Sintered body, solid electrolyte thereof, all-solid-state lithium ion battery thereof, and manufacturing method thereof

Abstract

To provide a sintered body having a cubic garnet type structure lithium metal oxide sintered at a temperature of 900°C or lower capable of being integrally sintered with an electrode and excellent in ionic conductivity, a solid electrolyte using the sintered body, an all-solid-state lithium-ion battery, and a method for manufacturing the sintered body, the solid electrolyte, and the all-solid-state lithium-ion battery.SOLUTION: Disclosed is a sintered body which includes particles comprising a lithium metal oxide of a cubic garnet structure represented by Li7-aLa3 A2O12 where the parameter a satisfies 0≤a≤0.9, and the element A is at least one element selected from the group consisting of Zr, Ta, Hf, Sn, Nb, Ti, V, Bi, Mo, and W, and lithium hydroxide located at grain boundaries of the particles. A volume ratio of the lithium metal oxide to the total of the lithium metal oxide and lithium hydroxide is in the range of 50 vol% or more and 95 vol% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sintered body, a solid electrolyte thereof, an all-solid-state lithium ion battery thereof, and methods for producing these. [Background technology]

[0002] Conventional commercially available lithium-ion batteries use organic electrolytes, which pose a risk of combustion due to temperature rise during short circuit. Therefore, all-solid-state lithium-ion batteries, which replace the organic electrolyte with a solid electrolyte, have attracted attention.

[0003] Lithium ion conductive oxides with a garnet-type structure can have a tetragonal crystal structure, which is stable at room temperature, and a cubic crystal structure, which is stable at high temperatures. It is known that the cubic crystal structure exhibits high ionic conductivity. For this reason, lithium ion conductive oxides with a cubic garnet-type structure are considered promising candidates for solid electrolytes.

[0004] When synthesizing a lithium ion conductive oxide having a cubic garnet structure using common oxide raw materials, it is generally necessary to carry out the synthesis at a firing temperature exceeding 900°C and then sintering at a higher temperature to densify the oxide.

[0005] In addition, when manufacturing an all-solid-state lithium-ion battery using such an oxide sintered body as a solid electrolyte, there is a technology in which the solid electrolyte and the electrode are sintered together at high temperatures to form a strong interface between them. However, when the above-mentioned lithium ion conductive oxide is used, if it is sintered together with the electrode at a high temperature exceeding 900°C, interdiffusion occurs between the electrode and the solid electrolyte, and a different phase is generated at the interface. Therefore, it is desired to lower the sintering temperature of the lithium ion conductive oxide and enable it to be sintered together with the electrode.

[0006] In recent years, techniques have been developed for producing a lithium ion conductive oxide sintered body having a garnet structure by using a precursor (see, for example, Patent Documents 1 and 2, and Non-Patent Documents 1 and 2).

[0007] According to Patent Document 1, Li showing a garnet crystal structure a M 1 b M 2 c O d (5 ≤ a ≤ 8, 2.5 ≤ b ≤ 3.5, 1.5 ≤ c ≤ 2.5, 10 ≤ d ≤ 14, M 1 is one or more elements selected from Al, Y, La, Pr, Nd, Sm, Lu, Mg, Ca, Sr, or Ba. M 2 is one or more elements selected from Zr, Hf, Nb, or Ta.) A method for manufacturing a structure, M 1 source and M 1 s M 2 t O u (0.3 < s < 2.7, 0.3 < t < 2.7, 3.7 ≤ s + t ≤ 4.3, 6.7 ≤ u ≤ 7.3) is heat-treated to form a first sintered body, and the first sintered body is heat-treated in contact with a Li source to form a second sintered body. A method for manufacturing a structure characterized by including these steps is disclosed. Patent Document 1 discloses, as a Li source, lithium metal alone, lithium oxide, lithium hydroxide, lithium halide, lithium phosphate, lithium carbonate, lithium acetate, lithium oxalate, lithium nitrate, and lithium sulfate.

[0008] However, the sintered body obtained in this way has a tetragonal crystal and is not a cubic crystal with excellent ionic conductivity. Also, in Patent Document 1, since the step of forming the first sintered body is performed at 1200 to 1400°C, it is still difficult to integrally sinter with an electrode.

[0009] Non-Patent Document 1 prepared a sintered body represented by La 0.6 Zr 0.3 Ta 0.1 O 1.75 and heat-treated this sintered body together with lithium nitrate (LiNO 3 ) at 700 to 1000°C for 10 hours to obtain a dense cubic crystal Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12However, there have been no reports of high ionic conductivity at low sintering temperatures below 900°C.

[0010] Patent Document 2 is A x E y La 3 G 2-z-q J z L q O 12-(7-2x-3y-z-2q) / 2 The present invention discloses a method for producing a garnet-type lithium composite metal oxide by firing a mixture of an amorphous composite metal oxide made of a compound represented by the following formula: (In the formula, A is an element that becomes a divalent cation, E is an element that becomes a trivalent cation, G is an element that becomes a tetravalent cation, J is an element that becomes a pentavalent cation, L is an element that becomes a hexavalent cation, x is 0 to 0.3, y is 0 to 0.3, z is 0 to 1.0, and q is 0 to 0.5) and a lithium salt.

[0011] In particular, according to Examples 4 and 8 of Patent Document 2, La is used as the amorphous composite metal oxide precursor. 3 Zr 1.5 Ta 0.5 O 8.75 The Li was obtained by mixing the lithium salt with lithium oxide or lithium peroxide and baking it at 400°C for 12 hours. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 The cubic garnet-type lithium composite metal oxide represented by the formula (I) is hot-pressed and sintered at 400°C. The ionic conductivity of the sintered body at room temperature is 3.6×10 -5 S / cm, showing high ionic conductivity.

[0012] Non-Patent Document 2 uses La as a precursor. 2+x Zr 2-2x Ta x O 7 Li (x=0.4) was calcined with lithium oxide at 400°C to 500°C for 12 hours. 6.5 La 3 Zr 1.5 Ta0.5 O 12 The paper discloses that the sintered body thus obtained has an ionic conductivity of 9.4×10 -4 S / cm, showing high ionic conductivity.

[0013] However, in both Patent Document 2 and Non-Patent Document 2, a precursor and a lithium salt are sintered to obtain cubic Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 After obtaining the powder, it is necessary to densify it by hot pressing, which is a complicated process. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] International Publication No. 2016 / 178321 [Patent Document 2] Patent Publication No. 2021-138554 [Non-patent literature]

[0015] [Non-Patent Document 1] Naoki Hamao et al., Journal of Alloys and Compounds, 865, 2021, 158223 [Non-Patent Document 2] Naoki Hamao et al.,Solid State Ionics,357,2020,115460 Summary of the Invention [Problem to be solved by the invention]

[0016] In view of the above, an object of the present invention is to provide a sintered body containing a cubic garnet-type lithium metal oxide having excellent ionic conductivity, which is sintered at a temperature of 900° C. or less at which integral sintering with an electrode is possible, a solid electrolyte and an all-solid-state lithium battery using the sintered body, and methods for producing the same. [Means for solving the problem]

[0017] The sintered body according to the present invention is Li 7-a La 3 A 2 O 12 The present invention contains particles made of a cubic garnet-type lithium metal oxide represented by the formula (1) where the parameter a satisfies 0≦a≦0.9, and the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W), and lithium hydroxide located at the grain boundaries of the particles, and the ratio of the volume of the lithium metal oxide to the total volume of the lithium metal oxide and the lithium hydroxide is in the range of 50% by volume or more and 95% by volume or less, thereby solving the above-mentioned problem. The lithium hydroxide may be amorphous. The volume ratio of the lithium metal oxide to the total volume of the lithium metal oxide and the lithium hydroxide may be in the range of 60 volume % or more and 80 volume % or less. The particles may have a size in the range of 1 μm to 70 μm. The ionic conductivity at room temperature is 5.0×10 -5 S / cm or more 2.0×10 -3 S / cm or less. The method for producing the sintered body according to the present invention comprises the steps of: 3 A 2 O 9-b(wherein parameter b satisfies -0.5≦b≦0.5, and element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W)), and contacting at least a portion of the green compact obtained by the powder pressing with lithium hydroxide powder and firing at a temperature in the range of 500°C to 900°C, thereby solving the above-mentioned problem. At least a portion of the green compact may be contacted with the lithium hydroxide powder in an amount such that the molar ratio of lithium in the lithium hydroxide powder is in the range of 1 to 16 times the molar ratio of lithium in the lithium metal oxide. The sintered body may be obtained by firing for a period of time of 2 hours or more and 72 hours or less. The solid electrolyte according to the present invention uses the above-mentioned sintered body, thereby solving the above-mentioned problems. The all-solid-state lithium ion battery according to the present invention comprises at least the above-mentioned solid electrolyte, thereby solving the above-mentioned problems. The all-solid-state lithium ion battery further includes a positive electrode layer and a negative electrode layer, the solid electrolyte being located between the positive electrode layer and the negative electrode layer, and the positive electrode layer is formed of a positive electrode active material and Li 7-a La 3 A 2 O 12 (wherein the parameter a satisfies 0≦a≦0.9, and the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W)) and a composite of lithium hydroxide. The positive electrode active material may be selected from the group consisting of lithium transition metal oxides and lithium sulfides. The anode layer may comprise an anode active material selected from the group consisting of carbon materials, metal materials, conductive polymers, sulfides, and oxides. The negative electrode layer may be a composite of the negative electrode active material, a cubic garnet-type structure lithium metal oxide, and lithium hydroxide. The method for producing the all-solid-state lithium-ion battery according to the present invention comprises the steps of: 3 A 2 O 9-b (wherein parameter b satisfies -0.5≦b≦0.5, and element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W)), placing a positive electrode mixed powder containing a positive electrode active material powder and the precursor powder on a powder compact obtained by the pressing, and pressing the powder compact; and bringing at least a portion of the laminated powder compact obtained by the pressing and placing the laminated powder compact on a lithium hydroxide powder, and firing the powder compact at a temperature in the range of 500°C to 900°C, thereby solving the above-mentioned problem. The method may further include placing a negative electrode mixed powder containing a negative electrode active material powder and the precursor powder on a side of a laminated green compact obtained by placing and compressing the positive electrode mixed powder on the side opposite to the side on which the positive electrode mixed powder was placed, and compressing the laminated green compact, subsequent to placing and compressing the positive electrode mixed powder. Following the firing, the method may further include forming a negative electrode layer on the side opposite to the side on which the positive electrode mixed powder is placed and compressed. Effect of the Invention

[0018] The sintered body of the present invention is Li 7-a La 3 A 2 O 12The sintered body of the present invention contains particles (LLAO particles) made of a lithium metal oxide having a cubic garnet structure represented by the formula (wherein the parameter a satisfies 0≦a≦0.9, and the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W), and lithium hydroxide located at the grain boundaries of the particles. Since the sintered body of the present invention contains LLAO particles in a range of 50% by volume to 95% by volume, the LLAO particles are connected to each other to form a path for ion conduction, and thus has high ionic conductivity. Furthermore, since the lithium hydroxide is located between the LLAO particles, the sintered body is densified, and thus has even better ionic conductivity. Such a sintered body functions as a solid electrolyte, and an all-solid-state lithium ion battery can be provided.

