Solid electrolyte and method for producing the same

Abstract

The purpose of the present invention is to provide a solid electrolyte which contains a garnet-type composite metal oxide phase and exhibits favorable lithium ion conductivity. The present invention is a solid electrolyte characterized by comprising a garnet-type composite metal oxide phase (L) and a phase (D) different from the phase (L), wherein the phase (L) contains Li, La, Zr, and O, and Ga that replaces a part of a Li site, and has a lattice constant of at least 12.96 Å, and the phase (D) contains at least one selected from the group consisting of LiF, BaZrO3, YF3, SrF2, and ScF3.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte.

Background Art

[0002] Research and development of lithium-ion secondary batteries are actively carried out in portable devices, hybrid vehicles, electric vehicles, and household power storage applications. Lithium-ion secondary batteries used in these fields are required to have high safety, long-term cycle stability, high energy density, etc.

[0003] Among them, all-solid-state batteries using solid electrolytes have attracted attention due to their high safety. For example, the lithium-ion conductor LIC of Patent Document 1 is manufactured by first preparing an ion conductor, and then mixing and heating the lithium halide and the ion conductor. For example, in the case of the powder of LLZ-MgSr obtained by substituting the elements of Mg and Sr for Li 7 La 3 Zr 2 O 12 raw materials containing each element of LLZ-MgSr (Li 2 CO 3 , MgO, La(OH) 3 , SrCO 3 , ZrO 2 , SrCO 3 , ZrO 2 ) are mixed for 15 hours and fired at 1000 °C for 10 hours. After that, the powder of lithium halide (for example, LiI) is further mixed to obtain a mixed powder, which is pressed by a press together with a stainless steel current collector to obtain a compact, and heat treatment is performed at 80 °C for 17 hours.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention provides a Li + ion-conductive solid electrolyte that contains a garnet-type composite metal oxide phase and exhibits good lithium-ion conductivity, which is different from that of Patent Document 1.

Means for Solving the Problems

[0006] The present invention that solves the above problems is as follows. [1] A solid electrolyte containing a garnet-type composite metal oxide phase (L) and a phase (D) different from the phase (L), wherein the phase (L) contains Li, La, Zr, and O, and Ga that substitutes for a part of the Li sites, the lattice constant is 12.96 Å or more, and the phase (D) contains at least one selected from the group consisting of LiF, BaZrO 3 , YF 3 , SrF 2 , and ScF 3 . A solid electrolyte characterized by this. [2] The solid electrolyte according to [1], wherein when the phase (D) contains the LiF, it further contains at least one of an Al element and a La element. [3] The solid electrolyte according to [1] or [2], wherein the phase (D) is present in at least a part of the interface of the phase (L). [4] A solid electrolyte containing a garnet-type composite metal oxide phase (L), wherein the solid electrolyte is in the presence of a reaction aid containing a mixture of LiX 1 and MX 2 p (X 1 and X 2 are both F, Cl, Br, or I, X 1 and X 2 may be the same or different, M is Ba, Y, Sr, or Sc, and p is a value equal to the valence of M)), and is synthesized by mechanochemical treatment of a raw material mixture containing a Li source powder, a La source powder, a Zr source powder, and a Ga source powder. The solid electrolyte characterized in that the phase (L) contains Li, La, Zr, O, and Ga that replaces a part of the Li sites. [5] The X 1 and X 2 are both F, as described in [4]. [6] A phase containing a compound containing at least a part of the constituent elements of the reaction assistant, wherein a phase (D) different from the phase (L) is present at at least a part of the interface of the phase (L), as described in [4] or [5]. [7] Li + ion conductivity is 1.0×10 -4 S / cm or more, as described in any one of [1] to [6]. [8] The solid electrolyte as described in any one of [4] to [7], wherein the reaction assistant is 15 parts by mass or less with respect to a total of 100 parts by mass of the raw material mixture. [9] After the mechanochemical treatment, firing is performed at 1100 to 1350 °C for 10 to 30 hours, as described in any one of [4] to [8].

Advantages of the Invention

[0007] The solid electrolyte of the present invention exhibits good Li + ion conductivity, and thus can be used as an excellent member for a solid electrolyte for a secondary battery.

Brief Description of the Drawings

[0008]

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Mode for Carrying Out the Invention

[0009] The solid electrolyte of the present invention is a solid electrolyte containing a garnet-type composite metal oxide phase (L) and a phase (D) different from the phase (L), wherein the phase (L) contains Li, La, Zr and O, and Ga substituting a part of the Li sites, and has a lattice constant of 12.96 Å or more, and the phase (D) is LiF, BaZrO 3 , YF 3 , SrF 2 and ScF 3 and contains at least one selected from the group consisting of.

[0010] The garnet-type composite metal oxide phase (L) containing Li, La, Zr and O usually contains Li 7 La3 Zr 2 O 12 It can be represented by the composition formula. The phase (L) is preferably cubic. Further, the garnet-type composite metal oxide phase (L) contains Ga that substitutes for a part of the Li sites. Hereinafter, the garnet-type composite metal oxide may be referred to as "LLZ". In the present invention, LLZ is preferably cubic.

