NASICON-type oxide powder and its manufacturing method

Abstract

To provide NASICON-based solid electrolyte powder having a low sintering initiation temperature.SOLUTION: An NASICON-based oxide powder contains lithium, aluminum, germanium, and phosphorus, with sodium content of 1 ppm or more and 500 ppm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a NASICON-type oxide powder and a method for producing the same. [Background technology]

[0002] Solid electrolyte powder with a NASICON-type crystal structure, which has high ionic conductivity, is used as the solid electrolyte material for all-solid-state batteries. As the solid electrolyte powder, a solid electrolyte powder containing lithium, aluminum, germanium, and phosphorus, as described in Patent Document 1, is known. Patent Document 1 describes a method for obtaining an all-solid-state battery through a firing process in which a laminate unit having a green sheet containing an oxide-based solid electrolyte powder, a paste coating for a first electrode layer formed on a first main surface of the green sheet, and a paste coating for a second electrode layer formed on a second main surface of the green sheet is laminated, and the laminate unit is fired at a high temperature of 400°C to 1000°C to form a laminated chip. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-187897 Summary of the Invention [Problem to be solved by the invention]

[0004] However, according to the investigations of the present inventors, it has been found that in the firing step in the manufacture of a stacked all-solid-state battery, the solid electrolyte powder constituting the solid electrolyte layer reacts with the positive electrode active material powder constituting the positive electrode active material layer, causing a change in composition, and making it impossible to obtain the desired battery characteristics.

[0005] Based on this finding, the inventors continued their research and came up with the idea of a solid electrolyte powder with a low sintering onset temperature. That is, by using a solid electrolyte powder with a low sintering onset temperature, the activation energy in the firing step is reduced, and the reaction between the solid electrolyte powder and the positive electrode active material powder is suppressed.

[0006] The present invention has been made under the above circumstances, and the problem to be solved by the present invention is to provide a NASICON-type solid electrolyte powder having a low sintering initiation temperature. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the inventors have conducted research and have come up with a NASICON-type oxide powder containing lithium, aluminum, germanium, phosphorus, and a predetermined amount of sodium.The inventors have also come up with the idea that the NASICON-type oxide powder has a low sintering initiation temperature, and have completed the present invention.

[0008] That is, the first invention for solving the above-mentioned problems is: A NASICON-type oxide powder containing lithium, aluminum, germanium, and phosphorus, Furthermore, the NASICON type oxide powder contains sodium in an amount of 1 ppm or more and 500 ppm or less. The second invention is: The BET value, which is the specific surface area measured by the BET single-point method, The ratio of D50, which is the cumulative 50% particle diameter on a volume basis measured by laser diffraction, to BET is 0.05 or more and 7.00 or less. The NASICON-type oxide powder is described in the first aspect of the present invention. The third invention is The specific surface area measured by the BET single-point method is 1.0 m 2 / g or more, 15.0m 2 / g or less, The D50 value, which is the cumulative 50% particle diameter on a volume basis measured by laser diffraction, is 0.5 μm or more and 7.0 μm or less. The NASICON-type oxide powder is as set forth in the first or second invention. The fourth invention is Lithium is 1.0 mass% or more and 4.0 mass% or less, Aluminum: 0.5 mass% or more and 6.0 mass% or less; germanium, 15 mass% or more and 35 mass% or less; Contains 10% by mass or more and 30% by mass or less of phosphorus, The NASICON-type oxide powder is according to any one of the first to third aspects of the present invention. The fifth invention is The value of D10, which is the cumulative 10% particle diameter on a volume basis measured by laser diffraction, is 0.1 μm or more and 4.0 μm or less. The D90 value, which is the cumulative 90% particle diameter on a volume basis measured by laser diffraction, is 2.0 μm or more and 14.0 μm or less. The NASICON-type oxide powder is according to any one of the first to fourth aspects of the present invention. The sixth invention is Tap density is 0.5g / cm 3 More than 2.0g / cm 3 Below is the The NASICON-type oxide powder is according to any one of the first to fifth aspects of the present invention. The seventh invention is The sintering start temperature is 750°C or less. The NASICON-type oxide powder is according to any one of the first to sixth aspects of the present invention. The eighth invention is Furthermore, it contains zirconium at 10 ppm or more and 10,000 ppm or less. The NASICON-type oxide powder is according to any one of the first to seventh aspects of the present invention. The ninth invention is obtaining a slurry containing lithium, aluminum, germanium, phosphorus, and sodium; drying the slurry to obtain a dry powder; calcining the dried powder at a temperature of 600°C or higher and 900°C or lower to obtain a calcined powder; The method for producing NASICON-type oxide powder includes a step of pulverizing the fired powder. [Effects of the Invention]

[0009] The present invention provides a NASICON-type oxide powder having a low sintering initiation temperature and a method for producing the same. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an XRD spectrum of the NASICON-type oxide powder according to Example 1. [Figure 2] 1 shows a TMA pattern of the NASICON-type oxide powder according to Example 1. [Figure 3] FIG. 3 is an enlarged view of part (A) in the TMA pattern of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] The NASICON-type oxide powder of the present invention has a NASICON-type crystal structure that exhibits high ionic conductivity in addition to a low sintering temperature. The powder having the NASICON-type crystal structure exhibits high ionic conductivity and can be used as a solid electrolyte for all-solid-state batteries. The following describes the embodiments of the invention in the following order: 1. NASICON-type oxide powder containing lithium, aluminum, germanium, phosphorus, and sodium; 2. Effects and content ratios of each constituent element in the NASICON-type oxide powder; 3. Properties of the NASICON-type oxide powder; 4. Sintering start temperature of the NASICON-type oxide powder; and 5. Manufacturing method of the NASICON-type oxide powder.

