JP6272229B2 - Solid electrolyte ceramic materials - Google Patents

Description

  The present invention relates to a solid electrolyte ceramic material having lithium ion conductivity.

  In recent years, with the development of portable devices such as personal computers and mobile phones, as well as low-emission vehicles (eco-cars) such as hybrid vehicles and electric vehicles, the demand for secondary batteries as their power source has been rapidly expanding. . In secondary batteries used for such applications, liquid electrolytes (electrolytic solutions) are widely used. From the viewpoint of improving safety, all battery elements are solidified using solid electrolytes instead of liquid electrolytes. Development of all-solid-state secondary batteries composed of is currently underway. Such an all-solid-state secondary battery is advantageous in that since the electrolyte is composed of a ceramic sintered body, there is no risk of ignition or leakage, and problems such as deterioration of battery performance due to corrosion are less likely to occur. In particular, an all-solid lithium secondary battery using lithium metal as an electrode is expected as a secondary battery that easily achieves a high energy density.

  In order to improve the battery characteristics of the secondary battery, it is important to increase the potential difference between the positive and negative electrode materials and to improve the capacity density of each material used for the positive and negative electrodes. Particularly for negative electrode materials, it is known that the use of lithium metal or lithium alloys greatly contributes to the improvement of characteristics. However, when lithium metal is used for the negative electrode, dendrites (dendritic crystals) are deposited on the negative electrode along with charge and discharge, and in the worst case, the separator is broken through, causing a short circuit between the positive and negative electrodes. As a result, current concentration occurs in the short-circuit portion and heat generation triggers thermal runaway of the battery, so there is a concern about safety issues. In this regard, an all-solid battery in which the electrolyte portion is formed of a solid electrolyte is expected to have higher safety because the deposit cannot penetrate the solid electrolyte.

  On the other hand, there are high expectations for high-capacity batteries such as those for electric vehicles, and one of such candidates is a lithium air battery. The lithium-air battery is a battery that can be expected to have a theoretical maximum capacity by using atmospheric oxygen as a positive electrode active material and lithium metal as a negative electrode active material. However, such an air battery also has the problem of the dendrite, and as described above, the solution is strongly desired.

As a solid electrolyte, a garnet-type ceramic material has attracted attention. For example, in Non-Patent Document 1 (Ramaswamy Murugan et al., Angew. Chem. Int. Ed. 2007, 46, 1-5), Li ₇ La ₃ Zr ₂ O ₁₂ (hereinafter referred to as LLZ) is lithium-resistant. It has been reported that it can be used as a solid electrolyte of an all-solid lithium secondary battery.

Patent Document 1 (Japanese Patent Publication No. 2007-528108) discloses a garnet-type solid ion conductor having a composition of L _{5 + x} A _y G _z M ₂ O ₁₂ . Patent Document 2 (Japanese Patent Laid-Open No. 2011-051800) discloses that the addition of Al in addition to Li, La and Zr, which are basic elements of LLZ, can improve the denseness and lithium ion conductivity. . Patent Document 3 (Japanese Patent Laid-Open No. 2011-073962) discloses that lithium ion conductivity can be further improved by adding Nb and / or Ta in addition to Li, La, and Zr, which are basic elements of LLZ. ing. Patent Document 4 (Japanese Patent Laid-Open No. 2011-073963) includes Li, La, Zr, and Al, and the density can be further improved by setting the molar ratio of Li to La to 2.0 to 2.5. Is disclosed. Patent Document 5 (Japanese Patent Laid-Open No. 2012-031025) describes Li _x Ln ₃ (M ¹ _y M ² _z ) O _t (where Ln is La, Pr, Nd, Sm, Lu, Y, K, mg, Ba, Ca, 1 or more elements selected from the group consisting of Sr, ^{M 1} is, Si, Sc, Ti, V , Ga, Ge, Y, Zr, Nb, in, Sb, Te, Hf, One or more elements selected from the group consisting of Ta, W, Bi, M ² is an element different from M ^1, and is Sc, Ti, V, Y, Nb, Hf, Ta, Si, Ga, and A garnet-type lithium ion conductive oxide containing Al in a skeleton represented by one or more elements selected from the group consisting of Ge is disclosed. Non-Patent Document 2 (Materials Science and Engineering B 143 (2007) 14-20) discloses Li ₅ La ₃ Bi ₂ O ₁₂ and reports a value of 0.04 mS / cm for the ionic conductivity in the grains. Has been. However, these solid electrolytes cannot be said to have sufficiently high conductivity, and further higher conductivity is desired.

