Amorphous powder, powder package containing the same, method for producing amorphous powder, and method for producing solid electrolyte

Abstract

To provide amorphous powder that shows reduced variation in a mixed state with electrode active material powder.SOLUTION: An amorphous powder contains lithium, aluminum, germanium, phosphorus and oxygen, with the amorphous powder having a moisture content of 0.08-4 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] This invention relates to an amorphous powder, a powder package containing the same, a method for producing the amorphous powder, and a method for producing a solid electrolyte.

Background Art

[0002] As a solid electrolyte used in all-solid-state batteries, there is an ion conductor having a NASICON-type crystal structure with high ionic conductivity. As one of the solid electrolytes having a NASICON-type crystal structure, for example, it contains lithium, aluminum, germanium, phosphorus and oxygen, and has the general formula Li 1+x Al x Ge 2-x (PO4)3 (the range of x is 0 < x ≤ 1, and may be hereinafter referred to as "LAGP") is known.

[0003] The solid electrolyte having a NASICON-type crystal structure may be provided as a film on the particle surface of the electrode active material in order to increase the ionic conductivity of the electrode layer of the all-solid-state battery. For example, in Patent Documents 1 and 2, as a method for forming this film, it has been proposed to use an amorphous powder containing lithium, aluminum, germanium, phosphorus and oxygen. Here, the amorphous powder is crystallized so that its crystal structure changes from amorphous to NASICON-type, and a NASICON-type solid electrolyte is formed as a film on the particle surface of the electrode active material. By having a NASICON-type crystal structure, the solid electrolyte exhibits ionic conductivity, and by having this solid electrolyte present as a film on the surface of the electrode active material, high ionic conductivity can be obtained in the electrode layer of the all-solid-state battery.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the mixing of electrode active material powder and amorphous powder, from the viewpoint of uniformly forming a solid electrolyte film on the particle surface of the electrode active material powder, it is important to uniformly mix each powder and reduce the variation in the mixing state. In this regard, when the amorphous powder is directly mixed with the electrode active material powder, it has been confirmed that uniform mixing cannot be achieved and the variation in the mixing state becomes large. Therefore, uneven ion conductivity occurs in the electrode layer, and in the finally manufactured all-solid-state battery, not only excellent battery characteristics cannot be obtained, but also the variation in battery characteristics may become large. That is, excellent battery characteristics may not be stably obtained in the all-solid-state battery.

[0006] Therefore, an object of the present invention is to provide a technique for reducing the variation in the mixing state when an amorphous powder is mixed with an electrode active material powder.

Means for Solving the Problems

[0007] The inventor of the present invention studied to solve the above problems and found that by adjusting the moisture content contained in the amorphous powder, the variation in the mixing state when the amorphous powder is mixed with the electrode active material powder can be reduced.

[0008] The first aspect of the present invention is an amorphous powder containing lithium, aluminum, germanium, phosphorus and oxygen, wherein the moisture content of the amorphous powder is 0.08 to 4% by mass.

[0009] The second aspect of the present invention is, in the first aspect, wherein the moisture content of the amorphous powder is 3% by mass or less.

[0010] The third aspect of the present invention is, in the first aspect, The water content of the amorphous powder is 0.3 to 1% by mass or less.

[0011] The fourth aspect of the present invention is, in any one of the first to third aspects, the amorphous powder is lithium in an amount of 1% by mass or more and 4% by mass or less, aluminum in an amount of 0.5% by mass or more and 6% by mass or less, germanium in an amount of 15% by mass or more and 35% by mass or less, and phosphorus in an amount of 10% by mass or more and 30% by mass or less.

[0012] The fifth aspect of the present invention is the amorphous powder according to any one of the first to fourth aspects, and a container for accommodating the amorphous powder in a sealed state, and is a powder package in which the amorphous powder is accommodated in the container so that its water content is maintained at 0.08 to 4% by mass.

[0013] The sixth aspect of the present invention is, in the fifth aspect, the container accommodates a member containing water together with the amorphous powder.

[0014] The seventh aspect of the present invention is a method for producing an amorphous powder containing lithium, aluminum, germanium, phosphorus, and oxygen, having a water content adjustment step of adjusting the water content of the amorphous powder to be 0.08% by mass to 4% by mass, which is a method for producing an amorphous powder.

[0015] The eighth aspect of the present invention is, in the seventh aspect, in the water content adjustment step, the water content of the amorphous powder is adjusted to 3% by mass or less.

[0016] The ninth aspect of the present invention is, in the seventh aspect, in the water content adjustment step, the water content of the amorphous powder is adjusted to 0.3% by mass to 1% by mass.

[0017] The tenth aspect of the present invention is, in any one of the seventh to ninth aspects, in the moisture content adjustment step, an amorphous powder having a moisture content of 0.05% by mass or less is exposed to an atmosphere containing moisture to absorb water into the amorphous powder.

[0018] The eleventh aspect of the present invention is, in any one of the seventh to tenth aspects, in the moisture content adjustment step, an amorphous powder having a moisture content of 0.05% by mass or less is stored in a container in a sealed state together with a member containing water, so that the amorphous powder absorbs water.