[0012] 1. NASICON-type oxide powder containing lithium, aluminum, germanium, phosphorus, and sodium The NASICON-type oxide powder according to the present invention contains lithium, aluminum, germanium, phosphorus, and sodium, and has a NASICON-type crystal structure. Whether the powder has a NASICON-type crystal structure can be determined by comparing the XRD profile obtained by measuring the powder using an XRD apparatus with the diffraction peaks of oxides having a NASICON-type crystal structure registered in a database using analysis software. For example, it can be determined by comparing with PDF (Powder Diffraction File) No. 01-080-1922 of ICDD (International Center for Diffraction Data). Incidentally, the NASICON-type oxide powder according to the present invention has a general formula Li 1+x Al x Ge 2-x (PO4)3 (where 0 < x ≤ 1. In the present invention, it may be described as "LAGP") as the main phase, or a mixed phase having LAGP as the main phase and other oxides as the secondary phase as long as the effects of the present invention are not impaired. Here, that LAGP is the main phase in the obtained solid electrolyte can be confirmed by the fact that the maximum peak obtained when the solid electrolyte is subjected to XRD measurement is LAGP. And the ratio of the secondary phase can be obtained from the ratio of the peak intensities of the strongest peaks of the main phase and the secondary phase, and it is preferable that the secondary phase / main phase ratio is 1 / 10 or less.

[0013] 2. Effects and Content Ratios of Each Constituent Element in NASICON-Type Oxide Powder The NASICON-type oxide powder according to the present invention contains at least lithium, aluminum, germanium, phosphorus, and sodium as constituent elements. Also, zirconium and other elements may be contained as desired. Hereinafter, the effects and content ratios of each constituent element will be described in the order of (1) lithium, (2) aluminum, (X) germanium, (4) phosphorus, (5) sodium, (6) zirconium, (7) moisture content, (8) carbon, (9) nitrogen, (10) other elements.

[0014] (1) Lithium The NASICON-type oxide powder of the present invention preferably contains 1.0% by mass or more and 4.0% by mass or less of lithium. This is because a lithium content of 1.0% by mass or more and 4.0% by mass or less ensures high ionic conductivity. The lithium content is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and even more preferably 1.8% by mass or more, while it is preferably 4.0% by mass or less, preferably 3.5% by mass or less, and even more preferably 3.3% by mass or less.

[0015] (2) Aluminum The NASICON-type oxide powder of the present invention preferably contains 0.5% by mass or more and 6.0% by mass or less of aluminum. By containing 0.5% by mass or more and 6.0% by mass or less of aluminum, a solid electrolyte with a NASICON-type crystal structure is obtained. The aluminum content is preferably 1.0% by mass or more, more preferably 1.5% by mass or more. On the other hand, it is preferably 5.5% by mass or less, more preferably 5.0% by mass or less.

[0016] (3) Germanium The NASICON-type oxide powder of the present invention preferably contains 15% by mass or more and 35% by mass or less of germanium. This concentration range results in a solid electrolyte with a NASICON-type crystal structure. The germanium content is preferably 20% by mass or more, more preferably 22% by mass or more, and most preferably 23.5% by mass or more, to obtain a solid electrolyte with higher ionic conductivity. On the other hand, the germanium content is preferably 33% by mass or less, more preferably 30% by mass or less.

[0017] (4) Phosphorus The NASICON-type oxide powder of the present invention preferably contains 10% by mass or more and 30% by mass or less of phosphorus. This concentration range results in a solid electrolyte with a NASICON-type crystal structure. The phosphorus content is preferably 15% by mass or more, more preferably 18% by mass or more. On the other hand, it is preferably 28% by mass or less, more preferably 25% by mass or less.

[0018] (5) Sodium The NASICON-type oxide powder of the present invention contains sodium in an amount of 1 ppm to 500 ppm. By adding sodium in an amount of 1 ppm to 500 ppm to the NASICON-type solid electrolyte powder, the sintering start temperature of the NASICON-type solid electrolyte powder can be lowered. R It is possible. From the above viewpoints, the sodium content should be 1 ppm or more and adjusted in ppm units. On the other hand, if the sodium content is 500 ppm or less, it is possible to avoid the influence of cation mixing with lithium ions on ionic conductivity. In addition, even if the sodium content is insufficient to lower the sintering initiation temperature of the NASICON-type oxide powder when it is 1 ppm or less, it may be possible to suppress the occurrence of localized sintering and achieve uniformity in sintering. In addition, the sodium content is preferably 300 ppm or less, and more preferably 200 ppm or less.

[0019] (6) Zirconium The NASICON-type oxide powder of the present invention preferably contains 10 ppm to 10,000 ppm of zirconium. This is because adding zirconium to the NASICON-type oxide powder improves ionic conductivity. The amount added can be adjusted to control the ionic conductivity. From the viewpoints of avoiding the formation of heterophases such as ZrO2 during firing and ensuring ionic conductivity, the zirconium content is preferably 10,000 ppm or less.

[0020] (7) Moisture content In the NASICON-type oxide powder of the present invention, the water content is preferably 0.10% by mass or more and 4.00% by mass or less. A water content of 0.10% by mass or more and 4.00% by mass or less improves the dispersibility of the electrode active material powder and the NASICON-type oxide powder when they are mixed in the process of producing an all-solid-state battery, enabling them to be mixed uniformly. On the other hand, a water content of 4.00% by mass or less prevents the NASICON-type oxide powder from agglomerating and reducing its dispersibility. As a result, agglomeration of the NASICON-type oxide powder is suppressed, allowing for high miscibility with the electrode active material powder to be maintained.

