Sintered body, solid electrolyte thereof, all-solid-state lithium-ion battery thereof, and methods for manufacturing the same.

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, its solid electrolyte, its all-solid-state lithium-ion battery, and methods for manufacturing the same. [Background technology]

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

[0003] Lithium-ion conductive oxides with a garnet-type structure can exist in a tetragonal crystal structure that is stable at room temperature, or in a cubic crystal structure that is stable at high temperatures. However, they are known to exhibit high ionic conductivity in the cubic crystal structure. For this reason, lithium-ion conductive oxides with a cubic garnet-type structure are considered promising candidate materials for solid electrolytes.

[0004] When synthesizing lithium-ion conductive oxides with this cubic garnet-type structure using common oxide raw materials, it is generally necessary to synthesize them at a firing temperature exceeding 900°C, and then densify them by sintering at even higher temperatures.

[0005] Furthermore, when manufacturing all-solid-state lithium-ion batteries using such oxide sintered bodies as solid electrolytes, there is a technique to integrally sinter the solid electrolyte and electrodes at high temperatures, forming a strong interface between them. However, when using the aforementioned lithium-ion conductive oxides, integral sintering with the electrodes at temperatures exceeding 900°C causes interdiffusion between the electrodes and the solid electrolyte, resulting in the formation of different phases at the interface. Therefore, it is desirable to lower the sintering temperature of the lithium-ion conductive oxides to enable integral sintering with the electrodes.

[0006] In recent years, techniques have been developed to produce lithium-ion conductive oxide sintered bodies having a garnet-type structure using precursors (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, comprising a step of heat-treating a mixture of 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) to obtain a first sintered body, and a step of heat-treating the first sintered body in contact with a Li source to obtain a second sintered body. A method for manufacturing a structure characterized by including the above steps is disclosed. Patent Document 1 discloses lithium metal alone, lithium oxide, lithium hydroxide, lithium halide, lithium phosphate, lithium carbonate, lithium acetate, lithium oxalate, lithium nitrate, and lithium sulfate as the Li source.

[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 obtaining the first sintered body is performed at 1200 to 1400 °C, it is still difficult to integrally sinter with the 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 (LiNO3) at 700 to 1000 °C for 10 hours to obtain a dense cubic crystal Li 6.5 La3Zr 1.5 Ta 0.5 O 12We report obtaining a layered structure. However, there are no reports of high ionic conductivity at sintering temperatures below 900°C.

[0010] Patent Document 2 is A x E y La3G 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 calcining a mixture of an amorphous composite metal oxide and a lithium salt, which consists of a compound represented by the formula (wherein A is an element that forms a divalent cation, E is an element that forms a trivalent cation, G is an element that forms a tetravalent cation, J is an element that forms a pentavalent cation, L is an element that forms a hexavalent cation, x is between 0 and 0.3, y is between 0 and 0.3, z is between 0 and 1.0, and q is between 0 and 0.5).

[0011] In particular, according to Examples 4 and 8 of Patent Document 2, La3Zr is used as the amorphous composite metal oxide precursor. 1.5 Ta 0.5 O 8.75 Then, lithium oxide or lithium peroxide is mixed as a lithium salt and calcined at 400°C for 12 hours to obtain Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The cubic garnet-type lithium composite metal oxide shown is hot-pressed and sintered at 400°C. The ionic conductivity of the sintered body obtained in this way at room temperature is 3.6 × 10⁻⁶. -5 It had a density of S / cm and exhibited high ionic conductivity.

[0012] Non-patent document 2 states that La is used as a precursor. 2+x Zr 2-2x Ta x Li obtained by calcining O7 (x=0.4) and lithium oxide at 400°C to 500°C for 12 hours. 6.5 La3Zr 1.5 Ta 0.5 O 12The material is pelletized and sintered at 1100°C for 4 hours. The ionic conductivity of the sintered body obtained in this way at room temperature is 9.4 × 10⁻⁶. -4 It had a density of S / cm and exhibited high ionic conductivity.

[0013] However, both Patent Document 2 and Non-Patent Document 2 describe calcining the precursor and lithium salt, and producing cubic Li 6.5 La3Zr 1.5 Ta 0.5 O 12 After obtaining the powder, it needs to be densified by hot pressing, making the process complicated. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] International Publication No. 2016 / 178321 [Patent Document 2] Japanese 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 [Overview of the project] [Problems that the invention aims to solve]

[0016] Therefore, the object of the present invention is to provide a sintered body containing a cubic garnet-type lithium metal oxide that can be sintered at a temperature of 900°C or less, which allows for integral sintering with electrodes, and which has excellent ionic conductivity; a solid electrolyte using the same; an all-solid-state lithium battery; and a method for manufacturing the same. [Means for solving the problem]

[0017] The sintered body according to the present invention is a Li 7-a La3A2O 12 The invention provides a solution to the above problem by providing particles made of a cubic garnet-type lithium metal oxide represented by (parameter a satisfies 0 ≤ a ≤ 0.9, and element A is an 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, wherein 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% by volume or more and 95% by volume or less. 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% by volume or more and 80% by volume or less. The particles may have a particle size in the range of 1 μm to 70 μm. The ionic conductivity at room temperature is 5.0 × 10⁻⁶. -5 S / cm or more 2.0×10 -3 The range of S / cm or less may be satisfied. The method for manufacturing the above-mentioned sintered body according to the present invention is La3A2O 9-b The present invention relates to a method that involves compacting a precursor powder represented by (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 then contacting at least a portion of the compact obtained by the compaction with lithium hydroxide powder and firing it at a temperature range of 500°C to 900°C, thereby solving the above problem. At least a portion of the compacted powder may be brought into contact with lithium hydroxide powder in an amount that satisfies the range of 1 to 16 times the molar ratio of lithium in the lithium metal oxide. The aforementioned sintered body may be obtained by firing for a period of 2 hours to 72 hours. 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 above all-solid-state lithium-ion battery further comprises a positive electrode layer and a negative electrode layer, the solid electrolyte is located between the positive electrode layer and the negative electrode layer, and the positive electrode layer comprises a positive electrode active material and Li 7-a La3A2O 12 The composite may consist of a cubic garnet-type lithium metal oxide represented by (parameter a satisfies 0 ≤ a ≤ 0.9, and element A is an 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. The positive electrode active material may be selected from the group consisting of lithium transition metal oxides and lithium sulfides. The negative electrode layer may comprise a negative electrode active material selected from the group consisting of carbon materials, metallic materials, conductive polymers, and sulfides and oxides. The negative electrode layer may be a composite of the negative electrode active material, a cubic garnet-type lithium metal oxide, and lithium hydroxide. The method for manufacturing the all-solid-state lithium-ion battery according to the present invention is La3A2O 9-bThe present invention relates to the following steps: compacting a precursor powder that satisfies the following conditions (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 mixed powder for a positive electrode containing positive electrode active material powder and the precursor powder onto the compact obtained by the above compaction, and compacting it; and contacting at least a portion of the laminated compact obtained by the above placement and compaction with lithium hydroxide powder and firing it in a temperature range of 500°C to 900°C, thereby solving the above problem. The process may include placing the positive electrode mixed powder and compacting it, followed by placing the negative electrode mixed powder containing the negative electrode active material powder and the precursor powder on the side of the laminated compact obtained by placing and compacting the positive electrode mixed powder that is opposite to the side on which the positive electrode mixed powder was placed, and then compacting it. Following the firing process, the method may further include placing the positive electrode mixed powder and forming a negative electrode layer on the side opposite to the compacted side. [Effects of the Invention]

[0018] The sintered body of the present invention is Li 7-a La3A2O 12The present invention contains particles (LLAO particles) made of a cubic garnet-type lithium metal oxide represented by (parameter a satisfies 0 ≤ a ≤ 0.9, and element A is an 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. The sintered body of the present invention has LLAO particles in a range of 50% to 95% by volume, so the LLAO particles are linked to each other and form ion conduction paths, resulting in high ionic conductivity. Furthermore, the presence of lithium hydroxide between the LLAO particles densifies the material, resulting in even better ionic conductivity. Such a sintered body can function as a solid electrolyte, providing an all-solid-state lithium-ion battery.