[0019] The twelfth aspect of the present invention is, in any one of the eighth to eleventh aspects, before the moisture content adjustment step, a mixed slurry forming step of obtaining a mixed slurry containing lithium, aluminum, germanium, and phosphorus; a drying step of drying the mixed slurry to obtain a dried powder; and a heat treatment step of heat-treating the dried powder at 300°C or higher and 500°C or lower to obtain an amorphous powder having a moisture content of 0.05% by mass or less.

[0020] The thirteenth aspect of the present invention is a method for producing a solid electrolyte having a NASICON-type crystal structure, which includes a firing step of firing and crystallizing the amorphous powder according to any one of the first to fourth aspects.

Advantages of the Invention

[0021] According to the present invention, for an amorphous powder, it is possible to reduce the variation in the mixing state when mixed with an electrode active material powder.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Embodiment for Carrying Out the Invention

[0023] <One Embodiment of the Present Invention> Hereinafter, one embodiment of the present invention will be described. In this specification, each “particle” constitutes “powder”, and “powder” refers to a collection of “particles”. In the following description, in principle, the term “particle” is used when focusing on each individual component constituting the powder, and the terms “powder” or “powder of particles” are used when focusing on the whole collection of particles.

[0024] (Amorphous Powder) The amorphous powder according to this embodiment contains at least lithium, aluminum, germanium, phosphorus, and oxygen as constituent elements. This amorphous powder is amorphous and is a precursor powder that forms a solid electrolyte having a NASICON-type crystal structure by crystallization. The powder having a NASICON-type crystal structure can be used as a solid electrolyte for an all-solid-state battery because it exhibits high ionic conductivity. Here, a solid electrolyte is a solid that can move ions (charged substances) by an externally applied electric field. And the amorphous powder of this embodiment can be uniformly mixed with the electrode active material powder by adjusting its moisture content to a predetermined range. Hereinafter, the composition and moisture content of the amorphous powder will be described in detail.

[0025] The amorphous powder contains lithium, aluminum, germanium, phosphorus, oxygen, and, if necessary, other elements. These contents are not particularly limited as long as they become a solid electrolyte having a NASICON-type crystal structure when crystallized. From the viewpoint of obtaining a solid electrolyte having a NASICON-type crystal structure that exhibits higher ionic conductivity, the content of each element in the amorphous powder preferably falls within the following ranges.

[0026] Lithium is an element that contributes to the formation of a NASICON-type crystal structure when the amorphous powder is crystallized. Regarding the lower limit of the lithium content, it is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and still more preferably 1.8% by mass or more. Regarding the upper limit, it is preferably 4.0% by mass or less, preferably 3.5% by mass or less, and still more preferably 3.3% by mass or less.

[0027] Aluminum is an element that contributes to the formation of a NASICON-type crystal structure when the amorphous powder is crystallized. Regarding the lower limit of the aluminum content, it is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and still more preferably 2.0% by mass or more. Regarding the upper limit, it is preferably 6.0% by mass or less, more preferably 5.5% by mass or less, and still more preferably 5.0% by mass or less.

[0028] Germanium contributes to the formation of the amorphous state in the amorphous powder and also contributes to the formation of a NASICON-type crystal structure when the amorphous powder is crystallized. Regarding the lower limit of the germanium content, it is preferably 15% by mass or more, more preferably 20% by mass or more, still more preferably 22% by mass or more, and most preferably 23.5% by mass or more. Regarding the upper limit, it is preferably 35% by mass or less, more preferably 33% by mass or less, and still more preferably 30% by mass or less.

[0029] Phosphorus contributes to the formation of the amorphous state in the amorphous powder and also contributes to the formation of a NASICON-type crystal structure when the amorphous powder is crystallized. Regarding the lower limit of the phosphorus content, it is preferably 10% by mass or more, more preferably 15% by mass or more, and still more preferably 20% by mass or more. Regarding the upper limit, it is preferably 30% by mass or less, more preferably 28% by mass or less, and still more preferably 25% by mass or less.

[0030] If the amorphous powder forms a NASICON-type crystal structure when crystallized, it may contain other elements other than lithium, aluminum, germanium, and phosphorus described above. As other elements, for example, at least one of titanium, zirconium, and silicon may be included. The total content of other elements is preferably 5% by mass or less, and more preferably 3% by mass or less.

[0031] Oxygen makes up the remainder of lithium, aluminum, germanium, phosphorus, and other elements. The oxygen content is obtained by subtracting the total content of each constituent element contained in the amorphous powder (100% by mass - the total value of the mass percentages of each constituent element), and is preferably 40% by mass or more and 55% by mass or less.

[0032] Note that the amorphous powder may contain impurity elements other than the above-described elements as long as the effects are not impaired.

[0033] The amorphous powder of this embodiment is configured such that the moisture content is 0.08% by mass to 4% by mass. Since the amorphous powder is produced through drying and heat treatment, in the state after heat treatment, the moisture content tends to decrease due to heating, and is at most about 0.05% by mass. In this regard, in this embodiment, as will be described later, the moisture content is adjusted to be 0.08% by mass or more. Thereby, the dispersibility of the amorphous powder in the electrode active material powder is enhanced, and they can be uniformly mixed. On the other hand, if the moisture content becomes excessively high, the amorphous powder may aggregate and the dispersibility may decrease. However, by setting the moisture content to 4% by mass or less, aggregation of the amorphous powder can be suppressed, and the mixability with the electrode active material powder can be maintained at a high level. From the viewpoint of further improving the mixability with the electrode active material, the moisture content is preferably 0.08% by mass to 3% by mass, and more preferably 0.3% by mass to 1% by mass.