[0021] (8) Carbon In the NASICON-type oxide powder of the present invention, the carbon content is preferably 0.35% by mass or less, and may be completely absent. However, by adjusting the carbon content, the amount of gas generated when sintering the NASICON-type oxide powder in the manufacturing process of an all-solid-state battery can be adjusted, and the sintered density can be controlled. From the viewpoint of increasing the sintered density, it is preferable to set the carbon content to 0.35% by mass or less, for example, 0.01% by mass or more, in order to suppress the amount of gas generated.

[0022] (9) Nitrogen In the NASICON-type oxide powder of the present invention, the nitrogen content is preferably 0.005% by mass or more and 3% by mass or less, because when the nitrogen content is 0.005% by mass or more and 3% by mass or less, it acts as a sintering accelerator when sintering the NASICON-type oxide powder, and reduces the grain boundaries of the crystals, thereby reducing the ionic conduction resistance and improving the ionic conductivity of the sintered solid electrolyte.

[0023] (10) Other elements The NASICON-type oxide powder of the present invention may contain elements other than the above-mentioned lithium, aluminum, germanium, phosphorus, sodium, zirconium, water, carbon, and nitrogen, as long as they form a NASICON-type crystal structure. The other elements are not particularly limited, and may include at least one of iron, silicon, calcium, potassium, and chlorine. In the NASICON-type oxide powder of the present invention, the total content of the other elements may be 3% by mass or less. Examples of the other elements that may be included include iron, potassium, calcium, silicon, titanium, gallium, lanthanum, indium, hafnium, and yttrium.

[0024] 3. Properties of NASICON-type oxide powder The properties of the NASICON-type oxide powder according to the present invention will be explained in the following order: (1) particle size, (2) specific surface area (BET), (3) D50 / BET value, and (4) tap density.

[0025] (1) Particle size The particle size of the NASICON-type oxide powder according to the present invention is preferably determined by measuring the volume-based particle size distribution using a laser diffraction / scattering particle size distribution analyzer, and the volume-based cumulative 50% particle size (D50) obtained by the measurement is preferably 0.5 μm or more and 7.0 μm or less. Furthermore, it is preferable that the volume-based particle size distribution be measured using a laser diffraction / scattering particle size distribution analyzer, and that the volume-based cumulative 10% particle size (D10) value obtained by the measurement be 0.1 μm to 4.0 μm, and the cumulative 90% particle size (D90) value be 2.0 μm or more and 14.0 μm or less.

[0026] (2) Specific surface area (BET) value The specific surface area (BET) of the NASICON-type oxide powder of the present invention measured by the BET single-point method is 1.0 m 2 / g or more, 15.0m 2 / g or less. 2 If the BET value is greater than 15.0m / g, the driving force for sintering is ensured and the sintering start temperature is suppressed, which is preferable. 2If the particle size is smaller than 1 / g, the cohesive force of the particles is suppressed and the sintered density is ensured, which is preferable.

[0027] (3) D50 / BET value For the NASICON-type oxide powder according to the present invention, the value of the relationship between the cumulative 50% particle diameter (D50) measured by a laser diffraction / scattering particle size distribution analyzer and the specific surface area (BET) measured by the single-point BET method (D50 / BET) is preferably 0.05 or more and 7.00 or less. A D50 / BET value of 0.05 or more is preferable because the specific surface area relative to the particle diameter is large (meaning the particles do not become too close to a perfect sphericity), and the sintering initiation temperature tends to be low. On the other hand, a D50 / BET value of 7.00 or less is preferable because the specific surface area relative to the particle diameter is not too large, suppressing the particle cohesion force and improving the sintering density, and a value of 5.00 or less is even more preferable.

[0028] (4) Tap density The tap density of the NASICON-type oxide powder of the present invention is 0.5 g / cm 3 More than 2.0g / cm 3 Preferably, the tap density is 0.5 g / cm or less. 3 In the above cases, the packing property of the powder is improved, and the sintered density is improved, which is preferable. Although there is no particular upper limit to the tap density, in the case of the particle structure and composition according to the present invention, the upper limit is 2.0 g / cm under normal production conditions. 2 It will be about that amount.

[0029] 4. Sintering start temperature of NASICON-type oxide powder The sintering start temperature of the NASICON-type oxide powder according to the present invention and a method for measuring it will be described in the following order: (1) sintering start temperature, and (2) a method for measuring the sintering start temperature.

[0030] (1) Firing start temperature In the manufacturing process of all-solid-state batteries, electrode active material powder and NASICON-type oxide powder are mixed to form a paste. During the process of firing this paste to produce a laminated electrode body, the electrode active material and NASICON-type oxide powder react with each other to form a heterogeneous phase that does not contribute to charge and discharge, which can result in the battery not performing as designed. Here, the inventors have realized that if the temperature at which the NASICON-type oxide powder starts to sinter (sometimes referred to as the "sintering start temperature" in the present invention) exceeds 750°C in the process of firing the paste to produce a laminated electrode body, the NASICON-type oxide powder will react with the electrode active material (for example, lithium vanadium phosphate (Li3V2(PO4)3) or lithium cobalt phosphate (LiCoPO4)) to form a different phase, which may have adverse effects on battery characteristics such as a decrease in lithium ion conductivity and deterioration of cycle characteristics due to instability of the crystal structure. From the above viewpoint, it has been found that the sintering initiation temperature of the NASICON-type oxide powder according to the present invention is preferably 750° C. or less. It has also been found that it is convenient to measure the sintering initiation temperature of the NASICON-type oxide powder according to the present invention as the temperature at which the volume change rate measured by a TMA apparatus described later reaches −0.5%.

