Lithium ion conductive solid electrolyte material, lithium ion conductive solid electrolyte, methods for producing them, and all-solid-state battery

Abstract

One embodiment of the present invention relates to: a lithium ion-conductive solid electrolyte material; a lithium ion-conductive solid electrolyte; a method for producing the lithium ion-conductive solid electrolyte material; a method for producing the lithium ion-conductive solid electrolyte; or an all-solid-state battery. The lithium ion-conductive solid electrolyte material has a crystal structure based on LiTa2PO8; and the method for producing a lithium ion-conductive solid electrolyte material, which contains at least Li, Ta, P, O and Zr as constituent elements, comprises a primary grinding step in which a primary ground material is obtained by grinding a starting material, a firing step in which a primary fired material is obtained by firing the primary ground material, and a secondary grinding step in which a lithium ion-conductive solid electrolyte material is obtained by grinding the primary fired material with use of a ball mill. In the secondary grinding step, zirconia balls having a diameter of more than 1 mm but less than 10 mm are used; and the half-value width of a diffraction peak having the maximum intensity within the range of 20° ≤ 2θ ≤ 40°, the diffraction peak being assigned to the crystal structure based on LiTa2PO8 of the lithium ion-conductive solid electrolyte material, is 0.160° or more in X-ray diffractometry.

Description

Technical Field

[0001] One embodiment of the present invention relates to a lithium ion conductive solid electrolyte material, a lithium ion conductive solid electrolyte, a method for producing these, or an all-solid-state battery.

Background Art

[0002] In recent years, development of high-output and high-capacity batteries has been demanded as power sources for notebook computers, tablet terminals, mobile phones, smartphones, electric vehicles (EVs), and the like. Among these, all-solid-state batteries using solid electrolytes instead of liquid electrolytes such as organic solvents have attracted attention as batteries excellent in charge-discharge efficiency, charging speed, safety, and productivity.

[0003] As the solid electrolyte, inorganic solid electrolytes have attracted attention, and as the inorganic solid electrolytes, mainly oxide-based and sulfide-based solid electrolytes are known. When using a sulfide-based solid electrolyte, although there are advantages such as the ability to fabricate a battery by cold pressing, etc., it is unstable to humidity and there is a possibility of generating harmful hydrogen sulfide gas. Therefore, development of oxide-based solid electrolytes (for example, Patent Documents 1 and 2) has been promoted from the viewpoint of safety and the like.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Oxide-based solid electrolytes have extremely high grain boundary resistance. To obtain ionic conductivity sufficient for use in all-solid-state batteries, it is necessary not only to pressure-mold powders of the solid electrolyte material but also to sinter them to increase the relative density (the percentage of the actual density relative to the theoretical density). However, it has been found that to obtain a solid electrolyte with a high relative density from conventional solid electrolyte materials such as those described in Patent Documents 1 and 2, sintering over a long period of time of 12 hours or more is required, and there was room for improvement in this regard.

[0006] One embodiment of the present invention provides a lithium-ion conductive solid electrolyte material capable of obtaining a lithium-ion conductive solid electrolyte with a high relative density and excellent reliability even with sintering for a short time of less than 12 hours. Further, one embodiment of the present invention provides a method for manufacturing the lithium-ion conductive solid electrolyte material by a method with excellent productivity.

Means for Solving the Problems

[0007] As a result of intensive studies by the present inventors, it has been found that the above problems can be solved according to the following configuration examples, and the present invention has been completed. The configuration example of the present invention is as follows.

[0008] [1] A method for manufacturing a lithium-ion conductive solid electrolyte material having a crystal structure based on LiTa2PO8 and having at least lithium, tantalum, phosphorus, oxygen, and zirconium as constituent elements, comprising a primary pulverization step of pulverizing a raw material substance to obtain a primary pulverized product, a firing step of firing the primary pulverized product to obtain a primary fired product, and a secondary pulverization step of pulverizing the primary fired product using a ball mill to obtain a lithium-ion conductive solid electrolyte material, wherein in the secondary pulverization step, zirconia balls having a diameter of more than 1 mm and less than 10 mm are used, the half-value width of the diffraction peak having the maximum intensity observed in the range of 20° ≦ 2θ ≦ 40°, which is derived from the crystal structure based on LiTa2PO8 of the lithium-ion conductive solid electrolyte material in X-ray diffraction, is 0.160° or more, Method for producing a lithium ion conductive solid electrolyte material.

[0009] [2] The method for producing a lithium ion conductive solid electrolyte material according to [1], wherein the raw material substance does not contain zirconium.

[0010] [3] A sintering step of obtaining a lithium ion conductive solid electrolyte by sintering the lithium ion conductive solid electrolyte material obtained by the method for producing a lithium ion conductive solid electrolyte material according to [1] or [2], wherein the relative density, which is the percentage of the ratio of the measured density calculated from the mass and volume of the lithium ion conductive solid electrolyte to the theoretical density of the lithium ion conductive solid electrolyte, is 75.0% or more. Method for producing a lithium ion conductive solid electrolyte.

[0011] [4] Having a crystal structure based on LiTa2PO8, having at least lithium, tantalum, phosphorus, oxygen and zirconium as constituent elements, in X-ray diffraction, the half-value width of the diffraction peak having the maximum intensity observed in the range of 20° ≤ 2θ ≤ 40° is 0.160° or more, and the content of zirconium is more than 0 atomic % and 3.0 atomic % or less. Lithium ion conductive solid electrolyte material.

[0012] [5] The lithium ion conductive solid electrolyte material according to [4], further having a boron element.

[0013] [6] Having a crystal structure based on LiTa2PO8, a lithium ion conductive solid electrolyte having at least lithium, tantalum, phosphorus, oxygen and zirconium as constituent elements, wherein the relative density, which is the percentage of the ratio of the measured density calculated from the mass and volume of the lithium ion conductive solid electrolyte to the theoretical density of the lithium ion conductive solid electrolyte, is 75.0% or more. Lithium ion conductive solid electrolyte.

[0014] [7] The lithium ion conductive solid electrolyte according to [6], further comprising a boron element.

[0015] [8] A positive electrode having a positive electrode active material, A negative electrode having a negative electrode active material, A solid electrolyte layer between the positive electrode and the negative electrode, and the solid electrolyte layer contains the lithium ion conductive solid electrolyte according to [6] or [7], All solid-state battery.

[0016] [9] The positive electrode active material is LiM3PO4 [M3 is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, Ti, and V, or two elements of V and O.], LiM5VO4 [M5 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, and Ti.], Li2M6P2O7 [M6 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, Ti, and V, or two elements of V and O.], LiVP2O7, Li x7 V y7 M7 z7 [2≤x7≤4, 1≤y7≤3, 0≤z7≤1, 1≤y7 + z7≤3, M7 is one or more elements selected from the group consisting of Ti, Ge, Al, Ga, and Zr.], Li 1+x8 Al x8 M8 2-x8 (PO4)3 [0≤x8≤0.8, M8 is one or more elements selected from the group consisting of Ti and Ge.], LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiCoO2, LiNiO2, LiMn2O4, Li2CoP2O7, Li3V2(PO4)3, Li3Fe2(PO4)3, LiNi 0.5 Mn 1.5 O4 and Li4Ti5O 12 The all-solid-state battery according to [8], comprising one or more compounds selected from the group consisting of.

[0017]

[10] The negative electrode active material is LiM3PO4 [M3 is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, Ti, and V, or two elements of V and O.], LiM5VO4 [M5 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, and Ti.], Li2M6P2O7 [M6 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, Ti, and V, or two elements of V and O.], LiVP2O7, Li x7 V y7 M7 z7 [2 ≤ x7 ≤ 4, 1 ≤ y7 ≤ 3, 0 ≤ z7 ≤ 1, 1 ≤ y7 + z7 ≤ 3, M7 is one or more elements selected from the group consisting of Ti, Ge, Al, Ga, and Zr.], Li 1+x8 Al x8 M8 2-x8 (PO4)3 [0 ≤ x8 ≤ 0.8, M8 is one or more elements selected from the group consisting of Ti and Ge.], (Li 3-a9x9+(5-b9)y9 M9 x9 )(V 1-y9 M10 y9 )O4 [M9 is one or more elements selected from the group consisting of Mg, Al, Ga, and Zn, M10 is one or more elements selected from the group consisting of Zn, Al, Ga, Si, Ge, P, and Ti, 0 ≤ x9 ≤ 1.0, 0 ≤ y9 ≤ 0.6, a9 is the average valence of M9, and b9 is the average valence of M10.], LiNb2O7, Li4Ti5O 12 、Li4Ti5PO 12 、TiO2, LiSi, and one or more compounds selected from the group consisting of graphite, the all-solid-state battery according to [8] or [9].

[0018]

[11] The all-solid-state battery according to any one of [8] to

[10] , wherein the positive electrode and the negative electrode contain the lithium ion conductive solid electrolyte according to [6] or [7].