[0019] The present invention provides a method for manufacturing a sintered body using La3A2O 9-b A precursor powder represented by (-0.5 ≤ b ≤ 0.5, element A is at least one element selected from the group consisting of Zr, Ta, Hf, Sn, Nb, Ti, V, Bi, Mo, and W) is compacted, and at least a portion of the resulting compact is brought into contact with lithium hydroxide powder and fired in a temperature range of 500°C to 900°C, thereby obtaining the sintered body described above. A sintered body containing a cubic garnet-type lithium metal oxide can be obtained from the precursor powder in one step, making the process simple. Furthermore, because low-temperature firing below 900°C is possible, it is advantageous for practical application as it enables integrated firing with electrodes such as positive and negative electrodes. [Brief explanation of the drawing]

[0020] [Figure 1] Schematic diagram showing the sintered body of the present invention. [Figure 2] Flowchart showing the process for manufacturing the sintered body of the present invention. [Figure 3] A schematic diagram showing the all-solid-state lithium-ion battery of the present invention. [Figure 4]Flowchart showing the manufacturing process of the all-solid-state lithium-ion battery of the present invention. [Figure 5] Sintering temperature dependence of actual density of sintered bodies in Examples 1, 6, and 7 [Figure 6] Figure showing the XRD pattern of the sintered body in Example 1. [Figure 7] Figure showing the XRD pattern of the sintered body in Example 2. [Figure 8] Figure showing the XRD pattern of the sintered body in Example 3. [Figure 9] Figure showing the XRD pattern of the sintered body in Example 6. [Figure 10] Figure showing the XRD pattern of the sintered body in Example 7. [Figure 11] Figure showing an SEM image of the cross-section of the sintered body in Example 1. [Figure 12] Figure showing EDS mapping of the cross-section of the sintered body in Example 1. [Figure 13] Figure showing a high-resolution TOF-SIMS image of the cross-section of the sintered body in Example 1. [Figure 14] Figure showing an SEM image of the cross-section of the sintered body in Example 2. [Figure 15] Figure showing an SEM image of the cross-section of the sintered body in Example 3. [Figure 16] Figure showing SEM images of cross-sections of sintered bodies in Examples 6 and 7. [Figure 17] Figure showing the dependence of the ionic conductivity of the sintered bodies in Examples 1, 6, and 7 on the firing temperature. [Figure 18] Figure showing the dependence of the ionic conductivity of sintered bodies in Examples 1 to 5 on the firing temperature. [Figure 19] Figure showing the Arrhenius plots of the ionic conductivity of the sintered bodies in Example 1 and Example 6. [Figure 20] Diagram showing the procedure for manufacturing all-solid-state lithium-ion batteries. [Figure 21] Figure showing an SEM image of the cross-section of the laminated sintered body in Example 8. [Figure 22] Figure showing the charge and discharge curves of the all-solid-state lithium-ion battery in Example 8. [Modes for carrying out the invention]

[0021] Embodiments of the present invention will be described below with reference to the drawings. Similar elements are denoted by the same reference numerals, and their descriptions are omitted.

[0022] (Embodiment 1) Embodiment 1 describes the sintered body and method for manufacturing the same according to the present invention.

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

[0024] The sintered body 100 of the present invention is Li 7-a La3A2O 12 The present invention contains particles (LLAO particles) 110 made of a cubic garnet-type lithium metal oxide represented by (parameter a satisfies 0 ≤ a ≤ 0.9, and element A is an 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 120 located at the grain boundaries of the particles 110. The sintered body 100 of the present invention has excellent ionic conductivity because it contains LLAO particles that have ionic conductivity.

[0025] Furthermore, in the sintered body 100 of the present invention, the ratio of the volume of lithium metal oxide to the total volume of lithium metal oxide (LLAO particles 110) and lithium hydroxide 120 satisfies the range of 50% to 95% by volume. By containing lithium metal oxide constituting the LLAO particles 110 within the above range, the LLAO particles can be linked to each other, forming a network structure that creates ion conduction paths. As a result, the high ion conductivity inherent in lithium metal oxide can be achieved in the sintered body 100. In addition, the position of lithium hydroxide 120 at the grain boundaries of the LLAO particles 110 enables a high sintering density.

[0026] The structure of the sintered body 100 of the present invention will be described in more detail. LLAO particles 110 consist of lithium metal oxide having a cubic garnet-type structure, and the general formula is Li7-a La3A2O 12 The following conditions are met: Parameter a satisfies the range 0 ≤ a ≤ 0.9, and within this range, a cubic garnet-type structure is maintained. Furthermore, element A is an 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. Composed of these elements, an oxide with excellent ionic conductivity is formed. For example, if Zr and Ta are selected as element A, any combination of Zr and Ta equaling 2 is permitted.

[0027] General formula Li 7-a La3A2O 12 One example of a cubic garnet-type lithium metal oxide is one where a=0.5 and A is Zr and Ta. 6.5 La3Zr 1.5 Ta 0.5 O 12 There is. Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The crystal structure parameters are shown in Table 1.

[0028] [Table 1]

[0029] Li 6.5 La3Zr 1.5 Ta 0.5 O 12 It belongs to the cubic crystal system, has a garnet-type structure, and belongs to the Ia3-d space group (3- is an overbar representation of 3, space group 230 in the International Tables for Crystallography), occupying the crystal parameters and atomic coordinate positions shown in Table 1. In Table 1, the lattice constants a, b, and c represent the lengths of the unit cell axes, and α, β, and γ represent the angles between the unit cell axes.

[0030] General formula Li7-a La3A2O 12 Whether it is a crystal represented by La3A2O can be identified by X-ray diffraction or neutron diffraction. In the general formula Li 7-a La3A2O 12 In the crystal represented by La3A2O, although the lattice constant varies depending on the value of the parameter a, the type and ratio of the A element, the atomic positions given by the crystal structure and the sites occupied by the atoms and their coordinates do not change significantly enough to break the chemical bonds between the framework atoms. In the present invention, when the bond lengths calculated from the lattice constants and atomic coordinates obtained by analyzing the results of X-ray diffraction or neutron diffraction in the space group of Ia3￣d are within ±5% compared to the bond lengths calculated from the crystal structure parameters shown in Table 1, it has the same crystal structure and can be determined to be a crystal represented by the general formula Li 7-a La3A2O 12 In addition, as a more convenient determination method, when the main peak positions (2θ) of the X-ray diffraction pattern of the sintered body of interest match the diffraction peak positions (2θ) calculated using the crystal structure parameters in Table 1, it may be determined to be a crystal satisfying the general formula Li

[0031] La3A2O 7-a La3A2O 12 For example, it may be determined using about 10 main peaks with strong diffraction intensity.

[0032] As examples of the crystal represented by the general formula Li 7-a La3A2O 12 In addition to the above-mentioned Li 6.5 La3Zr 1.5 Ta 0.5 O 12 there are Li 6.5 La3(Zr,Ta)2O 12 Li 6.5 La3(Zr,Nb)2O 12 etc. All of these are known to be excellent ion conductors. Here, (Zr,Ta) means that Zr and Ta exist at an arbitrary ratio at the site of the A element.

[0033] The general formula Li 7-a La3A2O 12In the crystal represented by [formula], the parameter a only needs to satisfy 0 ≤ a ≤ 0.9, but preferably satisfies 0.3 ≤ a ≤ 0.7. This stabilizes the cubic garnet-type structure, resulting in an excellent ionic conductor.

[0034] General formula Li 7-a La3A2O 12 In the crystal represented by , from the viewpoint of ionic conductivity, 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 La3Zr 2-x Ta x O 12 A crystal represented by (parameter a satisfies 0.3 ≤ a ≤ 0.7 and x satisfies 0.3 ≤ x ≤ 0.7) is preferable because it makes an excellent ion conductor.

[0035] Lithium hydroxide 120 is located at the grain boundaries of the LLAO particles 110, and can improve the sintering density while maintaining the connectivity of the LLAO particles 110, thus contributing to an improvement in ionic conductivity. Lithium hydroxide 120 is preferably amorphous. This allows for a denser sintered body 100.

[0036] The content of LLAO particles 110 in the sintered body 100, that is, the volume ratio of lithium metal oxide to the total of lithium metal oxide and lithium hydroxide, is preferably in the range of 60% to 80% by volume. This maintains a high sintering density while having excellent ionic conductivity. The volume ratio of lithium metal oxide is more preferably in the range of 64% to 68% by volume.

[0037] In this specification, the volume percentage of lithium metal oxide was calculated by multiplying the volume percentage of lithium metal oxide obtained from inductively coupled plasma atomic emission spectrometry (ICP-OES) by the relative density. In detail, the calculation was performed using the following procedure. 1) ICP-OES measurement is used to detect the molar ratio of elements excluding oxygen (e.g., Li, La, Zr, Ta). 2) The composition ratio of Li in the lithium metal oxide is calculated based on the composition ratio of Zr and Ta, so as to maintain charge neutrality (Li, La, and A are cations, and O is an anion. For example, if Zr is 1.5 and Ta is 0.5, then Li will be 6.5). 3) The molar ratio of LiOH·H2O is calculated by subtracting the number of moles of Li in the lithium metal oxide from the molar ratio of Li detected (for example, if Li=10, La=3, Zr=1.5, and Ta=0.5 are detected, the molar ratio of LiOH·H2O will be 10-6.5=3.5, and Li 6.5 La3Zr 1.5 Ta 0.5 O 12 (It will become a sintered body of +3.5LiOH·H2O). 4) Calculate the mass by multiplying the number of moles (mol) of each substance by its molecular weight (g / mol). 5) The density (g / cm³) of each mass (g) 3 The volume is calculated by dividing by ). 6) Convert the volume percentages from the respective volume ratios and multiply them by the relative densities obtained using the method described later.