[0019] The method for producing the sintered body of the present invention is 3 A 2 O 9-b (-0.5≦b≦0.5, A element is at least one element selected from the group consisting of Zr, Ta, Hf, Sn, Nb, Ti, V, Bi, Mo, and W) is compressed, and at least a part of the obtained compressed powder is brought into contact with lithium hydroxide powder and sintered at a temperature range of 500°C to 900°C, thereby obtaining the above-mentioned sintered body. Since a sintered body containing a cubic garnet-type lithium metal oxide can be obtained from the above-mentioned precursor powder in one step, the process is simple. In addition, since low-temperature sintering at 900°C or less is possible, it is possible to sinter it together with electrodes such as positive and negative electrodes, which is advantageous for practical use. [Brief description of the drawings]

[0020] [Figure 1] Schematic diagram showing the sintered body of the present invention. [Diagram 2] Flowchart showing the steps for producing the sintered body of the present invention [Diagram 3] Schematic diagram showing an all-solid-state lithium-ion battery of the present invention. [Figure 4]A flowchart showing the steps of manufacturing the all-solid-state lithium-ion battery of the present invention. [Diagram 5] Dependence of actual density of sintered bodies of Examples 1, 6 and 7 on sintering temperature [Figure 6] 1 shows an XRD pattern of the sintered body of Example 1. [Figure 7] 1 shows an XRD pattern of the sintered body of Example 2. [Figure 8] 1 shows an XRD pattern of the sintered body of Example 3. [Figure 9] FIG. 1 shows an XRD pattern of the sintered body of Example 6. [Figure 10] 1 shows an XRD pattern of the sintered body of Example 7. [Figure 11] FIG. 1 shows an SEM image of a cross section of the sintered body of Example 1. [Figure 12] FIG. 1 shows EDS mapping of a cross section of the sintered body of Example 1. [Figure 13] FIG. 1 shows a high-resolution TOF-SIMS image of a cross section of the sintered body of Example 1. [Figure 14] FIG. 1 shows an SEM image of a cross section of the sintered body of Example 2. [Figure 15] FIG. 1 shows an SEM image of a cross section of the sintered body of Example 3. [Figure 16] 1 shows SEM images of cross sections of the sintered bodies of Examples 6 and 7. [Figure 17] FIG. 1 is a graph showing the sintering temperature dependence of ionic conductivity of the sintered bodies of Examples 1, 6, and 7. [Figure 18] FIG. 1 shows the sintering temperature dependence of ionic conductivity of sintered bodies of Examples 1 to 5. [Figure 19] FIG. 1 shows Arrhenius plots of the ionic conductivity of the sintered bodies of Examples 1 and 6. [Figure 20] Diagram showing the procedure for manufacturing an all-solid-state lithium-ion battery [Figure 21] FIG. 13 is a SEM image of a cross section of the laminated sintered body of Example 8. [Figure 22] Graph showing the charge / discharge curves of the all-solid-state lithium-ion battery of Example 8 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that like elements are given like reference numerals and their description will be omitted.

[0022] (Embodiment 1) In the first embodiment, a sintered body and a method for producing the same according to the present invention will be described.

[0023] FIG. 1 is a schematic diagram showing a sintered body of the present invention.

[0024] The sintered body 100 of the present invention is Li 7-a La 3 A 2 O 12 (wherein the parameter a satisfies 0≦a≦0.9, and the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W)) (LLAO particles) 110, and lithium hydroxide 120 located at the grain boundaries of the particles 110. The sintered body 100 of the present invention has excellent ion conductivity because it contains LLAO particles having ion conductivity.

[0025] Furthermore, in the sintered body 100 of the present invention, the ratio of the volume of the lithium metal oxide to the total volume of the lithium metal oxide (LLAO particles 110) and the lithium hydroxide 120 satisfies the range of 50 volume % or more and 95 volume % or less. By containing the lithium metal oxide constituting the LLAO particles 110 in the above range, the LLAO particles can be connected to each other to form a network structure that forms a path for ion conduction. As a result, the high ion conductivity inherent to the lithium metal oxide can be achieved in the sintered body 100. In addition, the lithium hydroxide 120 is located at the grain boundaries of the LLAO particles 110, enabling a high sintering density.

[0026] The configuration of the sintered body 100 of the present invention will now be described in more detail. The LLAO particles 110 are made of lithium metal oxide having a cubic garnet-type structure and have the general formula Li 7-a La 3 A 2 O 12 The parameter a satisfies the range of 0≦a≦0.9, and within this range, the cubic garnet structure is maintained. The element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W), and may be a combination of two or more elements. If it is made of these elements, it becomes an oxide with excellent ion conductivity. For example, when Zr and Ta are selected as the element A, any combination in which Zr and Ta together make 2 is allowed.

[0027] General formula Li 7-a La 3 A 2 O 12 As one of the cubic garnet-type lithium metal oxides represented by the formula: Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 There is. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 The crystal structure parameters are shown in Table 1.

[0028] [Table 1]

[0029] Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12It belongs to the cubic crystal system, has a garnet-type structure, and belongs to the Ia3￣d space group (3￣ is an overbar notation for 3, space group number 230 in the International Tables for Crystallography), with the crystal parameters and atomic coordinate positions shown in Table 1. In Table 1, the lattice constants a, b, and c indicate the lengths of the axes of the unit cell, and α, β, and γ indicate the angles between the axes of the unit cell.

[0030] General formula Li 7-a La 3 A 2 O 12 The crystals represented by the general formula Li can be identified by X-ray diffraction or neutron diffraction. 7-a La 3 A 2 O 12 In the crystal represented by the formula, the lattice constant changes depending on the value of the parameter a and the type and ratio of the A element, but the atomic positions given by the crystal structure, the sites occupied by the atoms, and their coordinates do not change so much that the chemical bonds between the skeletal atoms are broken. In the present invention, if the bond lengths calculated from the lattice constants and atomic coordinates obtained by analyzing the results of X-ray diffraction and neutron diffraction in the space group Ia3￣d are within ±5% of the bond lengths calculated from the crystal structure parameters shown in Table 1, the crystals have the same crystal structure and are of the general formula Li 7-a La 3 A 2 O 12 It can be determined that the crystal is represented by the formula:

[0031] As a simpler method of judgment, if the main peak position (2θ) of the X-ray diffraction pattern of the target sintered body coincides with the diffraction peak position (2θ) calculated using the crystal structure parameters in Table 1, it is determined that the sintered body is composed of the general formula Li 7-a La 3 A 2 O 12 For example, it is advisable to judge whether the crystal satisfies about 10 main peaks with strong diffraction intensities.

[0032] General formula Li 7-a La 3 A 2 O12 As an example of a crystal represented by the above Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Besides, Li 6.5 La 3 (Zr,Ta) 2 O 12 , Li 6.5 La 3 (Zr, Nb) 2 O 12 All of these are known to be excellent ion conductors. Here, (Zr,Ta) means that Zr and Ta are present at any ratio on the A element site.

[0033] General formula Li 7-a La 3 A 2 O 12 In the crystal represented by the formula (1), the parameter a only needs to satisfy 0≦a≦0.9, and preferably satisfies 0.3≦a≦0.7, which stabilizes the cubic garnet-type structure and provides an excellent ion conductor.

[0034] General formula Li 7-a La 3 A 2 O 12 In the crystal represented by the formula (1), from the viewpoint of ionic conductivity, the element A is preferably selected from the group consisting of Zr, Ta, and Nb, and more preferably a combination of Zr and Ta. In particular, in the combination of Zr and Ta, Li 7-a La 3 Zr 2-x Ta x O 12 (wherein the parameter a satisfies 0.3≦a≦0.7 and the parameter x satisfies 0.3≦x≦0.7) is preferable because it is an excellent ion conductor.

[0035] The lithium hydroxide 120 is located at the grain boundaries of the LLAO particles 110 and can improve the sintered density while maintaining the connection of the LLAO particles 110, thereby contributing to an improvement in ionic conductivity. The lithium hydroxide 120 is preferably amorphous. This can result in a denser sintered body 100.

[0036] The content of the LLAO particles 110 in the sintered body 100, i.e., the volume ratio of the lithium metal oxide to the total of the lithium metal oxide and lithium hydroxide, is preferably in the range of 60 volume % to 80 volume %. This allows the body to have excellent ion conductivity while maintaining a high sintered density. The volume ratio of the lithium metal oxide is more preferably in the range of 64 volume % to 68 volume %.

[0037] In this specification, the volume fraction of lithium metal oxide was calculated by multiplying the volume percentage of lithium metal oxide determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) by the relative density. More specifically, the calculation was performed according to the following procedure. 1) Detect the molar ratio of elements other than oxygen (e.g., Li, La, Zr, Ta) by ICP-OES measurement. 2) The Li composition ratio in the lithium metal oxide is calculated based on the Zr and Ta composition ratio so that charge neutrality is maintained (Li, La, and A elements are cations, and O element is an anion. For example, in the case of Zr1.5 and Ta0.5, the Li composition ratio is 6.5). 3) By subtracting the number of moles of Li in the lithium metal oxide from the detected mole ratio of Li, LiOH H 2 Calculate the molar ratio of LiOH H when Li = 10, La = 3, Zr = 1.5, and Ta = 0.5 are detected. 2 O is 10-6.5=3.5, Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 +3.5LiOH H 2 O sintered body). 4) Calculate the mass by multiplying the number of moles (mol) of each by the molecular weight (g / mol). 5) Mass (g) of each is density (g / cm 3 ) to calculate the volume. 6) Convert each volume ratio into a volume percentage and multiply it by the relative density calculated using the method described below.