[0031] (2) Measurement method of sintering start temperature The sintering initiation temperature of the NASICON-type oxide powder according to the present invention was measured by molding the NASICON-type oxide powder in a press to obtain a green compact, setting the green compact in a thermomechanical analysis device, applying a predetermined load in an air atmosphere, raising the temperature from room temperature at a predetermined heating rate, and measuring the displacement of a piston jig. Specifically, the powder compact was placed in the sample holder (cylinder) of the TMA device, and a load of 980 mN was applied from the top of the cylinder in an air atmosphere using a piston-shaped jig. The temperature was raised from room temperature at a rate of 10°C / min, and the volume change (volume shrinkage rate) of the powder compact was measured from the displacement of the piston jig. The temperature at which the volume change (volume shrinkage rate) of the powder compact reached -0.5% was defined as the sintering start temperature of the NASICON-type oxide powder according to the present invention.

[0032] 5. Manufacturing method of NASICON type oxide powder The NASICON-type oxide powder according to the present invention can be obtained by mixing aqueous solutions of raw materials containing the respective constituent elements to obtain a slurry, drying the slurry to obtain a dry powder, and firing the dry powder.

[0033] The method for producing the NASICON-type oxide powder according to the present invention will be described below in the order of (1) preparation of raw material aqueous solution, (2) mixing, (3) drying, (4) calcination, and (5) particle size adjustment and specific surface area adjustment.

[0034] (1) Preparation of raw material aqueous solution The raw materials containing lithium, aluminum, germanium, phosphorus, sodium, and optionally zirconium, iron, potassium, calcium, silicon, titanium, gallium, lanthanum, indium, hafnium, and yttrium, which are the constituent elements of the NASICON-type oxide powder according to the present invention, are dissolved in water to form aqueous solutions. Nitrates are preferably used as the raw materials containing the constituent elements, since this makes it difficult for impurities to remain in the NASICON-type oxide powder. The amounts of raw materials containing lithium, aluminum, germanium, phosphorus, sodium, and optionally zirconium, iron, potassium, calcium, silicon, titanium, gallium, lanthanum, indium, hafnium, and yttrium may be appropriately adjusted in consideration of the composition of the NASICON-type oxide powder to be produced.

[0035] (2) Mixture This is a step of mixing the raw material aqueous solutions prepared in the above "(1) Preparation of raw material aqueous solution" to obtain a slurry containing the constituent elements of the NASICON-type oxide powder.

[0036] For example, adding an acidic aqueous solution containing lithium nitrate, aluminum nitrate nonahydrate, and ammonium dihydrogen phosphate to an alkaline aqueous solution of germanium dissolved in ammonia immediately turns cloudy, resulting in a slurry containing lithium, aluminum, germanium, phosphorus, and ammonia through coprecipitation. The liquid temperature during this mixing process does not need to be specifically considered, and heating may or may not be required. The slurry is believed to contain both constituent elements precipitated as hydroxides and those present as ions. The coprecipitation method is used to achieve a supersaturated state in which the ion concentration product of the constituent elements is higher than the solubility product, because improving the uniformity of the constituent elements is essential for obtaining NASICON-type oxide powder with a NASICON-type crystal structure. To obtain a slurry containing the constituent elements of NASICON-type oxide powder, it is preferable to adjust the pH of the mixed aqueous solution to between 2 and 5.

[0037] (3) Drying, This is the step of drying the water content of the slurry obtained in the "(2) mixing" step to obtain a dry powder. While the drying method is not particularly limited, spray drying using a spray dryer or the like is preferred. Spray drying rapidly precipitates the constituent elements present in the slurry as ions in a short period of time, thereby reducing the non-uniformity of precipitation resulting from differences in the solubility of the constituent elements. This allows for the production of a dry powder with a uniform composition, and more reliably produces a NASICON-type oxide powder in which the generation of germanium dioxide is suppressed. The drying temperature may be appropriately set so that no water remains in the resulting dry powder. For example, the inlet temperature of the spray dryer, which is a spray dryer, is preferably 150 to 250°C, and the hot air outlet temperature is preferably 60°C or higher.

[0038] (4) Firing This is the process of calcining the dried powder obtained in "(3) Drying" to obtain a calcined powder having a NASICON-type crystal structure. Specifically, the dried powder is placed in a container made of alumina or the like, and the temperature is raised from room temperature to 300°C to 500°C in an air atmosphere at a rate of 0.1°C / min to 20°C / min. The temperature is then raised further to 600°C to 900°C in an amount of 1°C / min to 40°C / min, where the dried powder is calcined to obtain a calcined powder having a NASICON-type crystal structure.

[0039] The obtained fired powder having a NASICON-type crystal structure can be used as the NASICON-type oxide powder according to the present invention, for example, as a solid electrolyte in an all-solid-state battery. The XRD profile of the resulting calcined powder can be used to determine whether it is the NASICON-type oxide powder of the present invention. Specifically, the XRD profile can be compared with ICDD (International Center for Diffraction Data) PDF (Powder Diffraction File) No. 01-080-1922 using a computer attached to the XRD device to identify the crystal structure. The product is preferably a single-phase LAGP powder having a NASICON-type crystal structure, but may contain a subphase to the extent that it does not impair the effects of the present invention. The subphase ratio can be determined from the peak intensity ratio between the most intense peak associated with the main phase and the most intense peak associated with the subphase. The subphase / main phase ratio is preferably 1 / 10 or less.

[0040] (5) Particle size adjustment, specific surface area adjustment In the production of a solid electrolyte having a NASICON-type crystal structure, when the solid electrolyte obtained by sintering a NASICON-type oxide powder is formed into a sheet, the particle size and specific surface area of the sintered powder having a NASICON-type crystal structure may be appropriately adjusted depending on the target sheet thickness to obtain a NASICON-type oxide powder. Although known methods can be used to adjust the particle size and specific surface area, wet grinding using a bead mill or the like is preferred.