[0034] Note that the moisture content of the amorphous powder is a value measured by a Karl Fischer moisture measuring device, as will be described later. The moisture content obtained by this measurement mainly indicates the amount of moisture adhering to the surface of the amorphous powder.

[0035] The fact that the amorphous powder is amorphous is indicated by the observation of a halo in the region of 2θ: 15° to 40° when the amorphous powder is subjected to powder X-ray diffraction (XRD) measurement. Note that the halo is a gentle fluctuation in the intensity of X-rays and is observed as a broad elevation in the X-ray chart. And the full width at half maximum of the halo is 2θ: 2° or more.

[0036] The particle size of the amorphous powder is not particularly limited, but for the amorphous powder, the volume-based particle size distribution is measured using a laser diffraction scattering type particle size distribution measuring device, and the volume-based cumulative 50% particle size (D50) obtained by the measurement is preferably 0.5 μm or more and 30 μm or less. By setting the particle size in this way, it becomes possible to suitably use it as a solid electrolyte of an all-solid-state battery.

[0037] The BET specific surface area of the amorphous powder is 10 m 2 / g or more and 100 m 2 / g or less is preferable. By setting the BET specific surface area in this way, it becomes possible to suitably use it as a solid electrolyte of an all-solid-state battery.

[0038] (Manufacturing method of amorphous powder) Subsequently, the manufacturing method of the amorphous powder described above will be described in the order of (1) raw material aqueous solution preparation step, (2) mixed slurry formation step, (3) drying step, (4) heat treatment step, and (5) moisture content adjustment step. Note that (1) to (4) are not limited to the following methods, and for example, amorphous powder obtained by using the manufacturing methods of JP 2018-37341 A and JP 2019-50083 A may be adjusted for moisture.

[0039] (1) Raw material aqueous solution preparation step First, raw materials containing lithium, aluminum, germanium, phosphorus, which are elements constituting the amorphous powder, and other elements as required are each dissolved in water to prepare an aqueous raw material solution containing each constituent element. As the raw materials containing each constituent element, conventionally known ones can be used. For example, it is advisable to prepare an aqueous solution in which a germanium oxide such as germanium dioxide is dissolved, and an aqueous solution in which, for example, lithium nitrate, aluminum nitrate nonahydrate, ammonium dihydrogen phosphate, etc. are dissolved.

[0040] (2) Mixed slurry formation step Subsequently, the aqueous raw material solution prepared in (1) is mixed according to the composition of the target amorphous powder, and a slurry containing the constituent elements of the solid electrolyte is obtained by a so-called coprecipitation method. For example, when an acidic aqueous solution in which lithium nitrate, aluminum nitrate nonahydrate, and ammonium dihydrogen phosphate are dissolved is added to an alkaline germanium aqueous solution dissolved with ammonia, a slurry containing lithium, aluminum, germanium, phosphorus, etc. can be obtained by the coprecipitation method.

[0041] According to the coprecipitation method, the ionic concentration product of the constituent elements in the slurry obtained by mixing the aqueous raw material solutions becomes a supersaturated state higher than the solubility product, and as a result, the number of nuclei of the precipitate to be formed increases, so that the particle size of the precipitate to be deposited can be reduced. Thereby, for example, the BET specific surface area of the amorphous powder can be made 20 m 2 / g or more.

[0042] (3) Drying step Subsequently, the slurry obtained in (2) is dried to evaporate the moisture in the slurry, thereby obtaining a dry powder. The drying method is not particularly limited, but spray drying using a spray dryer or the like is preferable. According to spray drying, the constituent elements existing as ions in the slurry can be rapidly precipitated in a short time, and the non-uniformity of precipitation caused by the difference in solubility between the constituent elements can be reduced. Thereby, a dry powder with a uniform composition can be obtained, and an amorphous powder with the formation of germanium dioxide suppressed can be more reliably formed. The drying temperature may be appropriately set to a temperature at which no moisture remains in the obtained dry powder. For example, the inlet temperature of a spray dryer, which is a spray drying machine, is preferably 150 to 250°C, and the hot air outlet temperature is 60°C or higher.

[0043] (4) Heat treatment step Subsequently, the dry powder obtained in (3) is heat-treated to be vitrified, thereby obtaining an amorphous powder. For example, the dry powder may be placed in a container made of alumina or the like and heated from room temperature to 300 to 500°C at a heating rate of 0.1 to 20°C / min in an air atmosphere.

[0044] The amorphous powder obtained by the heat treatment has a reduced moisture content due to the heating during the above-mentioned (3) drying step and (4) heat treatment step. For example, the moisture content in the amorphous powder after the heat treatment is 0.05 mass% or less.

[0045] (5) Moisture content adjustment step Subsequently, in this embodiment, the moisture content of the amorphous powder obtained in (4) is adjusted. Specifically, the amorphous powder after the heat treatment and having a moisture content of 0.05 mass% or less is exposed to an atmosphere containing moisture for a predetermined time to allow the amorphous powder to absorb water, and the moisture content of the amorphous powder is adjusted to 0.08 mass% to 4 mass%. Thereby, the amorphous powder of this embodiment is obtained.