[0038] The LLAO particles 110 preferably have a particle size in the range of 1 μm to 70 μm. This allows the LLAO particles 110 to be connected to each other. The particle size is the average particle size measured by a scanning electron microscope (SEM). The LLAO particles 110 more preferably have a particle size in the range of 5 μm to 30 μm. This allows the LLAO particles 110 to exhibit excellent ion conductivity. The particle size in the sintered body was calculated from the number of particles per unit area using an SEM image. In detail, the apparent average particle size of the crystal grains was measured from an SEM image of the mirror-polished sintered body surface, and the apparent average particle size was multiplied by a coefficient of 1.225 calculated based on morphometric analysis to calculate the particle size. The average particle size was the average value calculated from 100 or more crystal grains.

[0039] The sintered body 100 of the present invention preferably has a relative density of 90% or more. This allows it to exhibit excellent ion conductivity. The sintered body 100 of the present invention preferably has a relative density of 93% or more. The relative density is defined as the percentage of the bulk density of the sintered body relative to the theoretical density of the sintered body (bulk density of the sintered body / theoretical density of the sintered body×100). The bulk density of the sintered body (g / cm 3 ) is measured in accordance with JIS R 1634:1998. The sintered body 100 of the present invention preferably has a density of 4.0 g / cm 3 More than 4.3g / cm 3 It has an actual density in the following range. The theoretical density is 4.3 g / cm 3 Let us assume that.

[0040] The sintered body 100 of the present invention exhibits excellent ion conductivity, preferably 5.0×10 -5 S / cm or more 2.0×10 -3S / cm or less. This makes the sintered body 100 of the present invention particularly advantageous as a solid electrolyte for lithium ion secondary batteries. The sintered body 100 of the present invention more preferably satisfies the range of 1.0×10 -4 S / cm or more 2.0×10 -3 The sintered body 100 of the present invention preferably has an activation energy in the range of 0.3 eV or more and 0.5 eV or less, and is an excellent ion conductor.

[0041] Next, a method for producing the sintered body 100 of the present invention will be described. FIG. 2 is a flow chart showing the steps of producing the sintered body of the present invention.

[0042] The process for producing the sintered body of the present invention includes the following steps S210 to S220. Step S210: La 3 A 2 O 9-b (wherein the parameter b satisfies -0.5≦b≦0.5, and the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W)) is compressed. Step S220: At least a part of the green compact obtained by pressing in step S210 is brought into contact with lithium hydroxide powder and fired at a temperature in the range of 500° C. to 900° C.

[0043] According to the present inventors, the above-mentioned general formula La 3 A 2 O 9-bIt has been discovered that the above-mentioned sintered body 100 of the present invention can be obtained by liquid phase penetration sintering (LLPS) by sintering a green compact made of a precursor powder represented by the formula (1) while contacting it with a lithium hydroxide selected from among many lithium-containing materials. Surprisingly, it has been discovered that the method of the present invention makes it possible to directly obtain a sintered body having excellent ionic conductivity while maintaining a high sintered density even at a sintering temperature of 500°C to 900°C, which is lower than conventional temperatures.

[0044] Each step will now be described in more detail. In step S210, La 3 A 2 O 9-b In the precursor powder represented by the formula (1), considering that oxygen deficiency or excess occurs depending on the firing conditions, the parameter b may satisfy -0.5≦b≦0.5. As described above, the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W). The element A is omitted because it has been described with reference to FIG. 1.

[0045] General formula La 3 A 2 O 9-b As one of the precursor powders represented by the formula, La 3 Zr 1.5 Ta 0.5 O 8.75 There is. 3 Zr 1.5 Ta 0.5 O 8.75 The crystal structure parameters are shown in Table 2.

[0046] [Table 2]

[0047] La 3 Zr 1.5Ta 0.5 O 8.75 belongs to the cubic crystal system, has a fluorite structure, and belongs to the Fm3￣m space group (3￣ is an overbar notation for 3, space group number 225 in the International Tables for Crystallography), with the crystal parameters and atomic coordinate positions shown in Table 2. In Table 2, the lattice constants a, b, and c indicate the lengths of the axes of the unit cell, and α, β, and γ indicate the angles between the axes of the unit cell.

[0048] General formula La 3 Zr 1.5 Ta 0.5 O 8.75 The crystals represented by the general formula La can be identified by X-ray diffraction or neutron diffraction. 3 A 2 O 9-b In crystals that satisfy this condition, the lattice constants change depending on the value of parameter b and the selection and proportion of the type and type of A element, but the atomic positions given by the crystal structure, the sites occupied by the atoms, and their coordinates do not change so much that the chemical bonds between the skeletal atoms are broken. In this invention, if the bond lengths calculated from the lattice constants and atomic coordinates obtained by analyzing the results of X-ray diffraction and neutron diffraction in the space group Fm3￣m are within ±5% of the bond lengths calculated from the crystal structure parameters shown in Table 2, the crystals have the same crystal structure and are of the general formula La 3 A 2 O 9-b It can be determined that the crystal is represented by the formula:

[0049] As a simpler method of judgment, if the main peak position (2θ) of the X-ray diffraction pattern of the target sintered body coincides with the diffraction peak position (2θ) calculated using the crystal structure parameters in Table 2, it is determined that the sintered body has the general formula La 3 A 2 O 9-b For example, it is advisable to judge whether the crystal satisfies about 10 main peaks with strong diffraction intensities.

[0050] General formula La 3 A 2 O 9-b As an example of a crystal represented by the above formula, La3 Zr 1.5 Ta 0.5 O 8.75 Besides, La 3 (Zr,Ta) 2 O 8.75 , La 3 (Zr, Nb) 2 O 8.75 All of these are known to be excellent ion conductors. Here, (Zr,Ta) means that Zr and Ta are present at any ratio on the A element site.

[0051] General formula La 3 A 2 O 9-b In the crystal represented by the formula: the parameter b should satisfy -0.5≦b≦0.5, but preferably satisfies 0≦b≦0.25. This stabilizes the cubic fluorite structure, and Li is infiltrated during the liquid phase infiltration sintering method, and the crystal is represented by the formula: Li 7-a La 3 A 2 O 12 It is possible to promote the formation of crystals represented by the formula:

[0052] In addition, the general formula La 3 A 2 O 9-b The precursor powder represented by the formula (1) may be commercially available or may be synthesized by a solid-state reaction method. When synthesized by a solid-state reaction method, for example, a raw material containing La (e.g., lanthanum hydroxide, lanthanum oxide, etc.) and a raw material containing A element (e.g., oxide of A element, hydroxide of A, etc.) may be weighed out so that La and A element have a stoichiometric ratio of La:A=3:2, and then mixed and fired.

[0053] The particle size (primary particle size) of the precursor powder is preferably in the range of 0.005 μm to 10 μm. This allows a green compact having a high relative density to be obtained by compaction. The particle size of the precursor powder is more preferably in the range of 0.05 μm to 1 μm, and even more preferably in the range of 0.1 μm to 0.3 μm. This promotes sintering in the firing step described below, and allows a dense sintered body to be obtained. The primary particle size is measured by a laser scattering method.

[0054] The relative density of the green compact obtained in step S210 is preferably 50% or more. This allows a sintered body with a high relative density to be obtained by the subsequent firing. The relative density of the green compact is more preferably 60% or more, and even more preferably 65% ​​or more.

[0055] In step S210, the powder can be compressed by die pressing, cold isostatic pressing (cold isostatic pressing), or the like. The compacting pressure is preferably 5 MPa or more. This allows a green compact that satisfies the above-mentioned relative density to be obtained. The compacting pressure is more preferably 150 MPa or more, and even more preferably 180 MPa or more. There is no particular upper limit, but it may be 300 MPa or less.

[0056] In step S220, the amount of lithium hydroxide powder to be brought into contact with the green compact obtained in step S210 is preferably such that the amount of Li in the lithium hydroxide (1 mole) is represented by the above-mentioned general formula Li 7-a La 3 A 2 O 12 The amount of Li is adjusted to be in the range of 1 to 16 times the amount of Li ((7-a) moles) in the compact. By contacting the compact with lithium hydroxide powder in this range and sintering, lithium is permeated into the compact and the compact is converted into the lithium hydroxide powder of the general formula Li 7-a La 3 A 2 O 12 A phase represented by the formula: may be formed, which is a complex with lithium hydroxide.

[0057] The amount of lithium hydroxide powder is preferably such that the amount of Li in the lithium hydroxide (1 mole) is represented by the above general formula Li 7-a La 3 A 2 O 12 The amount of Li is adjusted to be in the range of 5 to 13 times the amount of Li ((7-a) moles) in the general formula Li 7-a La 3 A 2 O 12 This promotes the formation of a phase represented by the formula:

[0058] The amount of lithium hydroxide powder is even more preferably such that the amount of Li in the lithium hydroxide (1 mole) is represented by the above general formula Li 7-a La 3 A 2 O 12 The amount of Li is adjusted to be in the range of 6 to 10 times the amount of Li ((7-a) moles) in the general formula Li 7-a La 3 A 2 O 12 The formation of the phase represented by the formula (I) is further promoted and forms a complex with lithium hydroxide.

[0059] In step S220, the sintering temperature is not particularly limited as long as it is in the range of 500°C or more and 900°C or less, but may preferably be in the range of more than 600°C to 900°C or less. Within this range, a sintered body having a higher ion conductivity can be obtained. The sintering temperature may more preferably be in the range of 750°C or more and 850°C or less. Within this range, a sintered body having an even higher ion conductivity can be obtained.

[0060] In step S220, the sintering time is not particularly limited. For example, if the compact has a diameter of 3 mm to 10 mm and a thickness of 0.5 mm to 1.5 mm, sintering for 2 hours to 72 hours in the above temperature range will produce a powder having the general formula Li 7-a La 3 A 2 O 12 The firing time may preferably be in the range of 10 hours to 60 hours.

[0061] In step S220, two or more stages of firing may be performed within the above temperature range. For example, firing may be performed at a first temperature selected from a temperature range of 500°C to 700°C, and then at a second temperature selected from a temperature range of more than 600°C to 900°C and higher than the first temperature. In this case, the firing time may be any time as long as the total firing time is within the above range. This allows the sintering to proceed efficiently, and is expected to improve the sintered density.

[0062] In step S220, the firing atmosphere is not particularly limited as long as it contains oxygen, and may be air.