[0041] The particle size and specific surface area in wet grinding using a bead mill can be adjusted appropriately by known methods such as the material of the media (beads), the diameter of the media (beads), the ratio of media (beads) to slurry, the slurry concentration, the grinding time, and the rotation speed. When wet pulverization is carried out, solid-liquid separation is carried out after the wet pulverization treatment, and the recovered wet-pulverized NASICON-type oxide powder is dried.

[0042] As described above, the particle size of the dried NASICON-type oxide powder is preferably such that the volume-based cumulative 10% particle size (D10) determined by laser diffraction / scattering particle size distribution measurement is 0.1 μm to 4.0 μm, the cumulative 50% particle size (D50) is 0.5 μm to 7.0 μm, and the cumulative 90% particle size (D90) is 2 μm to 14 μm. The specific surface area (BET) is 1.0 m 2 / g or more 15.0m 2 The value of D50 / BET is preferably 0.05 or more and 7.00 or less, and more preferably 5.00 or less.

[0043] As a solvent for wet milling, an organic solvent is preferred, specifically IPA, to prevent lithium in the NASICON-type oxide powder from ion-exchanging with protons, thereby reducing the ionic conductivity of the solid electrolyte. This is because IPA volatilizes during drying after milling and does not remain in the NASICON-type oxide powder. When a bead mill is used for milling, alumina or zirconia is preferred as the bead material to prevent impurities from being mixed in. The NASICON-type oxide powder after wet milling is preferably dried at a temperature above the boiling point of the solvent used and below the calcination temperature used in the "(4) calcination" step to remove the solvent. If the moisture content of the NASICON-type oxide powder obtained above is excessively low, a step of adjusting the moisture content of the powder by exposing it to a moisture-containing atmosphere for a predetermined time may be included. [Example]

[0044] Example 1 The NASICON-type oxide powder of Example 1 was produced according to the flow chart showing the manufacturing process for the NASICON-type oxide powder described above. The steps are explained in the following order: (1) preparation of raw material aqueous solution, (2) mixing, (3) spray drying, (4) calcination, and (5) adjustment of particle size and specific surface area. The produced NASICON-type oxide powder of Example 1 was then analyzed and characterized. The steps are explained in the following order: (6) analysis and characterization of the NASICON-type oxide powder, and (7) preparation and characterization of a solid electrolyte having a NASICON-type crystal structure.

[0045] (1) Preparation of raw material aqueous solution In Example 1, (I) a germanium-containing aqueous solution and (II) a lithium, aluminum, phosphorus, sodium, and zirconium-containing aqueous solution were prepared as raw material aqueous solutions. Each of these will be described below.

[0046] (I) Germanium-containing aqueous solution 152 g of germanium dioxide (99.999% manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to 3160 g of pure water and heated to 40°C while stirring, and 77 g of 28% by mass aqueous ammonia (28% manufactured by Nacalai Tesque, Inc.) was added as an alkali to dissolve the germanium dioxide, thereby preparing a germanium-containing aqueous solution. The pH of the prepared aqueous solution was 10.7, which was alkaline.

[0047] (II) Aqueous solution containing lithium, aluminum, phosphorus, sodium, and zirconium To 675 g of pure water, 102 g of lithium nitrate (FUJIFILM Wako Pure Chemical Corporation, 98.0+%), 195 g of aluminum nitrate nonahydrate (FUJIFILM Wako Pure Chemical Corporation, 98.0+%), 360 g of ammonium dihydrogen phosphate (FUJIFILM Wako Pure Chemical Corporation, 98.0+%), 0.07 g of sodium nitrate (FUJIFILM Wako Pure Chemical Corporation, 98.0+%), and 1.9 g of zirconyl nitrate dihydrate (FUJIFILM Wako Pure Chemical Corporation, 97.0+%) were added to prepare an aqueous solution containing lithium, aluminum, phosphorus, sodium, and zirconium. The pH of the prepared aqueous solution containing lithium, aluminum, phosphorus, sodium, and zirconium was 1.8, making it acidic.

[0048] (2) Mixture The alkaline germanium-containing aqueous solution was heated to 40°C while stirring, and the entire amount of the acidic lithium-, aluminum-, phosphorus-, sodium-, and zirconium-containing aqueous solution was added thereto. The aqueous solution became cloudy immediately after the addition, and a white mixed slurry containing lithium, aluminum, germanium, phosphorus, sodium, zirconium, ammonia, and water was obtained. The pH of the resulting mixed slurry was 4.7.

[0049] (3) Spray drying The mixed slurry was spray-dried using a spray dryer (SD-1000 manufactured by Tokyo Rikakikai Co., Ltd.) to evaporate the water in the mixed slurry and precipitate it into a solid phase at once, thereby obtaining a white dry powder. The spray-drying conditions were an inlet temperature of 180°C, an outlet temperature of 90°C, and an addition rate of the mixed slurry of 10 g / min.

[0050] (4) Firing The dried powder obtained by the spray drying was placed in an alumina container, and the temperature was increased from room temperature to 400°C at a rate of 5°C / min in an air atmosphere, kept at 400°C for 2 hours, and then increased from 400°C to 800°C at a rate of 5°C / min, and calcined at 800°C for 120 minutes to obtain a calcined powder with a NASICON-type crystal structure.

[0051] (5) Particle size and specific surface area adjustment 40 g of the calcined powder having the NASICON-type crystal structure was loaded into a bead mill together with 160 g of φ1 mm Zr beads and 94.32 g of IPA, and wet-ground for 120 minutes. After that, the powder was placed in a dryer and dried at 100°C for 3 hours to obtain the NASICON-type oxide powder according to Example 1.