[0046] The water absorption method is not particularly limited. There are methods such as spraying water directly onto the amorphous powder to absorb moisture directly, and exposing the amorphous powder to an atmosphere containing moisture to absorb moisture indirectly. In the method of indirectly absorbing moisture, for example, it is advisable to enclose and seal a member containing water (such as paper containing moisture) together with the amorphous powder in a container. To adjust the moisture content of the amorphous powder, if it is the case of directly absorbing moisture, the amount of water sprayed may be adjusted. If it is the case of indirectly absorbing moisture, the moisture content of the member containing water may be adjusted. From the perspective of making the mixing property of the amorphous powder with the electrode active material powder higher, the method of indirectly absorbing moisture is preferred. This is because in the case of the method of indirectly absorbing moisture, compared with the case of directly absorbing moisture, it is easier to adjust the moisture content and the aggregation of the amorphous powder due to water absorption can be suppressed.

[0047] The container used in the case of indirectly absorbing moisture is not particularly limited as long as it can be sealed and suppress moisture permeation, and known containers can be used.

[0048] Note that a particle size adjustment step for adjusting the particle size of the amorphous powder may be provided between the (4) heat treatment step and the (5) moisture content adjustment step. For example, in the case of forming a solid electrolyte into a sheet shape, the particle size may be appropriately adjusted according to the target sheet thickness. Although known methods can be used for the particle size adjustment method, wet grinding using a bead mill or the like is preferred. When wet grinding is carried out, solid-liquid separation is performed after the wet grinding treatment, and the amorphous powder after wet grinding is dried. The particle size of the amorphous powder after particle size adjustment obtained by drying is not particularly limited, but the volume-based cumulative 50% particle diameter (D 50 ) is more preferably 0.5 μm to 5 μm.

[0049] (Powder package) The above-mentioned amorphous powder may vary due to a decrease or increase in the moisture content when exposed to the atmosphere. If the moisture content fluctuates excessively, it may cause aggregation of the amorphous powder and impair its miscibility with the electrode active material powder. Therefore, it is preferable to store the amorphous powder in a container to form a powder package so as to maintain the moisture content of the amorphous powder at 0.08% to 4% by mass from the viewpoint of ensuring long-term storage stability. Hereinafter, the powder package will be specifically described.

[0050] The powder package of this embodiment includes an amorphous powder and a container for storing the amorphous powder in a sealed state, and is configured such that the moisture content of the amorphous powder is maintained at 0.08 to 4% by mass. By sealing the amorphous powder in the container, even if moisture volatilizes from the amorphous powder, the moisture can be retained in the container. Thereby, reduction of the moisture content contained in the amorphous powder can be suppressed, and the moisture content can be maintained at 0.08% to 4% by mass.

[0051] It is preferable that the powder package contains a hydrated member together with the amorphous powder in the container. According to the hydrated member, the amorphous powder can absorb water in the container, and fluctuations in the moisture content can be more reliably suppressed. Thereby, the amorphous powder can be stored more reliably over a long period of time.

[0052] From the viewpoint of indirectly causing the amorphous powder to absorb water, it is preferable that the hydrated member does not come into direct contact with the amorphous powder. For example, a mat or a tray may be placed on the amorphous powder, and the hydrated member may be placed thereon. Also, the moisture content in the hydrated member may be appropriately changed according to the target moisture content in the amorphous powder.

[0053] Also, when accommodating a member containing water in the powder package, for example, after the heat treatment step, an amorphous powder with a water content of 0.05 mass% or less and a member containing a predetermined amount of water are accommodated in a container, and the amorphous powder is allowed to absorb water in the container and stored so as to maintain a predetermined water content. Also, for example, it may be stored in a container together with a member containing an amorphous powder adjusted in advance to a predetermined water content so as to maintain the predetermined water content.

[0054] The container used for the powder package is not particularly limited as long as it can be sealed and suppress moisture permeation. For example, known containers such as resin laminate aluminum bags can be used.

[0055] Also, the member to be hydrated is not particularly limited as long as it can impregnate and hold water, and for example, known materials such as paper may be used.

[0056] (Mixed Powder for Electrode Layer and Electrode Layer) Subsequently, the mixed powder for the electrode layer obtained by mixing the above-described amorphous powder and the electrode active material powder will be described.

[0057] The mixed powder for the electrode layer is obtained by mixing the above-described amorphous powder and the electrode active material powder. As described above, since the amorphous powder of the present embodiment is excellent in mixability (mixing uniformity) with the electrode active material powder, in the mixed powder for the electrode layer, it is possible to suppress the deviation in the dispersion of the amorphous powder and the electrode active material powder. Specifically, when a plurality of predetermined samples are collected from the mixed powder for the electrode layer and the concentration of the component derived from the amorphous powder or the concentration of the element derived from the electrode active material powder contained in each sample is measured, the standard deviation σ of these concentrations can be preferably 1.0 or less, more preferably 0.5 or less, and even more preferably 0.3 or less. That is, the variation in the concentration of the predetermined element in each sample can be suppressed, and the concentration can be made uniform.

[0058] The electrode active material powder is not particularly limited as long as it can be used as a positive electrode active material or a negative electrode active material, and conventionally known ones can be used. The particle size of the electrode active material powder is not particularly limited, and for example, it may be 0.5 μm to 20 μm.