[0063] In step S220, the lithium hydroxide powder is not particularly limited since it is melted, but for example, a range of 0.01 μm to 50 μm may be used. This allows lithium to penetrate by sintering and become the above-mentioned general formula Li 7-a La 3 A 2 O 12 A phase represented by the formula:

[0064] In step S220, the lithium hydroxide powder may be in contact with at least a portion of the powder compact, but for example, the powder compact may be covered with the lithium hydroxide powder, which allows lithium to permeate efficiently.

[0065] In this way, the Li 7-a La 3 A 2 O 12 The sintered body contains particles made of a cubic garnet-type lithium metal oxide represented by the formula (wherein the parameter a satisfies 0≦a≦0.9, and the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W), and lithium hydroxide located at the grain boundaries of the particles, and the ratio of the volume of the lithium metal oxide to the total volume of the lithium metal oxide and lithium hydroxide is in the range of 50 volume % or more and 95 volume % or less.

[0066] (Embodiment 2) In the second embodiment, an all-solid-state lithium ion battery and a manufacturing method thereof according to the present invention will be described. FIG. 3 is a schematic diagram showing an all-solid-state lithium ion battery of the present invention.

[0067] The all-solid-state lithium-ion battery 300 of the present invention includes at least a solid electrolyte 310. In particular, the all-solid-state lithium-ion battery 300 of the present invention includes a solid electrolyte 310, a positive electrode layer 320, and a negative electrode layer 330, and the solid electrolyte 310 is located between the positive electrode layer 320 and the negative electrode layer 330.

[0068] The thickness of the solid electrolyte 310 is not particularly limited, but is illustratively in the range of 1 μm to 1.5 mm. Within this range, the internal resistance of the solid electrolyte 310 can be reduced. The thickness of the solid electrolyte 310 may be set to be, for example, 3 to 5 times the particle diameter of the positive electrode active material described below. This makes it possible to prevent short circuits. In consideration of practical application, the thickness may be 1 μm to 10 μm. Note that the solid electrolyte 310 is made of the sintered body described in the first embodiment, and therefore further description will be omitted.

[0069] The positive electrode layer 320 contains at least a positive electrode active material. The positive electrode active material is a material capable of desorbing or inserting lithium ions, and any positive electrode active material that is used in known all-solid-state lithium ion batteries can be used.

[0070] Such a positive electrode active material is selected from the group consisting of lithium transition metal oxides and lithium sulfides. The lithium transition metal oxide is, for example, LiCoO 2 , LiNiO 2 , Li(Ni,Mn,Co)O 2 , Li(Ni,Co,Al)O 2 , Li 2 MnO 3 -Li(Ni,Mn,Co)O 2 , Li(Ni,Mn) 2 O 4 , Li(Co,Mn) 2 O 4 , Li(Mn,Al) 2 O 4 , LiFePO 4 , LiMnPO 4 , LiCoPO 4 , LiNiPO 4 Lithium sulfide may be, for example, Li 2 S., Li2 S x (x=4, 6, 8) etc.

[0071] The positive electrode layer 320 preferably comprises a positive electrode active material and Li 7-a La 3 A 2 O 12 The positive electrode contains a composite of a cubic garnet-type lithium metal oxide represented by the formula (wherein the parameter a satisfies 0≦a≦0.9, and the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W), and lithium hydroxide. 7-a La 3 A 2 O 12 The cubic garnet-type lithium metal oxide represented by the formula (I) is the same as the cubic garnet-type lithium metal oxide described in the first embodiment, and therefore the description thereof will be omitted. The positive electrode layer 320 containing such a positive electrode composite is advantageous in that the positive electrode layer 320 and the solid electrolyte 310 are joined together without forming an interface reaction phase between the positive electrode active material and the solid electrolyte, and a high-speed Li conduction path is formed in the positive electrode layer.

[0072] The content (volume %) of the positive electrode active material contained in the positive electrode composite is preferably in the range of 30 volume % or more and 95 volume % or less. In this range, the positive electrode active material can desorb / adsorb a sufficient amount of lithium ions. The content of the positive electrode active material is more preferably in the range of 40 volume % or more and 80 volume % or less. The content of the positive electrode active material is calculated by a scanning electron microscope (SEM). In detail, the content was measured from a cross-sectional SEM image of the positive electrode composite by Image J (ver. 1.51n; an open source and public domain image processing software).

[0073] The content (volume %) of the cubic garnet-type lithium metal oxide contained in the positive electrode composite is preferably in the range of 5 volume % or more and 70 volume % or less. In this range, the charge / discharge characteristics are excellent. The content of the cubic garnet-type lithium metal oxide is more preferably in the range of 40 volume % or more and 60 volume % or less.

[0074] The content (volume %) of lithium hydroxide contained in the positive electrode composite is preferably in the range of more than 0 volume % to 20 volume % or less. The content of lithium hydroxide is more preferably in the range of more than 0 volume % to 10 volume % or less. Within this range, excellent charge / discharge characteristics can be maintained without being affected by lithium hydroxide while performing co-firing.

[0075] The positive electrode composite may further contain a conductive material. This increases the internal conductivity of the positive electrode layer 320, thereby improving the charge / discharge efficiency and output characteristics. Such a conductive material may be a carbon material such as graphite powder, acetylene black, carbon black, or carbon fiber, or a metal, metal alloy, or metal oxide having electrical conductivity. The conductive material may be 5% by mass or more and 15% by mass or less with respect to 100% by mass of the positive electrode active material.

[0076] The thickness of the positive electrode layer 320 is not particularly limited, but is illustratively in the range of 5 μm to 100 μm. In consideration of practical application, the thickness of the positive electrode layer 320 may be 10 μm to 50 μm. The positive electrode layer 320 may further include a positive electrode current collector (not shown). This makes it easy to extract power to the outside. The positive electrode current collector may be a metal material such as aluminum (Al), nickel (Ni), stainless steel, or gold (Au). The positive electrode current collector may be in the form of a sheet.

[0077] The negative electrode layer 330 contains at least a negative electrode active material. The negative electrode active material is a material capable of desorbing or inserting lithium ions, and any negative electrode active material that is used in known all-solid-state lithium ion batteries can be used.

[0078] Such a negative electrode active material is selected from the group consisting of carbon materials, metal materials, conductive polymers, sulfides, and oxides. The carbon materials may be, for example, natural graphite, artificial graphite, resin carbon, carbon fiber, activated carbon, hard carbon, soft carbon, etc. The metal materials may be lithium (Li), tin (Sn), silicon (Si), gallium (Ga), indium (In), aluminum (Al), or alloys thereof. The conductive polymers may be, for example, polyacene, polyacetylene, or polypyrrole.

[0079] The sulfide is TiS x Titanium sulfide, VS x Vanadium sulfide, FeS x Iron sulfide, MoS x Molybdenum sulfide, SnS x Tin sulfide, WS x Tungsten sulfide, SbS x Antimony sulfide, SeS x The x's may be any positive real number.

[0080] The oxide is, for example, SiO x Silicon oxide, TiO x Titanium oxide, VO x Vanadium oxides such as FeO x Iron oxide, SnO x Tin oxide, WO x Tungsten oxide, spinel structure Li 4+r Ti 5 O 12 (-1≦r≦3), ramsteride structure Li 2+s Ti 3 O 7 Lithium titanium oxide (-1≦s≦3), LiVO 2 The oxide of lithium vanadium may be, for example, an oxide of lithium vanadium such as, for example,

[0081] Again, the negative electrode layer 330 preferably comprises a negative electrode active material and Li 7-a La 3 A 2 O12 The negative electrode may contain a negative electrode composite of a cubic garnet-type lithium metal oxide represented by the formula (wherein the parameter a satisfies 0≦a≦0.9, and the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W), and lithium hydroxide. Li 7-a La 3 A 2 O 12 The cubic garnet-type lithium metal oxide represented by the formula (I) is the same as the cubic garnet-type lithium metal oxide described in the first embodiment, and therefore the description thereof will be omitted. The negative electrode layer 330 containing such a complex is advantageous in that the negative electrode layer 330 and the solid electrolyte 310 are joined together without forming an interface reaction phase between the negative electrode active material and the solid electrolyte, and a high-speed Li conduction path is formed in the negative electrode layer.

[0082] The content (volume %) of the negative electrode active material contained in the negative electrode composite is preferably in the range of 30 volume % or more and 95 volume % or less. In this range, the negative electrode active material can desorb / adsorb a sufficient amount of lithium ions. The content of the negative electrode active material is more preferably in the range of 40 volume % or more and 80 volume % or less.

[0083] The content (volume %) of the cubic garnet-type lithium metal oxide contained in the negative electrode composite is preferably in the range of 5 volume % or more and 70 volume % or less. In this range, the charge / discharge characteristics are excellent. The content of the cubic garnet-type lithium metal oxide is more preferably in the range of 40 volume % or more and 60 volume % or less.

[0084] The content (volume %) of lithium hydroxide contained in the negative electrode composite is preferably in the range of more than 0 volume % to 20 volume % or less. The content of lithium hydroxide is more preferably in the range of more than 0 volume % to 10 volume % or less. Within this range, excellent charge / discharge characteristics can be maintained without being affected by lithium hydroxide while performing co-firing.

[0085] The negative electrode composite may further contain a conductive material. This increases the internal conductivity of the negative electrode layer 330, thereby improving the charge / discharge efficiency and output characteristics. Such a conductive material may be a carbon material such as graphite powder, acetylene black, carbon black, or carbon fiber, or a metal, metal alloy, or metal oxide having electrical conductivity. The conductive material may be 5% by mass or more and 15% by mass or less with respect to 100% by mass of the negative electrode active material.

[0086] The thickness of the negative electrode layer 330 is not particularly limited, but is illustratively in the range of 5 μm to 100 μm. In consideration of practical application, the thickness of the negative electrode layer 330 may be 10 μm to 50 μm. The negative electrode layer 330 may further include a negative electrode current collector (not shown). This makes it easy to extract power to the outside. The negative electrode current collector may be a metal material such as copper (Cu), nickel (Ni), stainless steel, or gold (Au). The negative electrode current collector may be in the form of a sheet.

[0087] The all-solid-state lithium-ion battery 300 of the present invention may be housed in a case (not shown). The case may be made of aluminum (Al), stainless steel, nickel-plated steel, or the like. The shape of the all-solid-state lithium-ion battery 300 may be a coin type, a button type, a sheet type, a cylindrical type, a square type, or the like. In FIG. 3, the all-solid-state lithium-ion battery 300 of the present invention shows a solid electrolyte 310 sandwiched between a pair of a positive electrode layer 320 and a negative electrode layer 330, but a plurality of these may be stacked together. Such modifications are within the scope of the present invention and will be understood by those skilled in the art.