Advantages of the Invention

[0019] According to the lithium ion conductive solid electrolyte material according to an embodiment of the present invention, even with sintering for a short time of less than 12 hours, a lithium ion conductive solid electrolyte having a high relative density and excellent reliability can be obtained. A high relative density means that there are few voids inside the formed solid electrolyte layer, the positive electrode active material layer, and the negative electrode active material layer described later, leading to a high mechanical strength of the all-solid-state battery to be manufactured and being less likely to be damaged. Further, the fact that there are few voids leads to the high possibility of suppressing the precipitation of lithium contained in these layers as dendrites and causing a short circuit. Further, according to an embodiment of the present invention, the lithium ion conductive solid electrolyte material can be manufactured by a method with excellent productivity. Furthermore, by using the lithium ion conductive solid electrolyte according to an embodiment of the present invention, an all-solid-state battery including a solid electrolyte having sufficient ionic conductivity while suppressing decomposition and alteration of other materials such as the positive electrode and negative electrode materials and preventing short circuits between the positive electrode and negative electrode materials can be easily manufactured with excellent economy.

Brief Description of Drawings

[0020]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0021] ≪Lithium Ion Conductive Solid Electrolyte Material≫ The lithium ion conductive solid electrolyte material according to an embodiment of the present invention (hereinafter also referred to as "this material 1") is It has a crystal structure based on LiTa₂PO₈ (hereinafter also referred to as "LTPO structure"). It has at least lithium, tantalum, phosphorus, oxygen and zirconium as constituent elements. In X-ray diffraction, the full width at half maximum of the diffraction peak having the maximum intensity observed in the range of 20° ≤ 2θ ≤ 40° is 0.160° or more. The content of zirconium is more than 0 atomic % and 3.0 atomic % or less.

[0022] Whether the present material 1 has the LTPO structure can be determined by analyzing the X-ray diffraction (XRD) pattern, specifically, the XRD pattern measured by the method described in the following examples. In the present material 1 having the LTPO structure, peaks similar to those of LiTa₂PO₈ crystal structure described in J. Kim et al., J. Mater. Chem. A, 2018, 6, p22478-22482 are observed.

[0023] In the X-ray diffraction (XRD pattern) of the present material 1, the full width at half maximum of the diffraction peak having the maximum intensity observed in the range of 20° ≤ 2θ ≤ 40° is 0.160° or more, preferably 0.180° or more, more preferably 0.200° or more. The upper limit of the full width at half maximum is not particularly limited, for example, it is 0.500°. Since the present material 1 has the above full width at half maximum, the lithium ion conductive solid electrolyte (sintered body) obtained by sintering the present material 1 tends to have higher ionic conductivity.

[0024] The shape, size, etc. of the present material 1 are not particularly limited, but it is preferably in the form of particles (powder). The average particle diameter (D50) of the present material 1 is preferably 0.1 - 10 μm, more preferably 0.1 - 5 μm. In the present invention, unless otherwise specified, the average particle diameter means the 50% particle diameter (D50) in the volume-based cumulative particle size distribution. Since the average particle diameter of the present material 1 is in the above range, the lithium ion conductive solid electrolyte (sintered body) obtained by sintering the present material 1 tends to have higher ionic conductivity.

[0025] The elements constituting the present material 1 are not particularly limited as long as they include lithium, tantalum, phosphorus, oxygen, and zirconium, and may include one or more elements selected from the group consisting of B, Bi, Nb, Ga, Sn, Hf, W, Mo, Si, Al, and Ge.

[0026] From the viewpoint of easily obtaining a lithium-ion conductive solid electrolyte (sintered body) having higher lithium-ion conductivity, the content of lithium element in the present material 1 is preferably 5.0 atomic % or more, more preferably 9.0 atomic % or more, preferably 20.0 atomic % or less, and more preferably 15.0 atomic % or less.

[0027] In addition, the content of each element in the present material 1 can be measured by, for example, the absolute intensity quantification method of Auger electron spectroscopy (AES) using a standard powder sample in which Mn, Co, and Ni are contained at a ratio of 1:1:1 as a lithium-containing transition metal oxide such as LiCoO2. Alternatively, it can be determined by conventionally known quantitative analysis. For example, after adding an acid to the sample and performing thermal decomposition, the thermal decomposition product is fixed in volume, and the content of each element in the present material 1 can be determined using a high-frequency inductively coupled plasma optical emission spectrometry (ICP-AES) apparatus.

[0028] From the viewpoint of easily obtaining a lithium-ion conductive solid electrolyte (sintered body) having higher lithium-ion conductivity, the content of tantalum element in the present material 1 is preferably 10.6 atomic % or more, more preferably 11.0 atomic % or more, preferably 16.6 atomic % or less, and more preferably 16.0 atomic % or less.

[0029] From the viewpoint of being able to lower the sintering temperature when obtaining a lithium-ion conductive solid electrolyte (sintered body) having sufficient ion conductivity, the content of phosphorus element in the present material 1 is preferably 5.3 atomic % or more, more preferably 5.5 atomic % or more, preferably 8.3 atomic % or less, and more preferably 8.2 atomic % or less.

[0030] The content of zirconium element in this Material 1 (zirconium content) is more than 0 atom% and 3.0 atom% or less, preferably 0.1 to 2.5 atom%, more preferably 0.1 to 2.0 atom% from the viewpoints such as being able to easily obtain a lithium ion conductive solid electrolyte (sintered body) having a high relative density and excellent reliability even with short-time sintering.

[0031] When this Material 1 contains one or more elements selected from the group consisting of B, Bi, Nb, Ga, Sn, Hf, W, Mo, Si, Al, and Ge, the content of each of the one or more elements selected from the group consisting of B, Bi, Nb, Ga, Sn, Hf, W, Mo, Si, Al, and Ge in this Material 1 is preferably 0.1 to 5.0 atom%, more preferably 0.1 to 3.0 atom% from the viewpoints such as having a tendency to easily obtain a lithium ion conductive solid electrolyte (sintered body) having higher ionic conductivity.

[0032] This Material 1 preferably contains a boron element from the viewpoints such as being able to lower the sintering temperature when obtaining a lithium ion conductive solid electrolyte (sintered body) having sufficient ionic conductivity and relative density. When this Material 1 contains a boron element, for the same reason, it is preferably 0.1 atom% or more, more preferably 0.5 atom% or more, preferably 5.0 atom% or less, more preferably 3.0 atom% or less.

[0033] ≪Method for producing lithium ion conductive solid electrolyte material≫ A method for producing a lithium ion conductive solid electrolyte material according to an embodiment of the present invention (hereinafter also simply referred to as "the production method of this Material 2") is A method for producing a lithium ion conductive solid electrolyte material (hereinafter also referred to as "this Material 2") having a crystal structure based on LiTa2PO8 and having at least lithium, tantalum, phosphorus, oxygen, and zirconium as constituent elements, and in the X-ray diffraction of the lithium ion conductive solid electrolyte material, the half-value width of the diffraction peak having the maximum intensity observed in the range of 20° ≤ 2θ ≤ 40° derived from the crystal structure based on LiTa2PO8 is 0.160° or more. A primary pulverization step of pulverizing a raw material to obtain a primary pulverized product, A firing step of firing the primary pulverized product to obtain a primary fired product, And a secondary pulverization step of pulverizing the primary fired product using a ball mill to obtain the present material 2, In the secondary pulverization step, zirconia balls having a diameter exceeding 1 mm and less than 10 mm are used.

[0034] In the X-ray diffraction (XRD pattern) of the present material 2, the full width at half maximum of the diffraction peak having the maximum intensity observed in the range of 20° ≤ 2θ ≤ 40° is 0.160° or more, preferably 0.180° or more, more preferably 0.200° or more, and the upper limit of the full width at half maximum is not particularly limited, but is, for example, 0.500°. Since the present material 2 has the full width at half maximum, the lithium ion conductive solid electrolyte (sintered body) obtained by sintering the present material 2 tends to exhibit higher ionic conductivity.

[0035] The elements constituting the present material 2 are not particularly limited as long as they include lithium, tantalum, phosphorus, oxygen, and zirconium, and may include one or more elements selected from the group consisting of B, Bi, Nb, Ga, Sn, Hf, W, Mo, Si, Al, and Ge. For the same reasons as described in the column of the present material 1, it is preferable that the elements constituting the present material 2 include lithium, tantalum, phosphorus, oxygen, boron, and zirconium.

[0036] The present material 2 is preferably the present material 1. The method for confirming the LTPO structure, shape, size, and content of each element of the present material 2 are the same as those described in the column of the present material 1.

[0037] <Primary pulverization step> The primary pulverization step is a step of pulverizing a raw material to obtain a primary pulverized product. In the primary pulverization step, it is preferable to pulverize so that the obtained primary pulverized product becomes amorphous by a mechanochemical reaction and so that the average particle diameter (D50) of the obtained primary pulverized product falls within the above range.

[0038] Examples of the primary pulverization process include a method of pulverizing using a roll rolling mill, a ball mill, a small-diameter ball mill (bead mill), a medium stirring mill, a jet mill, a mortar, an automatic kneading mortar, a tank disintegrator, a jet mill, etc. Among these, when obtaining a lithium ion conductive solid electrolyte (sintered body) from the present material 2, a method of pulverizing using a ball mill or a bead mill is preferable from the viewpoint of easily obtaining a lithium ion conductive solid electrolyte (sintered body) having a higher ionic conductivity. A method of pulverizing with a ball mill using balls having a diameter of 0.1 to 10 mm is more preferable.