Special table 2007-528108 gazette JP 2011-051800 A JP 2011-073962 A JP 2011-073963 A JP 2012-031025 A

Ramaswamy Murugan et al., Angew.Chem. Int. Ed.2007, 46, 1-5 Materials Science and Engineering B 143 (2007) 14-20

  The present inventors have recently found that in a garnet-type or garnet-like LLZ-based solid electrolyte ceramic material, a higher conductivity can be realized by using a composition in which a substitution element containing at least Bi coexists. Got.

  Accordingly, an object of the present invention is to achieve further higher conductivity in a garnet-type or garnet-type-like LLZ-based solid electrolyte ceramic material.

According to one aspect of the present invention, a solid electrolyte ceramic material having lithium ion conductivity,
Ceramics comprising the ceramic material comprising an oxide sintered body having a garnet-type or garnet-type similar crystal structure containing a main constituent element of Li, La, Zr and O and a substitution element containing at least Bi Material is provided.

Solid electrolyte ceramic material The ceramic material according to the present invention is a solid electrolyte ceramic material having lithium ion conductivity. This ceramic material is made of an oxide sintered body having a garnet-type or garnet-type crystal structure containing a main constituent element such as Li, La, Zr, and O and a substitution element containing at least Bi. The substitution element preferably further contains Ta or Nb. Typically, this crystal structure is a garnet-type or garnet-type crystal structure composed of at least Li, La, Zr and O (hereinafter referred to as LLZ crystal structure), and a part of the Zr site is Bi and It is optionally substituted with a substitution element containing Ta or Nb. By such substitution, the Zr site in the LLZ crystal structure is composed of a plurality of predetermined elements. According to the present knowledge of the present inventors, the ionic conductivity can be improved because the Zr site is composed of a plurality of predetermined elements. The partial substitution amount of Zr by the substitution element is preferably 5 to 30 mol%, more preferably 5 to 20 mol%, still more preferably 10 to 10 mol%, based on the total number of moles of elements constituting the Zr site. 20 mol%. Such a ceramic material of the present invention can be said to be a garnet-type or garnet-type-like LLZ-based solid electrolyte ceramic material, but other elements other than Li, La, Zr, Bi, Ta, Nb and O (for example, Al) may be included in the crystal lattice or other portions (for example, grain boundaries). Although Ta and Nb which may exist if desired are substituted into the Zr site as the same pentavalent element, since the ionic radii are equivalent, the same effect is brought about in the change of the crystal structure and hence the ionic conductivity. . Therefore, even if the Zr site is replaced with any of the combination of Bi and Ta, the combination of Bi and Nb, or the combination of Bi, Ta and Nb, the same effect can be obtained.

The ceramic material of the present invention is a garnet-type or garnet-type similar LLZ-based solid electrolyte ceramic material. As a feature of the LLZ crystal structure, as an example of a material having the same garnet crystal structure, an X-ray diffraction file No. of CSD (Cambridge Structural Database) is used. It includes that it has a similar XRD pattern to _{422259 (Li 7 La 3 Zr 2} O 12). In addition, No. Compared to 422259, the constituent elements are different and the Li concentration in the ceramics may be different, so the diffraction angle and the diffraction intensity ratio may be different.

The contents of the main constituent element and the substitution element are not particularly limited as long as the LLZ crystal structure is obtained. Each molar ratio of Li: La: (Zr + Bi + Ta + Nb) in the ceramic material of the present invention is a molar ratio of each element in Li ₇ La ₃ Zr ₂ O ₁₂ described in Non-Patent Document 1, Li: La: Zr = 7: It does not necessarily match 3: 2, but rather tends to deviate.

The garnet-type or garnet-like crystal structure in the ceramic material of the present invention has the general formula:
Li _7-xy La ₃ (Zr _{2 -xy} , M _x , Bi _y ) O _12-δ
(Where 0 ≦ x <0.6, 0.03 ≦ y ≦ 0.6 (eg, 0.05 ≦ y ≦ 0.6), 0.1 ≦ x + y ≦ 0.6, and M is Ta or Nb is included, and δ represents the amount of oxygen deficiency but may be 0)
Is preferably included, more preferably 0 ≦ x <0.4, 0.05 ≦ y ≦ 0.4, 0.1 ≦ x + y ≦ 0.4, and further preferably 0 <x. <0.4, 0.1 ≦ y ≦ 0.4, 0.1 ≦ x + y ≦ 0.4, particularly preferably 0.1 ≦ x <0.4, 0.1 ≦ y ≦ 0.4, 0.2 ≦ x + y ≦ 0.4. In such a range, the ionic conductivity is particularly improved. In light of the fact that the amount of oxygen deficiency (δ) cannot be quantitatively analyzed using the latest apparatus, the above general formula is conventionally Li _7-xy La ₃ (Zr _2-xy , M _x , Bi is abbreviated _{y) O 12} it is permissible. In any case, it is considered that there is no problem if 0 ≦ δ <1. Further, the above general formula defines the composition ratio of the main constituent element and the substitution element, and the crystal lattice of other elements (for example, Al and Mg) or other parts (for example, grain boundaries). This does not exclude the possibility of inclusion.