[0088] The all-solid-state lithium-ion battery 300 of the present invention is charged by connecting it to an external power source and applying a negative potential to the positive electrode layer 320 and a positive potential to the negative electrode layer 330. The all-solid-state lithium-ion battery 300 is discharged by connecting a discharge circuit to the positive electrode layer 320 and the negative electrode layer 330 and passing current through the discharge circuit of an electronic device, an electric vehicle, or the like.

[0089] Next, a method for manufacturing the all-solid-state lithium-ion battery 300 of the present invention will be described.

[0090] The all-solid-state lithium-ion battery 300 may be manufactured, for example, as follows. A solid electrolyte 310, a positive electrode layer 320, and a negative electrode layer 330 are manufactured. Here, the solid electrolyte 310 is manufactured by the manufacturing method of a sintered body described with reference to FIG. 2 in the first embodiment. The positive electrode layer 320 may be manufactured by sintering the above-mentioned positive electrode active material and laminating a current collector thereto. The negative electrode layer 330 may be manufactured by sintering the above-mentioned negative electrode active material and laminating a current collector thereto. These may be laminated in the order of the positive electrode layer 320, the solid electrolyte 310, and the negative electrode layer 330.

[0091] The all-solid-state lithium-ion battery may be manufactured, for example, as follows. The solid electrolyte 310 is manufactured by the method for manufacturing a sintered body described with reference to FIG. 2 in the first embodiment. Next, the positive electrode layer 320 may be formed on the solid electrolyte 310 by physical vapor deposition or chemical vapor deposition, and a current collector may be bonded thereto. The negative electrode layer 330 may be formed by physical vapor deposition or chemical vapor deposition on the side of the solid electrolyte 310 facing the positive electrode layer 320, and a current collector may be bonded thereto. The negative electrode layer 330 may be formed first, and then the positive electrode layer 320 may be formed.

[0092] In the all-solid-state lithium ion battery, the positive and negative electrode layers may be formed by a combination of the above-mentioned sintering method and a physical vapor deposition method or a chemical vapor deposition method.

[0093] Next, a method for manufacturing at least solid electrolyte 310 and positive electrode layer 320 by integral sintering in the all-solid-state lithium ion battery of the present invention will be described. FIG. 4 is a flow chart showing the steps of manufacturing the all-solid-state lithium ion battery of the present invention.

[0094] The process for producing the all-solid-state lithium-ion battery of the present invention includes the following steps S410 to S430. Step S410:La 3 A 2 O 9-b(The parameter b satisfies -0.5≦b≦0.5, and the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W)) is compressed into a precursor powder. Step S420: A positive electrode mixed powder containing a positive electrode active material powder and a precursor powder is placed on the green compact obtained in step S410 and compressed. Step S430: At least a portion of the laminated green compact obtained in step S420 is brought into contact with lithium hydroxide powder and fired at a temperature in the range of 500°C to 900°C.

[0095] As described in the first embodiment, the general formula Li 7-a La 3 A 2 O 12 Since the sintered body containing the crystal represented by the formula (I) is obtained by low-temperature sintering at 900°C or less, it is possible to provide an all-solid-state lithium-ion battery in which the solid electrolyte and the positive electrode layer are integrally sintered by low-temperature sintering at 900°C or less. In particular, since the sintering temperature is 900°C or less, no interdiffusion occurs between the solid electrolyte and the positive electrode layer, and a strong interface is obtained. Each process will be described in detail.

[0096] Step S410 is the same as step S210 described with reference to FIG. 2 in the first embodiment, and therefore will not be described here.

[0097] In step S420, the positive electrode active material powder is the above-mentioned positive electrode active material powder, and the precursor powder is the precursor powder described in the first embodiment, so the description will be omitted. The content (volume %) of the positive electrode active material powder in the positive electrode mixed powder is preferably in the range of 30 volume % or more and 95 volume % or less. Within this range, a positive electrode composite satisfying the above-mentioned positive electrode active material content can be obtained. The content (volume %) of the positive electrode active material powder in the positive electrode mixed powder is more preferably in the range of 40 volume % or more and 60 volume % or less.

[0098] In step S420, the compacting conditions may be the same as those in step S210 described with reference to Fig. 2 in embodiment 1. According to step S420, a laminated green compact in which the precursor powder and the positive electrode mixed powder are laminated is obtained, but in consideration of practical application, the positive electrode mixed powder may be placed so that the thickness of the layer made of the positive electrode mixed powder is preferably thicker than the thickness of the layer made of the precursor powder.

[0099] Step S430 is similar to step S220 described with reference to FIG. 2 in the first embodiment, except that the green compact is a laminated green compact, and the same firing conditions may be used. Here, too, the amount of lithium hydroxide powder brought into contact with the laminated green compact is preferably such that the amount of Li in lithium hydroxide hydrate (1 mole) is represented by the general formula Li 7-a La 3 A 2 O 12 The Li amount is adjusted to be in the range of 1 to 16 times the Li amount ((7-a) moles) of the above.

[0100] In this manner, an all-solid-state lithium ion battery (half cell) in which a solid electrolyte made of a sintered body containing a cubic garnet-type lithium metal oxide and lithium hydroxide and a positive electrode layer containing a positive electrode active material and a composite of a cubic garnet-type lithium metal oxide and lithium hydroxide are laminated is obtained by integral sintering.

[0101] Following step S420 and prior to step S430, a negative electrode mixed powder containing a negative electrode active material powder and a precursor powder may be placed on the side of the laminated green compact obtained in step S420 opposite to the layer of the positive electrode mixed powder, and compressed. This results in a laminated green compact in which the negative electrode mixed powder, the precursor powder, and the positive electrode mixed powder are laminated in this order. The compression conditions may be the same as those in step S420.

[0102] The mixed powder for the negative electrode may be any of the above-mentioned powders of the negative electrode active material, but preferably has low reactivity in the temperature range of 500°C to 900°C. Lithium titanium oxide is typically used. The precursor powder is the precursor powder described in the first embodiment, and so a detailed description is omitted. The content (volume %) of the negative electrode active material powder in the mixed powder for the negative electrode is preferably in the range of 30% to 95% by volume. This range allows the production of a negative electrode composite that satisfies the above-mentioned content of the negative electrode active material. The content (volume %) of the negative electrode active material powder in the mixed powder for the negative electrode is more preferably in the range of 40% to 80% by volume.

[0103] In the laminated green compact, the mixed powder for the negative electrode may be placed so that the thickness of the layer made of the mixed powder for the negative electrode is preferably greater than the thickness of the layer made of the precursor powder.

[0104] By firing the laminated compact obtained by laminating the negative electrode mixed powder, the precursor powder, and the positive electrode mixed powder in this order in step S430, an all-solid-state lithium ion battery (full cell) is obtained by integral sintering in which a negative electrode layer containing a composite of a cubic garnet-type lithium metal oxide and lithium hydroxide, a solid electrolyte made of a sintered body containing a cubic garnet-type lithium metal oxide and lithium hydroxide, and a positive electrode layer containing a composite of a positive electrode active material and a composite of a cubic garnet-type lithium metal oxide and lithium hydroxide are laminated.

[0105] Alternatively, following step S430, the anode layer 330 may be formed by physical vapor deposition or chemical vapor deposition or sintering to produce a full cell.

[0106] The present invention will now be described in detail with reference to specific examples, but it should be noted that the present invention is not limited to these examples. EXAMPLES

[0107] [La 3 Zr 1.5 Ta 0.5 O 8.75 : Preparation of precursor powder] The precursor powder, La 3 Zr 1.5 Ta 0.5 O 8.75 was synthesized by a solid-state reaction method. Lanthanum hydroxide hydrate (99.9%, Fujifilm Wako Pure Chemical Industries, Ltd.), zirconium oxide (99.0%, Tosoh Corporation), and tantalum oxide (99.9%, Fujifilm Wako Pure Chemical Industries, Ltd.) were weighed out so that the stoichiometric ratio of La, Zr, and Ta was La:Zr:Ta=3:1.5:0.5, and mixed in hexane for 6 hours using a planetary ball mill.

[0108] The mixed powder was mechanically compressed at 100 MPa to form a green compact. The green compact was placed on an MgO plate and sintered in air at 1200°C (heating rate: 10°C / min) for 12 hours. The obtained sintered body was again ball milled in hexane for 6 hours to powderize it. The particle size of the powder (primary particles) was measured by a laser scattering method, and the average particle size was 0.15 μm. Powder X-ray diffraction measurement (MiniFlex600, manufactured by Rigaku Corporation) was performed using the obtained powder, and it was confirmed that it has a fluorite structure and the X-ray diffraction pattern in Non-Patent Document 2 is in good agreement. The crystal structure was analyzed using single crystal structure analysis software from the results of the X-ray diffraction measurement, and the obtained powder belonged to the space group Fm3̂m (space group 225 of the International Tables for Crystallography), with lattice constants a = b = c = 0.5448 nm and angles α = β = γ = 90°. The atomic positions were as shown in Table 2. The powder was subjected to composition analysis using an inductively coupled plasma optical emission spectrometer (Agilent Technologies, 5800ICP-OES), and the detected contents of La, Zr, and Ta were 3.00, 1.50, and 0.50, respectively. 3 Zr 1.5 Ta 0.5 O 8.75 It was confirmed that the composition formula was satisfied.

[0109] [Example 1: Sintered body] In Example 1, Li was 6.5 La3 Zr 1.5 Ta 0.5 O 12 A sintered body containing (LLZTO) was produced.

[0110] Precursor powder (La 3 Zr 1.5 Ta 0.5 O 8.75 The powder) was uniaxially compressed at 6.25 MPa and then isostatically pressed at 200 MPa for 5 min to form a green compact (size: diameter 9 mm × thickness 1.3 mm) (step S210 in Figure 2). The green compact (300 mg, 0.00383 mol = 0.3 / 784.021, relative density 67%) was placed in a magnesia crucible and mixed with lithium hydroxide hydrate (LiOH·H 2 The powder was covered with a SiO2 blanket (99.0%, Fujifilm Wako Pure Chemical Industries, Ltd., primary particle diameter 40 μm) and sintered in air at 500° C., 600° C., 700° C., 800° C., and 900° C. (Step S220 in FIG. 2). The relative density of the green compact was 64%.