[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 connect with 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 them to exhibit excellent ionic conductivity. The particle size in the sintered body was calculated from the number of particles per unit area using SEM images. Specifically, the apparent average particle diameter of the crystal grains was measured from SEM images of the mirror-polished surface of the sintered body, and the particle size was calculated by multiplying this by a coefficient of 1.225 determined based on metric morphology. The average particle diameter was the average value obtained 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 results in excellent ionic 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 to the theoretical density of the sintered body (bulk density of the sintered body / theoretical density of the sintered body × 100). Bulk density of the sintered body (g / cm³ 3 The g / cm³ of the sintered body 100 of the present invention is preferably 4.0 g / cm³. 3 More than 4.3g / cm 3 The actual density is within the following range. The theoretical density is 4.3 g / cm³. 3 Let's assume that.

[0040] The sintered body 100 of the present invention exhibits excellent ionic conductivity, preferably 5.0 × 10⁻⁶. -5 S / cm or more 2.0×10 -3 The sintered body 100 of the present invention satisfies a range of S / cm or less. Therefore, the sintered body 100 of the present invention is particularly advantageous as a solid electrolyte for lithium-ion secondary batteries. The sintered body 100 of the present invention is more preferably 1.0 × 10⁻⁶ -4 S / cm or more 2.0×10 -3 The range of S / cm or less is satisfied. The sintered body 100 of the present invention preferably has an activation energy in the range of 0.3 eV to 0.5 eV and is an excellent ion conductor.

[0041] Next, a method for producing the sintered body 100 of the present invention will be described. Figure 2 is a flowchart showing the process for manufacturing the sintered body of the present invention.

[0042] The process for manufacturing the sintered body of the present invention includes the following steps S210 to S220. Step S210: La3A2O 9-bA precursor powder represented by (parameter b satisfies -0.5 ≤ b ≤ 0.5, and element A is an 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 compacted. Step S220: At least a portion of the compacted powder obtained by compacting in Step S210 is brought into contact with lithium hydroxide powder and fired at a temperature range of 500°C to 900°C.

[0043] According to the inventors of the present invention, the above general formula La3A2O 9-b We discovered that the sintered body 100 of the present invention described above can be obtained by liquid-phase penetration sintering (LLPS) by firing a compacted powder made from a precursor powder represented by [formula] in contact with lithium hydroxide, selected from among many lithium-containing materials. Surprisingly, we found that, according to the method of the present invention, a sintered body with excellent ionic conductivity and high sinter density can be obtained directly from the precursor powder even at a firing temperature of 500°C to 900°C, which is lower than conventional methods.

[0044] Each step will be explained in more detail. In step S210, La3A2O 9-b In the precursor powder represented by [formula], considering that oxygen deficiency or excess may occur depending on the calcination conditions, the parameter b should satisfy -0.5 ≤ b ≤ 0.5. Element A is, as mentioned above, an 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). Element A is explained with reference to Figure 1 and will therefore be omitted.

[0045] General formula La3A2O 9-b One of the precursor powders represented by is La3Zr, where b=0.25 and A is Zr and Ta. 1.5Ta 0.5 O 8.75 There is. La3Zr 1.5 Ta 0.5 O 8.75 The crystal structure parameters are shown in Table 2.

[0046] [Table 2]

[0047] La3Zr 1.5 Ta 0.5 O 8.75 It belongs to the cubic crystal system, has a fluorite-type structure, and belongs to the Fm3-m space group (3- is an overbar representation of 3, space group 225 in the International Tables for Crystallography), occupying the crystal parameters and atomic coordinate positions shown in Table 2. In Table 2, the lattice constants a, b, and c represent the lengths of the unit cell axes, and α, β, and γ represent the angles between the unit cell axes.

[0048] General formula La3Zr 1.5 Ta 0.5 O 8.75 Whether a crystal is represented by the formula La3A2O can be identified by X-ray diffraction or neutron diffraction. 9-b In a crystal satisfying the conditions, the lattice constant changes depending on the value of parameter b, the selection and proportion of the type of element A, but the atomic positions given by the crystal structure, the sites occupied by atoms, and their coordinates do not change so drastically that the chemical bonds between skeletal atoms are broken. In this invention, if the bond length calculated from the lattice constant and atomic coordinates obtained by analyzing the results of X-ray diffraction and neutron diffraction in the space group Fm3-m is within ±5% of the bond length calculated from the crystal structure parameters shown in Table 2, then the crystal has the same crystal structure and the general formula is La3A2O 9-b It can be determined that it is a crystal represented by [formula].

[0049] Furthermore, a simpler method of determination is to determine if the main peak position (2θ) of the X-ray diffraction pattern of the sintered body in question matches the diffraction peak position (2θ) calculated using the crystal structure parameters in Table 2, in which case the general formula La3A2O9-b It can be determined that the crystal satisfies the following conditions. For example, it is good to make this determination based on about 10 peaks with strong diffraction intensity as the main peaks.

[0050] General formula La3A2O 9-b As an example of a crystal represented by the above La3Zr 1.5 Ta 0.5 O 8.75 In addition, La3(Zr,Ta)2O 8.75 La3(Zr,Nb)2O 8.75 These are all known to be excellent ionic conductors. Here, (Zr,Ta) means that Zr and Ta are present in any ratio at the site of element A.

[0051] General formula La3A2O 9-b In the crystal represented by , the parameter b should satisfy -0.5 ≤ b ≤ 0.5, but preferably 0 ≤ b ≤ 0.25. This stabilizes the cubic fluorite-type structure, allowing Li to penetrate during the liquid-phase penetration sintering method, and the general formula Li 7-a La3A2O 12 This can promote the formation of crystals represented by [formula].

[0052] Note: The general formula is La3A2O 9-b The precursor powder represented by can be obtained commercially or synthesized by a solid-phase reaction method. When synthesized by a solid-phase reaction method, for example, raw materials containing La (e.g., lanthanum hydroxide, lanthanum oxide, etc.) and raw materials containing element A (e.g., oxide of element A, hydroxide of A, etc.) can be weighed so that the stoichiometric ratio of La and element A is La:A = 3:2, mixed, and calcined.

[0053] The particle size (primary particle diameter) of the precursor powder is preferably in the range of 0.005 μm to 10 μm. This allows for the acquisition of a compacted body with high relative density through compaction. More preferably, the particle size of the precursor powder is 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 during the firing process described later, resulting in a dense sintered body. The primary particle diameter is measured by laser scattering.

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

[0055] In step S210, methods such as die pressing and cold isostatic (cold hydrostatic) processing can be used to compact the powder. The molding pressure is preferably 5 MPa or higher. This yields a compact that satisfies the relative density described above. The molding pressure is more preferably 150 MPa or higher, even more preferably 180 MPa or higher, and there is no particular upper limit, but it may be 300 MPa or lower.

[0056] In step S220, the amount of lithium hydroxide powder to be contacted with the compacted powder obtained in step S210 is preferably such that the amount of Li (1 mole) in the lithium hydroxide is equal to the amount of Li in the general formula described above. 7-a La3A2O 12 The amount of Li is adjusted to satisfy a range of 1 to 16 times the amount of Li ((7-a) moles). By contacting lithium hydroxide powder in this range and firing it, lithium permeates the compacted powder, and the general formula Li 7-a La3A2O 12 A phase represented by [formula] can be formed, which then becomes a complex with lithium hydroxide.

[0057] The amount of lithium hydroxide powder is more preferably such that the amount of Li (1 mole) in the lithium hydroxide is equal to the amount of Li in the general formula described above. 7-a La3A2O 12The amount of Li is adjusted to satisfy a range of 5 to 13 times the amount of Li ((7-a) moles). This allows the general formula Li 7-a La3A2O 12 The formation of the phase represented by is promoted, and it becomes a complex with lithium hydroxide.