[0052] (6) Analysis and Characterization of NASICON-Type Oxide Powders The obtained NASICON-type oxide powder according to Example 1 was subjected to the following measurements: (I) particle size and particle size distribution measurement, (II) specific surface area measurement, (III) elemental analysis, (IV) nitrogen content analysis, carbon content analysis, (V) XRD measurement, (VI) tap density, (VII) sintering start temperature, and (VIII) moisture content measurement. Each method and result will be explained below.

[0053] (I) Particle size and particle size distribution measurement The volumetric particle size distribution of the NASICON-type oxide powder according to Example 1 was measured using a laser diffraction / scattering particle size distribution analyzer (SYMPATEC's HELOS particle size distribution analyzer (HELOS&RODOS (airflow dispersion module))) at a dispersion pressure of 5 bar, and the volumetric cumulative 10% particle size (D10), cumulative 50% particle size (D50), and cumulative 90% particle size (D90) were measured. The D10, D50, and D90 values of the NASICON-type oxide powder according to Example 1 are shown in Table 2.

[0054] (II) Specific surface area measurement The specific surface area (BET) value of the NASICON-type oxide powder obtained in Example 1 was measured using a BET specific surface area measuring device (Macsorb, manufactured by Mountec Co., Ltd.). After degassing by flowing nitrogen gas into the measuring device for 20 minutes at 105°C, the BET value was measured by the BET single-point method while flowing a mixed gas of nitrogen and helium (N2: 30 vol%; He: 70 vol%). The BET value of the NASICON-type oxide powder according to Example 1 is shown in Table 2. The D50 value of the NASICON-type oxide powder according to Example 1 divided by the BET value, or "D50 / BET," is also shown in Table 2.

[0055] (III) Elemental analysis Sodium carbonate was added as a flux to the NASICON-type oxide powder of Example 1 to prepare an alkali molten salt. This molten salt was then dissolved in nitric acid, and the resulting solution was subjected to elemental analysis using an ICP-OES device (ICP-720, manufactured by Agilent). Quantitative analysis values for each of the constituent elements, lithium, aluminum, phosphorus, germanium, zirconia, iron, silicon, calcium, and chlorine, are shown in Table 1. Regarding sodium, 1 g of the NASICON-type oxide powder according to Example 1 was weighed and quantitatively transferred to a 50 ml volumetric flask with pure water. The obtained solution was sonicated for 30 minutes and filtered through a filter with a pore size of 0.2 μm, and the amount of sodium in the filtered solution was measured using an atomic absorption spectrophotometer ZA3300 manufactured by HITACHI. The analytical values are shown in Table 1.

[0056] (IV) Nitrogen content analysis and carbon content analysis The nitrogen content in the NASICON-type oxide powder according to Example 1 was analyzed using a nitrogen analyzer (EMGA-920 manufactured by Horiba, Ltd.). The analytical values of the nitrogen content are shown in Table 1. In addition, the carbon content in the NASICON-type oxide powder according to Example 1 was analyzed using a trace carbon and sulfur analyzer (ETMA-U510 manufactured by Horiba, Ltd.). The analytical values of the carbon content are shown in Table 1.

[0057] (V) XRD measurement XRD measurement was performed on the NASICON-type oxide powder according to Example 1 under the following measurement conditions. The obtained XRD spectrum is shown in Figure 1. <XRD measurement conditions> Measuring device: XRD-6100 (manufactured by Shimadzu Corporation) Tube target: Cu Tube voltage: 40 kv Tube current: 30 mA Divergence slit: 1.0° Scattering slit: 1.0° Receiving slit: 0.3 mm Step width: 0.02° / step Measurement time: 0.25 sec

[0058] The XRD spectrum of the NASICON-type oxide powder of Example 1 shown in Figure 1 was compared with ICDD (International Center for Diffraction Data) PDF (Powder Diffraction File) No. 01-080-1922, and it was possible to identify a solid electrolyte with a NASICON-type crystal structure as the main phase. The ratio of the most intense peak associated with the main phase to the most intense peak associated with the subphase was calculated, and no subphase / main phase ratio exceeding 1 / 10 was confirmed. The results are shown in Table 2.

[0059] (VI) Tap density The tap density of the NASICON-type oxide powder according to Example 1 was determined by filling an oxide powder into a cylindrical container with a bottom having an inner diameter of 6 mm to form an oxide powder layer, and applying a pressure of 0.16 N / m from above to the oxide powder layer, in the same manner as in the method described in JP 2007-263860 A. 2 After applying a pressure of 1000 kJ / cm, the height of the oxide powder layer was measured, and the density of the oxide powder was calculated from the measured height of the oxide powder layer and the weight of the packed oxide powder. The tap density of the NASICON-type oxide powder according to Example 1 is shown in Table 2.

[0060] (VII) Sintering start temperature The NASICON-type oxide powder according to Example 1 was compacted using a manual press to obtain a green compact measuring 5 mm in diameter and approximately 5 mm in height. The resulting green compact was placed in the sample holder (cylinder) of a thermomechanical analyzer (TMA) (Hitachi High-Tech Science; TMA / SS6200). A load of 980 mN was applied from the top of the cylinder in an air atmosphere using a piston-shaped jig, and the temperature was increased from room temperature at a rate of 10°C / min. The displacement of the piston jig was measured to determine the volumetric change (volumetric shrinkage) of the green compact. A method for determining the sintering start temperature of the green compact from the volumetric change (volumetric shrinkage) of the green compact will be described with reference to FIGS. 2 and 3.