[0111] In this case, the amount of lithium hydroxide hydrate is set so that the amount of Li in the lithium hydroxide hydrate (1 mole) is equal to or larger than the amount of cubic garnet-type lithium oxide (Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 The Li amount was adjusted to be 8 times the Li amount (6.5 mol) of the sintered body. Here, the amount of lithium hydroxide hydrate was 835 mg (= 6.5 mol × 8 × 0.00383 × 41.96 g / mol). The sintering time was 12 hours or 40 hours in air at each temperature. The sintered bodies thus obtained are referred to as the sintered body of Example 1 or the sintered body (500) of Example 1 to the sintered body (900) of Example 1.

[0112] The actual density (bulk density) was calculated from the mass and outer diameter of the obtained sintered body. The results are shown in Table 4 and Figure 5. The sintered body was crushed in an agate mortar and subjected to powder X-ray diffraction measurement. The results are shown in Figure 6. The crushed powder was subjected to composition analysis using an inductively coupled plasma emission spectrometer. The cross section of the sintered body was observed with a scanning electron microscope (SEM, Keyence Corporation, VE-8800), and elemental analysis was performed using an energy dispersive X-ray electron spectroscope (EDS) attached to the SEM. Samples for cross-sectional observation were prepared by Ar ion milling using a cross-section polisher (CP, JEOL Ltd., IB-09020CP) and a mechanical polisher (Ikegami Seiki Co., Ltd., ISPP-1000). The results are shown in Figures 11 to 13.

[0113] The ionic conductivity of the sintered body was measured by impedance spectroscopy. The measurement sample was prepared as follows. The surface of the sintered body was polished with sandpaper (#400), and gold (Au) electrodes for blocking lithium ions were sputtered on both sides of the sintered body. The impedance spectrum was collected using a high-frequency impedance measuring device (E4990A impedance analyzer, manufactured by Keysight Technologies Inc.). The measurement conditions were a frequency range of 150 MHz to 20 Hz, a frequency amplitude of 10 mV, and a temperature range of -50°C to 50°C. The results are shown in Figures 17 to 19.

[0114] [Example 2: Sintered body] In Example 2, lithium carbonate (99.0%, Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of lithium hydroxide hydrate in Example 1. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 The procedure was the same as in Example 1, except that the firing temperatures were 800°C, 900°C, and 1000°C.

[0115] The sintered bodies thus obtained are referred to as the sintered body of Example 2, or the sintered body of Example 2 (800) to the sintered body of Example 2 (1000), and the density was measured, and the identification by powder X-ray diffraction, the composition analysis, the SEM observation, and the ion conductivity were measured in the same manner as in Example 1. The results are shown in Table 4, Fig. 7, Fig. 14, and Fig. 18.

[0116] [Example 3: Sintered body] In Example 3, lithium nitrate (99.0%, Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of lithium hydroxide hydrate in Example 1. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 The manufacturing procedure was the same as in Example 1.

[0117] The sintered bodies thus obtained are referred to as the sintered body of Example 3 or the sintered body (500) of Example 3 to the sintered body (900) of Example 3, and the density was measured, and the identification by powder X-ray diffraction, the composition analysis, the SEM observation, and the ion conductivity were measured in the same manner as in Example 1. The results are shown in Table 4, Fig. 8, Fig. 15, and Fig. 18.

[0118] [Example 4: Sintered body] In Example 4, lithium phosphate (99.0%, Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of lithium hydroxide hydrate in Example 1. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 The procedure was the same as in Example 1, except that the firing temperature was 800°C and 900°C.

[0119] The sintered bodies thus obtained are referred to as the sintered body of Example 4, or the sintered body (800) of Example 4 to the sintered body (900) of Example 4, and the density was measured, and the identification by powder X-ray diffraction, the composition analysis, the SEM observation, and the ion conductivity were measured in the same manner as in Example 1. The results are shown in Table 4 and FIG.

[0120] [Example 5: Sintered body] In Example 5, lithium acetate (99.0%, Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of lithium hydroxide hydrate in Example 1. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 The procedure was the same as in Example 1, except that the firing temperatures were 600°C, 700°C, 800°C, and 900°C.

[0121] The sintered bodies thus obtained are referred to as the sintered body of Example 5 or the sintered body of Example 5 (600) to the sintered body of Example 5 (900), and the density was measured, and the identification by powder X-ray diffraction, the composition analysis, the SEM observation, and the ion conductivity were measured in the same manner as in Example 1. The results are shown in Table 4 and FIG.

[0122] [Example 6: Sintered body] In Example 6, Li was produced by the conventional solid-phase sintering method. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 A sintered body containing the precursor powder (La 3 Zr 1.5 Ta 0.5 O 8.75 Powder) and stoichiometric composition (Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 ) and 10 wt.% excess lithium hydroxide hydrate, then calcined at 900°C for 12 hours to produce Li by solid-state reaction. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 The sintered body was synthesized. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 The fired body was powdered again, uniaxially compressed at 6.25 MPa, and then isostatically pressed at 200 MPa for 5 min to form a green compact, which was then sintered in air at 700°C, 800°C, 900°C, 1000°C, 1100°C, and 1150°C for 40 h to obtain a sintered compact.

[0123] The sintered bodies thus obtained are referred to as the sintered body of Example 6 or the sintered body of Example 6 (700) to the sintered body of Example 6 (1150), and the density was measured, and the identification by powder X-ray diffraction, the composition analysis, the SEM observation, and the ion conductivity were measured in the same manner as in Example 1. The results are shown in Table 4, Fig. 5, Fig. 9, Fig. 16 to Fig. 17, and Fig. 19.

[0124] [Example 7: Sintered body] In Example 7, Li was synthesized by the conventional liquid phase sintering method. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 A sintered body containing the precursor powder (La 3 Zr 1.5 Ta 0.5 O 8.75 Powder) and stoichiometric composition (Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 ) was mixed with 10 wt.% excess lithium hydroxide hydrate to obtain a mixed powder. The mixed powder was uniaxially compressed at 6.25 MPa and then isostatically pressed at 200 MPa for 5 minutes to obtain a green compact. The green compact was 3 Zr 1.5 Ta 0.5 O 8.75 The samples were covered with a powder mixture of lithium hydroxide and lithium hydroxide hydrate and sintered in air at 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, and 1150°C for 40 hours.

[0125] The sintered bodies thus obtained are referred to as the sintered body of Example 7 or the sintered body of Example 7 (500) to (1150), and the density was measured, and the identification by powder X-ray diffraction, the composition analysis, the SEM observation, and the ion conductivity were measured in the same manner as in Example 1. The results are shown in Table 4, Fig. 5, Fig. 10, and Fig. 16 to Fig. 17.

[0126] The results of Examples 1 to 7 are summarized in Tables 3 and 4 for simplicity and are explained below.

[0127] [Table 3]

[0128] [Table 4]

[0129] FIG. 5 shows the sintering temperature dependence of the actual density of the sintered bodies of Examples 1, 6 and 7.

[0130] According to FIG. 5, the sintered body of Example 1 sintered by the method of the present invention (liquid phase infiltration sintering method) had a density of 4.0 g / cm even at a low sintering temperature of 500° C. 3 It was found that the density exceeded 1000°C and was increased. On the other hand, in order to increase the density of the sintered bodies of Examples 6 and 7 by the solid phase sintering method or the liquid phase sintering method, a sintering temperature of about 1100°C was required. This is believed to be due to the fact that in step S220 of FIG. 2 of the method of the present invention, the precursor powder compact is sintered while being brought into contact with lithium hydroxide, so that Li and O (oxygen) of lithium hydroxide can be sufficiently diffused into the powder compact even at a low temperature due to the capillary phenomenon. As shown in Table 4, it was found that the sintered body of Example 1 (800-12) with a sintering time of 12 hours is comparable to the sintered body of Example 1 (800) with a sintering time of 40 hours. This suggests that the sintering time is preferably 10 hours or more.

[0131] FIG. 6 is a diagram showing an XRD pattern of the sintered body of Example 1. FIG. 7 is a diagram showing an XRD pattern of the sintered body of Example 2. FIG. 8 is a diagram showing an XRD pattern of the sintered body of Example 3. FIG. 9 is a diagram showing an XRD pattern of the sintered body of Example 6. FIG. 10 is a diagram showing an XRD pattern of the sintered body of Example 7.

[0132] According to FIG. 6, it was confirmed that the XRD patterns of the sintered bodies of Example 1, in which lithium hydroxide was used as the lithium source in the liquid phase infiltration sintering method, all had a cubic garnet structure and were in good agreement with the JCPDS card (#183686). From this, it was found that a sintered body whose main component was a lithium metal oxide having a cubic garnet structure could be obtained by firing at a firing temperature of 500°C or higher. In addition to the cubic garnet structure, the diffraction peaks of the unreacted precursor powder were observed in the XRD patterns of the sintered bodies (500) and (600) of Example 1, which were fired at 500°C and 600°C. From this, it was shown that a firing temperature higher than 600°C is more preferable.

[0133] In addition, the crystal structure of the sintered body (800) of Example 1 was analyzed using single crystal structure analysis software based on the results of X-ray diffraction measurement. The powder obtained belonged to the space group Ia3￣d (space group number 230 in the International Tables for Crystallography), with lattice constants a=b=c=1.29391 nm and angles α=β=γ=90°. The atomic positions were as shown in Table 1.

[0134] According to FIG. 7, in Example 2 in which lithium carbonate was used as the lithium source in the liquid phase infiltration sintering method, sintered bodies mainly composed of cubic garnet-type lithium metal oxide (sintered body (900) and sintered body (1000) of Example 2) were obtained at a sintering temperature of 900° C. or higher.

[0135] Similarly, according to FIG. 8, in Example 3 in which lithium nitrate was used as the lithium source in the liquid phase infiltration sintering method, sintered bodies (sintered body (800) and sintered body (900) of Example 3) mainly composed of a cubic garnet-type lithium metal oxide were obtained at a sintering temperature of 800° C. or higher.

[0136] Although not shown, even in Examples 4 and 5 in which lithium phosphate and lithium acetate were used as the lithium source, a firing temperature of 800° C. or higher was required to obtain a sintered body mainly composed of a cubic garnet-type lithium metal oxide.

[0137] On the other hand, Fig. 9 shows that the XRD patterns of the sintered bodies of Example 6 obtained by the solid phase sintering method all contain a cubic garnet-type lithium metal oxide as the main component. Fig. 10 shows that the XRD patterns of the sintered bodies of Example 7 obtained by the liquid phase sintering method all contain a cubic garnet-type lithium metal oxide as the main component, although the diffraction peaks of the unreacted precursor powder are observed at sintering temperatures of 500°C and 600°C.