[0058] The amount of lithium hydroxide powder is more preferably such that the amount of Li (1 mole) in the lithium hydroxide is equal to the amount of Li in the general formula described above. 7-a La3A2O 12 The amount of Li is adjusted to satisfy a range of 6 to 10 times the amount of Li ((7-a) moles). This makes the general formula Li 7-a La3A2O 12 The formation of the phase represented by is further promoted, resulting in a complex with lithium hydroxide.

[0059] In step S220, the firing temperature is not particularly limited as long as it is within the temperature range of 500°C to 900°C, but preferably it is within the temperature range of 600°C to 900°C. Within this range, a sintered body with higher ionic conductivity can be obtained. The firing temperature is more preferably within the temperature range of 750°C to 850°C. Within this range, a sintered body with even higher ionic conductivity can be obtained.

[0060] In step S220, there are no particular restrictions on the firing time, but for example, if the compacted powder has a diameter of 3 mm to 10 mm and a thickness of 0.5 mm to 1.5 mm, firing it for 2 hours or more and 72 hours or less within the above temperature range will result in a general formula Li 7-a La3A2O 12 A phase represented by is generated. The firing time may preferably be in the range of 10 hours to 60 hours.

[0061] In step S220, two or more firing stages may be performed within the above temperature range. For example, firing may be performed at a first temperature selected from the temperature range of 500°C to 700°C, and then at a second temperature selected from the temperature range of 600°C to 900°C, which is higher than the first temperature. In this case, the total firing time should be within the above range. This allows for efficient sintering and is expected to improve sinter 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, there are no particular restrictions on the lithium hydroxide powder to be melted, but for example, a size in the range of 0.01 μm to 50 μm may be used. This allows lithium to penetrate through firing, and the general formula Li described above is formed. 7-a La3A2O 12 A phase represented by can be generated.

[0064] In step S220, the lithium hydroxide powder only needs to be in contact with at least a portion of the compacted powder; however, for example, the compacted powder may be coated with the lithium hydroxide powder. This allows lithium to penetrate efficiently.

[0065] Thus described in Embodiment 1, Li 7-a La3A2O 12 A sintered body is produced which contains particles made of a cubic garnet-type lithium metal oxide represented by (parameter a satisfies 0 ≤ a ≤ 0.9, and element A is an 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, wherein the ratio of the volume of lithium metal oxide to the total volume of lithium metal oxide and lithium hydroxide is in the range of 50 volume% to 95 volume%.

[0066] (Embodiment 2) Embodiment 2 describes the all-solid-state lithium-ion battery of the present invention and a method for manufacturing the same. Figure 3 is a schematic diagram illustrating the all-solid-state lithium-ion battery of the present invention.

[0067] The all-solid-state lithium-ion battery 300 of the present invention comprises at least a solid electrolyte 310. More specifically, the all-solid-state lithium-ion battery 300 of the present invention comprises a solid electrolyte 310, a positive electrode layer 320, and a negative electrode layer 330, wherein 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 exemplary, it is 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, for example, 3 to 5 times the particle size of the positive electrode active material described later. This prevents short circuits. For practical use, it may be 1 μm to 10 μm. Note that the solid electrolyte 310 is made of the sintered body described in Embodiment 1, so further explanation is omitted.

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

[0070] Such positive electrode active materials are selected from the group consisting of lithium transition metal oxides and lithium sulfides. Examples of lithium transition metal oxides include LiCoO2, LiNiO2, Li(Ni,Mn,Co)O2, Li(Ni,Co,Al)O2, Li2MnO3-Li(Ni,Mn,Co)O2, Li(Ni,Mn)2O4, Li(Co,Mn)2O4, Li(Mn,Al)2O4, LiFePO4, LiMnPO4, LiCoPO4, LiNiPO4, etc. Examples of lithium sulfides include Li2S, Li2S x (x=4, 6, 8, etc.) are acceptable.

[0071] The positive electrode layer 320 preferably comprises a positive electrode active material and Li 7-a La3A2O 12 The material contains a cathode composite of a cubic garnet-type lithium metal oxide (where parameter a satisfies 0 ≤ a ≤ 0.9, 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 lithium hydroxide. 7-a La3A2O 12 The cubic garnet-type lithium metal oxide represented by is the same as the cubic garnet-type lithium metal oxide described in Embodiment 1, so its description is omitted. The inclusion of such a positive electrode composite in the positive electrode layer 320 is advantageous because it allows the positive electrode layer 320 and the solid electrolyte 310 to bond without the formation of an interfacial reaction phase between the positive electrode active material and the solid electrolyte, thereby forming a high-speed Li conduction path 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% to 95% by volume. Within this range, the positive electrode active material can desorb / adsorb a sufficient amount of lithium ions. More preferably, the content of the positive electrode active material is in the range of 40% to 80% by volume. The content of the positive electrode active material is calculated by scanning electron microscopy (SEM). Specifically, the content was measured from cross-sectional SEM images of the positive electrode composite using ImageJ (ver. 1.51n; open-source, public-domain image processing software).

[0073] The content (vol.) of cubic garnet-type lithium metal oxide contained in the positive electrode composite is preferably in the range of 5 vol% to 70 vol%. Within this range, excellent charge-discharge characteristics are obtained. More preferably, the content of cubic garnet-type lithium metal oxide is in the range of 40 vol% to 60 vol%.

[0074] The lithium hydroxide content (vol.) in the positive electrode composite is preferably in the range of more than 0 vol% and 20 vol% or less. More preferably, the lithium hydroxide content is in the range of more than 0 vol% and 10 vol% or less. Within this range, excellent charge-discharge characteristics can be maintained without the influence of lithium hydroxide while undergoing integral 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 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 an electrically conductive metal, metal alloy, or metal oxide. The conductive material may be present in an amount of 5% to 15% by mass relative to 100% by mass of the positive electrode active material.

[0076] The thickness of the positive electrode layer 320 is not particularly limited, but exemplary it is in the range of 5 μm to 100 μm. For practical use, 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 facilitates the extraction of power to the outside. The positive electrode current collector may be made of a metallic 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 that can detach or insert lithium ions, and can be a negative electrode active material used in known all-solid-state lithium-ion batteries.

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

[0079] Sulfides are TiS x Titanium sulfides, VS x Vanadium sulfide, FeS x Iron sulfides, MoS x Molybdenum sulfide, SnS x Tin sulfide, WS x Tungsten sulfide, SbS x Antimony sulfide, SeS x It may be a selenium sulfide. x is always a positive real number.

[0080] Oxides are, 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 Li tungsten oxide, spinel structure 4+r Ti5O 12 (-1≦r≦3), Li with a ramsteride structure 2+s The oxides can be lithium titanium oxide (Ti3O7, -1 ≤ s ≤ 3) or lithium vanadium oxide (LiVO2, etc.). x is always a positive real number.

[0081] Here too, the negative electrode layer 330 preferably comprises a negative electrode active material and Li 7-a La3A2O 12The negative electrode composite may contain a cubic garnet-type lithium metal oxide represented by (parameter a satisfies 0 ≤ a ≤ 0.9, 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 lithium hydroxide. 7-a La3A2O 12 The cubic garnet-type lithium metal oxide represented by is the same as the cubic garnet-type lithium metal oxide described in Embodiment 1, so its description is omitted. The inclusion of such a composite in the negative electrode layer 330 is advantageous because it allows the negative electrode layer 330 and the solid electrolyte 310 to bond without the formation of an interfacial reaction phase between the negative electrode active material and the solid electrolyte, thereby forming a high-speed Li conduction path 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% to 95% by volume. Within this range, the negative electrode active material can desorb / adsorb a sufficient amount of lithium ions. More preferably, the content of the negative electrode active material is in the range of 40% to 80% by volume.

[0083] The content (vol.) of cubic garnet-type lithium metal oxide contained in the negative electrode composite is preferably in the range of 5 vol% to 70 vol%. Within this range, excellent charge-discharge characteristics are obtained. More preferably, the content of cubic garnet-type lithium metal oxide is in the range of 40 vol% to 60 vol%.

[0084] The lithium hydroxide content (vol.) in the negative electrode composite is preferably in the range of more than 0 vol% and 20 vol% or less. More preferably, the lithium hydroxide content is in the range of more than 0 vol% and 10 vol% or less. Within this range, excellent charge-discharge characteristics can be maintained without the influence of lithium hydroxide while undergoing integral 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 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 an electrically conductive metal, metal alloy, or metal oxide. The conductive material may be present in an amount of 5% to 15% by mass relative to 100% by mass of the negative electrode active material.