[0011] In addition to the phase (L), the solid electrolyte of the present invention contains a phase (D) different from the phase (L). The phase (D) contains at least one selected from the group consisting of LiF, BaZrO 3 , YF 3 , SrF 2 and ScF 3 When the phase (D) contains LiF in a preferred embodiment, it further contains at least one of an Al element and a La element. At least one of the Al element and the La element may form an oxide, and examples of the oxide include an Al oxide, a La oxide, and a composite oxide of Al and La. Among them, when the phase (D) contains LiF, it is preferable to contain LiF and a La element, and more preferably to contain LiF, a La element, and an Al element. The La element contained in the phase (D) is usually derived from the La source powder described later. The Al element may be, for example, Al contained as an impurity in the raw material powder described later or derived from the crucible.

[0012] LiF, BaZrO 3 , YF 3 , SrF 2 and ScF 3 The presence of can be confirmed by the results measured by EDS (Energy dispersive X-ray spectroscopy), XRD (X-ray diffraction), TEM (Transmission Electron Microscopy)-EELS (Electron Energy-Loss Spectroscopy), or by appropriately combining these results.

[0013] In addition, the solid electrolyte of the present invention has a lattice constant of 12.96 Å or more. Usually, the lattice constant of LLZ partially substituted with Ga (hereinafter referred to as Ga-substituted LLZ) is about 12.95 Å, and the lattice constant of the solid electrolyte of the present invention is larger than that of Ga-substituted LLZ. The reason for this is not clear, but it is considered that a part of the Li site is substituted with an element derived from the reaction auxiliary component. The lattice constant is preferably 12.97 Å or more, more preferably 12.99 Å or more, and still more preferably 13.02 Å or more. The upper limit of the lattice constant is not particularly limited, and may be, for example, 13.10 Å.

[0014] The phase (D) is usually present in at least a part of the interface of the phase (L). That is, it is preferable that the phases (L) have a region where they exist via the phase (D), and in this region, they exist in contact with each other in the order of phase (L)-phase (D)-phase (L). By the phase (D) being present in at least a part of the interface of the phase (L), Li + ions can be favorably conducted from the phase (L) to the phase (L) through the phase (D).

[0015] The solid electrolyte of the present invention may be in the form of powder or a molded body (compression molded product) obtained by compression molding the powder or the like, and it is more preferable that it is a sintered body obtained by sintering the compression molded product. The solid electrolyte of the present invention preferably has a relative density of 60% or more, more preferably 70% or more, still more preferably 80% or more, even more preferably 90% or more, and the upper limit may be 100% or may be about 95%.

[0016] The solid electrolyte of the present invention is obtained by subjecting a mixture of raw material powders to mechanochemical treatment in the presence of a predetermined reaction assistant, and LLZ can be produced by reacting the raw material powders with each other by mechanochemical treatment. More specifically, the mechanochemical method can be carried out by shearing while compressing a mixture of raw material powders under dry conditions, and strain energy is accumulated in the raw material powders, and the energy is self-released to become thermal energy, or is consumed for surface modification, crystal structure transition, or solid-phase reaction. In the present invention, the raw material powders are subjected to mechanochemical treatment in the presence of a predetermined reaction assistant, which promotes the reaction between the raw material powders and improves the Li + ion conductivity of the obtained solid electrolyte.

[0017] More specifically, the mechanochemical treatment can be carried out by shearing while compressing a mixture containing the raw material powders and the reaction assistant under dry conditions. An example of this method will be described with reference to the drawings. FIG. 1 is a schematic diagram of a grinding mill capable of applying a compressive force and a shearing force to a mixture of raw material powders and a reaction assistant. FIG. 1(a) is a cross-sectional view perpendicular to the rotation axis, and FIG. 1(b) is a cross-sectional view taken along line A-A' of FIG. 1(a). The grinding mill of FIG. 1 includes a bottomed cylindrical container 1 and a rotor 2. The rotor 2 has a tip blade 3 with a curvature smaller than the inner circumference of the bottomed cylindrical container 1, and a clearance 4 is provided between the tip blade 3 and the inner circumference of the bottomed cylindrical container 1. By rotating the rotor 2, the mixture 5 of the raw material powders and the reaction assistant is subjected to a compressive force and a shearing force in the clearance 4.

[0018] If the mechanochemical treatment conditions are too weak, the reaction between the raw material powders will not occur, and if they are too strong, the once-formed LLZ crystals will become amorphous, which is not preferable. When the mechanochemical treatment conditions are inappropriate, the conditions can be appropriately changed according to the reason (unreacted, amorphous, etc.), the type and amount of the raw material, and the type and amount of the flux. For example, it is as follows.

[0019] The range of the clearance varies depending on the amount of raw material powder, the difference between the curvature of the tip blade of the rotor and the curvature of the inner circumference of the container, the processing power of the rotor, etc., but is preferably less than 1 mm, for example. By doing so, sufficient compressive force and shear force can be applied to the mixture of raw material powders, and the reaction between the raw material powders is promoted. The clearance is preferably 0.9 mm or less, more preferably 0.8 mm or less. The lower limit of the clearance is, for example, 100 μm or more, preferably 0.5 mm or more.

