JP7280815B2 - Sintered compact, power storage device, and method for producing sintered compact - Google Patents

Description

Disclosed herein are a sintered body, an electrical storage device, and a method of manufacturing the sintered body.

Conventionally, as a lithium secondary battery as an electricity storage device, a porous solid electrolyte exhibiting a lithium ion conductivity of 0.5 × 10 ^-4 S/cm or more and a battery active material filled inside the pores of the porous solid electrolyte There has been proposed a lithium secondary battery electrode composed of a composite of (see, for example, Patent Document 1). This lithium secondary battery has a composite electrode consisting of a porous solid electrolyte and a battery active material that fills the pores of the porous solid electrolyte. Batteries can be supplied. Also, as a sintered body that is a solid electrolyte, a first fine particle-containing solution is deposited on a substrate, dried to form a first fine particle aggregation layer, polymer particles are deposited on the first fine particle aggregation layer, and After the solution containing the second fine particles is filled so as to immerse the polymer particles, it is dried to form a second fine particle aggregation layer in which a large number of polymer particles are embedded, and is sintered to form a porous solid. A method for obtaining a structure in which an electrolyte and a solid electrolyte dense body are integrated has been proposed (see, for example, Patent Document 2). In this sintered body, it is possible to realize the integration of the porous solid electrolyte and the solid electrolyte. In addition, as a sintered body that is a solid electrolyte, a sintered body obtained by adding a pore-forming material to a Li-La-Zr garnet phase powder and sintering it has been proposed (see, for example, Non-Patent Document 1). . It is said that this sintered body can be charged and discharged at a high rate of 1 mA/cm ² .

JP 2006-260887 A JP 2009-238739 A

Nano Letter.2018,18,3926-3933

However, in the sintered bodies of Patent Documents 1 and 2 and Non-Patent Document 1, since the sintering temperature is 1000 ° C. or higher, the particles are coarsened, and the structure was not sufficient for charging and discharging at a high rate. . Although it can be said that the sintered body of Non-Patent Document 1 can handle a relatively high rate, it is still insufficient and further improvement has been desired. Thus, there has been a demand for a sintered body that has porosity and can be charged and discharged at a high rate exceeding 1 mA/cm ² .

The present disclosure has been made in view of such problems, and a sintered body, an electricity storage device, and a method for producing a sintered body that can realize charging and discharging at a higher rate in a lithium ion-conducting material. The main purpose is to provide

As a result of intensive research to achieve the above-described object, the present inventors have found that the base material particles of a solid electrolyte such as a garnet-type oxide have an average pore size larger than a predetermined value and a predetermined void The present inventors have found that a sintered body that conducts lithium ions can be charged and discharged at a higher rate, and have completed the invention disclosed herein.

That is, the sintered body of the present disclosure is
A sintered body containing matrix particles that conduct lithium ions,
A porous layer having a porosity of 20% by volume or more and 60% by volume or less and an average pore diameter of less than 10 μm and having an average pore diameter larger than that of the base material particles is provided on the outer surface side.

The power storage device of the present disclosure is
a positive electrode;
a negative electrode;
the above-mentioned sintered body interposed between the positive electrode and the negative electrode to conduct lithium ions and having the porous layer at least on the negative electrode side;
is provided.

The method for producing a sintered body of the present disclosure includes
A method for producing a sintered body containing matrix particles that conduct lithium ions,
A dense porous layer containing the base material particles, in which a pore-forming material having an average particle size equal to or larger than the average particle size of the base material particles and having an average particle size of less than 10 μm is added in a range of 20% by volume or more and 60% by volume or less. A sintering step of obtaining a sintered body by sintering the raw material compact present on the outer surface side of the layer at a temperature of 900 ° C. or less;
includes.

In the sintered body, the electricity storage device, and the method for manufacturing the sintered body of the present disclosure, charging and discharging at a higher rate can be realized. The reason why such an effect is obtained is presumed as follows. For example, when the porosity is within a desired range, it can be used as a buffer for containing lithium deposited from the electrode, and can prevent separation between the electrode and the sintered body. In addition, when the particle diameter of the base material particles is smaller than the pore diameter of the pores and the pore diameter of the pores is less than 10 μm, the pore channels and the ion conducting channels are in a more preferable range, and the ionic conductivity is further improved. It is presumed that this is because it can be ensured.

FIG. 2 is an explanatory diagram showing an example of the structure of the lithium battery 10; X-ray diffraction measurement result of base material particles. FIG. 3 is a relational diagram between the amount of LiOH added and the volume fraction of each phase contained in the sintered body. SEM photograph of a sintered body obtained by sintering base material particles. A scheme of the manufacturing process of a sintered body using a pore-forming material. Cross-sectional SEM photographs of porous layer/dense layer/porous layer of Experimental Example 4. FIG. SEM photograph of the porous layer after electrochemical property evaluation in Experimental Example 4. FIG. Impedance measurement results of Experimental Examples 1 to 8. FIG. 2 is a diagram showing the relationship between the particle size of a pore-forming material and the porosity. An example of the structure of a porous body. FIG. 4 is a diagram showing the relationship between the average particle size of the pore-forming material and the average radius of void channels in the porous layer. FIG. 2 is a diagram showing the relationship between the ratio of the grain size of the pore-forming material to the grain size of the base material and the apparent conductivity of the sintered body.

(sintered body)
The sintered body of the present disclosure is a sintered body containing matrix particles that conduct lithium ions. This sintered body may be used as a solid electrolyte used in an electricity storage device using lithium ions as carriers. This sintered body has a porous layer on the outer surface side. This sintered body may have a dense layer in the central portion. Also, this sintered body may have a three-layer structure of porous layer/dense layer/porous layer. Electrodes of an electric storage device may be formed adjacent to the porous layer. This sintered body may be integrally formed with the electrode and fired. The thickness of this sintered body may be set according to the performance required for the electricity storage device used, and may be, for example, 100 μm or more, 250 μm or more, or 500 μm or more. The thickness of this sintered body may be 1000 μm or less, 750 μm or less, or 600 μm or less. Moreover, the thickness of the porous layer may be 10 μm or more, 50 μm or more, or 100 μm or more. The thickness of this porous layer may be 200 μm or less, 150 μm or less, or 100 μm or less. Also, the thickness of the dense layer may be 50 μm or more, 100 μm or more, or 2500 μm or more. The thickness of this dense layer may be 500 μm or less, 250 μm or less, or 100 μm or less.