[0059] The electrode layer can be produced, for example, by forming a mixed powder for the electrode layer into a sheet shape and firing it at a temperature exceeding 500°C to crystallize the amorphous powder. The obtained electrode layer is configured such that a solid electrolyte having a NASICON-type crystal structure uniformly coats the surface of the electrode active material powder. Therefore, in the electrode layer, while obtaining high ionic conductivity, the deviation thereof can be reduced. Moreover, when a plurality of electrode layers are produced, the variation in ionic conductivity of each can be reduced. By adopting such an electrode layer in an all-solid-state battery, it becomes possible to stably obtain excellent battery characteristics in the all-solid-state battery.

[0060] The reason for obtaining high ionic conductivity in the electrode layer of the present embodiment is that the solid electrolyte forms a NASICON-type crystal structure and exhibits high ionic conductivity, and the variation in the mixing state of the mixed powder for the electrode layer is small, that is, each powder is not unevenly distributed and the deviation in each concentration is small. Therefore, it is presumed that the interface between the solid electrolyte and the active material in the electrode layer formed from the mixed powder for the electrode layer increases compared to the case where the variation in the mixing state is large, and ionic conduction is more likely to occur.

[0061] The solid electrolyte having a NASICON-type crystal structure contains lithium, aluminum, germanium, and phosphorus, which are the constituent elements of the amorphous powder before crystallization described above. Whether it is a solid electrolyte having a NASICON-type crystal structure can be determined from the XRD profile by measuring it using an XRD apparatus. Specifically, the obtained XRD profile can be identified by comparing it with PDF (Powder Diffraction File) No. 01-080-1922 of ICDD (International Center for Diffraction Data) using the electronic computer attached to the XRD apparatus.

Examples

[0062] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto in any way.

[0063] <Production of Amorphous Powder> In this example, as shown below, the amorphous powders of Examples 1 to 6 and Comparative Examples 1 and 2 were produced in the order of (1) raw material aqueous solution preparation step, (2) mixed slurry formation step, (3) drying step, (4) heat treatment step, (5) particle size adjustment step, and (6) moisture content adjustment step.

[0064] <Example 1> (1) Raw material aqueous solution preparation step First, as the raw material aqueous solution, (I) a germanium aqueous solution and (II) an aqueous solution containing lithium, aluminum, and phosphorus were prepared. Each will be described below.

[0065] (I) Aqueous solution of germanium compound 385 g of germanium dioxide (99.999% manufactured by Fujifilm Wako Pure Chemical Corporation) was added to 8000 g of pure water, heated to 40 °C while stirring, and then 195 g of 28 mass% aqueous ammonia (28% manufactured by Nacalai Tesque) as an alkali was added to dissolve germanium dioxide to prepare an aqueous solution of germanium compound. The pH value of the prepared aqueous solution was 10.7 and it was alkaline.

[0066] (II) Aqueous solution containing lithium, aluminum, and phosphorus 217 g of lithium nitrate (98.0+% manufactured by Fujifilm Wako Pure Chemical Corporation), 394 g of aluminum nitrate nonahydrate (98.0+% manufactured by Fujifilm Wako Pure Chemical Corporation), and 725 g of ammonium dihydrogen phosphate (98.0+% manufactured by Fujifilm Wako Pure Chemical Corporation) were added to 1500 g of pure water to prepare an aqueous solution containing lithium, aluminum, and phosphorus. The pH value of the prepared aqueous solution containing lithium, aluminum, and phosphorus was 1.4 and it was acidic.

[0067] (2) Mixed slurry formation step 7,200 g of an alkaline germanium aqueous solution was separated and heated to 40 °C while stirring. When the total amount (2,837 g) of the prepared lithium, aluminum, and phosphorus-containing aqueous solution was added thereto, the aqueous solution became turbid immediately after the addition, and a white mixed slurry of lithium, aluminum, germanium, phosphorus, ammonia, and water was obtained. The pH value of the obtained white slurry was 4.3.

[0068] (3) Drying step The mixed slurry was spray-dried using a spray dryer (SD-1000 manufactured by Tokyo Rika Kikai Co., Ltd.) to evaporate the moisture in the mixed slurry and precipitate the solid phase at once, obtaining a white powder. The conditions for spray drying were an inlet temperature of 180 °C, an outlet temperature of 90 °C, and a feeding rate of the mixed slurry of 10 g / min.

[0069] (4) Heat treatment step 50 g of the dried powder obtained by spray drying was placed in an alumina container, heated from room temperature to 400 °C at a heating rate of 5 °C / min, and heat-treated for 120 minutes in an air atmosphere after reaching 400 °C to obtain a heat-treated powder.

[0070] (5) Particle size adjustment step 400 g of the heat-treated powder was charged into a bead mill together with 1,600 g of φ1 mm Zr beads and 943.2 g of isopropyl alcohol (IPA), and wet-milled for 120 minutes. Subsequently, the wet-milled heat-treated powder was put into a dryer and dried at 100 °C for 3 hours to remove IPA and obtain a dried powder with adjusted particle size. When the moisture content of the dried powder with adjusted particle size obtained in this step was measured in the same manner as the moisture content analysis described below, it was 0.04% by mass.