[0039] The time of the primary pulverization process is preferably 0.5 to 48 hours, more preferably 2 to 48 hours, from the viewpoint of easily obtaining the present material 2 which becomes amorphous by a mechanochemical reaction and has an average particle diameter (D50) within the above range.

[0040] During the primary pulverization process, it may be pulverized and mixed while heating if necessary, but it is usually carried out at room temperature. The primary pulverization process may be carried out in the air, but it is preferably carried out in an atmosphere of nitrogen gas and / or argon gas with the oxygen gas content adjusted in the range of 0 to 20% by volume.

[0041] The raw material used in the primary pulverization process is preferably an inorganic compound from the viewpoint of ease of handling. The raw material may be obtained by manufacturing by a conventionally known method or a commercially available product may be used.

[0042] As the raw material, for example, it is preferable to use a compound containing a lithium atom, a compound containing a tantalum atom, and a compound containing a phosphorus atom. Since the present material 2 has zirconium as a constituent element, a compound containing a zirconium atom may be used as the raw material. However, since zirconia balls are used in the secondary pulverization process, zirconium elements derived from the zirconia balls will be contained in the present material 2. Preferably, the raw material substance does not contain zirconium.

[0043] Examples of the compound containing a lithium atom include lithium carbonate (Li2CO3), lithium oxide (Li2O), lithium hydroxide (LiOH), lithium acetate (LiCH3COO), and hydrates thereof. Among these, lithium carbonate, lithium hydroxide, and lithium acetate are preferred because they are easy to decompose and react. As the compound containing a lithium atom, one kind may be used, or two or more kinds may be used.

[0044] Examples of the compound containing a tantalum atom include tantalum pentoxide (Ta2O5) and tantalum nitrate (Ta(NO3)5). Among these, tantalum pentoxide is preferred from the viewpoint of cost. As the compound containing a tantalum atom, one kind may be used, or two or more kinds may be used.

[0045] As the compound containing a phosphorus atom, phosphate is preferred. As the phosphate, examples include diammonium hydrogen phosphate ((NH4)2HPO4) and ammonium dihydrogen phosphate (NH4H2PO4) because they are easy to decompose and react. As the compound containing a phosphorus atom, one kind may be used, or two or more kinds may be used.

[0046] As the compound containing a zirconium atom, an inorganic compound is preferred from the viewpoint of ease of handling, and examples include oxides and nitrates of zirconium. Among these, oxides are preferred from the viewpoint of cost. Examples of the compound containing a zirconium atom include zirconium oxide (ZrO2) and zirconium hydroxide (Zr(OH)4). As the compound containing a zirconium atom, one kind may be used, or two or more kinds may be used.

[0047] When this material contains one or more elements M1 selected from the group consisting of Bi, Nb, Ga, Sn, Hf, W, and Mo, and / or when it contains one or more elements M2 selected from the group consisting of B, Si, Al, and Ge, it is preferable to use, as the raw material substance, a compound containing lithium atoms, a compound containing tantalum atoms, a compound containing phosphorus atoms, and further a compound containing element M1 and / or a compound containing element M2.

[0048] The compound containing element M1 is not particularly limited, but from the viewpoint of ease of handling, an inorganic compound is preferable, and examples thereof include oxides and nitrates of M1. Among these, oxides are preferable from the viewpoint of cost. As the compound containing element M1, one kind may be used, or two or more kinds may be used.

[0049] When M1 is Nb, examples of the compound containing niobium atoms include Nb2O5, LiNbO3, LiNb3O8, and NbPO5. As the compound containing niobium atoms, one kind may be used, or two or more kinds may be used.

[0050] When M1 is Bi, examples of the compound containing bismuth atoms include LiBiO2, Li3BiO3, Li4Bi2O5, Li 2.4 Al 0.2 BiO3, and Bi2O3. As the compound containing bismuth atoms, one kind may be used, or two or more kinds may be used.

[0051] When M1 is Ga or Sn, examples of the oxides include gallium oxide (Ga2O3), tin oxide (SnO2), etc., respectively.

[0052] When M1 is Hf, W or Mo, examples of the oxide include hafnium oxide (HfO2), tungsten oxide (WO3), molybdenum oxide (MoO3), etc. When M1 is Hf, W or Mo, in addition to the oxide, hafnium hydroxide (Hf(OH)4), tungstic acid (H2WO4), molybdic acid (H2MoO4) can also be used from the viewpoint of ease of reaction.

[0053] The compound containing element M2 is not particularly limited, but from the viewpoint of ease of handling, an inorganic compound is preferable, and examples thereof include the oxide of M2. As the compound containing element M2, one kind may be used, or two or more kinds may be used.

[0054] When M2 is B, examples of the compound containing a boron atom include LiBO2, LiB3O5, Li2B4O7, Li3B 11 O 18 , Li3BO3, Li3B7O 12 , Li4B2O5, Li6B4O9, Li 3-x5 B 1-x5 C x5 O3 (0 < x < 1), Li 4-x6 B 2-x6 C x6 O5 (0 < x6 < 2), Li 2.4 Al 0.2 BO3, Li 2.7 Al 0.1 BO3, B2O3, H3BO3. As the compound containing a boron atom, one kind may be used, or two or more kinds may be used.

[0055] When M2 is Si, examples of the compound containing a silicon atom include SiO2, Li2SiO3, Li2Si2O5, Li2Si3O7, Li4SiO4, Li6Si2O7, Li8SiO6. As the compound containing a silicon atom, one kind may be used, or two or more kinds may be used.

[0056] When M2 is Ge or Al, examples of the oxide include germanium oxide (GeO2), aluminum oxide (Al2O3), and the like.

[0057] The mixing ratio of the raw material substances may be, for example, an amount such that the content of each constituent element in the obtained present material 2 falls within the above range. In addition, in the firing process described later, since lithium atoms tend to flow out of the system, the compound containing the lithium atoms may be used in an excess of about 1 to 2%. Also, in the firing process described later, in order to suppress the generation of by-products, the compound containing the phosphorus atoms may be used in an excess of about 0.1 to 1%.

[0058] In the primary pulverization step, the raw material substances may be mixed in advance before pulverization, but it is preferable to mix (pulverize and mix) while pulverizing each raw material substance.

[0059] As the raw material substances, for example, a compound (a) containing lithium, tantalum, phosphorus, and oxygen as constituent elements may be used. At this time, a compound containing zirconium atoms, a compound containing element M1, and / or a compound containing element M2 may be further used.

[0060] ·Compound (a) Compound (a) is a compound containing lithium, tantalum, phosphorus, and oxygen as constituent elements, preferably an oxide containing these elements, and more preferably a lithium ion conductive compound containing these elements. One kind or two or more kinds of the compound (a) may be used.

[0061] Compound (a) preferably has a monoclinic crystal structure. Whether compound (a) has a monoclinic crystal structure can be specifically determined, for example, by performing Rietveld analysis on the X-ray diffraction (XRD) pattern of compound (a), specifically, by the method of the following examples.

[0062] As the compound (a), specifically, a compound (a1) containing lithium, tantalum, phosphorus, and oxygen as constituent elements, and further optionally containing one or more elements M1' selected from the group consisting of Bi, Nb, Zr, Ga, Sn, Hf, W, and Mo, a compound (a2) containing lithium, tantalum, phosphorus, and oxygen as constituent elements, and further optionally containing one or more elements M2 selected from the group consisting of B, Si, Al, and Ge, etc. may be mentioned. Among these, from the viewpoint of more effectively exhibiting the effects of the present invention, as the compound (a), a compound consisting only of lithium, tantalum, phosphorus, and oxygen as constituent elements is preferable, and LiTa2PO8 is more preferable.

[0063] The compound (a1) is preferably LiTa2PO8 or a compound in which part of Ta in LiTa2PO8 is substituted with the element M1', and preferably has a monoclinic crystal structure. Specifically, the compound (a1) has the composition formula Li 〔1+(5-a)x〕 Ta 2-x M1’ x PO8 [M1' is one or more elements selected from the group consisting of Bi, Nb, Zr, Ga, Sn, Hf, W, and Mo, 0.0 ≦ x < 1.0, and a is the average valence of M1'.] and is preferably a compound represented by.

[0064] In the obtained lithium ion conductive solid electrolyte (sintered body), from the viewpoint of increasing the lithium ion conductivity at the grain boundaries, M1' is more preferably Bi, Nb, Zr, W, Mo, further preferably Bi, Nb, Zr, W, and particularly preferably Bi, Nb, Zr.

[0065] The x is preferably 0.95 or less, more preferably 0.90 or less, further preferably 0.85 or less, more preferably 0.80 or less, and particularly preferably 0.75 or less. When x is in the above range, in the obtained lithium ion conductive solid electrolyte (sintered body), the lithium ion conductivity at the grain boundaries tends to increase.