[0020] Also, the power of the rotation of the rotor is, for example, 0.05 kW / g or more with respect to the total mass of the raw material powder. By increasing the rotational power, the solid-phase reaction between the raw material powders is promoted. The rotational power is preferably 0.06 kW / g or more, more preferably 0.08 kW / g or more, and particularly preferably 0.1 kW / g or more. The upper limit of the rotational power is not particularly limited, but is, for example, 0.5 kW / g. The rotational speed of the rotor varies depending on the size of the apparatus, the shape of the rotor, etc., but with the rotational power in the above range, it is, for example, 2000 - 6000 rpm, preferably 3000 - 5000 rpm.

[0021] The rotation time of the rotor can be appropriately set according to the rotational power of the rotor, but is, for example, 5 minutes or more, preferably 10 minutes or more, more preferably 15 minutes or more. By rotating the rotor for 5 minutes or more (preferably 10 minutes or more), sufficient compressive force and shear force can be applied to the raw material powder, so that the solid-phase reaction of the raw material powder proceeds and LLZ can be obtained. The upper limit of the rotation time of the rotor is not particularly limited, but if it is too long, the crystallinity of LLZ will instead decrease and unnecessary energy will be consumed, so it is preferably 40 minutes or less, more preferably 30 minutes or less.

[0022] In mechanochemical treatment, strain energy is accumulated in the raw material powder by shear, and the energy is self-released to become thermal energy, resulting in heat generation. Therefore, it is also possible to implement the manufacturing method of the present invention without heating by an external heat source. The mechanochemical treatment may be carried out in a heat-generating state or may be carried out by cooling with water cooling or the like. In mechanochemical treatment, the temperature reached in the cylindrical container may be, for example, 50°C or higher, preferably 130°C or higher, and may be 500°C or lower.

[0023] The atmosphere for mechanochemical treatment is not particularly limited, and it may be either an oxygen-containing atmosphere such as air or an inert gas atmosphere. Examples of the inert gas include nitrogen, helium, argon, etc. (nitrogen gas is particularly preferred).

[0024] The material of the bottomed cylindrical container described above is not particularly limited, and examples include stainless steel such as SUS304 and carbon steel. Alternatively, a coating may be applied so that impurities do not mix into the generated LLZ. The inner diameter of the container is, for example, 50 to 500 mm. Also, there may be one or more tip vanes, preferably two or more, and usually eight or less.

[0025] The raw material powder is a Li source powder, a La source powder, a Zr source powder, and a Ga source powder. As the Li source powder, La source powder, Zr source powder, and Ga source powder, for example, oxides, carbonates, hydroxides, chlorides, alkoxides, etc. of each metal (Li, La, Zr, or Ga) can be used. The Li source powder is preferably a Li oxide or a Li carbonate, the La source powder is preferably a La oxide or a La hydroxide, the Zr source powder is preferably a Zr oxide or a Zr hydroxide, and the Ga source powder is preferably a Ga oxide or a Ga hydroxide. It is preferable that all of the Li source powder, La source powder, Zr source powder, and Ga source powder are powders of oxides of each metal (Li oxide, La oxide, Zr oxide, and Ga oxide).

[0026] The use ratios of the Li source powder, La source powder, Zr source powder, and Ga source powder may be the stoichiometric ratios of the target composition. In particular, the amount of Ga relative to the amount of Li is preferably 0.02 or more in terms of molar ratio, and by doing so, the crystal system of LLZ obtained can be made cubic. The molar ratio is more preferably 0.03 or more, still more preferably 0.04 or more, even more preferably 0.06 or more, particularly preferably 0.08 or more, and the upper limit is not limited, for example, it is 0.2 or less.

[0027] It is also preferable that the powder characteristics of each raw material powder are appropriately adjusted. For example, the specific surface area S w (m 2 / g) is preferably 0.5 to 25 m 2 / g. Further, the specific surface area diameter d w can be calculated from the specific surface area S BET (nm) by the following formula. d BET = 6 / (ρ·S w ) (In the above formula, ρ represents the theoretical density)

[0028] The preferable specific surface area diameter d BET (nm) is 250 to 400 nm for the Li source powder, 30 to 150 nm for the La source powder, 20 to 100 nm for the Zr source powder, and 20 to 100 nm for the Ga source powder.

[0029] The reaction assistant includes a mixture of LiX 1 and MX 2 p (X 1 and X 2 are both F, Cl, Br, or I, X 1 and X 2 may be the same or different, M is Ba, Y, Sr, or Sc, and p is a value equal to the valence of M). The amount of LiX 1 relative to the total amount of LiX 2 p and MX 1 is preferably 40 mol% or more. By increasing the ratio of LiX 1 , the Li + of the obtained solid electrolyteIonic conductivity can be improved. LiX 1 The ratio is more preferably 50 mol% or more, still more preferably 60 mol% or more, and the upper limit is, for example, 95 mol% or less, and may be 90 mol% or less.