[0061] Fig. 2 is a graph showing the TMA pattern of the powder compact according to Example 1, with the volumetric shrinkage rate of the powder compact on the vertical axis and the temperature of the powder compact on the horizontal axis. Fig. 3 is an enlarged view of part (A) in Fig. 2 where the TMA pattern begins to change. 3, the temperature at which the compact underwent a volume change (volume shrinkage rate) of -0.5% was determined and used as the sintering start temperature. The sintering start temperature of the NASICON-type oxide powder according to Example 1 is shown in Table 2.

[0062] (VIII) Measurement of water content The moisture content of the NASICON-type oxide powder according to Example 1 was measured under the following measurement conditions. The measured moisture content is shown in Table 1. <Moisture content measurement conditions> Measurement equipment: Karl Fischer moisture analyzer (Hiranuma trace moisture analyzer AQ-2100 and moisture vaporizer EV-2000, manufactured by Hiranuma Sangyo Co., Ltd.) Measurement sample amount: 0.3g Carrier gas: Nitrogen gas Carrier gas flow rate: 0.3 L / min interval time: 15 seconds Vaporization chamber temperature: 100℃

[0063] (7) Preparation and characterization of solid electrolytes with NASICON-type crystal structure A compact of the NASICON-type oxide powder according to Example 1 was sintered to produce a solid electrolyte having a NASICON-type crystal structure according to Example 1. The ionic conductivity of the solid electrolyte was then evaluated. The following describes (I) the production of a solid electrolyte having a NASICON-type crystal structure, and (II) the evaluation of the ionic conductivity of the solid electrolyte having a NASICON-type crystal structure, in that order.

[0064] (I) Preparation of solid electrolyte with NASICON-type crystal structure 0.5 g of the NASICON-type oxide powder according to Example 1 was placed in a cylindrical container with a diameter of 10 mm and pressed at 360 MPa using a press to obtain a green compact. The green compact obtained was placed in a furnace and sintered in the air for 120 minutes after the furnace temperature reached 800°C, producing a sintered green compact, which is a solid electrolyte having a NASICON-type crystal structure according to Example 1.

[0065] (II) Evaluation of ionic conductivity of solid electrolytes with NASICON-type crystal structure The solid electrolyte having a NASICON-type crystal structure according to Example 1 was measured in an air atmosphere at a temperature of 25°C using a potentio / galvanostat (1470E manufactured by Solartron) and a frequency response analyzer (1255B manufactured by Solartron) by an AC impedance method in the range of 100 Hz to 4 MHz. The resistance value of the solid electrolyte having a NASICON-type crystal structure according to Example 1 was then calculated from the obtained resistance value using a Cole-Cole plot (complex impedance plane plot) of the measured values. The calculated ionic conductivity values are shown in Table 2.