[0066] Depending on the valence and content of M1', the amount of Li varies according to the average valence of M1' so that the charge neutrality of the aforementioned compound (a) can be achieved. The average valence represented by a can be determined as follows. When M1' is composed of two or more elements, a is calculated by weighted averaging using the valence of each element and the content of each element. For example, when M1' is composed of 80 atomic% Nb and 20 atomic% Zr, a is calculated as (+5×0.8)+(+4×0.2)=+4.8. Also, when M1' is composed of 80 atomic% Nb and 20 atomic% W, a is calculated as (+5×0.8)+(+6×0.2)=+5.2.

[0067] The compound (a2) is preferably LiTa2PO8 or a compound in which a part of P in LiTa2PO8 is substituted with element M2, and preferably has a monoclinic crystal structure. The compound (a2) is specifically a compound represented by the composition formula Li 〔1+(5-b)y〕 Ta2P 1-y M2 y O8 [M2 is one or more elements selected from the group consisting of B, Si, Al, and Ge, 0.0≦y<0.7, and b is the average valence of M2.] is preferably such a compound.

[0068] In the obtained lithium ion conductive solid electrolyte (sintered body), from the viewpoint of increasing the lithium ion conductivity at the grain boundaries, M2 is more preferably B, Si, Al, and even more preferably B, Si.

[0069] The y is preferably 0.65 or less, more preferably 0.60 or less, and even more preferably 0.55 or less. When y is in the above range, in the obtained lithium ion conductive solid electrolyte (sintered body), the total ion conductivity, which is the sum of the lithium ion conductivities in the grains and at the grain boundaries, tends to increase.

[0070] The average valence represented by b can be determined in the same manner as the method for calculating the average valence a described above.

[0071] The production method of the compound (a) is not particularly limited, and for example, conventionally known production methods such as solid-phase reaction and liquid-phase reaction can be adopted. Specifically, the production method includes, for example, a method including at least a one-step mixing process and a firing process respectively.

[0072] As the mixing process in the production method of the compound (a), for example, a process of mixing a compound containing a lithium atom (e.g., oxide, carbonate), a compound containing a tantalum atom (e.g., oxide, nitrate), a compound containing a phosphorus atom (e.g., ammonium salt), and, if necessary, a compound containing element M1’ (e.g., oxide), and / or a compound containing element M2 (e.g., oxide), which are raw materials, can be mentioned. Each of the above raw materials may be used alone or in combination of two or more.

[0073] Examples of the mixing method of the raw materials include a method of mixing using a roll rolling mill, a ball mill, a small-diameter ball mill (bead mill), a medium stirring mill, a jet mill, a mortar, an automatic kneading mortar, a tank breaker, a jet mill, etc.

[0074] The mixing ratio of the raw materials may be, for example, mixed in a stoichiometric ratio so as to obtain a desired composition of the compound (a). In addition, in the firing process in the production method of the compound (a) described later, since the lithium atom is likely to flow out of the system, the compound containing the lithium atom may be used in an excess of about 1 to 20%. Also, in the firing process in the production method of the compound (a) described later, in order to suppress the generation of by-products, the compound containing the phosphorus atom may be used in an excess of about 0.1 to 1%.

[0075] When mixing the raw materials, it may be mixed while heating if necessary, but usually it is carried out at room temperature. Also, the mixing of the raw materials may be carried out in the air, but it is preferably carried out in an atmosphere of nitrogen gas and / or argon gas with the oxygen gas content adjusted in the range of 0 to 20% by volume.

[0076] In the firing step in the method for producing the compound (a), the mixture obtained in the mixing step is fired. When the firing step is performed multiple times, a grinding step using a ball mill, a mortar, or the like may be provided for the purpose of grinding or reducing the particle size of the fired product obtained in the firing step. In particular, since the reaction rate of phase formation of the compound (a) is slow, reaction intermediates may be present in the first firing. In this case, it is preferable to perform the first firing, perform the grinding step, and then perform the firing step again.

[0077] The firing step in the method for producing the compound (a) may be performed in air, but it is preferably performed in an atmosphere of nitrogen gas and / or argon gas with the oxygen gas content adjusted in the range of 0 to 20% by volume.

[0078] The firing temperature in the firing step in the method for producing the compound (a) depends on the firing time, but is preferably 800°C or higher, more preferably 950°C or higher, preferably 1200°C or lower, more preferably 1100°C or lower, and even more preferably 1000°C or lower. When the firing temperature is within the above range, lithium atoms are less likely to flow out of the system, and a compound (a) with high ionic conductivity is likely to be obtained.

[0079] The firing time (total firing time when the firing step is performed several times) in the firing step in the method for producing the compound (a) depends on the firing temperature, but is preferably 1 hour or longer, more preferably 3 hours or longer, preferably 16 hours or shorter, and more preferably 12 hours or shorter. When the firing time is within the above range, lithium atoms are less likely to flow out of the system, and a compound with high ionic conductivity is likely to be obtained.

[0080] The fired product obtained after the firing step in the method for producing the compound (a) may absorb moisture or react with carbon dioxide and deteriorate when left in the air. Therefore, the fired product obtained after the firing step is preferably transferred and stored in a dehumidified inert gas atmosphere when the temperature reaches 200°C or lower during the cooling after the firing step.

[0081] <Firing process> In the manufacturing method of the present material 2, the firing process is a process of firing the primary pulverized material to obtain a primary fired product. The firing temperature in the firing process depends on the firing time, but is preferably 800 °C or higher, more preferably 950 °C or higher, preferably 1200 °C or lower, more preferably 1100 °C or lower, and even more preferably 1000 °C or lower. When the firing temperature is within this range, lithium atoms are less likely to flow out of the system, and a lithium-ion conductive solid electrolyte (sintered body) with high ionic conductivity is likely to be obtained. The firing time in the firing process (total firing time when the firing process is performed multiple times) depends on the firing temperature, but is preferably 1 hour or longer, more preferably 3 hours or longer, preferably 16 hours or shorter, and more preferably 12 hours or shorter.

[0082] <Secondary pulverization process> The secondary pulverization process is a process of pulverizing the primary fired product using a ball mill with zirconia balls having a diameter of more than 1 mm and less than 10 mm to obtain the present material 2. The diameter of the zirconia balls is preferably 1.5 mm or more, more preferably 2.0 mm or more, preferably 9.0 mm or less, and more preferably 8.0 mm or less. By using zirconia balls with a diameter within the above range, a lithium-ion conductive solid electrolyte (sintered body) with high relative density and excellent reliability can be obtained even with short-time sintering, and the lithium-ion conductive solid electrolyte (sintered body) can be manufactured by a method with excellent productivity.

[0083] The time of the secondary pulverization process is preferably 0.1 to 48 hours, more preferably 0.5 to 48 hours, from the viewpoint of easily obtaining the present material 2 with a half-value width and an average particle diameter (D50) within the above range.

[0084] During the secondary pulverization process, it may be pulverized and mixed while heating if necessary, but it is usually carried out at room temperature. Also, the secondary grinding process may be performed under the atmosphere, but it is preferably performed under an atmosphere of nitrogen gas and / or argon gas with the oxygen gas content adjusted in the range of 0 to 20% by volume.

[0085] ≪Lithium Ion Conductive Solid Electrolyte (Sintered Body)≫ The lithium ion conductive solid electrolyte (sintered body) (hereinafter also referred to as "this electrolyte 1") according to an embodiment of the present invention is has a crystal structure based on LiTa2PO8, is a lithium ion conductive solid electrolyte having at least lithium, tantalum, phosphorus, oxygen and zirconium as constituent elements, The relative density, which is the percentage of the ratio of the measured density calculated from the mass and volume of the lithium ion conductive solid electrolyte to the theoretical density of the lithium ion conductive solid electrolyte, is 75.0% or more. This electrolyte 1 is preferably an electrolyte obtained by using the above-mentioned this material 1 or 2, and more preferably a sintered body obtained by sintering this material 1 or 2.

[0086] This electrolyte 1 has an LTPO structure. The crystallinity of the LTPO structure of this electrolyte 1 (= crystal amount of LTPO × 100 / total crystal amount of all confirmed crystals) is preferably 60% or more, more preferably 70% or more, still more preferably 80% or more, and the upper limit is not particularly limited but less than 100%. When the crystallinity of the LTPO structure of this electrolyte 1 is within the above range, the ionic conductivity is high both in the crystal grains and at the grain boundaries, and as a result, the total ionic conductivity is high, and it tends to become a lithium ion conductive solid electrolyte (sintered body) with a high relative density.

[0087] The crystallinity of the LTPO structure in the electrolyte 1 can be calculated, for example, by performing Rietveld analysis on the XRD pattern of the electrolyte 1 using known analysis software RIETAN-FP (which can be obtained from the homepage of Fujio Izumi, "RIETAN-FP·VENUS system distribution file" (http: / / fujioizumi.verse.jp / download / download.html)).

[0088] The relative density of the electrolyte 1 is 75.0% or more, preferably 80% or more, particularly preferably 85% or more, and the upper limit is not particularly limited, but is 100%, and for example, it may be 99%. The electrolyte 1 having the relative density within the above range is excellent in balance between total ion conductivity and reliability.