[0030] X 1 and X 2 are both preferably F. M is preferably Ba or Sr. LiX 1 and MX 2 p The mixture is most preferably a mixture of LiF and BaF 2 or a mixture of LiF and SrF 2 2

[0031] It is also preferable to appropriately adjust the BET specific surface area diameter of the compound contained in the reaction aid. For example, the specific surface area diameter d 2 obtained from the BET specific surface area of BaF BET is, for example, 100 to 200 nm, and the specific surface area diameter d BET obtained from the BET specific surface area of LiF is, for example, 550 to 700 nm.

[0032] With respect to 100 parts by mass of the mixture of the raw material powders containing the above-mentioned Li source powder, La source powder, Zr source powder and Ga source powder, the reaction aid is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, still more preferably 10 parts by mass or less, and may be 4 parts by mass or more. The addition procedure of the reaction aid is not particularly limited, but it is preferable to add the reaction aid to the mixture of the above-mentioned raw material powders to start the mechanochemical treatment.

[0033] LLZ is generated only by the above-mentioned mechanochemical treatment, but after the mechanochemical treatment, firing is preferably performed. Li +Ionic conductivity can be further improved. The firing temperature is preferably 1100 to 1350 °C, more preferably 1150 to 1300 °C, and still more preferably 1200 to 1300 °C. The firing time is preferably 10 to 30 hours, more preferably 12 to 27 hours, and still more preferably 15 to 25 hours. Note that it is also preferable to perform firing after molding the mixture after mechanochemical treatment.

[0034] The solid electrolyte of the present invention that can be produced by the above method, that is, a solid electrolyte containing a garnet-type composite metal oxide phase (L), wherein the solid electrolyte is LiX 1 and MX 2 p (X 1 and X 2 are both F, Cl, Br or I, X 1 and X 2 may be the same or different, M is Ba, Y, Sr, or Sc, and p is a value equal to the valence of M), a raw material mixture containing a Li source powder, a La source powder, a Zr source powder, and a Ga source powder is synthesized by mechanochemical treatment in the presence of a reaction aid, and the phase (L) is a solid electrolyte containing Li, La, Zr, and O, and Ga substituting a part of the Li sites. It can also be said that. The reaction aid is LiX 1 and MX 2 p may contain other than the mixture of, but it is preferable that the reaction aid is a mixture of LiX 1 and MX 2 p . The total amount of LiX 1 and MX 2 p in the reaction aid is preferably 90% by mass or more, more preferably 95% by mass or more, and also preferably 100% by mass.

[0035] By using the above reaction aid, a phase containing a compound containing at least a part of the constituent elements of the reaction aid, and a phase (D) different from the phase (L) are preferably present in at least a part of the interface of the phase (L).

[0036] When the reaction aid contains a mixture of LiF and BaF 2 in the case of, at least one of LiF and BaZrO is preferably included in a compound containing at least a part of the constituent elements of the reaction aid. When LiF is included in the compound containing at least a part of the constituent elements of the reaction aid, it is more preferable that the phase (D) further contains at least one of Al element and La element. In particular, when the target chemical composition is Li 3 Ga 7-x Ga x / 3 La 3 Zr 2 O 12 (0 < x ≤ 1.5, preferably 0.3 ≤ x ≤ 0.8), when using Li source powder, La source powder, Zr source powder, and Ga source powder, and the reaction aid is a mixture of LiF and BaF 2 in particular, the molar ratio of LiF and BaF is 50:50 to 90:10, preferably 80:20 to 90:10), and the reaction aid is 8 to 10 parts by mass with respect to 100 parts by mass of the mixture of raw material powders, it is preferable that the compound containing at least a part of the constituent elements of the reaction aid contains BaZrO 2 in particular, the molar ratio of LiF and BaF is 50:50 to 90:10, preferably 80:20 to 90:10), and the reaction aid is 8 to 10 parts by mass with respect to 100 parts by mass of the mixture of raw material powders, it is preferable that the compound containing at least a part of the constituent elements of the reaction aid contains BaZrO 3 When the target chemical composition is Li 7-x Ga x / 3 La 3 Zr 2 O 12 (0 < x ≤ 1, preferably 0.3 ≤ x ≤ 0.8), when using Li source powder, La source powder, Zr source powder, and Ga source powder, and the reaction aid is a mixture of LiF and BaF 2 in particular, the molar ratio of LiF and BaF is 80:20 to 90:10), and the reaction aid is 8 to 10 parts by mass with respect to 100 parts by mass of the mixture of raw material powders, and further fired at 1100 to 1350 °C for 10 to 30 hours after mechanochemical treatment, it is preferable that the compound containing at least a part of the constituent elements of the reaction aid contains LiF and BaZrO 2 in particular, the molar ratio of LiF and BaF is 80:20 to 90:10), and the reaction aid is 8 to 10 parts by mass with respect to 100 parts by mass of the mixture of raw material powders, and further fired at 1100 to 1350 °C for 10 to 30 hours after mechanochemical treatment, it is preferable that the compound containing at least a part of the constituent elements of the reaction aid contains LiF and BaZrO 3 in the case of, at least one of LiF and BaZrO is preferably included in a compound containing at least a part of the constituent elements of the reaction aid. When LiF is included in the compound containing at least a part of the constituent elements of the reaction aid, it is more preferable that the phase (D) further contains at least one of Al element and La element. In particular, when the target chemical composition is Li