[0086] The thickness of the negative electrode layer 330 is not particularly limited, but exemplary it is in the range of 5 μm to 100 μm. For practical use, 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 facilitates the extraction of power to the outside. The negative electrode current collector may be made of a metallic 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 coin-shaped, button-shaped, sheet-shaped, cylindrical, or prismatic. In Figure 3, the all-solid-state lithium-ion battery 300 of the present invention shows a solid electrolyte 310 sandwiched between a pair of positive electrode layers 320 and a negative electrode layer 330, but multiple such arrangements may be integrated. 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 energizing the discharge circuit of an electronic device, electric vehicle, etc.

[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 separately. Here, the solid electrolyte 310 is manufactured by the sintering method described with reference to Figure 2 of Embodiment 1. The positive electrode layer 320 may be made by sintering the positive electrode active material described above and bonding a current collector to it. The negative electrode layer 330 may be made by sintering the negative electrode active material described above and bonding a current collector to it. These can then be stacked in the order of positive electrode layer 320, solid electrolyte 310, and negative electrode layer 330.

[0091] An all-solid-state lithium-ion battery may be manufactured, for example, as follows: A solid electrolyte 310 is manufactured by the method for manufacturing a sintered body described with reference to Figure 2 of Embodiment 1. A positive electrode layer 320 may then be formed on the solid electrolyte 310 by physical vapor deposition or chemical vapor deposition, and a current collector may be bonded to it. A negative electrode layer 330 may be formed on the side of the solid electrolyte 310 opposite the positive electrode layer 320 by physical vapor deposition or chemical vapor deposition, and a current collector may be bonded to it. Alternatively, the negative electrode layer 330 may be formed first, and then the positive electrode layer 320 may be formed.

[0092] In an all-solid-state lithium-ion battery, the positive electrode layer and the negative electrode layer may be formed by a combination of the above-described sintering method and either a physical vapor phase growth method or a chemical vapor phase growth method.

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

[0094] The process for manufacturing the all-solid-state lithium-ion battery of the present invention comprises the following steps S410 to S430. Step S410: La3A2O 9-bA precursor powder satisfying the following conditions is compacted: (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)). Step S420: A mixed powder for the positive electrode, containing positive electrode active material powder and precursor powder, is placed on the compacted powder obtained in step S410 and compacted. Step S430: At least a portion of the laminated compact obtained in step S420 is brought into contact with lithium hydroxide powder and fired at a temperature range of 500°C to 900°C.

[0095] As described in Embodiment 1, the general formula Li 7-a La3A2O 12 Since the sintered body containing the crystal represented by [the formula] is obtained by low-temperature firing at 900°C or below, 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 firing at 900°C or below. In particular, because the firing temperature is 900°C or below, interdiffusion does not occur 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 in Embodiment 1 with reference to Figure 2, so it is omitted.

[0097] In step S420, the positive electrode active material powder is the positive electrode active material powder described above, and the precursor powder is the precursor powder described in Embodiment 1, so its description is omitted. The content (volume %) of the positive electrode active material powder in the mixed powder for the positive electrode is preferably in the range of 30 volume% to 95 volume%. Within this range, a positive electrode composite that satisfies the above-mentioned content of positive electrode active material can be obtained. The content (volume %) of the positive electrode active material powder in the mixed powder for the positive electrode is more preferably in the range of 40 volume% to 60 volume%.

[0098] In step S420, the compaction conditions may be the same as those in step S210, which was described in Embodiment 1 with reference to Figure 2. Step S420 yields a laminated compact in which the precursor powder and the positive electrode mixed powder are stacked. However, considering practical application, it is preferable to place the positive electrode mixed powder so that the thickness of the layer made of the positive electrode mixed powder is greater than the thickness of the layer made of the precursor powder.

[0099] Step S430 is the same as in step S220, which was described with reference to Figure 2 of Embodiment 1, except that the compacted body becomes a laminated compacted body, and the same firing conditions may be used. Here as well, the amount of lithium hydroxide powder to be brought into contact with the laminated compacted body is preferably such that the amount of Li (1 mole) in the lithium hydroxide hydrate is the amount of Li of the general formula described above. 7-a La3A2O 12 The amount of Li is adjusted to satisfy a range of 1 to 16 times the amount of Li ((7-a) moles).

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

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

[0102] The mixed powder for the negative electrode can be the negative electrode active material powder described above, but among them, one that is less reactive in the temperature range of 500°C to 900°C is preferred, and typically lithium titanium oxide can be used. The precursor powder is the precursor powder described in Embodiment 1, so its 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 volume% to 95 volume%. Within this range, a negative electrode composite that satisfies the above-mentioned negative electrode active material content can be obtained. 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 volume% to 80 volume%.

[0103] In a laminated compact, the negative electrode mixed powder should be placed such that the thickness of the layer made of the negative electrode mixed powder is preferably greater than the thickness of the layer made of the precursor powder.

[0104] When a laminated compact of powders, such as a negative electrode mixed powder, a precursor powder, and a positive electrode mixed powder, is fired in step S430, an all-solid-state lithium-ion battery (full cell) is obtained by integral sintering. This battery consists of a negative electrode layer containing a composite of a negative electrode active material, a cubic garnet-type lithium metal oxide, and lithium hydroxide; a solid electrolyte consisting 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, a cubic garnet-type lithium metal oxide, and lithium hydroxide.

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

[0106] The present invention will now be described in detail using specific examples, but please note that the present invention is not limited to these examples. [Examples]

[0107] [La3Zr 1.5 Ta 0.5 O 8.75 [Preparation of precursor powder] La3Zr, a precursor powder 1.5 Ta 0.5 O 8.75 It was synthesized by a solid-phase reaction method. Lanthanum hydroxide hydrate (99.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), zirconium oxide (99.0%, manufactured by Tosoh Corporation), and tantalum oxide (99.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were weighed in such a stoichiometric ratio of La, Zr, and Ta as La:Zr:Ta = 3:1.5:0.5, and mixed in hexane using a planetary ball mill for 6 hours.

[0108] The mixed powder was mechanically compressed at 100 MPa to form a compact. The compact was placed on an MgO plate and sintered in air at 1200°C (heating rate: 10°C / min) for 12 hours. The resulting sintered body was again ball-milled in hexane for 6 hours to produce a powder. The particle size of the powder (primary particles) was measured by laser scattering and found to be an average particle size of 0.15 μm. Powder X-ray diffraction (MiniFlex600, Rigaku Corporation) was performed using the obtained powder and confirmed that it had a fluorite-type structure and that the X-ray diffraction pattern was in good agreement with that of Non-Patent Document 2. The crystal structure was analyzed using single-crystal structure analysis software based on the X-ray diffraction results and found that the obtained powder belonged to space group Fm3￣m (space group 225 in the International Tables for Crystallography), with lattice constants of a=b=c=0.5448 nm and angles α=β=γ=90°. The atomic positions are as shown in Table 2. Compositional analysis of the powder using an inductively coupled plasma emission spectrometer (Agilent Technologies, Inc., 5800ICP-OES) revealed the presence of La, Zr, and Ta, with values ​​of 3.00, 1.50, and 0.50, respectively. Therefore, the precursor powder is La3Zr 1.5 Ta 0.5 O 8.75 We confirmed that it satisfies the following chemical formula.

[0109] [Example 1: Sintered body] In Example 1, Li is produced by the method shown in Figure 2. 6.5 La3Zr 1.5 Ta 0.5 O 12A sintered body containing (LLZTO) was manufactured.

[0110] Precursor powder (La3Zr 1.5 Ta 0.5 O 8.75 The powder was uniaxially compressed at 6.25 MPa, then hydrostatically pressed at 200 MPa for 5 minutes to form a compact (size: diameter 9 mm × thickness 1.3 mm) (step S210 in Figure 2). The compact (300 mg, 0.00383 mol = 0.3 / 784.021, relative density 67%) was placed in a magnesia crucible, covered from the outside with lithium hydroxide hydrate (LiOH·H2O, 99.0%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., primary particle size 40 μm), and calcined in air at 500°C, 600°C, 700°C, 800°C, and 900°C (step S220 in Figure 2). The relative density of the compact was 64%.

[0111] At this time, the amount of lithium hydroxide hydrate is such that the amount of Li (1 mole) in lithium hydroxide hydrate is cubic garnet-type structure lithium oxide (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The amount of Li was adjusted to eight times the amount of Li in the original mixture (6.5 mol). Here, the lithium hydroxide hydrate was 835 mg (= 6.5 mol × 8 × 0.00383 × 41.96 g / mol). The firing time was 12 hours or 40 hours in air at each temperature. The sintered body obtained in this way is referred to as the sintered body of Example 1, or the sintered body of Example 1 (500) to the sintered body of Example 1 (900).