[0089] The relative density is the percentage (measured density / theoretical density × 100) obtained by dividing the measured density calculated from the mass and volume of the electrolyte 1 by the theoretical density of the electrolyte 1, and specifically, it can be measured by the method described in the following examples. Note that the theoretical density of the electrolyte 1 is specifically calculated by weighted averaging using the theoretical density of the crystal structure constituting the electrolyte 1 and the content of the crystal structure. For example, when the electrolyte 1 has a crystal structure 1 with a content of h% and a crystal structure 2 with a content of k%, the theoretical density of the electrolyte can be calculated as (theoretical density of crystal structure 1 × h + theoretical density of crystal structure 2 × k) / 100. For example, when crystal structures based on LiTa3O8, Ta2O5, TaPO5, etc. are confirmed, the theoretical density can be calculated by weighted averaging the theoretical densities of these crystal structures and the theoretical density of the LTPO structure using the content of each crystal structure obtained by Rietveld analysis. The content of each crystal structure can be obtained by Rietveld analysis.

[0090] The constituent elements of the electrolyte 1 are not particularly limited as long as they include lithium, tantalum, phosphorus, oxygen, and zirconium. However, from the viewpoint of being able to lower the sintering temperature when obtaining a lithium ion conductive solid electrolyte (sintered body) having sufficient ionic conductivity and relative density, it is preferable to contain a boron element, and it may contain one or more elements Ma selected from the group consisting of Nb, Ga, Sn, Hf, Bi, W, Mo, Si, Al, and Ge.

[0091] From the viewpoint of obtaining a lithium ion conductive solid electrolyte (sintered body) having higher lithium ion conductivity, the content of lithium element in the electrolyte 1 is preferably 5.0 atomic% or more, more preferably 9.0 atomic% or more, preferably 20.0 atomic% or less, and more preferably 15.0 atomic% or less.

[0092] Note that the content of each element in the electrolyte 1 can be measured by the same method as the content of each element in the material 1.

[0093] From the viewpoint of obtaining a lithium ion conductive solid electrolyte (sintered body) having higher lithium ion conductivity, the content of tantalum element in the electrolyte 1 is preferably 10.6 atomic% or more, more preferably 11.0 atomic% or more, preferably 16.6 atomic% or less, and more preferably 16.0 atomic% or less.

[0094] From the viewpoint of obtaining a lithium ion conductive solid electrolyte (sintered body) having higher lithium ion conductivity, the content of phosphorus element in the electrolyte 1 is preferably 5.3 atomic% or more, more preferably 5.8 atomic% or more, preferably 8.3 atomic% or less, more preferably less than 8.3 atomic%, and still more preferably 8.0 atomic% or less.

[0095] From the viewpoint of obtaining a lithium ion conductive solid electrolyte (sintered body) having a high relative density and excellent reliability even with short-time sintering, the content of zirconium element (content of zirconium) in the electrolyte 1 is more than 0 atomic% and 3.0 atomic% or less, preferably 0.1 to 2.5 atomic%, and more preferably 0.1 to 2.0 atomic%.

[0096] When the electrolyte 1 contains a boron element, the content of the boron element in the electrolyte 1 is preferably 0.1 atomic % or more, more preferably 0.5 atomic % or more, from the viewpoint that the sintering temperature for obtaining a lithium ion conductive solid electrolyte (sintered body) having sufficient ionic conductivity and relative density can be lowered, and is preferably 5.0 atomic % or less, more preferably 3.0 atomic % or less.

[0097] When the electrolyte 1 contains the element Ma, the content of each of the element Ma in the electrolyte 1 is preferably 0.1 to 5.0 atomic %, more preferably 0.1 to 3.0 atomic %, from the viewpoint that the sintering temperature for obtaining a lithium ion conductive solid electrolyte (sintered body) having sufficient ionic conductivity and relative density tends to be lowered.

[0098] The total ionic conductivity of the electrolyte 1 is preferably 2.00×10 -4 S·cm -1 or more, more preferably 3.00×10 -4 S·cm -1 or more. The electrolyte 1 having the total ionic conductivity within the above range is preferable because it has sufficient ionic conductivity.

[0099] Specifically, the total ionic conductivity can be measured by the following method. By forming a gold layer on both surfaces of the electrolyte 1 (sintered body) using a sputtering machine, a measurement pellet for evaluating ionic conductivity is obtained, and the obtained measurement pellet is held in a thermostatic bath at 25°C for 2 hours before measurement. Then, at 25°C, using an impedance analyzer (manufactured by Solartron Analytical, model number: 1260A), AC impedance measurement is performed in the range of a frequency of 1 Hz to 10 MHz under the condition of an amplitude of 25 mV. The obtained impedance spectrum is fitted with an equivalent circuit using the equivalent circuit analysis software ZView attached to the apparatus to obtain the respective lithium ion conductivities in the crystal grains and at the grain boundaries, and the total conductivity is calculated by summing these.

[0100] ≪Method for Producing Lithium Ion Conductive Solid Electrolyte≫ A method for producing a lithium ion conductive solid electrolyte according to an embodiment of the present invention (hereinafter also referred to as "the production method of the present electrolyte 2") is as follows: It has a sintering step of sintering the present material 2 obtained by the production method of the present material 2 to obtain a lithium ion conductive solid electrolyte (hereinafter also referred to as "the present electrolyte 2"). The relative density, which is the percentage of the ratio of the measured density calculated from the mass and volume of the present electrolyte 2 to the theoretical density of the present electrolyte 2, is 75.0% or more.

[0101] It is preferable that the present electrolyte 2 is the present electrolyte 1. It is preferable that the present electrolyte 2 has an LTPO structure similar to that of the present electrolyte 1. The relative density, the types and contents of the constituent elements, and the total ionic conductivity of the present electrolyte 2 are the same as those described in the column of the present electrolyte 1.

[0102] <Sintering Step> The sintering step is a step of sintering the present material 2 to obtain the present electrolyte 2.

[0103] The sintering temperature in the sintering step is preferably 500°C or higher, more preferably 600°C or higher, still more preferably 700°C or higher, and preferably 1200°C or lower, more preferably 1000°C or lower, still more preferably 900°C or lower. Since the present material 2 is used, a sintered body with sufficient ionic conductivity can be obtained even when sintered at such a low temperature.

[0104] The sintering time in the sintering step depends on the sintering temperature, but is preferably 0.5 hours or more, more preferably 1 hour or more, and preferably less than 12 hours, more preferably 10 hours or less. When using this Material 2, even if sintering is performed in such a short time, a lithium-ion conductive solid electrolyte (sintered body) with a high relative density and excellent reliability can be obtained. Further, since a desired lithium-ion conductive solid electrolyte (sintered body) can be obtained even with such short-time sintering, the lithium-ion conductive solid electrolyte (sintered body) can be manufactured by a method excellent in productivity and economy.

[0105] The sintering may be performed in the air, but it is preferably performed in an atmosphere of nitrogen gas and / or argon gas with the oxygen gas content adjusted in the range of 0 to 20% by volume. Further, the sintering may be performed in a reducing gas atmosphere such as a nitrogen-hydrogen mixed gas containing a reducing gas such as hydrogen gas. Examples of the ratio of hydrogen gas contained in the nitrogen-hydrogen mixed gas include 1 to 10% by volume. As the reducing gas, in addition to hydrogen gas, ammonia gas, carbon monoxide gas, etc. may be used.

[0106] In the sintering step, from the viewpoint of easily obtaining a lithium-ion conductive solid electrolyte (sintered body) with higher ionic conductivity, it is preferable to sinter a molded body formed from this Material 2, and it is more preferable to sinter a molded body obtained by press-molding this Material 2. The pressure during press-molding of this Material 2 is not particularly limited, but it is preferably 50 MPa or more, more preferably 100 MPa or more, preferably 500 MPa or less, and more preferably 400 MPa or less. The shape of the molded body obtained by press-molding this Material 2 is not particularly limited, but it is preferably a shape according to the use of the lithium-ion conductive solid electrolyte (sintered body) obtained by sintering the molded body, such as pellet shape, coin shape, film shape, etc.

[0107] In addition, when manufacturing this Electrolyte 2, other components other than this Material 2 may be used. Examples of such other components include conventionally known materials used for the solid electrolyte of all-solid-state batteries. For example, as lithium-ion conductive compounds, lithium-ion conductive materials having structures such as NASICON type and LISICON type are included. Each of the other components may be used alone or in combination of two or more. The amount of the other component used is preferably 50% by mass or less, more preferably 30% by mass or less, based on 100% by mass in total with the present material 2, and it is preferable not to use the other component.

[0108] ≪All-solid-state battery≫ The all-solid-state battery according to one embodiment of the present invention (hereinafter also referred to as "the present battery") includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a solid electrolyte layer between the positive electrode and the negative electrode, and the solid electrolyte layer contains the present electrolyte 1 or 2. The present battery may be a primary battery or a secondary battery, but from the viewpoint of more effectively exhibiting the effects of the present invention, etc., it is preferably a secondary battery, and more preferably a lithium-ion secondary battery. The structure of the present battery is not particularly limited as long as it includes a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode, and may be any of a so-called thin film type, laminated type, and bulk type.