This porous layer has a porosity of 20% by volume or more and 60% by volume or less, an average pore diameter of less than 10 μm, and has a structure in which the average pore diameter is larger than the average particle diameter of the base material particles. The porosity of the porous layer may be 25% by volume or more, or may be 30% by volume or more. Moreover, the porosity may be 50% by volume or less, or may be 45% by volume or less. This porosity may be, for example, in the range of 25% by volume or more and 50% by volume or less. The average pore diameter of the porous layer is preferably 7.0 μm or less, more preferably 5.0 μm or less. This average pore diameter is preferably 1.0 μm or more, and may be 2.0 μm or more. For example, the average pore diameter may range from 1.0 μm to 7.0 μm. The average particle size of the base material particles is preferably in the range of, for example, 0.1 μm or more and 5 μm or less. The average particle size of the base material particles is preferably 4.0 μm or less, more preferably 2.0 μm or less, and may be 1.0 μm or less. Also, the average particle diameter of the base material particles may be 0.2 μm or more, or may be 0.5 μm or more. Here, the average pore diameter is obtained by observing the cut surface of the sintered body with a scanning electron microscope (SEM), obtaining a circle inscribed in the voids contained in the image for each void, and calculating the diameter of the inscribed circle. The pore diameter of the voids is an average value obtained by accumulating and dividing by the number of voids. In addition, the average particle size of the particles is obtained by observing the powder with a scanning electron microscope (SEM), drawing 7 test lines vertically and horizontally in the observation field (5000 times or 1000 times), and the test lines cross the pores Assuming that the length of the intercept is the particle size and the particle is a sphere, the volume-weighted average particle size is calculated. P/B, which is the ratio of the average pore diameter P (μm) to the average particle diameter B (μm) of the base material particles, is 1.0 or more, preferably 1.5 or more, and may be 2.0 or more. . Alternatively, the ratio P/B is preferably 5.0 or less, and may be 4.0 or less. The porosity and the average pore size ratio P/B within the ranges described above are suitable as a buffer for accommodating lithium deposited from the electrode, and can sufficiently secure ion conduction channels.

The sintered body may contain base material particles that conduct lithium ions, but may also contain base material particles of a garnet-type oxide containing at least Li, La, and Zr. This base material particle has a basic composition of Li7.0 _+xy (La3 _-x , _Ax )( _Zr2-y , _Ty ) _O12 . However, A is at least one of Sr and Ca, and T is at least one of Nb and Ta, satisfying 0<x≦1.0 and 0<y<0.75. Alternatively, the base material particles may have a basic composition of ( _{Li7-3z+xyMz )} ( _{La3-xAx )} ( _{Zr2-yTy ) O12} or ( _{Li7-3z+xyMz )} ( It may be a garnet-type oxide represented by _{La3-xAx )} (Y2 _{-yTy ) O12} . However, in the formula, element M is one or more of Al and Ga, element A is one or more of Ca and Sr, T is one or more of Nb and Ta, and 0 ≤ z ≤ 0.2, 0 ≤ x ≤0.2, 0≤y≤2. In this basic composition formula, it is more preferable to satisfy 0.05≦z≦0.1. In this basic composition formula, it is more preferable to satisfy 0.05≦x≦0.1. Moreover, in this basic composition formula, it is more preferable to satisfy 0.1≦y≦0.8. Within such a range, the ionic conductivity can be made more suitable.

Alternatively, _the matrix particles may be particles of _a common solid electrolyte, such as _Li3N , _{Li14Zn ( GeO4} ) ₄ called LISICON, sulfide _{Li3.25Ge0.25P0.75S4} , perovskite type La _0.5 Li _0.5 TiO ₃ , (La _2/3 Li _3x □ _1/3-2x ) TiO ₃ (□: atomic vacancies), garnet-type Li ₇ La ₃ Zr ₂ O ₁₂ , NASICON-type LiTi ₂ (PO ₄ ) ₃ , Li _1.3 M _0.3 Ti _1.7 (PO ₃ ) ₄ (M=Sc, Al) and the like. In addition, Li ₇ P ₃ S ₁₁ obtained from glass having a composition of 80Li ₂ S·20P ₂ S ₅ (mol %), which is a glass-ceramic, and Li ₁₀ Ge ₂ PS, which is a sulfide-based substance with high electrical conductivity. ₂ are also mentioned. Li ₂ S--SiS ₂ , Li ₂ S--SiS ₂ --LiI, Li ₂ S--SiS ₂ --Li ₃ PO ₄ , Li ₂ S--SiS ₂ --Li ₄ SiO ₄ , and Li ₂ S-- as glass-based inorganic solid electrolytes. P ₂ S ₅ , Li ₃ PO ₄ —Li ₄ SiO ₄ , Li ₃ BO ₄ —Li ₄ SiO ₄ , and SiO ₂ , GeO ₂ , B ₂ O ₃ , and P ₂ O ₅ as glass-based materials, and Li ₂ O Examples include those used as network modifiers. Li ₂ S--GeS ₂ system, Li ₂ S--GeS ₂ --ZnS system, Li ₂ S--Ga ₂ S ₂ system, Li ₂ S--GeS ₂ --Ga ₂ S ₃ system, and Li ₂ S as thiolysicone solid electrolytes. _{-GeS2- P2S5} system _, Li2S _{- GeS2} - _SbS5 system _{, Li2S - GeS2} - _Al2S3 system, _Li2S - _SiS2 system _{, Li2SP2S5} system, Li ₂ S--Al ₂ S ₃ system, LiS--SiS ₂ --Al ₂ S ₃ system, and Li ₂ S--SiS ₂ --P ₂ S ₅ system.

In this sintered body, the grain boundaries of the base material particles may contain lithium borate. Sintering of the sintered body can be further accelerated by lithium borate. This sintered body may have an ion conductivity of 1.0×10 ⁻⁴ S/cm or more at 25° C. The ionic conductivity of the sintered body is preferably higher, and the conductivity at 25 ° C. is preferably 1.0 × 10 ^-4 (S / cm) or more, and 2.5 × 10 ^-4 S / cm or more is more preferable. This conductivity may be 1.0×10 ⁻² S/cm or less. In addition, in the garnet-type oxide containing Li, La and Zr, the electrical conductivity represents the ionic conductivity. Since this sintered body has, for example, ionic conductivity, it can be used, for example, as a sintered body or a separator for an electric storage device such as a lithium secondary battery.

This sintered body may be chargeable and dischargeable at 2.0 mA/cm ² or higher. Since this sintered body has the structure described above, it can be charged and discharged at a high rate. A higher rate is more preferable, but from the viewpoint of production difficulty, the sintered body may be chargeable and dischargeable at 5.0 mA/cm ² or less.

(Manufacturing method of sintered body)
The method for producing a sintered body of the present disclosure includes a sintering step of sintering a molded body obtained by molding base material particles to obtain a sintered body. Moreover, a base material preparation step of synthesizing unsintered base material particles may be included before the sintering step.