[0071] (6) Moisture content adjustment step The water content adjustment process was carried out as shown in Figure 1. Specifically, first, a nylon inner bag and an outer bag (width 450 mm, length 700 mm) were prepared, and the inner bag was placed inside the outer bag to double it, thereby forming the container 11. Subsequently, 200 g of the dried powder 10 with adjusted particle size after the above particle size adjustment was taken and placed in the nylon inner bag in the container 11. Also, after preparing a paper wipe (trade name JK Wiper, manufactured by Nippon Paper Crecia Co., Ltd.) containing 0.12 g of pure water to make it water-containing, a stainless-steel deep-type vat 13 containing the water-containing member was prepared, placed on the dried powder 10 with adjusted particle size in the inner bag, and the entrances of the inner bag and the outer bag were sealed and left standing for 12 hours. After standing, the stainless-steel deep-type vat 13 containing the water-containing member 12 was taken out from the inner bag, the entrance of the container 11 was sealed again, the container 11 was shaken, left standing for 1 hour, and the amorphous powder of Example 1 was obtained.

[0072] <Example 2> In Example 2, in the (6) water content adjustment of Example 1, except that the amount of pure water impregnated in the paper wipe was changed from 0.12 g to 0.52 g as the water content adjustment condition, it was the same as Example 1, and an amorphous powder was obtained.

[0073] <Example 3> In Example 3, in the (6) water content adjustment of Example 1, except that the amount of pure water impregnated in the paper wipe was changed from 0.12 g to 0.92 g as the water content adjustment condition, it was the same as Example 1, and an amorphous powder was obtained.

[0074] <Example 4> In Example 4, in the (6) water content adjustment of Example 1, except that the amount of pure water impregnated in the paper wipe was changed from 0.12 g to 1.52 g as the water content adjustment condition, it was the same as Example 1, and an amorphous powder was obtained.

[0075] <Example 5> In Example 5, in the (6) water content adjustment of Example 1, except that the amount of pure water impregnated in the paper wipe was changed from 0.12 g to 1.92 g as the water content adjustment condition, it was the same as Example 1, and an amorphous powder was obtained.

[0076] <Example 6> In Example 6, in the (6) moisture content adjustment of Example 1, except that the amount of pure water impregnated into the paper-made wick was changed from 0.12 g to 5.92 g as the moisture content adjustment condition, the same procedure as in Example 1 was followed to obtain an amorphous powder.

[0077] <Comparative Example 1> In Comparative Example 1, in the (6) moisture content adjustment of Example 1, except that the amount of pure water impregnated into the paper-made wick was changed from 0.12 g to 9.92 g as the moisture content adjustment condition, the same procedure as in Example 1 was followed to obtain an amorphous powder.

[0078] <Comparative Example 2> In Comparative Example 2, in the (6) moisture content adjustment of Example 1, except that the amount of pure water impregnated into the paper-made wick was changed from 0.12 g to 0.02 g as the moisture content adjustment condition, the same procedure as in Example 1 was followed to obtain an amorphous powder.

[0079] <Evaluation Method> Subsequently, for the obtained amorphous powders of the examples and comparative examples, moisture content analysis, XRD measurement of the amorphous powder, elemental analysis, particle size D 50 measurement, and BET specific surface area measurement were performed. In addition, the obtained amorphous powders of the examples and comparative examples were mixed with the electrode active material to evaluate the mixability. Furthermore, a compact sintered body obtained by crystallizing the obtained amorphous powders of the examples and comparative examples was fabricated, and XRD measurement of the compact sintered body was carried out to evaluate whether it is a solid electrolyte with a NASICON-type crystal structure. Hereinafter, each method and result will be described.

[0080] (Moisture Content Analysis) The moisture content of the amorphous powder was measured under the following measurement conditions, and the measurement results are shown in Table 1. Measuring device: Karl Fischer moisture measuring device (Hiranuma Sangyo Co., Ltd. Hiranuma micro moisture measuring device AQ-2100 and moisture vaporization device EV-2000) Measured sample amount: 0.3 g Carrier gas: Nitrogen gas Carrier gas flow rate: 0.3 L / min Interval time: 15 sec Vaporization chamber temperature: 100 °C

[0081] (XRD measurement of amorphous powder) XRD measurement of the amorphous powder was carried out under the following measurement conditions. Measuring device: XRD-6100 (manufactured by Shimadzu Corporation) X-ray tube: 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

[0082] (Elemental analysis) 0.1 g of the obtained amorphous powder according to the examples and comparative examples and 1 g of NaK carbonate were weighed into a platinum crucible, melted at about 900 °C, leached with warm water after melting, and 10 mL of nitric acid was added to dissolve it. A dissolved sample solution diluted 500 times was prepared. One dissolved sample solution was subjected to elemental analysis using ICP-OES, and the analytical values of each constituent element are shown in Table 1. It should be noted that (100 mass% - the total value of the mass% of each constituent element) obtained by subtracting the total content of the analytical values of each constituent element contained in the amorphous powder by elemental analysis is considered to be the amount of oxygen present. The same applies to Examples 2 to 6 and Comparative Examples 1 to 2 described later.