[0109] <Solid electrolyte layer> The solid electrolyte layer is not particularly limited as long as it contains the present electrolyte 1 or 2, and may contain, if necessary, conventionally known additives used in the solid electrolyte layer of the all-solid-state battery, but it is preferably composed of only the present electrolyte 1 or 2. The thickness of the solid electrolyte layer may be appropriately selected according to the structure of the battery to be formed (such as thin film type), but is preferably 50 nm or more, more preferably 100 nm or more, and preferably 1000 μm or less, more preferably 100 μm or less.

[0110] <Positive electrode> The positive electrode is not particularly limited as long as it has a positive electrode active material, but preferably includes a positive electrode current collector and a positive electrode active material layer.

[0111] [Positive electrode active material layer] The positive electrode active material layer is not particularly limited as long as it contains a positive electrode active material, but preferably contains a positive electrode active material and a solid electrolyte, and may further contain additives such as a conductive aid and a sintering aid. The thickness of the positive electrode active material layer may be appropriately selected according to the structure of the battery to be formed (such as thin film type), but is preferably 10 μm or more, more preferably 30 μm or more, still more preferably 50 μm or more, and preferably 200 μm or less, more preferably 150 μm or less, still more preferably 100 μm or less.

[0112] · Positive electrode active material Examples of the positive electrode active material include lithium cobalt oxide, lithium nickel cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium manganese oxide, lithium manganese - based spinel, lithium manganese nickel oxide, lithium manganese aluminum oxide, lithium manganese magnesium oxide, lithium manganese cobalt oxide, lithium manganese iron oxide, lithium manganese zinc oxide, lithium chromium nickel manganese oxide, lithium chromium manganese oxide, lithium titanate, lithium metal phosphate, transition metal oxide, titanium sulfide, graphite, hard carbon, transition metal - containing lithium nitride, silicon oxide, lithium silicate, lithium metal, lithium alloy, Li - containing solid solution, and lithium - storage intermetallic compound. Among these, lithium nickel cobalt manganese oxide, lithium nickel cobalt oxide, and lithium cobalt oxide are preferable, and lithium nickel cobalt manganese oxide is more preferable, because they have good affinity with the solid electrolyte, excellent balance of macro - conductivity, micro - conductivity, and ion conductivity, high average potential, and can increase the energy density and battery capacity in terms of the balance between specific capacity and stability. Further, the surface of the positive electrode active material may be coated with lithium niobate, lithium phosphate, lithium borate, etc., which are ion - conductive oxides. The positive electrode active material used in the positive electrode active material layer may be one type or two or more types.

[0113] Preferable examples of the positive electrode active material include LiM3PO4 [M3 is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, Ti, and V, or two elements of V and O.], LiM5VO4 [M5 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, and Ti.], Li2M6P2O7 [M6 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, Ti, and V, or two elements of V and O.], LiVP2O7, Li x7 V y7 M7 z7 [2 ≤ x7 ≤ 4, 1 ≤ y7 ≤ 3, 0 ≤ z7 ≤ 1, 1 ≤ y7 + z7 ≤ 3, M7 is one or more elements selected from the group consisting of Ti, Ge, Al, Ga, and Zr.], Li 1+x8 Al x8 M8 2-x8 (PO4)3 [0 ≤ x8 ≤ 0.8, M8 is one or more elements selected from the group consisting of Ti and Ge.], LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiCoO2, LiNiO2, LiMn2O4, Li2CoP2O7, Li3V2(PO4)3, Li3Fe2(PO4)3, LiNi 0.5 Mn 1.5 O4, Li4Ti5O 12 can also be mentioned.

[0114] The positive electrode active material is preferably particulate. The 50% diameter in its volume-based particle size distribution is preferably 0.1 μm or more, more preferably 0.3 μm or more, still more preferably 0.4 μm or more, and particularly preferably 0.5 μm or more, and is preferably 30 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less, and particularly preferably 3 μm or less. Also, the ratio of the length of the major axis to the length of the minor axis (length of major axis / length of minor axis), that is, the aspect ratio of the positive electrode active material is preferably less than 3, more preferably less than 2.

[0115] The positive electrode active material may form secondary particles. In that case, the 50% diameter in the number-based particle size distribution of the primary particles is preferably 0.1 μm or more, more preferably 0.3 μm or more, still more preferably 0.4 μm or more, particularly preferably 0.5 μm or more, and preferably 20 μm or less, more preferably 15 μm or less, still more preferably 10 μm or less, particularly preferably 2 μm or less.

[0116] The content of the positive electrode active material in the positive electrode active material layer is preferably 20% by mass or more, more preferably 30% by mass or more, and preferably 80% by mass or less, more preferably 70% by mass or less. When the content of the positive electrode active material is within the above range, the positive electrode active material functions suitably, and there is a tendency that a battery with a high energy density can be easily obtained.

[0117] ·Solid electrolyte The solid electrolyte that can be used for the positive electrode active material layer is not particularly limited, and a conventionally known solid electrolyte can be used. However, from the viewpoint of more effectively exhibiting the effects of the present invention, it is preferable to use the present electrolyte 1 or 2. The solid electrolyte used for the positive electrode active material layer may be one kind or two or more kinds.

[0118] ·Additive Preferable examples of the conductive auxiliary agent include metal materials such as Ag, Au, Pd, Pt, Cu, and Sn, and carbon materials such as acetylene black, ketjen black, carbon nanotubes, and carbon nanofibers. As the sintering auxiliary agent, a compound containing a boron atom, a compound containing a niobium atom, a compound containing a bismuth atom, and a compound containing a silicon atom are preferable. Each of the additives used for the positive electrode active material layer may be one kind or two or more kinds.

[0119] ·Positive electrode current collector The positive current collector is not particularly limited as long as its material conducts electrons without undergoing an electrochemical reaction. Examples of the material of the positive current collector include simple metals such as copper, aluminum, and iron, alloys containing these metals, and conductive metal oxides such as antimony-doped tin oxide (ATO) and indium tin oxide (ITO). In addition, as the positive current collector, a current collector provided with a conductive adhesive layer on the surface of a conductor can also be used. Examples of the conductive adhesive layer include a layer containing a granular conductive material, a fibrous conductive material, or the like.

[0120] <Negative electrode> The negative electrode is not particularly limited as long as it has a negative electrode active material, but preferably, a negative electrode having a negative electrode current collector and a negative electrode active material layer can be mentioned.

[0121] [Negative electrode active material layer] The negative electrode active material layer is not particularly limited as long as it contains a negative electrode active material, but preferably contains a negative electrode active material and a solid electrolyte, and may further contain additives such as a conductive aid and a sintering aid. The thickness of the negative electrode active material layer may be appropriately selected according to the structure of the battery to be formed (such as a thin film type), but is preferably 10 μm or more, more preferably 30 μm or more, still more preferably 50 μm or more, and preferably 200 μm or less, more preferably 150 μm or less, still more preferably 100 μm or less.

[0122] ·Negative electrode active material Examples of the negative electrode active material include lithium alloys, metal oxides, graphite, hard carbon, soft carbon, silicon, silicon alloys, silicon oxides SiO n (0 < n ≤ 2), silicon / carbon composites, composites in which silicon is encapsulated in the pores of porous carbon, lithium titanate, and graphite coated with lithium titanate. Among these, composites in which silicon / carbon composites or silicon domains are encapsulated within the pores of porous carbon are preferable because they have a high specific capacity and can increase the energy density and battery capacity. More preferably, it is a composite in which a silicon domain is encapsulated within the pores of porous carbon, which is excellent in relaxing the volume expansion associated with the lithium storage / discharge of silicon and can maintain a good balance of macro conductivity, micro conductivity, and ionic conductivity. Particularly preferably, it is a composite in which a silicon domain is encapsulated within the pores of porous carbon, where the silicon domain is amorphous, the size of the silicon domain is 10 nm or less, and pores derived from porous carbon are present in the vicinity of the silicon domain.

[0123] Preferable examples of the negative electrode active material include LiM3PO4 [M3 is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, Ti, and V, or two elements of V and O.], LiM5VO4 [M5 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, and Ti.], Li2M6P2O7 [M6 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, Ti, and V, or two elements of V and O.], LiVP2O7, Li x7 V y7 M7 z7 [2 ≤ x7 ≤ 4, 1 ≤ y7 ≤ 3, 0 ≤ z7 ≤ 1, 1 ≤ y7 + z7 ≤ 3, M7 is one or more elements selected from the group consisting of Ti, Ge, Al, Ga, and Zr.], Li 1+x8 Al x8 M8 2-x8 (PO4)3 [0 ≤ x8 ≤ 0.8, M8 is one or more elements selected from the group consisting of Ti and Ge.], (Li 3-a9x9+(5-b9)y9 M9 x9 )(V 1-y9 M10 y9 )O4 [M9 is one or more elements selected from the group consisting of Mg, Al, Ga, and Zn, M10 is one or more elements selected from the group consisting of Zn, Al, Ga, Si, Ge, P, and Ti, 0 ≤ x9 ≤ 1.0, 0 ≤ y9 ≤ 0.6, a9 is the average valence of M9, and b9 is the average valence of M10.], LiNb2O7, Li4Ti5O 12, Li4Ti5PO 12 , TiO2, LiSi, graphite can also be mentioned.