In the base material preparation step, powder obtained by mixing base material particles and lithium hydroxide is fired to synthesize unsintered base material particles. In this step, a raw material synthesis process for synthesizing base material particles of a garnet-type oxide, a pulverization process for making the base material particles into fine particles, a mixing process for mixing the base material particles and lithium hydroxide, and the mixed powder Firing treatment for firing may also be included. In this step, it is preferable to produce base particles of a garnet-type oxide containing at least Li, La, and Zr. Note that the base material particles may be the general solid electrolyte described above. In this treatment, the basic composition is Li7.0 _+xy (La3 _-x , _Ax )(Zr2 _-y , _Ty ) _O12 (where A is one or more of Sr and Ca, and T is Nb , Ta and satisfies 0<x≦1.0 and 0<y<0.75). Addition of the element A or element T can make the ionic conductivity more suitable. Element A is preferably Ca, and element T is preferably Nb. Alternatively, the base material has a basic composition of ( _{Li7-3z+xyMz )} ( _{La3-xAx )} ( _{Zr2-yTy ) O12} or ( _{Li7-3z+xyMz )} (La _3- xA _x )(Y _2-y T _y )O ₁₂ may be a garnet-type oxide. However, in the formula, element M is one or more of Al and Ga, element A is one or more of Ca and Sr, T is one or more of Nb and Ta, and 0 ≤ z ≤ 0.2, 0 ≤ x ≤0.2, 0≤y≤2. In this basic composition formula, it is more preferable to satisfy 0.05≦z≦0.1. In this basic composition formula, it is more preferable to satisfy 0.05≦x≦0.1. Moreover, in this basic composition formula, it is more preferable to satisfy 0.1≦y≦0.8.

In the raw material synthesizing process, for example, a raw material containing at least a Li compound, a La compound and a Zr compound may be used and fired to obtain base material particles. The raw materials are blended by appropriately adjusting the amount of each compound so as to obtain a desired composition. Each compound may be, for example, a hydroxide, carbonate, oxide, or the like. Further, the raw material may include an additive compound containing at least one of Al and Ga, an additive compound containing at least one of Ca and Sr, and an additive compound containing at least one of Nb and Ta. These additive compounds may also be hydroxides, carbonates, oxides, and the like. The baking treatment for synthesizing raw materials may be performed at a temperature of 700° C. or higher and 900° C. or lower, for example.

In the pulverization treatment, for example, wet or dry ball mill pulverization, planetary mill pulverization, or attrition mill pulverization is performed on the base material so that the average particle size is in the range of 0.1 μm or more and 5 μm or less. As the pulverization treatment, wet ball mill pulverization is preferable. In wet pulverization, water or an organic solvent can be used as a solvent. Examples of organic solvents include alcohols and acetone, and alcohols such as ethanol are preferred. The average particle size of the base material particles obtained by the pulverization process is preferably 4.0 μm or less, more preferably 2.0 μm or less, and may be 1.0 μm or less. Also, the average particle diameter of the base material particles may be 0.2 μm or more, or may be 0.5 μm or more.

In the mixing process, base material particles and lithium hydroxide are mixed. Mixing methods include, for example, wet or dry ball mill mixing and mortar mixing. This mixing treatment may be performed in the same manner and under the same conditions as the pulverization treatment, or may be performed together with the pulverization treatment, that is, the mixing treatment may be part of the pulverization treatment. As for the amount of lithium hydroxide to be blended, the ratio Lh/Lg of the lithium number Lh of the lithium hydroxide to the lithium number Lg of the garnet-type oxide is preferably in the range of 0.05 or more and 0.35 or less. When Lh/Lg is in this range, it is possible to promote neck growth between base material particles during sintering, which will be described later, and to further increase ion conductivity. The Lh/Lg ratio is more preferably 0.1 or more, more preferably 0.15 or more, and may be 0.2 or more. Sinterability is improved when the amount of lithium hydroxide compounded is increased, which is preferable. Moreover, it is more preferable that Lh/Lg of this compounding amount is less than 0.3, and more preferably 0.25 or less. When Lh/Lg is less than 0.3, promotion of sintering can be suppressed, and coarsening of base material particles can be further suppressed.

In the firing process, the mixed powder is fired at a predetermined temperature lower than the sintering temperature. The firing temperature may be, for example, a temperature range of 650° C. or higher and 800° C. or lower. This temperature is more preferably in the range of 700° C. or higher and 750° C. or lower. By carrying out the sintering in this manner, base particles can be obtained. By firing the base particles, Li ₂ O, which is a decomposed product of lithium hydroxide, and Li ₂ CO ₃ , which has absorbed carbonic acid in the air, are present on the surface of the base particles. In the base material particles having such a component on the surface, the bonding of the base material particles is promoted during sintering, and the particles can be made porous.

In the sintering step, the raw material obtained by adding the pore-forming material to the base material particles is molded so that at least one or more of the raw materials are present on the outer surface side, and the obtained molded body is sintered at a temperature of 900 ° C. or less to obtain a sintered body. obtain. The sintering step includes an addition process of adding a pore-forming material and/or a sintering aid to the base material particles, a molding process of molding the raw material powder into a raw material compact, and a sintering process of sintering the compact. may be

In the addition treatment, a pore-forming material and a sintering aid are added and mixed. In the addition treatment, a pore-forming material having an average particle size equal to or larger than that of the base material particles and having an average particle size of less than 10 μm is added in a range of 20% by volume or more and 60% by volume or less. This addition treatment may be performed in an inert atmosphere such as nitrogen gas or rare gas. Examples of the pore-forming material to be added to the base particles include organic substances such as particulate polymers. The polymer is not particularly limited as long as it is burnt off during sintering, and examples thereof include acrylic particles and organic fibers. The average particle size of the pore-forming material is preferably 7.0 μm or less, more preferably 5.0 μm or less. The average particle size is preferably 1.0 μm or more, and may be 2.0 μm or more. For example, the average particle diameter of the pore-forming material is preferably in the range of 1.0 μm or more and 7.0 μm or less. Since the pores of the sintered body are formed where the pore-forming material exists, the average particle diameter of the pore-forming material is related to the average pore diameter of the sintered body, and these values are close to each other. The amount of the pore-forming material to be added may be appropriately set according to the desired void amount, and may be, for example, 25% by volume or more, or may be 30% by volume or more. Also, the amount of the pore-forming material added may be 50% by volume or less, or may be 45% by volume or less. The amount of the pore-forming material added may be, for example, in the range of 25% by volume or more and 50% by volume or less. The resulting sintered body can have an ion conductivity of 1.0×10 ⁻⁴ S/cm or more at 25° C. Examples of the sintering aid added to the base particles include lithium borate, aluminum oxide, and gallium oxide. Examples of lithium borate include Li ₃ BO ₃ , Li ₂ B ₄ O ₇ , and LiBO ₂ , among which Li ₃ BO ₃ (hereinafter also referred to as LBO) is more preferable. LBO is preferred because it is less reactive with the matrix. Regarding the amount of lithium borate added, the volume fraction of lithium borate to the total volume of the base material particles and lithium borate is preferably in the range of 5% by volume or more and 15% by volume or less, and 8% by volume or more and 12% by volume. The following ranges are more preferred. Moreover, Al and Ga of the sintering aid may be contained in the Li site of the Li-containing garnet-type oxide. Aluminum oxide is preferably added in a range of 0.08 mol or more and 0.12 mol or less per 1 mol of the garnet-type oxide. When the amount of aluminum oxide added is 0.08 mol or more, the effect of promoting sintering can be exhibited, and when the amount is 0.12 mol or less, the added Al can replace the Li site.