[0066] Example 2 The same procedure as in Example 1 was carried out, except that the amount of sodium nitrate added in Example 1 was 0.03 g, the amount of zirconyl nitrate dihydrate added was 0.95 g, and the bead material used during grinding was SUS304, to obtain the NASICON-type oxide powder of Example 2. The properties of the obtained NASICON-type oxide powder according to Example 2 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0067] Example 3 A NASICON-type oxide powder according to Example 3 was obtained by carrying out the same operation as in Example 1, except that the amount of sodium nitrate added was 0.08 g and the amount of zirconia nitrate dihydrate added was 0.80 g. The properties of the obtained NASICON-type oxide powder according to Example 3 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0068] Example 4 A NASICON-type oxide powder according to Example 4 was obtained by carrying out the same operation as in Example 1, except that the amount of sodium nitrate added was 0.10 g and the amount of zirconia nitrate dihydrate added was 0.15 g. The properties of the obtained NASICON-type oxide powder according to Example 4 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0069] Example 5 The same operation as in Example 1 was carried out, except that the amount of sodium nitrate added in Example 1 was 0.02 g, the amount of zirconia nitrate dihydrate added was 0.30 g, and the grinding process was carried out for 100 minutes, to obtain a NASICON-type oxide powder according to Example 5. The properties of the obtained NASICON-type oxide powder according to Example 5 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0070] Example 6 The same operation as in Example 1 was carried out, except that the amount of sodium nitrate added in Example 1 was 0.03 g, the amount of zirconia nitrate dihydrate added was 0.40 g, and the grinding process was carried out for 60 minutes, to obtain a NASICON-type oxide powder according to Example 6. The properties of the obtained NASICON-type oxide powder according to Example 6 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0071] Example 7 The amount of lithium nitrate added in Example 1 was 98 g, the amount of aluminum nitrate nonahydrate added was 116.7 g, the amount of sodium nitrate added was 0.23 g, and the amount of zirconia nitrate dihydrate added was 0.02 g. Furthermore, for firing, the temperature was increased from room temperature to 400°C at a rate of 5°C / min in an air atmosphere, and 400°C was maintained for 2 hours. The temperature was then increased from 400°C to 600°C at a rate of 5°C / min, and firing was performed at 600°C for 120 minutes. Furthermore, the crushing process was carried out for 30 minutes. Except for the above, the same operation as in Example 1 was carried out to obtain a NASICON-type oxide powder according to Example 7. The properties of the obtained NASICON-type oxide powder according to Example 7 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0072] Example 8 The amounts of lithium nitrate, aluminum nitrate nonahydrate, sodium nitrate, and zirconia nitrate dihydrate added in Example 1 were 110 g, 116.7 g, 0.08 g, and 0.02 g, respectively. The grinding process was carried out for 30 minutes. Other than the above, the same operation as in Example 1 was carried out to obtain a NASICON-type oxide powder according to Example 8. The properties of the obtained NASICON-type oxide powder according to Example 8 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0073] Example 9 A NASICON-type oxide powder according to Example 9 was obtained by carrying out the same operation as in Example 1, except that the amount of sodium nitrate added was changed to 0.30 g. The properties of the obtained NASICON-type oxide powder according to Example 9 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0074] Example 10 A NASICON-type oxide powder according to Example 10 was obtained by carrying out the same operation as in Example 1, except that the amount of sodium nitrate added was changed to 0.02 g. The properties of the obtained NASICON-type oxide powder according to Example 10 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0075] Example 11 A NASICON-type oxide powder according to Example 11 was obtained by carrying out the same operation as in Example 1, except that the amount of zirconium nitrate dihydrate added was changed to 0.02 g. The properties of the obtained NASICON-type oxide powder according to Example 11 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0076] Example 12 A NASICON-type oxide powder according to Example 12 was obtained by carrying out the same operation as in Example 1, except that the amount of zirconium nitrate dihydrate added was changed to 2.80 g. The properties of the obtained NASICON-type oxide powder according to Example 12 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0077] Comparative Example 1 Lithium carbonate (Fujifilm Wako Pure Chemical Industries, Ltd., 99.0+%), aluminum oxide (Fujifilm Wako Pure Chemical Industries, Ltd., 99.999%), germanium dioxide (Fujifilm Wako Pure Chemical Industries, Ltd., 99.999%), and ammonium dihydrogen phosphate (Fujifilm Wako Pure Chemical Industries, Ltd., 98.0+%) were prepared and used as LAGP powder. 1.5 Al 0.5 Ge 1.5 A predetermined amount of each powder was weighed out so as to obtain (PO4)3. The weighed powders were mixed in a dry bead mill to obtain a mixed powder. The mixed powder was heat-treated at 400°C for 1 hour, and then pulverized in a bead mill using isopropyl alcohol as a dispersion medium until the D50 particle size reached 0.04 μm. The pulverized powder was fired at 800°C to obtain a NASICON-type oxide powder according to the comparative example. The properties of the obtained NASICON-type oxide powder according to Comparative Example 1 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0078] Comparative Example 2 The same operation as in Comparative Example 1 was carried out, except that the pulverization treatment after the 400°C heat treatment in Comparative Example 1 was carried out until the D50 particle size became 0.08 μm, to obtain a NASICON-type oxide powder according to Comparative Example 2. The properties of the obtained NASICON-type oxide powder according to Comparative Example 2 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0079] Comparative Example 3 The same operation as in Comparative Example 1 was carried out, except that the pulverization treatment after the 400°C heat treatment in Comparative Example 1 was carried out until the D50 particle size became 0.30 μm, to obtain a NASICON-type oxide powder according to Comparative Example 3. The properties of the obtained NASICON-type oxide powder according to Comparative Example 3 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0080] Comparative Example 4 The same operation as in Comparative Example 1 was carried out, except that the pulverization treatment of the 400°C heat treatment in Comparative Example 1 was carried out until the D50 particle size became 6.8 μm, to obtain a NASICON-type oxide powder according to Comparative Example 4. The properties of the obtained NASICON-type oxide powder according to Comparative Example 4 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0081] Comparative Example 5 A NASICON-type oxide powder according to Comparative Example 5 was obtained by carrying out the same operation as in Example 1, except that the amount of sodium nitrate added was 0 g and the amount of zirconium nitrate dihydrate added was 0 g. The properties of the obtained NASICON-type oxide powder according to Comparative Example 1 were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0082] [Table 1] [Table 2]

Claims

1. A NASICON-type oxide powder containing lithium, aluminum, germanium, and phosphorus, Further, the NASICON-type oxide powder contains sodium in an amount of 1 ppm or more and 500 ppm or less.

2. A BET value, which is a specific surface area value measured by a BET single-point method; a D50 / BET ratio, which is the ratio of the D50 value, which is the cumulative 50% particle diameter on a volume basis, measured by laser diffraction, to the D50 value, is 0.05 or more and 7.00 or less; 2. The NASICON-type oxide powder according to claim 1.

3. The BET value, which is the specific surface area measured by the BET single-point method, is 1.0 m ２ / g or more, 15.0m ２ / g or less, The value of D50, which is the cumulative 50% particle diameter on a volume basis measured by laser diffraction, is 0.5 μm or more and 7.0 μm or less.

3. The NASICON-type oxide powder according to claim 1 or 2.

4. Lithium is 1.0 mass % or more and 4.0 mass % or less, Aluminum is 0.5 mass% or more and 6.0 mass% or less, germanium in an amount of 15% by mass or more and 35% by mass or less; Contains 10% by mass or more and 30% by mass or less of phosphorus, 4. The NASICON-type oxide powder according to claim 1.

5. The value of D10, which is the cumulative 10% particle diameter on a volume basis measured by laser diffraction, is 0.1 μm or more and 4.0 μm or less; The value of D90, which is the cumulative 90% particle diameter on a volume basis measured by laser diffraction, is 2.0 μm or more and 14.0 μm or less.

5. The NASICON-type oxide powder according to claim 1.

6. Tap density is 0.5 g / cm ３ Above, 2.0g / cm ３ Below is the 6. The NASICON-type oxide powder according to claim 1.

7. The sintering start temperature is 750°C or less.

7. The NASICON-type oxide powder according to claim 1.

8. Further, zirconium is contained in an amount of 10 ppm or more and 10,000 ppm or less.

8. The NASICON-type oxide powder according to claim 1.

9. obtaining a slurry containing lithium, aluminum, germanium, phosphorus, and sodium; drying the slurry to obtain a dry powder; calcining the dried powder at 600°C or higher and 900°C or lower to obtain a calcined powder; pulverizing the fired powder; A method for producing a NASICON-type oxide powder containing lithium, aluminum, germanium, and phosphorus, which further contains 1 ppm or more and 500 ppm or less of sodium.

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