[0138] These results indicate that when using lithium hydroxide as the lithium source in the liquid phase infiltration sintering method to obtain a sintered body mainly composed of a cubic garnet-type structure lithium metal oxide, the sintering temperature needs only to be 500°C or higher and 900°C or lower, and therefore it is possible to lower the sintering temperature.

[0139] FIG. 11 is a diagram showing an SEM image of a cross section of the sintered body of Example 1. FIG. 12 is a diagram showing EDS mapping of a cross section of the sintered body of Example 1. FIG. 13 is a diagram showing a high-resolution TOF-SIMS image of a cross section of the sintered body of Example 1. FIG. 14 is a diagram showing an SEM image of a cross section of the sintered body of Example 2. FIG. 15 is a diagram showing an SEM image of a cross section of the sintered body of Example 3. FIG. 16 is a diagram showing SEM images of the cross sections of the sintered bodies of Examples 6 and 7.

[0140] 11(a) to (c) show SEM images of the sintered body (700) of Example 1, the sintered body (800) of Example 1, and the sintered body (900) of Example 1, respectively. In FIG. 11, it was found that the sintered body of Example 1 is a composite of grains in bright regions and dark regions located so as to fill the grain boundaries of the grains. Furthermore, remarkable grain growth was confirmed in the sintered body (700) of Example 1. Although not shown, grain growth was also confirmed in the sintered body (500) of Example 1. The average grain size of the grains of the sintered body (700), the sintered body (800), and the sintered body (900) of Example 1 was in the range of 5 μm to 20 μm, and no sintering temperature dependency was observed.

[0141] In Fig. 12, the EDS mapping of the sintered body (800) of Example 1 is shown in gray scale, and the regions where each element is present are shown brightly. Focusing on the parts corresponding to the particles, it was found that La, Zr, Ta and O are distributed. The results of Fig. 6, Fig. 11 and Fig. 12 suggest that the particles are lithium metal oxides with a cubic garnet structure, and the grain boundary regions are lithium hydroxide phases.

[0142] FIG. 13 shows the LaO + and Li 2 OH - The high-resolution TOF-SIMS images of the fragments are shown in grayscale. According to Fig. 13, the bright areas are Li 2 OH - The darkened regions are LaO + It was a fragment of LaO + The distribution of fragments is similar to that of the bright particles in Fig. 11 and that of Zr in Fig. 12, for example, and is similar to that of LaO + The fragments were distributed in the cubic garnet-type structure lithium metal oxide particles. 2 OH - The distribution of the fragments was strongly detected in the grain boundary region. From the results in Figures 6 and 13, it was found that the grain boundaries were amorphous lithium hydroxide.

[0143] The volume percentage of the cubic garnet-type lithium metal oxide particles in the sintered body was calculated from the results of Fig. 13 and ICP-OES by multiplying the volume percentage of the cubic garnet-type lithium metal oxide particles obtained by ICP-OES by the relative density.

[0144] According to the sintered body (800) of Example 1, when the volume percentage (71%) measured by ICP-OES is multiplied by the relative density (93%), it was found that the sintered body contains 66 volume% of cubic garnet-type lithium metal oxide particles and 34 volume% of lithium hydroxide. It was found that the sintered body (500) of Example 1 to the sintered body (700) of Example 1 and the sintered body (900) of Example 1 all contain 64 volume% to 68 volume% of cubic garnet-type lithium metal oxide particles and 32 volume% to 36 volume% of lithium hydroxide.

[0145] 14, it was found that the sintered body (800) of Example 2 was also a composite of brightly colored grains and darkly colored grains that filled the grain boundaries. Although not shown, TOF-SIMS revealed that the grains were a cubic garnet-type structure lithium metal oxide phase, and the grain boundaries were lithium carbonate, similar to Example 1.

[0146] Similarly, in Fig. 15, the sintered body (800) of Example 3 had bright regions of grains and dark regions, but the dark regions were voids. This is because the sintering temperature (800°C) exceeded the boiling point of lithium nitrate, which was the lithium source, and lithium nitrate evaporated before diffusing into the precursor.

[0147] 16(a)-(f) show SEM images of the sintered body (700) of Example 6 to the sintered body (1100) of Example 6 and the sintered body (700) of Example 7 to the sintered body (1100) of Example 7, respectively. According to FIG. 16(a)-(c), in the sintered body of Example 6 by the solid phase sintering method, grain growth is promoted at a sintering temperature of 900°C, and the grains grow rapidly at 1100°C, resulting in an extremely dense single phase. Considering the results of FIG. 10, it was found that the sintered body (1100) of Example 6 is composed of a single phase of lithium metal oxide with a cubic garnet structure.

[0148] According to Figs. 16(d) to (e), in the sintered body of Example 7 produced by the liquid phase sintering method, grain growth was promoted at a sintering temperature of 700°C, but at 900°C, voids remained, resulting in a mesh-like structure.

[0149] The element ratios of the sintered body (1150) of Example 6 produced by the solid phase sintering method and the sintered body (1150) of Example 7 produced by the liquid phase sintering method by EDS were (Li, La, Zr, Ta) = (6.40, 3.00, 1.48, 0.49) when La was normalized to 3. 6.5 La 3 Zr 1.5 Ta 0.5 O 12 13. On the other hand, the element ratio of the sintered body (800) of Example 1 by the liquid phase infiltration sintering method, normalized with La at 3, was (Li, La, Zr, Ta) = (10.45, 3.00, 1.51, 0.50), and the Li content was significantly high. This indicates the presence of lithium hydroxide at the grain boundaries, which coincides with the results shown in FIG. 13. In addition, considering the element ratio and the lithium hydroxide content (34 volume%), the particles are 6.5 La 3 Zr 1.5 Ta 0.5 O 12 The particles were identified as lithium metal oxide particles with a cubic garnet structure, and the grain boundaries were found to be amorphous lithium hydroxide.

[0150] The theoretical density of a composite of cubic garnet-type lithium metal oxide and lithium hydroxide is 4.3 g / cm. 3 The relative density of the sintered body (800) of Example 1 was calculated as 93%. On the other hand, the relative density of the sintered body (1100) of Example 6, which does not contain lithium hydroxide, was calculated as Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 Theoretical density (5.4g / cm 3 ) was calculated to be 92.5%. This shows that by employing the method of the present invention, an extremely dense sintered body can be obtained even by low-temperature sintering.

[0151] FIG. 17 is a graph showing the firing temperature dependence of the ionic conductivity of the sintered bodies of Examples 1, 6 and 7. FIG. 18 is a graph showing the firing temperature dependence of the ionic conductivity of the sintered bodies of Examples 1 to 5.

[0152] Figures 17 and 18 show the ionic conductivity of each sintered body at room temperature. Figures 17, 18 and Table 1 show that the ionic conductivity of the sintered body of Example 1, which used lithium hydroxide as the lithium source in the liquid phase penetration sintering method, is two orders of magnitude higher than the ionic conductivity of the sintered bodies of Examples 2 to 5, which used a lithium source other than lithium hydroxide, and Examples 6 and 7, which were produced by the solid phase sintering method or the liquid phase sintering method, particularly at low sintering temperatures of 500°C to 900°C.

[0153] In detail, the ionic conductivity of the sintered bodies of Examples 6 and 7 produced by the solid phase sintering method and the liquid phase sintering method both tended to increase with increasing sintering temperature, reaching 2 to 4 × 10 at a sintering temperature of 1100 °C. -4 The ionic conductivity of the sintered body of Example 2, which used lithium carbonate as the lithium source, also increased with increasing sintering temperature, reaching 1×10 -4 The sintered bodies of Examples 3 to 5, in which lithium nitrate, lithium phosphate and lithium acetate were used as the lithium source, did not show an increase in ionic conductivity regardless of the firing temperature.

[0154] On the other hand, the sintered body of Example 1, in which lithium hydroxide was used as the lithium source, had a melting point of 1×10 -4 It has an ionic conductivity of 2×10 S / cm or more, especially at a sintering temperature of 800°C. -4 It should be noted that the fact that the ionic conductivity increases only when lithium hydroxide is used among the various lithium sources is something that the present inventors discovered only through their own experiments and was therefore unexpected.

[0155] FIG. 19 is a graph showing Arrhenius plots of the ionic conductivity of the sintered bodies of Examples 1 and 6.

[0156] The measurement temperature range is -50℃ to 50℃, and the total ionic conductivity including the contribution of the bulk and grain boundaries in the sintered body is shown. The lithium ionic conductivity follows the Arrhenius equation: σ T = σ 0 exp(-E a / (K B T)) Here, σ T is the lithium ion conductivity, and σ 0 is the pre-exponential factor, E a is the activation energy, K B is the Boltzmann constant and T is the absolute temperature.

[0157] According to Fig. 19, the ionic conductivity of all sintered bodies is T -1 It was found that the ionic conduction path did not change within the measured temperature range, and was linear with respect to the function. Even more surprisingly, it was found that the activation energy of the sintered body (700) and the sintered body (800) of Example 1 was 0.42 eV, which was significantly smaller than that of the sintered body (800) of Example 6 (0.7 eV). Although not shown, the activation energy of the sintered body of Example 1 was smaller than those of the sintered bodies of Examples 2 to 5 and Example 7. From this, it was found that the grain boundary resistance of the sintered body of Example 1 was smaller than those of the sintered bodies of Examples 2 to 7.

[0158] Referring again to Tables 3 and 4, when the ionic conductivity of the sintered body (800) of Example 1, in which the volume content of the cubic garnet-type structure lithium metal oxide particles is 66%, is compared with that of the sintered body (1000) of Example 6, in which the volume content (62%) is the same, the ionic conductivity of the sintered body (800) of Example 1 is 10 times or more higher than that of the sintered body (1000) of Example 6. The ionic conductivity of lithium hydroxide is extremely low (1×10 at 150° C. -9From the above, it is considered that lithium hydroxide does not contribute to the ionic conductivity in the sintered body of Example 1. Rather, it is considered that in the sintered body of Example 1, the cubic garnet-type structure lithium metal oxide particles are connected to each other to efficiently form a network for ionic conduction paths, while the amorphous lithium hydroxide fills the grain boundaries, thereby achieving a high sintered density. In particular, in the present invention, the precursor powder compact is sintered while being brought into contact with lithium hydroxide from the outside, which can promote the formation of continuous ionic conduction paths between the cubic garnet-type structure lithium metal oxide particles.