In the molding process, a mold may be used to mold the raw material powder containing the base material particles. In the molding process, for example, a raw material molded body having a two-layer structure of porous layer/dense layer or a raw material molded body having a three-layer structure of porous layer/dense layer/porous layer can be formed. The thickness of the porous layer and the dense layer can be within the range described for the sintered body. At this time, the raw material powder for forming the dense layer is composed of base material particles, and the raw material powder for forming the porous layer formed outside the dense layer contains the pore-forming material after the above addition treatment. use. In this forming process, the raw materials for the porous layer and the dense layer may be formed simultaneously, or the raw materials for the porous layer and the dense layer may be formed separately. That is, in this treatment, the raw material powder for the porous layer and the dense layer may be molded, or the raw material powder for the porous layer containing the pore-forming material may be molded on the surface of the sintered dense layer. Alternatively, the raw material powder for the dense layer may be formed on the surface of the porous layer made into a sintered body. The amount of pressure applied during molding may be appropriately set according to the shape and size of the molded product, and may be, for example, in the range of 1 MPa to 100 MPa, or in the range of 5 MPa to 20 MPa. The shape of the molded body is not particularly limited, and can be any shape.

In the sintering process, the compact is sintered at a temperature of 800°C or higher and 900°C or lower. By sintering the molded body in this temperature range, it is possible to obtain a sintered body having voids and further suppressing a decrease in ionic conductivity. In addition, in this temperature range, since the temperature is relatively low, volatilization and reduction of Li in the base material is further suppressed. The sintering temperature may be 820° C. or higher or 835° C. or higher, or may be 880° C. or lower or 850° C. or lower. The sintering time is not particularly limited as long as a sintered body having a desired strength can be obtained. For example, it may be 10 hours or longer, or 20 hours or longer. Moreover, it may be 50 hours or less, or may be 24 hours or less. A shorter sintering time is preferable from the viewpoint of energy saving and porosity, and a longer sintering time is preferable from the viewpoint of improving sintering strength and ion conductivity. This sintering treatment is preferably performed in the air because the sintered body is an oxide. In this way, it is possible to produce a sintered body that contains voids and base material particles having a specific structure, has higher ionic conductivity, and can be charged and discharged at a high rate.

(storage device)
An electricity storage device of the present disclosure includes a positive electrode, a negative electrode, and the above-described sintered body interposed between the positive electrode and the negative electrode to conduct lithium ions and having a porous layer at least on the negative electrode side. This electricity storage device may be any one of a lithium secondary battery, a lithium ion secondary battery, an electric double layer capacitor, a hybrid capacitor, an air battery, and the like. Moreover, it is preferable that this electric storage device is an all-solid-state secondary battery.

The positive electrode may contain a positive electrode active material. For the positive electrode, for example, a positive electrode active material, a conductive material, and a binder are mixed, and an appropriate solvent is added to make a paste-like positive electrode material. It may be formed by compression to increase its density. A sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used as the positive electrode active material. Specifically, transition metal sulfides such as TiS ₂ , TiS ₃ , MoS ₃ and FeS ₂ , and basic compositional formulas of Li _(1-x) MnO ₂ (0<x<1, etc., the same applies hereinafter) and Li _{(1 -x)} Lithium-manganese composite oxides such as Mn ₂ O ₄ , Lithium-cobalt composite oxides such as Li _(1-x) CoO ₂ with a basic composition formula, Li _(1-x) NiO ₂ with a basic composition formula, etc. a lithium-nickel composite oxide having a basic composition formula of Li _(1-x) Ni _a Co _b Mn _c O ₂ (a+b+c=1) or the like, a basic composition formula of LiV ₂ O ₃ Lithium vanadium composite oxides such as V ₂ O 5 , transition metal oxides having a basic composition formula of V 2 O ₅ , and the like can be used. Among these, transition metal composite oxides of lithium such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ are preferred. It should be noted that the “basic composition formula” means that other elements may be included. Alternatively, the positive electrode active material may be a carbonaceous material used in capacitors, lithium ion capacitors, and the like. Carbonaceous materials include, for example, activated carbons, cokes, vitreous carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, and polyacenes. Among these, activated carbons exhibiting a high specific surface area are preferred. The activated carbon as the carbonaceous material preferably has a specific surface area of 1000 m ² /g or more, more preferably 1500 m ² /g or more. When the specific surface area is 1000 m ² /g or more, the discharge capacity can be further increased. The specific surface area of this activated carbon is preferably 3000 m ² /g or less, more preferably 2000 m ² /g or less, for ease of production.

The conductive material contained in the positive electrode is not particularly limited as long as it is an electronically conductive material that does not adversely affect the battery performance of the positive electrode. , carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, metals (copper, nickel, aluminum, silver, gold, etc.), or a mixture of two or more thereof can be used. Among these, carbon black and acetylene black are preferable as the conductive material from the viewpoint of electronic conductivity and coatability. The binder plays a role of binding the active material particles and the conductive material particles, and is, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing resin such as fluororubber, polypropylene, Thermoplastic resins such as polyethylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM rubber, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. Cellulose-based or styrene-butadiene rubber (SBR) aqueous dispersions, which are water-based binders, can also be used. Examples of solvents for dispersing the positive electrode active material, conductive material, and binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, and N,N-dimethylaminopropylamine. , ethylene oxide, and tetrahydrofuran can be used. Alternatively, a dispersant, a thickener, or the like may be added to water, and the active material may be slurried with a latex such as SBR. As the thickening agent, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used singly or as a mixture of two or more. Application methods include, for example, roller coating such as applicator roll, screen coating, doctor blade method, spin coating, and bar coater, and any thickness and shape can be obtained using any of these methods. Current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, and conductive glass. The surface of which is treated with carbon, nickel, titanium, silver, or the like can be used. For these, it is also possible to oxidize the surface. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded, lath, porous, foam, and fiber group formed bodies. The current collector used has a thickness of, for example, 1 to 500 μm.