[0037] When the reaction aid contains a mixture of LiF and YF 3 in the case of, the compound containing at least a part of the constituent elements of the reaction aid contains YF3 is preferred. In particular, when the target chemical composition is Li 7-x Ga x / 3 La 3 Zr 2 O 12 (0 < x ≤ 1, preferably 0.3 ≤ x ≤ 0.8), and Li source powder, La source powder, Zr source powder, and Ga source powder are used, and the reaction assistant is a mixture of LiF and YF 3 (in particular, the molar ratio of LiF to YF 3 is 80:20 to 90:10), and the reaction assistant is 8 to 10 parts by mass with respect to 100 parts by mass of the mixture of raw material powders. Further, when calcined at 1100 to 1350 °C for 10 to 30 hours after mechanochemical treatment, it is preferable that the compound containing at least a part of the constituent elements of the reaction assistant contains YF 3 .

[0038] When the reaction assistant contains a mixture of LiF and SrF 2 , it is preferable that the compound containing at least a part of the constituent elements of the reaction assistant is SrF 2 . In particular, when the target chemical composition is Li 7-x Ga x / 3 La 3 Zr 2 O 12 (0 < x ≤ 1, preferably 0.3 ≤ x ≤ 0.8), and Li source powder, La source powder, Zr source powder, and Ga source powder are used, and the reaction assistant is a mixture of LiF and SrF 2 (in particular, the molar ratio of LiF to SrF 2 is 80:20 to 90:10), and the reaction assistant is 8 to 10 parts by mass with respect to 100 parts by mass of the mixture of raw material powders. Further, when calcined at 1100 to 1350 °C for 10 to 30 hours after mechanochemical treatment, it is preferable that the compound containing at least a part of the constituent elements of the reaction assistant contains SrF 2 . In this case, it is preferable to contain Li 2 O together with SrF 2 .

[0039] When the reaction assistant contains a mixture of LiF and ScF 3When including the mixture, a compound containing at least a part of the constituent elements of the reaction auxiliary is ScF 3 is preferable. In particular, when the target chemical composition is Li 7-x Ga x / 3 La 3 Zr 2 O 12 (0 < x ≦ 1, preferably 0.3 ≦ x ≦ 0.8), when using a Li source powder, a La source powder, a Zr source powder, and a Ga source powder so as to be, and the reaction auxiliary is a mixture of LiF and ScF 3 (especially the molar ratio of LiF and ScF 3 is 80:20 to 90:10), and the reaction auxiliary is 8 to 10 parts by mass with respect to 100 parts by mass of the mixture of the raw material powders, and further when calcined at 1100 to 1350 ° C. for 10 to 30 hours after mechanochemical treatment, it is preferable that a compound containing at least a part of the constituent elements of the reaction auxiliary contains ScF 3 .

[0040] The solid electrolyte of the present invention can have a Li + ion conductivity at room temperature by impedance measurement of 1.0 × 10 -4 S / cm or more, preferably 1.5 × 10 -4 S / cm or more, more preferably 2.0 × 10 -4 S / cm or more, and the upper limit is not limited, for example, 8.0 × 10 -4 S / cm or less. Also, the activation energy Ea by impedance measurement can be 0.4 eV or less, preferably 0.35 eV or less, more preferably 0.30 eV or less, and the lower limit may be, for example, 0.10 eV. Note that the above-mentioned Li + ion conductivity may be measured by using the solid electrolyte of the present invention as a molded body having a relative density within the above-mentioned preferable relative density range.

[0041] This application claims the benefit of priority based on Japanese Patent Application No. 2020-018115 filed on February 5, 2020. The entire contents of the specification of Japanese Patent Application No. 2020-018115 filed on February 5, 2020 are incorporated herein by reference.

Examples

[0042] Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited by the following examples, and it is of course possible to appropriately modify and implement it within the scope that conforms to the above-mentioned and following spirits, and all of them are included in the technical scope of the present invention.