[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 powder X-ray diffraction was performed. The results are shown in Figure 6. In addition, the crushed powder was subjected to compositional analysis using an inductively coupled plasma emission spectrometer. The cross-section of the sintered body was observed with a scanning electron microscope (SEM, VE-8800, Keyence Corporation), and elemental analysis was performed using an energy-dispersive X-ray electron spectrometer (EDS) attached to the SEM. Samples for cross-sectional observation were prepared using Ar ion milling with a cross-sectional polishing machine (CP, IB-09020CP, JEOL Ltd.) and a mechanical polishing machine (ISPP-1000, Ikegami Seiki Co., Ltd.). The results are shown in Figures 11 to 13.

[0113] The ionic conductivity of the sintered body was measured by impedance spectroscopy. The sample for measurement was prepared as follows: The surface of the sintered body was polished with sandpaper (#400), and lithium ion-blocking gold (Au) electrodes were sputtered onto both sides of the sintered body. The impedance spectrum was collected using a high-frequency impedance analyzer (E4990A impedance analyzer, 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%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of lithium hydroxide hydrate as in Example 1. 6.5 La3Zr 1.5 Ta 0.5 O 12 A sintered body containing [the substance] was manufactured. The procedure was the same as in Example 1, except that the firing temperature was set to 800°C, 900°C, and 1000°C.

[0115] The sintered bodies obtained in this manner are referred to as the sintered bodies of Example 2, or the sintered bodies of Example 2 (800) to the sintered bodies of Example 2 (1000). Similar to Example 1, their density was measured, identification was performed by powder X-ray diffraction, compositional analysis was conducted, SEM observation was performed, and their ionic conductivity was measured. The results are shown in Table 4, Figure 7, Figure 14, and Figure 18.

[0116] [Example 3: Sintered body] In Example 3, lithium nitrate (99.0%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of lithium hydroxide hydrate as in Example 1. 6.5 La3Zr 1.5 Ta 0.5 O 12 A sintered body containing [the substance] was manufactured. The manufacturing procedure was the same as in Example 1.

[0117] The sintered bodies obtained in this manner are referred to as the sintered bodies of Example 3, or the sintered bodies of Example 3 (500) to the sintered bodies of Example 3 (900). Similar to Example 1, their density was measured, identification was performed by powder X-ray diffraction, compositional analysis was conducted, SEM observation was performed, and their ionic conductivity was measured. The results are shown in Table 4, Figure 8, Figure 15, and Figure 18.

[0118] [Example 4: Sintered body] In Example 4, lithium phosphate (99.0%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of lithium hydroxide hydrate as in Example 1. 6.5 La3Zr 1.5 Ta 0.5 O 12 A sintered body containing [the substance] was manufactured. The procedure was the same as in Example 1, except that the firing temperature was set to 800°C and 900°C.

[0119] The sintered bodies obtained in this manner are referred to as the sintered bodies of Example 4, or the sintered bodies of Example 4 (800) to the sintered bodies of Example 4 (900). Similar to Example 1, their density was measured, identification was performed by powder X-ray diffraction, compositional analysis was conducted, SEM observation was performed, and their ionic conductivity was measured. The results are shown in Table 4 and Figure 18.

[0120] [Example 5: Sintered body] In Example 5, lithium acetate (99.0%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of lithium hydroxide hydrate as in Example 1. 6.5 La3Zr 1.5 Ta 0.5 O 12 A sintered body containing [the substance] was manufactured. The procedure was the same as in Example 1, except that the firing temperature was set to 600°C, 700°C, 800°C, and 900°C.

[0121] The sintered bodies obtained in this manner are referred to as the sintered bodies of Example 5, or the sintered bodies of Example 5 (600) to the sintered bodies of Example 5 (900). Similar to Example 1, their density was measured, identification was performed by powder X-ray diffraction, compositional analysis was conducted, SEM observation was performed, and their ionic conductivity was measured. The results are shown in Table 4 and Figure 18.

[0122] [Example 6: Sintered body] In Example 6, Li is produced by an existing solid-state sintering method. 6.5 La3Zr 1.5 Ta 0.5 O 12 A sintered body containing the precursor powder (La3Zr) was manufactured. 1.5 Ta 0.5 O 8.75 (Powder) and stoichiometric composition (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 ) is mixed with lithium hydroxide hydrate in an excess of 10 wt.% and calcined at 900°C for 12 hours, and Li is obtained by solid-phase reaction. 6.5 La3Zr 1.5 Ta 0.5 O 12 A calcined body was synthesized. This Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The calcined body was again pulverized, uniaxially compressed at 6.25 MPa, and then hydrostatically pressed at 200 MPa for 5 minutes to form a compact. The compact was sintered in air at 700°C, 800°C, 900°C, 1000°C, 1100°C, and 1150°C for 40 hours to obtain a sintered body.

[0123] The sintered bodies obtained in this manner are referred to as the sintered bodies of Example 6, or the sintered bodies of Example 6 (700) to the sintered bodies of Example 6 (1150). Similar to Example 1, their density was measured, identification was performed by powder X-ray diffraction, compositional analysis was conducted, SEM observation was performed, and their ionic conductivity was measured. The results are shown in Table 4, Figures 5, 9, 16-17, and 19.

[0124] [Example 7: Sintered body] In Example 7, Li is produced by an existing liquid-phase sintering method. 6.5 La3Zr 1.5 Ta 0.5 O 12 A sintered body containing the precursor powder (La3Zr) was manufactured. 1.5 Ta 0.5 O 8.75 (Powder) and stoichiometric composition (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 A mixture of lithium hydroxide hydrate (La3Zr) and a 10 wt.% excess was obtained by mixing the mixture with the hydrate to obtain a mixed powder. The mixed powder was uniaxially compressed at 6.25 MPa, and then hydrostatically pressed at 200 MPa for 5 minutes to obtain a compact. 1.5 Ta 0.5 O 8.75 The material was covered with a mixed powder of 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 obtained in this manner are referred to as the sintered bodies of Example 7, or the sintered bodies of Example 7 (500) to the sintered bodies of Example 7 (1150). Similar to Example 1, their density was measured, identification was performed by powder X-ray diffraction, compositional analysis was conducted, SEM observation was performed, and their ionic conductivity was measured. The results are shown in Table 4, Figure 5, Figure 10, and Figures 16 to 17.

[0126] For simplicity, the results of Examples 1 to 7 are summarized and explained in Tables 3 and 4.

[0127] [Table 3]

[0128] [Table 4]

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

[0130] As shown in Figure 5, the sintered body of Example 1, sintered by the method of the present invention (liquid-phase penetration sintering method), has a density of 4.0 g / cm³ even at low-temperature sintering of 500°C. 3 It was found that the density exceeded the limit and was increased. On the other hand, for the sintered bodies in Examples 6 and 7 obtained by the solid-phase sintering method and the liquid-phase sintering method, a sintering temperature of about 1100°C was required to increase the density. This is thought to be because, in step S220 of Figure 2 of the method of the present invention, lithium hydroxide is brought into contact with the precursor powder molded body while sintering, so that the Li and O (oxygen) of lithium hydroxide can sufficiently diffuse into the powder molded body even at low temperatures due to capillary action. As shown in Table 4, it was found that the sintered body of Example 1 (800-12) with a sintering time of 12 hours was comparable to the sintered body of Example 1 (800) with a sintering time of 40 hours. From this, it is suggested that a sintering time of 10 hours or more is preferable.

[0131] Figure 6 shows the XRD pattern of the sintered body in Example 1. Figure 7 shows the XRD pattern of the sintered body in Example 2. Figure 8 shows the XRD pattern of the sintered body in Example 3. Figure 9 shows the XRD pattern of the sintered body of Example 6. Figure 10 shows the XRD pattern of the sintered body of Example 7.

[0132] As shown in Figure 6, the XRD patterns of the sintered bodies in Example 1, where lithium hydroxide was used as the lithium source in the liquid-phase penetration sintering method, all exhibited a cubic garnet-type structure and were confirmed to closely match the JCPDS cart (#183686). This indicates that sintering at temperatures above 500°C yields sintered bodies in which the main component is a lithium metal oxide with a cubic garnet-type structure. In addition to the cubic garnet structure, diffraction peaks of unreacted precursor powder were observed in the XRD patterns of the sintered bodies (500) and (600) of Example 1, which were sintered at 500°C and 600°C, respectively. This suggests that temperatures higher than 600°C are more preferable for sintering.

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

[0134] As shown in Figure 7, in Example 2, where lithium carbonate was used as the lithium source in the liquid-phase penetration sintering method, a sintered body mainly composed of cubic garnet-type lithium metal oxide (sintered body (900) and sintered body (1000) in Example 2) was obtained at a firing temperature of 900°C or higher.