[0124] The negative electrode active material is preferably particulate. The 50% diameter in the volume-based particle size distribution, the aspect ratio, and the 50% diameter in the number-based particle size distribution of the primary particles when the negative electrode active material forms secondary particles are preferably in the same range as the positive electrode active material.

[0125] The content of the negative electrode active material in the negative electrode active material layer is preferably 20% by mass or more, more preferably 30% by mass or more, preferably 80% by mass or less, and more preferably 70% by mass or less. When the content of the negative electrode active material is within the above range, the negative electrode active material functions suitably, and there is a tendency that a battery with high energy density can be easily obtained.

[0126] · Solid electrolyte The solid electrolyte that can be used for the negative electrode active material layer is not particularly limited, and conventionally known solid electrolytes can be used. However, from the viewpoint of more exerting the effects of the present invention, it is preferable to use the present electrolyte 1 or 2. The solid electrolyte used for the negative electrode active material layer may be one kind or two or more kinds.

[0127] · Additive Preferable examples of the conductive assistant include metal materials such as Ag, Au, Pd, Pt, Cu, Sn, and carbon materials such as acetylene black, ketjen black, carbon nanotubes, and carbon nanofibers. As the sintering assistant, a compound containing a boron atom, a compound containing a niobium atom, a compound containing a bismuth atom, and a compound containing a silicon atom are preferable. Each of the additives used for the negative electrode active material layer may be one kind or two or more kinds.

[0128] · Negative electrode current collector As the negative electrode current collector, the same current collector as the positive electrode current collector can be used.

[0129] <Method for manufacturing all-solid-state battery> An all-solid-state battery can be formed, for example, by a known powder molding method. For example, a positive electrode current collector, a powder for a positive electrode active material layer, a powder for a solid electrolyte layer, a powder for a negative electrode active material layer, and a negative electrode current collector are stacked in this order, and they are simultaneously powder-molded, whereby the formation of each layer of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer and the connection between each of the positive electrode current collector, the positive electrode active material layer, the solid electrolyte layer, the negative electrode active material layer, and the negative electrode current collector can be performed simultaneously.

[0130] During this powder molding, it is preferable to sinter at a temperature similar to the sintering temperature in the sintering step while applying a pressure comparable to the pressure when press-molding the main material in the sintering step. According to one embodiment of the present invention, even when the sintering temperature during the production of this all-solid-state battery is performed at a low temperature for a short time, an all-solid-state battery having sufficient ionic conductivity can be obtained. Therefore, while suppressing decomposition and alteration of other materials such as the positive electrode and negative electrode materials, an all-solid-state battery can be produced with excellent economic efficiency and less equipment.

[0131] Each layer of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer may be powder-molded respectively. However, when manufacturing an all-solid-state battery using the obtained layers, it is preferable to press and sinter each layer.

[0132] Also, an all-solid-state battery can be manufactured, for example, by the following method. By appropriately mixing a solvent, a resin, etc. with a material for forming a positive electrode active material layer, a material for forming a solid electrolyte layer, and a material for forming a negative electrode active material layer, a paste for forming each layer is prepared. The paste is applied onto a base sheet and dried to produce a green sheet for a positive electrode active material layer, a green sheet for a solid electrolyte layer, and a green sheet for a negative electrode active material layer. Next, the green sheet for a positive electrode active material layer, the green sheet for a solid electrolyte layer, and the green sheet for a negative electrode active material layer from which the base sheet has been peeled are sequentially laminated, thermocompression-bonded at a predetermined pressure, and then enclosed in a container and pressurized by hot isostatic pressing, cold isostatic pressing, hydrostatic pressing, etc. to produce a laminated structure.

[0133] Thereafter, if necessary, the laminated structure is degreased at a predetermined temperature and then sintered to produce a laminated sintered body. The sintering temperature in this sintering process is preferably the same temperature as the sintering temperature in the sintering step.

[0134] Next, if necessary, a positive electrode current collector and a negative electrode current collector are formed on both main surfaces of the laminated sintered body by sputtering, vacuum deposition, application of a metal paste, dipping, or the like, whereby a all-solid-state battery can also be produced.

Example

[0135] Hereinafter, an embodiment of the present invention will be specifically described based on examples. Note that the present invention is not limited to these examples.

[0136] [Comparative Example 1] ·Primary pulverization process Lithium carbonate (Li2CO3) (manufactured by Merck Sigma-Aldrich, purity 99.0% or more), tantalum pentoxide (Ta2O5) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9%), boric acid (H3BO3) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.5% or more), and diammonium hydrogen phosphate ((NH4)2HPO4) (manufactured by Merck Sigma-Aldrich, purity 98% or more) were weighed so that the atomic ratio of lithium, tantalum, boron, and phosphorus (Li:Ta:B:P) of the resulting lithium-ion conductive solid electrolyte was 1.15:1.90:0.10:0.95. Further, considering the lithium atoms that flow out of the system in the firing process, lithium carbonate was weighed so that the amount was 1.05 times the atomic weight of lithium of the resulting lithium-ion conductive solid electrolyte. Further, in order to suppress the generation of by-products in the firing process, diammonium hydrogen phosphate was weighed so that the amount was 1.06 times the atomic weight of phosphorus of the resulting lithium-ion conductive solid electrolyte. At this time, the remaining elements to be weighed were weighed on the assumption that they do not flow out of the system at the firing temperature. To each of the weighed raw material powders, an appropriate amount of toluene was added, and the mixture was pulverized and mixed for 2 hours using a zirconia ball mill with zirconia balls (manufactured by Nikkato Corporation, diameter 1 mm) to obtain a primary pulverized product.

[0137] ·Firing process The obtained primary pulverized product was placed in an alumina boat, and using a rotary firing furnace (manufactured by Motoyama Co., Ltd.), the temperature was raised to 1000 °C at a rate of 10 °C / min under an atmosphere of air (flow rate: 100 mL / min), and firing was performed at this temperature for 4 hours to obtain a primary fired product.

[0138] ·Secondary pulverization process An appropriate amount of toluene was added to the obtained primary fired product, and the mixture was pulverized and mixed for 30 minutes (350 rpm) using a zirconia ball mill with zirconia balls (manufactured by Nikkato Corporation, diameter 1 mm) to obtain a secondary pulverized product (lithium ion conductive solid electrolyte material).

[0139] Using a tablet molding machine, a pressure of 40 MPa was applied to the obtained secondary pulverized product by hydraulic pressing to form a disk-shaped molded body with a diameter of 10 mm and a thickness of 1 mm. Then, a pellet was produced by applying a pressure of 300 MPa to the disk-shaped molded body by CIP (cold isostatic pressing).

[0140] ·Sintering process The obtained pellet was placed in an alumina boat, and using a rotary firing furnace (manufactured by Motoyama Co., Ltd.), the temperature was raised to 900 °C at a rate of 10 °C / min under an atmosphere of air (flow rate: 100 mL / min), and sintering was performed at this temperature for 2 hours to obtain a sintered body. After the obtained sintered body was cooled to room temperature, it was taken out from the rotary firing furnace and transferred to a dehumidified nitrogen gas atmosphere for storage to obtain a lithium ion conductive solid electrolyte. The atomic ratio of lithium, tantalum, boron, phosphorus, and oxygen (Li:Ta:B:P:O) of the obtained lithium ion conductive solid electrolyte was 1.15:1.90:0.10:0.95:8.0.

[0141] [Example 1] Instead of the zirconia balls used in the secondary pulverization step in Comparative Example 1, zirconia balls with a diameter of 2 mm were used, and in the same manner as in Comparative Example 1, a secondary pulverized product (lithium ion conductive solid electrolyte material) and a lithium ion conductive solid electrolyte were obtained.

[0142] [Example 2] Instead of the zirconia balls used in the secondary pulverization step in Comparative Example 1, zirconia balls with a diameter of 3 mm were used, and in the same manner as in Comparative Example 1, a secondary pulverized product (lithium ion conductive solid electrolyte material) and a lithium ion conductive solid electrolyte were obtained.

[0143] [Example 3] Instead of the zirconia balls used in the secondary pulverization step in Comparative Example 1, zirconia balls with a diameter of 5 mm were used, and in the same manner as in Comparative Example 1, a secondary pulverized product (lithium ion conductive solid electrolyte material) and a lithium ion conductive solid electrolyte were obtained.

[0144] [Comparative Example 2] Instead of the zirconia balls used in the secondary pulverization step in Comparative Example 1, zirconia balls with a diameter of 10 mm were used, and in the same manner as in Comparative Example 1, a secondary pulverized product (lithium ion conductive solid electrolyte material) and a lithium ion conductive solid electrolyte were obtained.