[0043] Production Example 1-1 Li 5.5 Ga 0.5 La 3 Zr 2 O 12 As raw materials for, Li having the following characteristics respectively 2 O, La 2 O 3 , ZrO 2 , and Ga 2 O 3 , powders of, were each weighed in a total of 20 g at a stoichiometric ratio such that the composition of the composite metal oxide to be produced was Li 5.5 Ga 0.5 La 3 Zr 2 O 12 becomes. Li 2 O: Manufactured by High Purity Chemical Co., Ltd., purity: 99%, specific surface area S w : 2.1 m 2 / g, specific surface area diameter d BET : 1421 nm of Li 2 O was added to a 100 cc zirconia container together with 50 cc of zirconia balls and dry milled at 96 rpm for 24 h (inside a glove box: dew point value -90°C) to obtain a specific surface area S w : 8.4 m 2 / g, specific surface area diameter d BET : 355 nm of Li 2 O was used. La 2 O 3 : 5 mm and 500 cc of zirconia balls were added to a 1 L zirconia container, and ethanol and La manufactured by High Purity Chemical Co., Ltd., purity: 99.9%, specific surface area S w : 1.7 m 2 / g, specific surface area diameter d BET : 543 nm of La2 O 3 The specific surface area S obtained by wet grinding for 24 hours at 80 rpm in an air atmosphere is w :11.5m 2 / g, specific surface area diameter d BET :80nm La 2 O 3 was used. ZrO 2 : Kojundo Kagaku Co., Ltd., purity: 98%, specific surface area S w :18.4m 2 / g, specific surface area diameter d BET : 57nm ZrO 2 was used. Ga 2 O 3 : Kojundo Kagaku Co., Ltd., purity: 99.99%, specific surface area S w :10.4m 2 / g, specific surface area diameter d BET : 90nm Ga 2 O 3 was used.

[0044] Next, these raw materials and LiF and BaF as reaction aids were mixed. 2 A mixture of LiF and BaF 2 The molar ratio of LiF is 50:50, and the specific surface area diameter d BET : 649 nm, BaF 2 Specific surface area diameter d BET The reaction aid was added to the grinding mill shown in FIG. 1 in an amount of 10 parts by mass relative to 100 parts by mass of the total amount of the raw materials. The bottomed cylindrical vessel 1 was made of SUS304 and had an inner diameter of 80 mm, and the clearance 4 between the inner circumference of the vessel 1 and the tip blade 3 of the rotor 2 was 0.8 mm. The grinding mill was rotated in the atmosphere at a rotation speed of 4500 rpm and a required power of 3 kW for 12 minutes to perform mechanochemical treatment. The temperature reached in the vessel was approximately 143.8°C.

[0045] Manufacturing Example 1-2 The reaction aids used were LiF and BaF 2 LiF and BaF in a molar ratio of 75:25 2 The mechanochemical treatment was carried out in the same manner as in Production Example 1-1, except that the mixture was changed to the above mixture.

[0046] Production Examples 1-3 The reaction auxiliary used was changed to a mixture of LiF and BaF 2 with a molar ratio of 85:15 of LiF and BaF 2 and mechanochemical treatment was carried out in the same manner as in Production Example 1-1, except that the attrition mill was rotated at 3 kW for 20 minutes.

[0047] Production Example 2-1 Li 2 O, La 2 O 3 ZrO 2 Ga 2 O 3 powders were each weighed out in a total of 20 g in a stoichiometric ratio such that the composition of the composite metal oxide to be produced was Li 6.25 Ga 0.25 La 3 Zr 2 O 12 and mechanochemical treatment was carried out in the same manner as in Production Example 1-1, except that the reaction auxiliary used was changed to a mixture of LiF and BaF 2 with a molar ratio of 85:15 of LiF and BaF 2

[0048] Production Example 2-2 Mechanochemical treatment was carried out in the same manner as in Production Example 2-1, except that the reaction auxiliary used was changed to a mixture of LiF and BaF 2 with a molar ratio of 75:25 of LiF and BaF 2

[0049] Production Example 2-3 Mechanochemical treatment was carried out in the same manner as in Production Example 2-1, except that the amount of the reaction auxiliary added was 6 parts by mass with respect to 100 parts by mass of the total amount of the raw materials, and the attrition mill was rotated at 3 kW for 17 minutes.

[0050] ​​The results of analyzing the crystal structures of the samples obtained in Production Examples 1-1 to 1-3 using an XRD (X-ray Diffraction analysis) apparatus manufactured by Bruker are shown in Fig. 2. The measurement was performed using CuKα radiation, with λ = 1.5418 nm and θ = 10 to 50°. As a result, it can be seen that a cubic LLZ in which part of the Li sites are substituted with Ga was formed in the obtained samples. Also, in Production Examples 1-1 to 1-3, the presence of BaZrO 3 was also confirmed. Similarly, the results of analyzing the crystal structures of the samples obtained in Production Examples 2-1 to 2-2 are shown in Fig. 3. As a result, it can be seen that in Production Examples 2-1 to 2-2 as well, a cubic LLZ in which part of the Li sites are substituted with Ga was formed in the obtained samples.

[0051] Production Example 3-1 Li 2 O, La 2 O 3 、ZrO 2 、Ga 2 O 3 powders were each weighed to a total of 20 g in a stoichiometric ratio such that the composition of the resulting complex metal oxide was Li 6.4 Ga 0.2 La 3 Zr 2 O 12 and the reaction aids used were changed to a mixture of LiF and YF 3 with a molar ratio of LiF to YF 3 of 75:25 (specific surface area diameter d BET of LiF: 649 nm. The same applies to LiF used below.), and mechanochemical treatment was carried out in the same manner as in Production Example 1-1 except that the attrition mill was rotated at 3 kW for 39 minutes.