[0135] Similarly, as shown in Figure 8, in Example 3, where lithium nitrate was used as the lithium source in the liquid-phase penetration sintering method, a sintered body mainly composed of cubic garnet-type lithium metal oxide (sintered body (800) and sintered body (900) in Example 3) was obtained at a firing temperature of 800°C or higher.

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

[0137] On the other hand, as shown in Figure 9, the XRD patterns of the sintered bodies of Example 6, produced by the solid-phase sintering method, all confirmed to be mainly composed of cubic garnet-type lithium metal oxide. As shown in Figure 10, the XRD patterns of the sintered bodies of Example 7, produced by the liquid-phase sintering method, showed diffraction peaks of unreacted precursor powder at firing temperatures of 500°C and 600°C, but confirmed to be mainly composed of cubic garnet-type lithium metal oxide.

[0138] These findings demonstrate that, in the liquid-phase penetration sintering method, when lithium hydroxide is used as the lithium source and a sintered body mainly composed of cubic garnet-type lithium metal oxide is obtained, the firing temperature can be as low as 500°C to 900°C.

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

[0140] Figures 11(a) to (c) show SEM images of the sintered body of Example 1 (700), the sintered body of Example 1 (800), and the sintered body of Example 1 (900), respectively. In Figure 11, it was found that the sintered body of Example 1 is a composite of particles in the brightly shown region and darkly shown regions that fill the grain boundaries of those particles. Significant grain growth was also observed in the sintered body of Example 1 (700). Although not shown, grain growth was also observed in the sintered body of Example 1 (500). The average particle size of the particles in the sintered bodies of Example 1 (700), Example 1 (800), and Example 1 (900) were all in the range of 5 μm to 20 μm, and no dependence on sintering temperature was observed.

[0141] Figure 12 shows the EDS mapping of the sintered body (800) of Example 1 in grayscale, with the regions where each element is present highlighted. Focusing on the parts corresponding to the particles, it was found that La, Zr, Ta, and O are distributed there. The results from Figures 6, 11, and 12 suggest that the particles are cubic garnet-type lithium metal oxides, and the grain boundary regions are lithium hydroxide phases.

[0142] Figure 13 shows the LaO in the sintered body (800) of Example 1. + and Li2OH - High-resolution TOF-SIMS images of the fragment are shown in grayscale. As shown in Figure 13, the brightly lit region is Li2OH - This is a fragment of LaO, and the darkly indicated region is LaO + It was a fragment of LaO. + The distribution of the fragments shows a similar distribution to, for example, the distribution of brightly shown particles in Figure 11 and the distribution of Zr in Figure 12, and LaO + The fragments were distributed in lithium metal oxide particles with a cubic garnet structure. On the other hand, Li2OH - 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 cubic garnet-type lithium metal oxide particles in the sintered body was calculated from Figure 13 and the ICP-OES results. The volume percentage was calculated by multiplying the volume percentage of 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 relative density (93%) was multiplied by the volume percentage (71%) measured by ICP-OES, it was found that it contained 66% by volume of cubic garnet-type structure lithium metal oxide particles and 34% by volume of lithium hydroxide. The sintered bodies (500) to (700) and (900) of Example 1 were all found to contain cubic garnet-type structure lithium metal oxide particles in the range of 64% to 68% by volume and lithium hydroxide in the range of 32% to 36% by volume.

[0145] In FIG. 14, it was also found that the sintered body (800) of Example 2 is a composite of particles in the brightly shown region and a darkly shown region located so as to fill the grain boundaries of the particles. Although not shown, similar to Example 1, according to TOF-SIMS, the particles were a cubic garnet-type structure lithium metal oxide phase and the grain boundaries were lithium carbonate.

[0146] Similarly, in FIG. 15, the sintered body (800) of Example 3 also had particles in the brightly shown region and a darkly shown region, but the darkly shown region was a void. This is because the firing temperature (800 °C) exceeded the boiling point of lithium nitrate which is the lithium source, and thus lithium nitrate evaporated before diffusing into the precursor.

[0147] FIGS. 16(a) to (f) show SEM images of the sintered bodies (700) to (1100) of Example 6 and the sintered bodies (700) to (1100) of Example 7, respectively. According to FIGS. 16(a) to (c), in the sintered body of Example 6 using the solid-phase sintering method, grain growth was promoted at a firing temperature of 900 °C, and the particles rapidly grew 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 consisted of a single phase of cubic garnet-type structure lithium metal oxide.

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

[0149] For the sintered bodies (1150) of Example 6 by the solid-phase sintering method and the sintered bodies (1150) of Example 7 by the liquid-phase sintering method, when the element ratios by EDS were normalized with La being 3, both were (Li, La, Zr, Ta) = (6.40, 3.00, 1.48, 0.49), and Li 6.5 La3Zr 1.5 Ta 0.5 O 12 showed good agreement. On the other hand, for the sintered body (800) of Example 1 by the liquid-phase infiltration sintering method, when the element ratio was normalized with La being 3, it 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 and is consistent with the results shown in FIG. 13. Also, considering the results of the element ratio and the content of lithium hydroxide (34 vol%), the particles were 6.5 La3Zr 1.5 Ta 0.5 O 12 represented by and were identified as cubic garnet-type structure lithium metal oxide particles, and it was found that the grain boundaries were amorphous lithium hydroxide.

[0150] When the relative density of the sintered body (800) of Example 1 was calculated assuming the theoretical density of the composite of cubic garnet-type structure lithium metal oxide and lithium hydroxide to be 4.3 g / cm 3 , it was 93%. On the other hand, when the relative density of the sintered body (1100) of Example 6 containing no lithium hydroxide was calculated using the theoretical density of Li 6.5 La3Zr 1.5 Ta 0.5 O 12 (5.4 g / cm 3 ), it was 92.5%. From this, it was found that by adopting the method of the present invention, a very dense sintered body can be obtained even by low-temperature firing.

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

[0152] Figures 17 and 18 show the ionic conductivity of each sintered body at room temperature. According to Figures 17, 18 and Table 1, the ionic conductivity of the sintered body of Example 1, which uses lithium hydroxide as the lithium source in the liquid-phase penetration sintering method, was found to be more than two orders of magnitude greater than that of the sintered bodies of Examples 2 to 5, which use a lithium source other than lithium hydroxide, and of Examples 6 and 7, which use solid-phase sintering or liquid-phase sintering methods, particularly at low firing temperatures of 500°C to 900°C.

[0153] In detail, the ionic conductivity of the sintered bodies in Examples 6 and 7, obtained by solid-phase sintering and liquid-phase sintering, both tended to increase with increasing firing temperature, reaching 2 to 4 × 10⁻¹⁶ at a firing temperature of 1100°C. -4 The ionic conductivity of the sintered body in Example 2, which used lithium carbonate as the lithium source, also increased with increasing firing temperature, reaching 1 × 10⁻⁶ at a firing temperature of 1100°C. -4 The conductivity reached S / cm. Sintered bodies in Examples 3 to 5, using lithium nitrate, lithium phosphate, and lithium acetate as lithium sources, did not show an increase in ionic conductivity regardless of the firing temperature.

[0154] On the other hand, the sintered body in Example 1, which uses lithium hydroxide as the lithium source, produces 1 × 10⁻¹⁶ units even at a firing temperature of 600°C. -4 It has an ionic conductivity of S / cm or higher, and in particular, at a firing temperature of 800°C, it has an ionic conductivity of 2 × 10⁻⁶. -4 The ionic conductivity was observed to be greater than S / cm. It should be noted that the increase in ionic conductivity only occurred when lithium hydroxide was used among various lithium sources, and this was discovered only after the inventors of this application conducted their own tests, making it unpredictable.

[0155] Figure 19 shows the Arrhenius plots of the ionic conductivity of the sintered bodies in Example 1 and Example 6.

[0156] The measurement temperature range is -50°C to 50°C, and the total ionic conductivity, including the contributions of bulk and grain boundaries in the sintered body, is shown. The lithium ion conductivity follows the following Arrhenius equation. σ T =σ0exp(-Ea / (K B T)) Here, σ T σ0 is the lithium-ion conductivity, and E is the pre-exponential factor. a This is the activation energy, and K B is the Boltzmann constant, and T is the absolute temperature.