The negative electrode may contain a negative electrode active material. The negative electrode may be formed, for example, by adhering a negative electrode active material and a current collector, or may be formed by mixing a negative electrode active material, a conductive material, and a binder, and adding an appropriate solvent to prepare a pasty negative electrode. The material may be coated on the surface of the current collector, dried, and compressed to increase the electrode density, if necessary. Examples of negative electrode active materials include inorganic compounds such as lithium, lithium alloys and tin compounds, carbonaceous materials capable of intercalating and deintercalating lithium ions, composite oxides containing multiple elements, and conductive polymers. Examples of carbonaceous materials include cokes, vitreous carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Among them, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, and suppress self-discharge when lithium salt is used as a supporting salt. Moreover, the irreversible capacity during charging can be reduced, which is preferable. Examples of composite oxides include lithium-titanium composite oxides and lithium-vanadium composite oxides. Among them, carbonaceous materials are preferable as the negative electrode active material from the viewpoint of safety. As the conductive material, binder, solvent, and the like used for the negative electrode, those exemplified for the positive electrode can be used. The current collector of the negative electrode includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc. For that purpose, for example, copper or the like whose surface is treated with carbon, nickel, titanium, silver, or the like can also be used. For these, it is also possible to oxidize the surface. A current collector having the same shape as that of the positive electrode can be used.

FIG. 1 is an explanatory diagram showing an example of the structure of the electricity storage device 10. As shown in FIG. This electricity storage device 10 has a positive electrode 12 , a negative electrode 15 and a solid electrolyte layer 20 . The positive electrode 12 has a positive electrode active material layer 13 and a current collector 14 . The negative electrode 15 has a negative electrode active material layer 16 and a current collector 17 . Solid electrolyte layer 20 is the sintered body described above and includes porous layer 24 and dense layer 25 . This sintered body includes base material particles 21 made of a garnet-type oxide containing at least Li, La and Zr, grain boundaries 22 containing components such as a sintering aid, and voids 23 are formed.

With the sintered body, the electricity storage device, and the method for manufacturing the sintered body described in detail above, charging and discharging at a higher rate can be realized. The reason why such an effect is obtained is presumed as follows. For example, when the porosity is within a desired range, it can be used as a buffer for containing lithium deposited from the electrode, and can prevent separation between the electrode and the sintered body. In addition, when the particle diameter of the base material particles is smaller than the pore diameter of the pores and the pore diameter of the pores is less than 10 μm, the pore channels and the ion conducting channels are in a more preferable range, and the ionic conductivity is further improved. It is presumed that this is because it can be ensured.

It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure.

An example in which the sintered body of the present disclosure was specifically produced will be described below as an experimental example. Experimental Examples 1, 2, 7, and 8 correspond to comparative examples, and Experimental Examples 4 to 6 correspond to examples of the present disclosure.

[Preparation of fine LLZ-CaNb powder]
LiOH (manufactured by ALDRICH), La(OH) ₃ , Ca(OH) ₂ , ZrO ₂ , Nb ₂ O ₅ (all manufactured by Kojundo Chemical) were used as powdery reagents, and the base material composition was Li _6.8 (La _2.95 Ca _0.05 )(Zr _1.75 Nb _0.25 )O ₁₂ , these were weighed, pulverized in a wet ball mill, mixed and dried. A wet ball mill was performed using an 80 mL zirconia pot and 1 mmf zirconia balls, using ethanol as a solvent, and rotating at 700 rpm for 1 hour. Drying was performed at 80°C. Thereafter, calcination was performed in the atmosphere to obtain LLZ-CaNb powder, which is a garnet-type oxide as base material particles. Temporary firing was performed at 700° C. for 48 hours using an alumina crucible lined with Au foil. LiOH is additionally added to this LLZ-CaNb powder, and after going through the same mixing and pulverizing process, the second calcination is performed at 700 ° C. for 10 hours, and the resulting fine powder is unsintered base material particles. (LLZ-CaNb-LiOH powder). The amount of LiOH added was such that the ratio Lh/Lg of the lithium number Lh of LiOH to the lithium number Lg of LLZ—CaNb was 0.1.

[Evaluation of base material particles]
When the obtained base material particles were observed with a scanning electron microscope (SEM), it was confirmed that submicron-sized fine powder particles could be obtained without depending on Lh/Lg. In addition, X-ray diffraction measurement was performed on base material particles with Lh/Lg of 0, 0.1, 0.2, 0.3, and 0.4. The X-ray diffraction measurement was performed using a Rigaku XRD apparatus smart-Lab with a Cu tube in the range of 2θ = 10° to 80° at a speed of 5°/min. FIG. 2 shows the results of X-ray diffraction measurement of base material particles. As shown in FIG. 2, in addition to the peaks from the garnet structure (cubic crystal) of the main phase, it was confirmed that as the amount of LiOH added increased, the peaks of Li ₂ CO ₃ appeared clearly. It was speculated that LiOH was converted to Li ₂ O when the base material particles were sintered, and that Li 2 O was produced by absorbing carbon dioxide in the atmosphere. In addition, when the LiOH addition amount is "0", a peak attributed to La ₂ Zr ₂ O ₇ is observed, and the LiOH addition amount is preferably 0.05 or more in Lh/Lg, and 0.1 or more. judged to be more preferable.

[Study of LiOH addition amount in sintered body: Reference Examples 1 to 6]
As described above, it was presumed that LiOH added to the base material would exist as lithium carbonate (Li ₂ CO ₃ ) in the atmosphere through the process of preparing the base material particles. It was presumed that this lithium carbonate was present in the form of fine powder adhering to the surface of the base material particles. Since this lithium carbonate releases CO ₂ at the sintering temperature of the molded body and changes to Li ₂ O, the presence of this Li ₂ O prevents the growth of necks between the LLZ-CaNb base particles. expected to be promoted. Here, sintered bodies were produced using base material particles with varying amounts of LiOH added, and their characteristics were evaluated. A raw material powder containing base material particles and Li ₃ BO ₃ (LBO) and γ-Al ₂ O ₃ as sintering aids was formed into pellets to obtain a sintered body. As for the blending ratio of the raw materials, the amount of γ-Al ₂ O ₃ added to 1 mol of the base material particles was 0.1 mol, and the volume fraction of LBO with respect to the total volume of the base material particles and LBO was 10% by volume. Sintering of the pellets was carried out at 835° C. for 48 hours. As the amount of LiOH added to the base material particles, the sintered bodies of Reference Examples 1 to 6 were obtained with Lh / Lg of 0, 0.1, 0.15, 0.2, 0.3, and 0.4. bottom. FIG. 3 is a diagram showing the relationship between the amount of LiOH added and the volume fraction of each phase contained in the sintered body. The volume fraction of each phase was obtained from the apparent density of the sintered body and the preparation composition when the sintered body was produced. As shown in FIG. 3, the void volume fraction decreased in inverse proportion to the increase in the amount of LiOH added, that is, the increase in Li ₂ CO ₃ . As shown in FIG. 3, it was confirmed that the amount of voids (the amount of defects) in the sintered body was reduced by adding LiOH.