[0052] Production Example 3-2 The reaction aids used were changed to a mixture of LiF and YF 3 with a molar ratio of LiF to YF 3 of 85:15, and mechanochemical treatment was carried out in the same manner as in Production Example 3-1 except that the attrition mill was rotated at 3 kW for 40 minutes.

[0053] Production Example 4-1 Li2 O, La 2 O 3 , ZrO 2 , Ga 2 O 3 powders of each were weighed to a total of 20 g at a stoichiometric ratio such that the composition of the composite metal oxide to be formed was Li 6.4 Ga 0.2 La 3 Zr 2 O 12 and mechanochemical treatment was carried out in the same manner as in Production Example 1-1, except that the reaction aids used were changed to a mixture of LiF and SrF 2 with a molar ratio of 85:15 of LiF and SrF 2 .

[0054] Production Example 5-1 Li 2 O, La 2 O 3 , ZrO 2 , Ga 2 O 3 powders of each were weighed to a total of 20 g at a stoichiometric ratio such that the composition of the composite metal oxide to be formed was Li 6.55 Ga 0.15 La 3 Zr 2 O 12 and the reaction aids used were changed to a mixture of LiF and ScF 3 with a molar ratio of 85:15 of LiF and ScF 3 , and mechanochemical treatment was carried out in the same manner as in Production Example 1-1, except that the attrition mill was rotated at 3 kW for 30 minutes.

[0055] Examples 1-1 to 1-3, Examples 2-1 to 2-3, Examples 3-1 to 3-2, Examples 4-1 to 4-2, Example 5-1 The sample obtained in the above production example was put into a mold, and a pressure of 375 MPa was applied to form a pellet with a diameter of 10 mm and a thickness of about 1 mm. Tetragonal LLZO powder was spread at the bottom of an alumina crucible to suppress the volatilization of Li during firing, and the pellet formed on the spread LLZO powder was allowed to stand. Further, the pellet was covered with LLZO powder and fired at 1230 °C for 20 hours in a dry nitrogen atmosphere to obtain a pellet sintered body. The weight of this pellet sintered body was measured, and the density was calculated from the dimensions and the weight of the pellet, and this was divided by 5.11 g / cm 3 which is the theoretical density of LLZ to calculate the relative density (%). Then, both sides of the pellet sintered body were polished in a dry room with a dew point value of -60 °C, and Au was sputtered to form an electrode with a diameter of 8 mm. In Example 4-2, after subjecting the sample after the mechanochemical treatment to a pulverization treatment, the above pellet forming and firing were performed to increase the relative density. Also, the pellet sintered body sample with the electrode formed was set in a all-solid-state battery evaluation cell manufactured by Hosen Co., Ltd., connected to a potentiostat galvanostat, and impedance measurement was performed in the temperature range of room temperature to 100 °C for Li + ion conductivity (S / cm) evaluation. Further, the activation energy E a (eV) was calculated from the Arrhenius plot using the ion conductivity values at each temperature.

[0056] Also, the pellet sintered body was pulverized using a mortar in a glove box, and crystal structure analysis was performed using an XRD (X-ray Diffraction analysis) apparatus manufactured by Bruker. Using the peak of the (400) plane of the obtained X-ray diffraction peak of LLZO, the interplanar spacing d value was obtained from the following formula, and the lattice constant was calculated. 2dSinθ=nλ (1) 1 / d 2 =(h 2 +k 2 +l 2 ) / a 2 (2) d: interplanar spacing, a: lattice constant

[0057] The results are shown in Table 1.

[0058]

Table 1

[0059] According to Table 1, all the examples showed good Li -4 ion conductivity of 1.0×10 + S / cm or more. Also, it was found that the Li + ion conductivity improved as the ratio of LiF increased.

[0060] For Example 2-1, substitute drawings showing images obtained by observing the pellet cross-section with a TEM (Transmission electron microscope, magnification 10,000 times) are shown in FIGS. 4 and 5. FIG. 4(a) is an SE (Secondary electron) detector image, and FIG. 4(b) is an ESB detector (Energy selected backscatter detector) image (composite image). A phase clearly different from LLZ is observed near the center of the portion surrounded by the dotted line in FIGS. 4 and 5.

[0061] FIG. 6 is a diagram showing the results of EDS analysis of the pellet cross-section for Example 2-1. Locations where La, Zr, and Ba are present, locations where Ba and Zr are present, and locations where Al is present were observed near the LLZ particle interface. In the XRD analysis results of Example 2-1 described later, BaZrO 3 was detected, and the locations where Ba and Zr are present are considered to be BaZrO 3 .

[0062] FIG. 7 is a diagram showing the results of TEM-EDS (Energy dispersive X-ray spectrometry) analysis of the cross-section of Example 2-1. According to FIG. 7, a phase containing La was observed at the interface of the LLZ phase, and Al was also detected in this La-containing phase.