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

[0158] Referring again to Tables 3 and 4, comparing the ionic conductivity of the sintered body (800) of Example 1, which has a volume content of cubic garnet-type lithium metal oxide particles of 66%, with the sintered body (1000) of Example 6, which has a similar volume content (62%), the ionic conductivity of the sintered body (800) of Example 1 was more than 10 times greater than that of the sintered body (1000) of Example 6. The ionic conductivity of lithium hydroxide is extremely low (1 × 10⁻⁶ at 150°C). -9 Given the S / cm ratio, it is unlikely that lithium hydroxide contributes to the ionic conductivity in the sintered body of Example 1. Rather, in the sintered body of Example 1, it is thought that high sintering density can be achieved by the cubic garnet-type structure lithium metal oxide particles linking to each other and efficiently forming a network for ion conduction paths, while amorphous lithium hydroxide fills the grain boundaries. In particular, in the present invention, since the precursor powder compact is fired while in contact with lithium hydroxide from the outside, the formation of continuous ion conduction paths between cubic garnet-type structure lithium metal oxide particles can be promoted.

[0159] As explained above with reference to Examples 1 to 7, by carrying out the manufacturing method shown in Figure 2 of the present invention, Li 7-a La3A2O 12 It has been shown that a sintered body can be obtained that contains particles made of a cubic garnet-type lithium metal oxide represented by (parameter a satisfies 0 ≤ a ≤ 0.9, and element A is an 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 is in the range of 50 volume% to 95 volume%.

[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 shown in Figure 20.

[0161] Figure 20 shows the procedure for manufacturing an all-solid-state lithium-ion battery.

[0162] Using a mold press, the precursor powder (La3Zr 1.5 Ta 0.5 O 8.75 The powder was uniaxially compressed at 6.25 MPa (step S410 in Figure 4). The resulting compact was 9 mm in diameter and 1.3 mm thick. Next, lithium cobalt oxide powder (99.0%, manufactured by Nippon Chemical Industrial Co., Ltd.) and the precursor powder were mixed in a volume ratio of 1:1 to prepare a cathode mixed powder. This cathode mixed powder was placed on top of the precursor powder compact and uniaxially compressed at 6.25 MPa (step S420 in Figure 4). This resulted in a laminated compact in which a layer of precursor powder and a layer of cathode mixed powder were stacked.

[0163] The laminated powder compact was densified further by hydrostatic pressing at 200 MPa for 5 minutes. At this time, the thickness of the mixed powder portion in the laminated powder compact was 50 μm. The densified laminated powder compact was placed in a magnesia crucible, covered with lithium hydroxide hydrate (lithium hydroxide hydrate, 99.0%, Wako Pure Chemical Industries, Ltd.), and calcined in air at 500°C for 40 hours, and then at 700°C for 10 hours (step S430 in Figure 4). Here again, the amount of Li in the lithium hydroxide hydrate is the stoichiometric composition of cubic garnet-type structure lithium hydroxide (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 It was adjusted to satisfy eight times the amount of )

[0164] In this manner, a laminated sintered body was obtained comprising a sintered body containing a cubic garnet-type structure lithium metal oxide and lithium hydroxide, and a positive electrode layer containing a positive electrode active material, a cubic garnet-type structure lithium metal oxide, and lithium hydroxide. The cross-section of the obtained laminated sintered body was observed using SEM. The results are shown in Figure 21.

[0165] Figure 21 shows an SEM image of a cross-section of the stacked sintered body of Example 8.

[0166] As shown in Figure 21, the laminated sintered body consisted of two layers: a positive electrode layer and a solid electrolyte. More specifically, the solid electrolyte consisted of particles (here, Li) made of cubic garnet-type structure lithium metal oxide, as described with reference to the sintered body of Example 1. 6.5 La3Zr 1.5 Ta 0.5 O 12 The phase consisted of particles (LLZTO) represented by the formula, and lithium hydroxide located at their grain boundaries. On the other hand, the positive electrode layer was a composite consisting of particles made of lithium cobalt oxide, which is the positive electrode active material, particles made of cubic garnet-type lithium metal oxide (LLZTO), and lithium hydroxide located at their grain boundaries. Here too, the lithium hydroxide was amorphous.

[0167] Next, the battery performance was measured using the laminated sintered body as a half cell. For measurement, a gold (Au) electrode was formed on the positive electrode side of the laminate by magnetron sputtering. Next, a lithium metal (Li) electrode was formed on the negative electrode side of the laminate by vacuum evaporation inside a glove box. The battery performance of the all-solid-state lithium-ion battery thus obtained was evaluated using a charge-discharge device (manufactured by Bio-Logic Science Instruments, SP-200). The measurement was carried out in a constant temperature furnace at 60 °C with the all-solid-state lithium-ion battery enclosed in a container filled with argon gas. The C rate during the charge-discharge test was 0.025C, and the current value was 0.53 mAcm -2 and the voltage range was 3 to 4.2 V. The results are shown in Fig. 22.

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

[0169] According to Fig. 22, the charge capacity was 101 mAhg -1 and the discharge capacity was 85 mAhg -1 Thus, the charge and discharge of the all-solid-state lithium-ion battery of Example 8 were 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-discharge voltage (about 3.7 V) of lithium cobaltate as the positive electrode active material. 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. This is thought to be because the electron conductivity of lithium cobaltate is low in the charged state.

[0170] As described above with reference to Example 8, the sintered body of the present invention is used as a solid electrolyte of an all-solid-state lithium-ion battery, and it has been shown that by implementing the manufacturing method shown in Fig. 4 of the present invention, 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 ionic conductivity by containing a predetermined amount of cubic garnet-type lithium metal oxide particles and lithium hydroxide at their grain boundaries. Such a sintered body is effective as a solid electrolyte for all-solid-state lithium-ion batteries. Furthermore, according to the method of the present invention, the above-mentioned sintered body can be manufactured at a low temperature of 500°C to 900°C, making integrated sintering with the electrode layer possible, which is advantageous for the practical application of all-solid-state lithium-ion batteries. [Explanation of Symbols]

[0172] 100 Sintered body 110 Lithium metal oxide (LLAO particles) 120 Lithium hydroxide 300 All-solid-state lithium-ion batteries 310 Solid electrolyte 320 Positive electrode layer 330 Negative electrode layer

Claims

1. Li ７－ａ La ３ A ２ O １２ Particles made of a cubic garnet-type lithium metal oxide represented by (parameter a satisfies 0 ≤ a ≤ 0.9, and element A is an 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)), Lithium hydroxide located at the grain boundary of the aforementioned particles It contains, A sintered body in which 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.

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 to 70 μm.

5. The ionic conductivity at room temperature is 5.0 × 10⁻⁶. －５ S / cm or more 2.0×10 －３ A sintered body according to claim 1, satisfying the range of S / cm or less.

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 by At least a portion of the compacted powder obtained by the aforementioned compaction process is brought into contact with lithium hydroxide powder and fired at a temperature range of 500°C to 900°C. A method for manufacturing a sintered body according to claim 1, comprising:

7. The manufacturing method according to claim 6, wherein at least a portion of the compacted powder is brought into contact with lithium hydroxide powder in an amount that satisfies the range of 1 to 16 times the molar ratio of lithium in the lithium metal oxide.

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

9. A solid electrolyte using the sintered body described in claim 1.

10. An all-solid-state lithium-ion battery comprising at least the solid electrolyte described in claim 9.

11. Further comprising a positive electrode layer and a negative electrode layer, The solid electrolyte is located between the positive electrode layer and the negative electrode layer. The positive electrode layer comprises a positive electrode active material and Li ７－ａ La ３ A ２ O １２ The all-solid-state lithium-ion battery according to claim 10, comprising a composite of a cubic garnet-type lithium metal oxide (where parameter a satisfies 0 ≤ a ≤ 0.9, 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 lithium hydroxide.

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 comprises a negative electrode active material selected from the group consisting of carbon material, metal material, conductive polymer, and sulfide and oxide.

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 structured lithium metal oxide, and lithium hydroxide.

15. La ３ A ２ O ９－ｂ The process involves compacting a precursor powder that satisfies the following conditions: (parameter b satisfies -0.5 ≤ b ≤ 0.5, and element A is an 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 process involves placing a mixed powder for the positive electrode, containing the positive electrode active material powder and the precursor powder, onto the compacted powder obtained by the aforementioned compaction, and then compacting it. The layered powder compact obtained by placing and compacting the powder is brought into contact with lithium hydroxide powder and fired at a temperature range of 500°C to 900°C. A method for manufacturing an all-solid-state lithium-ion battery according to any one of claims 10 to 14, encompassing the present invention.

16. The manufacturing method according to claim 15, further comprising placing the positive electrode mixed powder and compacting it, followed by placing the negative electrode mixed powder containing the negative electrode active material powder and the precursor powder on the side of the laminated compact obtained by placing the positive electrode mixed powder and compacting it, opposite to the side on which the positive electrode mixed powder was placed, and compacting it.

17. The manufacturing method according to claim 15, further comprising the steps of placing the positive electrode mixed powder on the side opposite to the compacted side, following the firing process.

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