[0083] (Particle size D 50 measurement) The obtained amorphous powders of the examples and comparative examples were measured for the volume-based particle size distribution at a dispersion pressure of 5 bar using a laser diffraction / scattering particle size distribution measuring device (HELOS & RODOS (pneumatic dispersion module) manufactured by SYMPATEC), and the volume-based cumulative 50% particle size (D 50 ) was determined. The measurement results are shown in Table 1.

[0084] (BET specific surface area measurement) The BET specific surface areas of the obtained amorphous powders of the examples and comparative examples were measured using a BET specific surface area measuring instrument (Macsorb manufactured by Mountech Co., Ltd.). After degassing by flowing nitrogen gas at 105°C for 20 minutes in the measuring instrument, the measurement was performed by the BET one-point method while flowing a mixed gas of nitrogen and helium (N2: 30% by volume, He: 70% by volume). The measured values of the BET specific surface areas are listed in Table 1.

[0085] (Mixability) Regarding the obtained amorphous powders of the examples and comparative examples, they were mixed with the electrode active material, and the uniformity of the mixture with the electrode active material was analyzed. The uniformity of the mixture was determined by preparing five samples of the mixed powder obtained by mixing the electrode active material powder containing Co element, which is an element not contained in the obtained amorphous powder of Example 1, dissolving the five samples of the mixed powder, and obtaining the standard deviation σ of the Co element content contained in the dissolved solution. The smaller the value of the standard deviation σ, the more uniformly the amorphous powder and the electrode active material are mixed, indicating a higher mixing uniformity. The reason for measuring the Co element content is that Co is an element not common to the amorphous powder and the electrode active material powder, and the variation in the Co content can be used to grasp the variation in the mixing state of the amorphous powder and the electrode active material powder.

[0086] Specifically, first, 16 g of the amorphous powder of the example or comparative example and D as the electrode active material 504 g of LiNiCoMnO2 powder (manufactured by MTI) with a particle size of 6.9 μm was mixed with a micro perspective V-type mixer (manufactured by Tsutsui Rikagaku Kikai Co., Ltd., model VM-2, mixing container V-C) under the conditions of a rotation speed of 70 rpm and a rotation time of 5 minutes. Subsequently, five samples of 0.5 g were taken from the obtained mixed powder. Subsequently, for the five samples, 0.1 g of the sample and 1 g of NaK carbonate were weighed into a platinum crucible, melted at about 900 °C, leached with warm water after melting, and 10 mL of nitric acid was added to dissolve it. Five dissolved sample solutions diluted 500 times were prepared. The amount of Co in the five dissolved sample solutions was measured using ICP-OES. The standard deviation σ of the amount of Co in the five obtained dissolved solutions was determined, and the determined standard deviation σ is described in Table 2. When preparing the dissolved sample solution by diluting the dissolved solution, the obtained dissolved solution was transferred to a 250 mL volumetric flask, fixed with pure water, then 5 mL of the fixed solution was taken, 5 mL of nitric acid was added, and it was fixed with pure water in a 100 mL volumetric flask.

[0087] (XRD Measurement of the Compressed Powder Sintered Body) First, for each of the obtained amorphous powders of the examples and comparative examples, 0.5 g was collected, put into a cylindrical container with a diameter of 10 mm, and pressed at 360 MPa with a press to obtain a compressed powder body. The compressed powder body of the obtained amorphous powder was fired for 120 minutes after the furnace temperature reached 800 °C to produce a compressed powder sintered body that was crystallized.

[0088] For the obtained compressed powder sintered body, XRD measurement of the compressed powder sintered body was performed under the same measurement conditions as the above-mentioned "XRD measurement of amorphous powder", and it was compared with the JCPDS card No. 01-080-1922 of LAGP, which is a solid electrolyte with a NASICON-type crystal structure, to confirm whether the crystal structure of the compressed powder sintered body is of the NASICON type.

[0089] <Evaluation Results> The results obtained by the above evaluation method are summarized in Tables 1 and 2 below.

[0090]

Table 1

[0091]

Table 2

[0092] As shown in Table 1, it was confirmed that all of the amorphous powders in Examples 1 to 6, Comparative Example 1 and Comparative Example 2 contained 2.43% by mass of Li, 3.02% by mass of Al, 25.1% by mass of Ge, and 21.7% by mass of P as constituent elements. Also, the particle diameter D 50 was 1.8 μm, and the BET specific surface area was 27 m 2 / g. Also, in the adjustment of the moisture content, by changing the moisture content impregnated into the paper-made wipes, the moisture content of the amorphous powder was 0.1% by mass in Example 1, 0.3% by mass in Example 2, 0.5% by mass in Example 3, 0.08% by mass in Example 4, 1% by mass in Example 5, 3% by mass in Example 6, 5% by mass in Comparative Example 1, and 0.05% by mass in Comparative Example 2.

[0093] Also, XRD measurement was performed on the amorphous powder of Example 1, and the XRD spectrum shown in FIG. 2 was obtained. In the XRD spectrum of FIG. 2, in the region of 2θ: 15° to 40°, a halo with a half-value width of 2θ: 2° or more was observed. From this, it was confirmed that the amorphous powder of Example 1 was amorphous. Also, it was confirmed that the amorphous powders of the other examples and comparative examples were also amorphous.