The cross sections of the sintered bodies of Reference Examples 1 to 6 were observed by SEM. First, after the fracture surface of the sintered pellet was surfaced with abrasive paper, it was fixed to the sample stage with conductive paste, and a thin film/cross-section sample preparation device (cross section polisher, JEOL SM-09010) was used. A smooth cross section was obtained. SU3500 manufactured by Hitachi (accelerating voltage: 5 to 15 kV) was used for SEM observation of this processed product. FIG. 4 is a SEM photograph of a sintered body obtained by sintering the base material particles, FIG. 4A is Reference Example 2, FIG. 4B is Reference Example 4, FIG. 4C is Reference Example 5, and FIG. 4E is an enlarged view of the grain boundary portion of FIG. 4D. As shown in FIG. 4, it was confirmed that when the material was sintered in the air at a temperature of 835° C. for 48 hours, sintering progressed when the amount of LiOH added was large, resulting in coarse grains and grain growth into large grains. It is preferable that sintering proceed, but excessive grain growth causes a reduction in voids, which is not preferable.

Next, from the viewpoint of lithium ion conductivity, the optimum range of the amount of LiOH to be added was examined. Ionic conductivity was measured as follows. The sintered body obtained by sintering the base material particles was subjected to impedance measurement at 100 mV in the range of 40 Hz to 110 MHz using an AC impedance measuring instrument (Agilent 4294A) in a constant temperature bath at 25°C. Then, the resistance value was obtained from the arc of the Nyquist plot, and the lithium ion conductivity was calculated from this resistance value. Table 1 summarizes the amount of LiOH added, the volume fraction of each phase, and the lithium ion conductivity (electrical conductivity) of the sintered bodies in Reference Examples 1 to 6. As shown in Table 1, the sintered bodies of Reference Example 1, in which the amount of LiOH added is 0, and Reference Example 6, in which the amount of LiOH is 0.4, show low values of ionic conductivity, between 0.05 and 0.35. It was found that a high conductivity exceeding 1×10 ⁻⁴ S/cm can be stably obtained in the range of . When the amount of LiOH added was 0, neck growth was insufficient and sintering did not proceed, so it was presumed that low conductivity was exhibited. Moreover, when the LiOH addition amount is 0.4, as shown in FIG. It was speculated that the degree of From the viewpoint of preventing coarsening of the base material particles, the amount of LiOH added is preferably in the range of Lh/Lg of 0.1 or more and less than 0.3. , X-ray diffraction, structure observation, and ionic conductivity, it was determined that the amount of LiOH to be added is suitable when Lh/Lg is in the range of 0.05 or more and 0.35 or less.

[Consideration of sintering temperature]
A sintered body was produced by changing the sintering temperature for the base material particles having a LiOH addition amount Lh/Lg of 0.1. The sintering conditions were 835° C. for 48 hours and 915° C. for 12 hours. When the cross section of the sintered body was observed with an SEM, it was found that sintering at 915.degree. Although sintering is accelerated by raising the temperature, it was presumed to be unsuitable for making porous because the crystal grains also become significantly coarser. On the other hand, when the sintering temperature is 835° C., grain growth is suppressed even if the sintering time is held for a long time of 48 hours, and the grain size can be maintained at about 1 to 2 μm even after sintering, which is good. The retention of the fine grain structure of the base material was satisfied. In addition, sintering at a temperature of less than 800 ° C. causes insufficient neck growth, and the added Al ₂ O ₃ may remain unreacted. It was surmised that the following would be suitable.

[Production of LLZ-CaNb Sintered Porous Body]
An attempt was made to produce a sintered body using LLZ-CaNb powder for which fine particle conditions after sintering were examined. Base material particles with a particle size of 0.5 to 1.0 μm and acrylic pore former powder with a particle size of 0.8 μm to 20 μm were used. As the base material particles, a fine powder of LLZ-CaNb powder with a LiOH addition amount Lh/Lg of 0.1 was used. The amount of γ-Al ₂ O ₃ added to 1 mol of the base material (LLZ-CaNb) is 0.1 mol, and the volume fraction of Li ₃ BO ₃ with respect to the total volume of the base material and Li ₃ BO ₃ is 10% by volume. and Porous bodies were produced by the procedure shown in FIG. FIG. 5 is a scheme of a manufacturing process of a sintered body using a pore-forming material. The fabrication process includes a mixing process, a molding process and a sintering process. In the mixing treatment, base material particles obtained by adding LiOH to LLZ-CaNb fine powder and firing, γ-Al ₂ O ₃ and Li ₃ BO ₃ as sintering aids, and an acrylic pore former were mixed in an Ar atmosphere. Mortar mixed in the glove box. In the molding process, the raw material containing the pore-forming material was filled in the range of 80 µm from the outer surface of the outer shape having a diameter of 11.0 mm and a thickness of 660 µm, and base particles containing a sintering aid were filled in the other areas. Uniaxial molding was performed. As a result, a sintered body having a three-layer structure of porous layer/dense layer/porous layer, in which porous layers were provided on both end surfaces of a layer containing no pore-forming material, was produced. The thickness of the porous layer was 80 μm, and the thickness of the dense layer was 500 μm. The press pressure was 10 MPa. In the sintering treatment, the temperature was raised at a rate of temperature rise of 1° C./min and held at 820° C. for 48 hours to obtain a sintered body. A sintered body using the pore-forming material was obtained as having a three-layer structure of porous layer/dense layer/porous layer. This sintered body was subjected to surface polishing, SEM observation, X-ray diffraction measurement, impedance measurement (25, 60° C.), and density measurement.

(Experimental Examples 1 to 8)
A laminate of a layer containing LLZ and Al ₂ O ₃ (thickness: 500 μm) and a layer of LBO was formed without using a pore-forming material. It was formed. A sintered body of Experimental Example 2 was obtained by forming an integral body of LLZ, Al ₂ O ₃ and LBO without using a pore-forming material, setting the pressing pressure to 10 MPa, and setting the thickness to 500 μm. A sintered body of Experimental Example 3 was obtained by using 45% by volume of acrylic powder (manufactured by Soken Kagaku Co., Ltd., average particle size 0.8 μm) as a pore-forming material and having a thickness of 600 μm. A sintered body of Experimental Example 4 was obtained by using 45% by volume of acrylic powder (average particle size: 1.8 μm) as a pore-forming material. A sintered body of Experimental Example 5 was obtained by using 25% by volume of acrylic powder (average particle size: 5.0 μm) as a pore-forming material. A sintered body of Experimental Example 6 was obtained by using 45% by volume of acrylic powder (average particle size: 5.0 μm) as a pore-forming material. A sintered body of Experimental Example 7 was obtained by using 45% by volume of acrylic powder (average particle size: 10 μm) as a pore-forming material. A sintered body of Experimental Example 8 was obtained by using 45% by volume of acrylic powder (average particle diameter: 20 μm) as a pore-forming material.

(Density measurement: porosity)
The mass of the sintered body was measured using an electronic balance, and the volume was measured using a micrometer. Density values were obtained by dividing the measured mass by the volume. The porosity of the porous layer in the three-layer structure of porous layer/dense layer/porous layer was estimated using the density of the dense sintered body without using a pore-forming material.