[0145] <X-ray Diffraction (XRD)> The obtained solid electrolyte was pulverized for 30 minutes using an agate mortar to obtain a powder for XRD measurement. Using a powder X-ray diffractometer PANalytical MPD (manufactured by Spectris Co., Ltd.), the obtained powder for XRD measurement was subjected to X-ray diffraction measurement (Cu-Kα ray (output: 45 kV, 40 mA), diffraction angle 2θ = 10 to 50°, step width: 0.013°, incident side Soller slit: 0.04 rad, incident side anti-scatter slit: 2°, receiving side Soller slit: 0.04 rad, receiving side anti-scatter slit: 5 mm) to obtain an X-ray diffraction (XRD) pattern. The obtained XRD pattern was subjected to Rietveld analysis using known analysis software RIETAN-FP (which can be obtained from the homepage of its author Fujio Izumi, "RIETAN-FP·VENUS system distribution file" (http: / / fujioizumi.verse.jp / download / download.html)) to confirm the crystal structure and the content of each crystal structure.

[0146] The full width at half maximum (hereinafter also referred to as "XRD full width at half maximum") of the diffraction peak having the maximum intensity observed in the range of 20° ≤ 2θ ≤ 40°, which is derived from the crystal structure based on LiTa2PO8, was confirmed. The results are shown in Table 1. The XRD patterns of the lithium ion conductive solid electrolyte materials obtained in Example 1 and Comparative Example 1 are shown in FIG. 1. Furthermore, in the XRD patterns of the solid electrolyte materials obtained in Comparative Example 1 and Example 1, the fitting results of the diffraction peaks having the maximum intensity that can be confirmed in the range of 20° ≤ 2θ ≤ 40° using the above-mentioned software are shown in FIGS. 2 and 3, respectively.

[0147] <Relative density> The mass of the prepared lithium ion conductive solid electrolyte was measured using an electronic balance. Next, the volume was measured from the actual dimensions of the lithium ion conductive solid electrolyte using a micrometer. By dividing the measured mass by the volume, the density (measured value) of the lithium ion conductive solid electrolyte was calculated, and the relative density (%) which is the percentage of the ratio of the measured value to the theoretical value of the density of the lithium ion conductive solid electrolyte (measured value of density / theoretical value of density × 100) was determined. The results are shown in Table 1. The theoretical density of the lithium-ion conductive solid electrolyte was taken as the theoretical density of the crystal structure based on LiTa2PO8 that constitutes the lithium-ion conductive solid electrolyte.

[0148] <Content of zirconium (Zr content)> Approximately 20 mg of the prepared lithium-ion conductive solid electrolyte material was precisely weighed into a platinum crucible, 1 g of sodium potassium carbonate and 0.5 g of boric acid were added, and it was melted with a gas burner for 15 minutes. After washing the outside of the crucible, the melt together with the crucible was warm-soaked with 3 mL of 10% citric acid solution and 2 mL of 30% hydrogen peroxide solution. After adding 3 mL of dilute sulfuric acid, the sample was dissolved by gently heating. Since there was a residue in the crucible, it was washed with hydrofluoric acid + sulfuric acid + hydrogen peroxide solution, and after adding internal standard elements (Co, Zn), the volume was made up to 100 mL to obtain a sample solution. Using the obtained sample solution, the Zr content in the lithium-ion conductive solid electrolyte material was measured twice using ICP-AES (Agilent 5110: manufactured by Agilent technologies), and the average value of the two measurement values was taken as the analysis result. The results are shown in Table 1.

[0149]

Table 1

[0150] From Table 1, it can be seen that the lithium-ion conductive solid electrolyte produced by sintering the lithium-ion conductive solid electrolyte material obtained by the production method of this Material 2 has a high relative density and is considered to be excellent in reliability.

Claims

1. LiTa 2 PO 8 A method for manufacturing a lithium ion conductive solid electrolyte material having a crystal structure based on [LiTa(PO₄)₂] and having at least lithium, tantalum, phosphorus, oxygen, and zirconium as constituent elements, comprising: A primary pulverization step of pulverizing a raw material substance to obtain a primary pulverized product, a firing step of firing the primary pulverized product to obtain a primary fired product, and a secondary pulverization step of pulverizing the primary fired product using a ball mill to obtain a lithium ion conductive solid electrolyte material; In the secondary pulverization step, using zirconia balls having a diameter of 1.5 mm or more and 9.0 mm or less; In X-ray diffraction, the half-value width of the diffraction peak having the maximum intensity observed in the range of 20° ≤ 2θ ≤ 40°, which is derived from the crystal structure based on [LiTa(PO₄)₂] of the lithium ion conductive solid electrolyte material, is 0.160° or more; 2 PO 8 A method for manufacturing a lithium ion conductive solid electrolyte material.

2. The method for manufacturing a lithium ion conductive solid electrolyte material according to claim 1, wherein the raw material substance does not contain zirconium.

3. A sintering step of sintering the lithium ion conductive solid electrolyte material obtained by the method for manufacturing a lithium ion conductive solid electrolyte material according to claim 1 or 2 to obtain a lithium ion conductive solid electrolyte; The relative density, which is the percentage of the ratio of the measured density calculated from the mass and volume of the lithium ion conductive solid electrolyte to the theoretical density of the lithium ion conductive solid electrolyte, is 75.0% or more; A method for manufacturing a lithium ion conductive solid electrolyte.

4. LiTa 2 PO 8 Having a crystal structure based on [LiTa(PO₄)₂]; Having at least lithium, tantalum, phosphorus, oxygen, and zirconium as constituent elements; In X-ray diffraction, the full width at half maximum of the diffraction peak having the maximum intensity observed in the range of 20° ≤ 2θ ≤ 40° is 0.160° or more, and the zirconium content is more than 0 atomic % and 3.0 atomic % or less, A lithium ion conductive solid electrolyte material.

5. The lithium ion conductive solid electrolyte material according to claim 4, further having a boron element.

6. LiTa 2 PO 8 having a crystal structure based on, A lithium ion conductive solid electrolyte having at least lithium, tantalum, phosphorus, oxygen, and zirconium as constituent elements, The relative density, which is the percentage of the ratio of the measured density calculated from the mass and volume of the lithium ion conductive solid electrolyte to the theoretical density of the lithium ion conductive solid electrolyte, is 93.2% or more, A lithium ion conductive solid electrolyte.

7. The lithium ion conductive solid electrolyte according to claim 6, further having a boron element.

8. A positive electrode having a positive electrode active material, A negative electrode having a negative electrode active material, A solid electrolyte layer between the positive electrode and the negative electrode, and including, The solid electrolyte layer includes the lithium ion conductive solid electrolyte according to claim 6 or 7, An all-solid-state battery.

9. The positive electrode active material is LiM3PO 4 、LiM5VO 4 、Li 2 M6P 2 O 7 、LiVPO 2 O 7 、Li x7 V y7 M7 z7 、Li 1+x8 Al x8M8 2-x8 (PO 4 ) 3 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , Li 2 CoP 2 O 7 , Li 3 V 2 (PO 4 ) 3 , Li 3 Fe 2 (PO 4 ) 3 , LiNi 0.5 Mn 1.5 O 4 and Li 4 Ti 5 O 12 and contains one or more compounds selected from the group consisting of M3 is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, Ti and V, or the two elements V and O, M5 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al and Ti, M6 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, Ti and V, or the two elements V and O, 2 ≤ x7 ≤ 4, 1 ≤ y7 ≤ 3, 0 ≤ z7 ≤ 1, 1 ≤ y7 + z7 ≤ 3, M7 is one or more elements selected from the group consisting of Ti, Ge, Al, Ga and Zr, 0 ≤ x8 ≤ 0.8, M8 is one or more elements selected from the group consisting of Ti and Ge, The all-solid-state battery according to claim 8.

10. The negative electrode active material is LiM3PO 4 , LiM5VO 4 , Li 2 M6P 2 O 7 , LiVP 2 O 7, Li x7 V y7 M7 z7 , Li 1+x8 Al x8 M8 2-x8 (PO 4 ) 3 , (Li 3-a9x9+(5-b9)y9 M9 x9 ) (V 1-y9 M10 y9 ) O 4 , LiNb 2 O 7 , Li 4 Ti 5 O 12 , Li 4 Ti 5 PO 12 , TiO 2 , and contains one or more compounds selected from the group consisting of LiSi and graphite, M3 is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, Ti, and V, or two elements of V and O, M5 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, and Ti, M6 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, Ti, and V, or two elements of V and O, 2 ≤ x7 ≤ 4, 1 ≤ y7 ≤ 3, 0 ≤ z7 ≤ 1, 1 ≤ y7 + z7 ≤ 3, M7 is one or more elements selected from the group consisting of Ti, Ge, Al, Ga, and Zr, 0 ≤ x8 ≤ 0.8, M8 is one or more elements selected from the group consisting of Ti and Ge, M9 is one or more elements selected from the group consisting of Mg, Al, Ga, and Zn, M10 is one or more elements selected from the group consisting of Zn, Al, Ga, Si, Ge, P, and Ti, 0 ≤ x9 ≤ 1.0, 0 ≤ y9 ≤ 0.6, a9 is the average valence of M9, and b9 is the average valence of M10, The all-solid-state battery according to claim 8.

11. A positive electrode having a positive electrode active material, A negative electrode having a negative electrode active material, A solid electrolyte layer is provided between the positive electrode and the negative electrode, and includes the positive electrode, the negative electrode, and the solid electrolyte layer include the lithium ion conductive solid electrolyte according to claim 6 or 7, all-solid-state battery.

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