[0094] Also, when XRD measurement was performed on the compacted sintered body formed using the amorphous powders of the examples and comparative examples, a crystal peak of LAGP, which is a solid electrolyte having a NASICON-type crystal structure, was observed in any of the compacted sintered bodies. From this, it was confirmed that the amorphous powders of the examples and comparative examples were precursor powders capable of forming a solid electrolyte having a NASICON-type crystal structure by crystallization.

[0095] In addition, when the miscibility of the amorphous powders of the examples and comparative examples was evaluated, as shown in Table 2, in Examples 1 to 6 where the water content of the amorphous powder was in the range of 0.08% to 4% by mass, when five samples were collected respectively, it was confirmed that the standard deviation σ of the Co content in each sample was 0.5 or less. That is, the variation in the Co content in each sample was small, the variation in the mixing state of the amorphous powder and the electrode active material was small, and it was confirmed that they were uniformly mixed. On the other hand, in Comparative Example 1 where the water content of the amorphous powder was 5% by mass and Comparative Example 2 where it was 0.05% by mass, the standard deviation σ was 1.43 and 1.49 respectively, and it was confirmed that the amorphous powder and the electrode active material were not uniformly mixed. This is presumably because when the water content of the amorphous powder is excessively low or high, the amorphous powder aggregates and the miscibility with the electrode active material powder is low.

[0096] In addition, in Examples 2 to 5, since the standard deviation σ could be made smaller, it was confirmed that by setting the water content of the amorphous powder to 0.3% to 1% by mass, the amorphous powder and the electrode active material could be mixed more uniformly.

[0097] As described above, according to the amorphous powder with a water content of 0.08% to 4% by mass, it can be uniformly mixed with the electrode active material, and when the electrode layer is formed, a film formed from the solid electrolyte can be uniformly formed on the surface of the electrode active material. Thereby, the deviation of the ionic conductivity in the electrode layer can be suppressed, and excellent battery characteristics can be realized.

Claims

1. An amorphous powder containing lithium, aluminum, germanium, phosphorus and oxygen, wherein the water content of the amorphous powder is 0.08 to 4% by mass, and the amorphous powder is a precursor powder for forming a solid electrolyte having a NASICON-type crystal structure.

2. The amorphous powder according to claim 1, which is used for mixing with an electrode active material powder and firing the mixed powder for an electrode layer obtained by the mixing.

3. The water content of the amorphous powder is 3% by mass or less, The amorphous powder according to claim 1 or 2.

4. The water content of the amorphous powder is 0.3 to 1% by mass or less, The amorphous powder according to any one of claims 1 to 3.

5. The amorphous powder is lithium in an amount of 1% by mass or more and 4% by mass or less, aluminum in an amount of 0.5% by mass or more and 6% by mass or less, germanium in an amount of 15% by mass or more and 35% by mass or less, phosphorus in an amount of 10% by mass or more and 30% by mass or less, The amorphous powder according to any one of claims 1 to 4.

6. An amorphous powder according to any one of claims 1 to 5, and a container for accommodating the amorphous powder in a sealed state, wherein the amorphous powder is accommodated in the container so that its water content is maintained at 0.08 to 4% by mass, Powder package.

7. The container accommodates a member containing water together with the amorphous powder, The powder package according to claim 6.

8. A method for producing an amorphous powder containing lithium, aluminum, germanium, phosphorus and oxygen, comprising a water content adjusting step of adjusting the water content of the amorphous powder to 0.08% by mass to 4% by mass, wherein the amorphous powder is a precursor powder for forming a solid electrolyte having a NASICON-type crystal structure, Method for producing amorphous powder.

9. The method for producing an amorphous powder according to claim 8, which is used for mixing with an electrode active material powder and firing the mixed powder for an electrode layer obtained by the mixing.

10. In the water content adjusting step, the water content of the amorphous powder is adjusted to 3% by mass or less, The method for producing an amorphous powder according to claim 8 or 9.

11. In the water content adjusting step, the water content of the amorphous powder is adjusted to 0.3% by mass to 1% by mass, The method for producing an amorphous powder according to any one of claims 8 to 10.

12. In the moisture content adjustment step, an amorphous powder having a moisture content of 0.05% by mass or less is exposed to an atmosphere containing moisture to cause the amorphous powder to absorb water. The method for producing an amorphous powder according to any one of claims 8 to 11.

13. In the moisture content adjustment step, an amorphous powder having a moisture content of 0.05% by mass or less is contained in a container in a sealed state together with a member containing water to cause the amorphous powder to absorb water. The method for producing an amorphous powder according to any one of claims 8 to 12.

14. Before the moisture content adjustment step, a mixed slurry formation step of obtaining a mixed slurry containing lithium, aluminum, germanium, and phosphorus; a drying step of drying the mixed slurry to obtain a dried powder; and a heat treatment step of heat-treating the dried powder at 300°C or higher and 500°C or lower to obtain an amorphous powder having a moisture content of 0.05% by mass or less. The method for producing an amorphous powder according to any one of claims 8 to 13.

15. It has a firing step of firing a mixed powder for an electrode layer obtained by mixing the amorphous powder according to any one of claims 1 to 5 and an electrode active material powder, A method for producing a solid electrolyte having a NASICON-type crystal structure, wherein in the firing step, an amorphous powder, which is a precursor powder for forming a solid electrolyte having a NASICON-type crystal structure, is fired and crystallized.

Images