(Evaluation of electrochemical properties)
Li was thermally deposited on both sides of the sintered body in a glove box and subjected to electrochemical property evaluation. Metal Li had a diameter of 6 mm and a thickness of several tens of μm. It was placed in a constant temperature bath at 60° C., and current was applied to a capacity of 1 mAh/cm ² at current densities of 0.1, 1.0 and 2.0 mA/cm ² using a potentiogalvanostat (VMP3 manufactured by Biologic). This energization was performed in one set of forward and reverse directions. Then, the impedance was measured when the current direction was switched.

(SEM observation)
After polishing the fracture surface of the sintered body with abrasive paper, it is fixed to the sample table with conductive paste, and a thin film and cross-section sample preparation device (cross section polisher, JEOL SM-09010) is used to smooth the cross section. got SU3500 manufactured by Hitachi was used for SEM observation of this processed product. The acceleration voltage was 5-15 kV. Also, the average pore diameter of the voids was obtained from the obtained SEM image. A circle inscribed in the voids was obtained, and this was used as the diameter of the voids. In addition, the average particle size of the particles is obtained by observing the powder with a scanning electron microscope (SEM), drawing 7 test lines vertically and horizontally in the observation field (5000 times or 10000 times), and the test lines cross the pores The length of the intercept was defined as the particle size, and the particle size was calculated as the volume-weighted average particle size, assuming that the particles were spherical.

(Results and discussion)
Table 2 shows the particle size (μm) of the pore-forming materials of Experimental Examples 1 to 8, the amount added (% by volume), the ratio P/B of the average particle size P of the pore-forming material to the average particle size B of the base material particles, and the The average pore diameter (μm) of the body, the porosity (% by volume) of the porous layer, and the possibility of outputting at 2 mA/cm ² were summarized. In addition, in the ratio P/B, the average particle size of the LLZ particles as the base material was evaluated as 1.0 μm from the SEM image after sintering. Also, Experimental Examples 1 to 4 and 6 were evaluated from 5000x SEM images, and Experimental Example 7 was evaluated with two fields of view of 5000x (upper) and 1000x (lower) because of the large void size. In Experimental Example 8, cracks occurred in the sample after charging and discharging, so the average pore diameter could not be evaluated, but the presence of coarse pores of 10 μm or more was confirmed from the SEM image. Moreover, Table 2 shows the designed value as the porosity of Experimental Example 8. Regarding the average pore size of Experimental Example 5, since the same pore-forming material as in Experimental Example 6 is used, the value is expected to be similar to that of Experimental Example 6, so the evaluation thereof is omitted. As for the porosity, since Experimental Examples 1 and 2 do not have a porous layer, the porosity of the whole was used. In addition, evaluation of whether or not output is possible was performed as follows. For example, growth of precipitated Li in the thickness direction of the sintered body leads to short-circuiting of the cell. In addition, since the growth of precipitated Li in the thickness direction of the sintered body causes a decrease in the initial resistance, it is possible to grasp the signs of a short circuit from the change in the initial resistance. Therefore, evaluation of whether or not the output is possible is performed by repeating charging and discharging at a current density of 2 mA / cm ² , and if the change from the initial resistance is within 20% and the state is almost the same as the initial resistance, "A ", and when the initial resistance is greatly reduced in a range exceeding 20%, it is judged as "B".

6 is a cross-sectional SEM photograph of the porous layer/dense layer/porous layer of Experimental Example 4. FIG. FIG. 7 is an SEM photograph of the porous layer after electrochemical property evaluation in Experimental Example 4. FIG. As shown in FIG. 6, it was confirmed that porous layers with a thickness of 80 μm could be formed on both sides of the sintered body without peeling. Further, as a result of observing the state inside the structure of the porous layer, as shown in FIG. 7, a substance filling the voids was confirmed. Elemental analysis of this substance revealed that B contained in the sintering aid was not detected, but C was detected. Therefore, this substance was presumed to be lithium carbonate. It was speculated that this lithium carbonate was produced by lithium metal deposited by charging and discharging absorbing carbon dioxide in the air. Thus, it was confirmed that the voids of the porous layer functioned as a buffer for accommodating lithium metal deposited by charging and discharging. Moreover, as shown in FIG. 7, it was confirmed that the skeleton structure of the base material particles, which are fine particles, was maintained even after charging and discharging.

FIG. 8 shows impedance measurement results of Experimental Examples 1 to 8, and FIGS. 8A to 8H are Experimental Examples 1 to 8, respectively. As shown in FIG. 8, in Experimental Examples 1 to 3, 7, and 8, charging/discharging was not possible at 1 mA/cm ² or more, or the Li conduction resistance greatly fluctuated by more than 20% from the initial stage. On the other hand, in Experimental Examples 4 to 6, it was found that the batteries could be stably charged and discharged even at a high output of 2 mA/cm ² or more. FIG. 9 is a diagram showing the relationship between the particle size of the pore-forming material and the porosity. When the results summarized in Table 2 and the results in FIG. 8 are combined, the region indicated by the dotted line in FIG. 9, that is, the porosity range of 20% by volume or more and 60% by volume or less and the average pore diameter of less than 10 μm. Then, a high output of 2 mA/cm ² or more could be expected. In other words, it was confirmed that charging/discharging at a rate of 30% became possible by providing a porous layer in the sintered body of the sintered body.

(Validity verification by calculation)
The consideration of the optimum range for the void size in FIG. 9 was examined by simulation calculation. FIG. 10 shows an example of the structure of a porous body with a porosity of 50% by volume used in the calculation. This is an example of a porous body. LLZ as the base material, the average particle size of the pore-forming material, and the compounding ratio of the base material/pore-forming material were variously set, and the 3D structure image of the porous polycrystal as exemplified in FIG. 10 was obtained by the multiphase field method. (calculation method capable of simulating structural change in the direction of free energy decrease in the sintering process). Next, this void channel radius was evaluated as the maximum diameter of the inscribed sphere, and its average value was obtained. This relationship between pore former particle size and void channel radius is illustrated in FIG. Next, based on this structural image, we set the conductivity and permittivity of each space and calculated the potential distribution inside the object induced by the AC electric field to evaluate the impedance. Assuming that the electric field inside the object induced by the alternating electric field (frequency ω) is E, this electric field must satisfy the formula (1) at various places inside the object. Here, σ _R (r) and ε(r) represent the electrical conductivity and dielectric constant at the position r, respectively, and are set in conjunction with the material structure image. The real and imaginary components of the complex electrostatic potential were evaluated by numerical calculation from this formula (1). The current obtained from the local potential and the local conductivity is integrated in a section parallel to the electrodes, and the real component Z _R and the imaginary component Z _I of the impedance can be evaluated from the potential modulation width given as the boundary condition. By performing this evaluation under each AC frequency condition, a Nyquist diagram of the impedance spectrum was obtained. The reciprocal of the total resistance of the evaluated real component Z _R was taken as the apparent lithium ion conductivity of this porous structure.