[0159] As described above with reference to Examples 1 to 7, by carrying out the production method of the present invention shown in FIG. 7-a La 3 A 2 O 12 It was shown that a sintered body can be obtained, which contains particles made of a cubic garnet-type lithium metal oxide represented by the formula (wherein the parameter a satisfies 0≦a≦0.9, and the element A is at least one element selected from the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W), and lithium hydroxide located at the grain boundaries of the particles, and the volume ratio of the cubic garnet-type lithium metal oxide to the total of the lithium metal oxide and lithium hydroxide satisfies the range of 50 vol % to 95 vol %.

[0160] [Example 8: All-solid-state lithium-ion battery] In Example 8, an all-solid-state lithium ion battery was manufactured according to the procedure of FIG.

[0161] FIG. 20 is a diagram illustrating a procedure for manufacturing an all-solid-state lithium-ion battery.

[0162] The precursor powder (La 3 Zr 1.5 Ta 0.5 O 8.75Powder) was uniaxially compressed at 6.25 MPa (step S410 in FIG. 4). The obtained green compact had a diameter of 9 mm and a thickness of 1.3 mm. Next, lithium cobalt oxide powder (99.0%, manufactured by Nippon Chemical Industry Co., Ltd.) as a positive electrode active material and the precursor powder were mixed at a volume ratio of 1:1 to prepare a positive electrode mixed powder. This positive electrode mixed powder was placed on the green compact of the precursor powder and uniaxially compressed at 6.25 MPa (step S420 in FIG. 4). As a result, a laminated green compact was obtained in which a layer made of the precursor powder and a layer made of the positive electrode mixed powder were laminated.

[0163] The laminated green compact was isostatically pressed at 200 MPa for 5 minutes to further densify the laminated green compact. At this time, the thickness of the mixed powder portion in the laminated green compact was 50 μm. The densified laminated green compact was placed in a magnesia crucible, covered with lithium hydroxide hydrate (lithium hydroxide hydrate, 99.0%, Wako Pure Chemical Industries, Ltd.), and fired in air at 500°C for 40 hours and then at 700°C for 10 hours (step S430 in FIG. 4). Here too, the lithium hydroxide hydrate was fired in such a way that the amount of Li in the lithium hydroxide hydrate was in the stoichiometric composition of cubic garnet-type lithium hydroxide (Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 ) was adjusted to fill eight times the amount of

[0164] In this way, a laminated sintered body was obtained, which was a sintered body containing a cubic garnet-type lithium metal oxide and lithium hydroxide, and a positive electrode layer containing a positive electrode active material, a cubic garnet-type lithium metal oxide, and lithium hydroxide. The cross section of the obtained laminated sintered body was observed by SEM. The results are shown in FIG.

[0165] FIG. 21 is a diagram showing an SEM image of a cross section of the laminated sintered body of Example 8.

[0166] As shown in FIG. 21, the laminated sintered body was composed of two layers, a positive electrode layer and a solid electrolyte. In detail, the solid electrolyte was composed of particles of a cubic garnet-type lithium metal oxide (here, Li 6.5La 3 Zr 1.5 Ta 0.5 O 12 The positive electrode layer was composed of particles of a phase represented by LLZTO (Li-ZrO2) and lithium hydroxide located at the grain boundaries. On the other hand, the positive electrode layer was a composite of particles of lithium cobalt oxide, the positive electrode active material, particles of lithium metal oxide with a cubic garnet structure (LLZTO), and lithium hydroxide located at the grain boundaries. Here too, the lithium hydroxide was amorphous.

[0167] Next, the laminated sintered body was used as a half cell to measure the battery performance. For the measurement, a gold (Au) electrode was formed on the positive electrode side of the laminated body by magnetron sputtering. Then, a lithium metal (Li) electrode was formed on the negative electrode side of the laminated body by vacuum deposition inside a glove box. The battery performance of the all-solid-state lithium-ion battery thus obtained was evaluated using a charge / discharge device (SP-200, manufactured by Bio-Logic Science Instruments). The measurement was performed in a constant temperature furnace at 60°C, with the C rate during the charge / discharge test being 0.025C and the current value being 0.53mAcm. -2 The voltage range was 3 to 4.2 V. The results are shown in FIG.

[0168] FIG. 22 is a diagram showing charge / discharge curves of the all-solid-state lithium ion battery of Example 8.

[0169] According to Figure 22, the charging capacity is 101mAhg -1 and the discharge capacity is 85mAhg -1 The charge and discharge of the all-solid-state lithium-ion battery of Example 8 was confirmed. The discharge voltage of the all-solid-state lithium-ion battery of Example 8 was about 3.7 V, which was consistent with the charge and discharge voltage (about 3.7 V) of the positive electrode active material lithium cobalt oxide. On the other hand, the charge voltage of the all-solid-state lithium-ion battery of Example 8 was about 4.0 V, which was slightly higher, but this is believed to be due to the low electronic conductivity of lithium cobalt oxide in the charged state.

[0170] As described above with reference to Example 8, it has been shown that the sintered body of the present invention is used as a solid electrolyte of an all-solid-state lithium ion battery, and that by carrying out the production method of the present invention shown in FIG. 4, an all-solid-state lithium ion battery can be provided by integrally sintering the solid electrolyte and the electrode layer. [Industrial Applicability]

[0171] The sintered body of the present invention achieves excellent ion conductivity by containing a predetermined amount of cubic garnet-type lithium metal oxide particles and lithium hydroxide at the grain boundaries. Such a sintered body is effective as a solid electrolyte for an all-solid-state lithium ion battery. In addition, according to the method of the present invention, the above-mentioned sintered body can be produced at a low temperature of 500°C to 900°C, so that it can be sintered together with an electrode layer, which is advantageous for practical use of an all-solid-state lithium ion battery. [Explanation of symbols]

[0172] 100 Sintered body 110 Lithium Metal Oxide (LLAO Particles) 120 Lithium Hydroxide 300 All-solid-state lithium-ion battery 310 Solid electrolyte 320 Positive electrode layer 330 Negative electrode layer

Claims

1. Li ７－ａ La ３ A ２ O １２ (The parameter a satisfies 0 ≦ a ≦ 0.9, and the A element is an element selected from at least one of the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W)), and particles composed of a cubic garnet-type lithium metal oxide represented by containing lithium hydroxide located at the grain boundaries of the particles and and, a sintered body in which the volume ratio of the lithium metal oxide to the total volume of the lithium metal oxide and the lithium hydroxide is in the range of 50% by volume or more and 95% by volume or less.

2. The sintered body according to claim 1, wherein the lithium hydroxide is amorphous.

3. The sintered body according to claim 1, wherein the volume ratio of the lithium metal oxide to the total volume of the lithium metal oxide and the lithium hydroxide is in the range of 60% by volume or more and 80% by volume or less.

4. The sintered body according to claim 1, wherein the particles have a particle size in the range of 1 μm or more and 70 μm or less.

5. The ionic conductivity at room temperature satisfies the range of 5.0×10 －５ S / cm or more and 2.0×10 －３ S / cm or less. The sintered body according to claim 1.

6. La ３ A ２ O ９－ｂ (The parameter b satisfies -0.5 ≤ b ≤ 0.5, and the A element is an element selected from at least one of the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W)), compacting the precursor powder represented thereby.) bringing at least a part of the green compact obtained by the compacting into contact with lithium hydroxide powder and firing in a temperature range of 500°C or more and 900°C or less and a method for producing the sintered body according to claim 1, including.

7. bringing at least a part of the green compact into contact with the lithium hydroxide powder in an amount such that the lithium in the lithium hydroxide powder satisfies a range of 1 to 16 times the molar ratio of the lithium in the lithium metal oxide, the method for producing according to claim 6.

8. The method for producing according to claim 6 or 7, wherein obtaining the sintered body is firing for a time of 2 hours or more and 72 hours or less.

9. A solid electrolyte using the sintered body according to claim 1.

10. An all-solid-state lithium-ion battery including at least the solid electrolyte according to claim 9.

11. further including a positive electrode layer and a negative electrode layer, wherein the solid electrolyte is located between the positive electrode layer and the negative electrode layer, The positive electrode layer includes a positive electrode active material and Li ７－ａ La ３ A ２ O １２ (where parameter a satisfies 0 ≦ a ≦ 0.9, and element A is an element selected from at least one of the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W)) and a complex of lithium hydroxide, the all-solid-state lithium-ion battery according to claim 10.

12. The all-solid-state lithium-ion battery according to claim 11, wherein the positive electrode active material is selected from the group consisting of lithium transition metal oxides and lithium sulfides.

13. The all-solid-state lithium-ion battery according to claim 11, wherein the negative electrode layer includes a negative electrode active material selected from the group consisting of a carbon material, a metal material, a conductive polymer, and sulfides and oxides.

14. The all-solid-state lithium-ion battery according to claim 13, wherein the negative electrode layer is a composite of the negative electrode active material, a cubic garnet-type structure lithium metal oxide, and lithium hydroxide.

15. La ３ A ２ O ９－ｂ (The parameter b satisfies -0.5 ≤ b ≤ 0.5, and the A element is an element selected from at least one of the group consisting of zirconium (Zr), tantalum (Ta), hafnium (Hf), tin (Sn), niobium (Nb), titanium (Ti), vanadium (V), bismuth (Bi), molybdenum (Mo), and tungsten (W)), compacting a precursor powder that satisfies this condition.) placing a positive electrode mixed powder containing a positive electrode active material powder and the precursor powder on the green compact obtained by the compacting and compacting, At least a part of the laminated compact obtained by placing and compacting the above is brought into contact with lithium hydroxide powder and fired in a temperature range of 500°C or higher and 900°C or lower, and A method for manufacturing an all-solid-state lithium-ion battery according to any one of claims 10 to 14, including.

16. The method for manufacturing according to claim 15, including placing the mixed powder for the positive electrode and compacting it, and then placing the mixed powder for the negative electrode containing the negative electrode active material powder and the precursor powder on the side opposite to the side on which the mixed powder for the positive electrode is placed and compacting the laminated compact obtained by placing and compacting the mixed powder for the positive electrode.

17. The method for manufacturing according to claim 15, further including forming a negative electrode layer on the side opposite to the side on which the mixed powder for the positive electrode is placed and compacted after the firing.

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