[0063] Furthermore, FIG. 8 shows TEM-EELS maps at positions (I) and (II) in FIG. 7. In FIG. 8, in both positions (I) and (II), the presence of LiF was confirmed in the central part of the EELS map (the bright part in the center of the EELS map), and the presence of LiF was confirmed in a phase different from the LLZ phase that exists at the interface of the LLZ phase.

[0064] FIG. 9 shows the results of analyzing the crystal structures of the samples obtained in Production Example 2-1 and Example 2-1 using an XRD (X-ray Diffraction analysis) apparatus manufactured by Bruker. In Example 2-1, which was further fired from Production Example 2-1, the full width at half maximum of the corresponding peak of LLZ became smaller, indicating that the crystallinity was improved by firing. Also, in both Production Example 2-1 and Example 2-1, the presence of BaZrO 3 was confirmed.

[0065] FIG. 10 shows the results of analyzing the crystal structures of the samples obtained in Production Example 3-2 and Example 3-2 using an XRD (X-ray Diffraction analysis) apparatus manufactured by Bruker. In Example 3-2, which was further fired from Production Example 3-2, the full width at half maximum of the corresponding peak of LLZ became smaller, indicating that the crystallinity was improved by firing.

[0066] FIG. 11 shows the results of EDS analysis of the pellet cross-section for Example 3-2. The presence of Y and F was confirmed, and Y and F were observed at the same position at the LLZ interface, suggesting that YF 3 was formed.

[0067] FIG. 12 shows the results of analyzing the crystal structures of the samples obtained in Production Example 4-1 and Example 4-1 using an XRD (X-ray Diffraction analysis) apparatus manufactured by Bruker. In Example 4-1, which was further fired from Production Example 4-1, the full width at half maximum of the corresponding peak of LLZ became smaller, indicating that the crystallinity was improved by firing. Also, in Example 4-1, the presence of Li 2 O was also confirmed.

[0068] Figure 13 is a diagram showing the result of EDS analysis of the pellet cross-section for Example 4-1. The presence of Sr and F is confirmed, and Sr and F are observed at the same position at the LLZ interface, suggesting that SrF 2 is formed. Also, no other elements are observed at the position where O is observed, and Li is a light element, making it difficult to confirm its presence by EDS analysis. Considering the result of FIG. 12 above, it is considered that Li 2 O exists at a part of the position where O exists.

[0069] Figure 14 shows the result of analyzing the crystal structures of the samples obtained in Production Example 5-1 and Example 5-1 using an XRD (X-ray Diffraction analysis) apparatus manufactured by Bruker. In Example 5-1, which was further fired from Production Example 5-1, the full width at half maximum of the corresponding peak of LLZ is smaller, indicating that the crystallinity has been improved by firing. Also, the presence of ScF 3 could also be confirmed in Example 5-1.

Explanation of Signs

[0070] 1 Bottomed cylindrical container 2 Rotor 3 Tip wing 4 Clearance 5 Mixture of raw material powder and reaction assistant

Claims

1. A solid electrolyte comprising a garnet-type composite metal oxide phase (L) and a phase (D) different from the phase (L), wherein the phase (L) contains Li, La, Zr, and O, and Ga that replaces a part of the Li sites, and has a lattice constant of 12.96 Å or more, The phase (D) is at least one selected from the group consisting of LiF, BaZrO 3 , YF 3 , SrF 2 and ScF 3 A solid electrolyte characterized by containing at least one selected from the group consisting of

2. The solid electrolyte according to claim 1, wherein when the phase (D) contains the LiF, it further contains at least one of an Al element and a La element.

3. The solid electrolyte according to claim 1 or 2, wherein the phase (D) is present at at least a part of the interface of the phase (L).

4. The solid electrolyte according to any one of claims 1 to 3, having an Li+ ion conductivity of 1.0×10−4 S / cm or more.

5. A method for producing a solid electrolyte containing a garnet-type composite metal oxide phase (L), wherein the phase (L) contains Li, La, Zr, and O, and Ga that replaces a part of the Li sites, LiX 1 and MX 2 ｐ (X 1 and X 2 are each F, Cl, Br, or I, X 1 and X 2 may be the same or different, M is Ba, Y, Sr, or Sc, and p is a value equal to the valence of M) in the presence of a reaction auxiliary containing a mixture characterized by subjecting a raw material mixture containing Li source powder, La source powder, Zr source powder, and Ga source powder to mechanochemical treatment.

6. Said X 1 and X 2 The method for producing a solid electrolyte according to claim 5, wherein both are F.

7. A phase containing a compound containing at least a part of the constituent elements of the reaction assistant, wherein a phase (D) different from the phase (L) is present at at least a part of the interface of the phase (L). The method for producing a solid electrolyte according to claim 5 or 6.

8. The method for producing a solid electrolyte according to any one of claims 5 to 7, wherein the reaction assistant is 15 parts by mass or less with respect to a total of 100 parts by mass of the raw material mixture.

9. The method for producing a solid electrolyte according to any one of claims 5 to 8, wherein after the mechanochemical treatment, it is fired at 1100 to 1350 °C for 10 to 30 hours.

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