FIG. 11 is a diagram showing the relationship between the average particle size of the pore-forming material and the average radius of void channels in the porous layer. FIG. 12 is a diagram showing the relationship between the ratio of the grain size of the pore-forming material to the grain size of the base material and the apparent conductivity of the sintered body. A symmetrical cell composed of metal Li/LLZ/metal Li using a garnet-type lithium ion conductive oxide (LLZ) without a porous layer was found to be 0.7 mAh/ at a current density of 0.4 mA/cm ^{2 .} It was confirmed that a current could flow at a stable potential up to a capacity of cm ² . Further, it was confirmed that Li depletion occurs at the metal Li/LLZ interface when the current is pulled out beyond that level. This capacity of 0.7 mAh/cm ² is estimated to be 3.4 μm in terms of Li thickness, and the upper limit of the radius of the voids where Li metal precipitates is set at 3.4 μm. When various porous structure models were created and the pore channel radii thereof were evaluated, it was derived that the average particle diameter of the pore-forming material should be designed in the range of less than 10 μm. This was consistent with the range of less than 10 μm, which is the upper limit of the particle size of the pore-forming material in Table 2. On the other hand, when the relationship between the lithium ion conductivity of the porous structure and the structure was evaluated, as shown in FIG. It was suggested that when the temperature is lower than that, the formation of ionic conduction paths in the base material particles, which is the electrolyte, is inhibited, resulting in a decrease in ionic conductivity performance. For this reason, it was inferred that it is important to design the average particle diameter of the pore-forming material in a range equal to or greater than the average particle diameter of the matrix particles that are the electrolyte. This was inconsistent with the lower limit of 1.0 μm for the average particle size of the pore-forming material in Table 2. That is, when the average particle size of the base material particles is 1 μm, it is assumed that the average particle size of the pore-forming material is required to be 1 μm or more.

The sintered body, the electric storage device, and the method for manufacturing the sintered body of the present disclosure are not limited to the above-described embodiments, and can be implemented in various modes as long as they fall within the technical scope of the present disclosure. Needless to say.

INDUSTRIAL APPLICABILITY The present disclosure is applicable to technical fields using materials that conduct Li ions, such as the technical field of the battery industry.

10 electricity storage device, 12 positive electrode, 13 positive electrode active material layer, 14 current collector, 15 negative electrode, 16 negative electrode active material layer, 17 current collector, 20 solid electrolyte layer, 21 base material particles, 22 grain boundaries, 23 voids.

Claims (19)

A sintered body containing matrix particles that conduct lithium ions,
A porous layer having a porosity of 20% by volume or more and 60% by volume or less and an average pore size of less than 10 μm and having an average pore size larger than the average particle size of the base material particles on the outer surface side,
A sintered body containing lithium borate at grain boundaries of the base material particles. A sintered body containing matrix particles that conduct lithium ions,
A porous layer having a porosity of 20% by volume or more and 60% by volume or less and an average pore size of less than 10 μm and having an average pore size larger than the average particle size of the base material particles on the outer surface side,
A sintered body having a dense layer at least in the central portion of the sintered body. 3. The sintered body according to claim 2, wherein the grain boundaries of the base material particles contain lithium borate. The sintered body according to any one of claims 1 to 3, comprising the base material particles of a garnet-type oxide containing at least Li, La and Zr. The base material particles have a basic composition of Li _7.0+xy (La _3-x , A _x ) (Zr _2-y , T _y ) O ₁₂ (where A is one or more of Sr and Ca, T is one or more of Nb and Ta, and satisfies 0<x≦1.0 and 0<y<0.75). The sintered body according to any one of claims 1 to 5, wherein the average pore diameter is in the range of 1.0 µm or more and 7.0 µm or less. The sintered body according to any one of claims 1 to 6, wherein the porosity is in the range of 25% by volume or more and 50% by volume or less. The sintered body according to any one of claims 1 to 7, which can be charged and discharged at 2.0 mA/cm ² or more. a positive electrode;
a negative electrode;
The sintered body according to any one of claims 1 to 8, which is interposed between the positive electrode and the negative electrode to conduct lithium ions and has the porous layer at least on the negative electrode side;
A storage device with A method for producing a sintered body containing matrix particles that conduct lithium ions,
A dense porous layer containing the base material particles, in which a pore-forming material having an average particle size equal to or larger than the average particle size of the base material particles and having an average particle size of less than 10 μm is added in a range of 20% by volume or more and 60% by volume or less. A sintering step of obtaining a sintered body by sintering the raw material compact present on the outer surface side of the layer at a temperature of 900 ° C. or less;
A method for producing a sintered body comprising: In the sintering step, the basic composition is Li _7.0+xy (La _3-x , A _x ) (Zr _2-y , T _y ) O ₁₂ (where A is one or more of Sr and Ca, T is one or more of Nb and Ta, and satisfies 0 < x ≤ 1.0, 0 < y < 0.75). Method. 12. The method for producing a sintered body according to claim 10, wherein the sintering step uses the pore-forming material having an average particle diameter in the range of 1.0 [mu]m to 7.0 [mu]m. The method for producing a sintered body according to any one of claims 10 to 12, wherein in the sintering step, the base material particles having an average particle size in the range of 0.1 µm or more and 5.0 µm or less are used. The method for producing a sintered body according to any one of claims 10 to 13, wherein in the sintering step, the pore-forming material is added in a range of 25% by volume or more and 50% by volume or less. The method for producing a sintered body according to any one of claims 10 to 14, wherein in the sintering step, lithium borate is further added to obtain the raw material molded body. The method for producing a sintered body according to any one of claims 10 to 15, wherein in the sintering step, the raw material compact is sintered at a temperature of 800°C or higher and 900°C or lower. The sintered body contains a garnet-type oxide,
The sintering step according to any one of claims 10 to 16, wherein a sintered body containing aluminum oxide in the range of 0.08 mol or more and 0.12 mol or less per 1 mol of the garnet-type oxide is obtained. A method for producing a sintered body. A method for producing a sintered body according to any one of claims 10 to 17,
Before the sintering step, a garnet-type oxide containing at least Li, La, and Zr, and lithium hydroxide are mixed with each other, and the ratio Lh/Lg of the lithium number Lh of the lithium hydroxide to the lithium number Lg of the garnet-type oxide a base material preparation step of obtaining unsintered base material particles by sintering a mixed powder obtained by mixing in a range of 0.05 or more and 0.35 or less. 19. The method for producing a sintered body according to claim 18, wherein said mixed powder is fired at a temperature of 650[deg.] C. or higher and 800[deg.] C. or lower in said base material preparing step.

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