  The oxide sintered body preferably contains Al as an additive element for the sintering aid. Al is an element effective in obtaining a highly compact sintered pellet capable of handling a ceramic material having an LLZ crystal structure, and also improves lithium ion conductivity. The form of Al is not particularly limited. As long as the LLZ crystal structure can be confirmed, Al may exist in the crystal lattice or may exist in other than the crystal lattice. The presence of Al can be detected by, for example, ICP (high frequency inductively coupled plasma) emission spectroscopic analysis, EPMA (electron beam microanalyzer) or the like, and the content thereof can be determined. The amount of Al added is not particularly limited as long as it is an amount that can improve the density and lithium ion conductivity without impairing the basic properties of the LLZ-based solid electrolyte ceramic material, but is finally limited to LLZ-Al It is preferable to set it as 0.01-1 mass% with respect to the total weight of a system ceramic powder or a sintered compact pellet, More preferably, it is 0.05 mass% or more. When aluminum is contained in such amounts, improved density and lithium ion conductivity are obtained. On the other hand, when the Al content exceeds 2% by mass, grain growth becomes remarkable and pores remain, resulting in a decrease in density, resulting in a decrease in lithium ion conductivity, preferably 1.2% by mass or less. It is.

  The oxide sintered body may further contain Mg as an additive element. Mg is an element that improves density and strength, preferably by adding together with Al to suppress or avoid the occurrence of defects such as uneven firing, cracks, vacancies, and abnormal grain growth. The form of Mg is not particularly limited. As long as the LLZ crystal structure can be confirmed, Mg may exist in the crystal lattice or may exist in other than the crystal lattice. The presence of Mg can be detected by, for example, ICP (high frequency inductively coupled plasma) emission spectroscopic analysis, EPMA (electron beam microanalyzer) or the like, and the content thereof can be determined. The amount of Mg added is not particularly limited as long as it is an amount that can improve the density and strength without impairing the basic characteristics of the LLZ-based solid electrolyte ceramic material, but is not limited to the total weight of the oxide sintered body. When 0.01% by mass or more of magnesium is contained, improved density and lithium ion conductivity are obtained. Further, when the Mg content as an additive element other than the substitution element greatly exceeds 1% by mass, the lithium ion conductivity tends to decrease, and is preferably 0.50% by mass or less. A more preferable Mg content is 0.05 to 0.30 mass%.

  According to a particularly preferred embodiment of the present invention, the oxide sintered body comprises both Al and Mg as additive elements. Thus, by adding Al and Mg in combination, generation of defects such as uneven firing, cracks, vacancies, abnormal grain growth and the like can be suppressed or avoided, and high density and high strength can be realized. In that sense, it can be said that Al and Mg are added as a sintering aid and / or a particle growth inhibitor. When a garnet-type or garnet-like LLZ-based solid electrolyte ceramic material is increased in size for practical use, defects such as uneven firing, cracks, vacancies, abnormal grain growth, etc. occur, resulting in a decrease in denseness and strength. However, such a problem is solved by the combined addition of Al and Mg. Therefore, the ceramic material of the present invention is not limited to a laboratory-sized small material, and even if it is a large material suitable for practical use or mass production, defects such as uneven firing, cracks, voids, and abnormal grain growth Etc. can be reduced or avoided to achieve high density and high strength. The ceramic material of the present invention preferably has a sintered body size of more than 20 mm × 20 mm, more preferably more than 25 mm × 25 mm, and still more preferably more than 50 mm × 50 mm. . The thickness of the ceramic material of the present invention is preferably 1 mm or less, more preferably 0.5 mm or less, and further preferably 0.2 mm or less, from the viewpoint of reducing internal resistance when the battery is applied.

The ceramic material of the present invention preferably has a density of 4.8 g / cm ³ or more, more preferably 5.0 g / cm ³ or more, and still more preferably 5.1 g / cm ³ or more. In particular, when the density is 5.0 g / cm ³ or more, the handling property is good and good lithium ion conductivity can be obtained, and even when the plate is thinned, the through holes caused by defects such as vacancies can be obtained. Generation can be suppressed, and it is effective for suppressing lithium dendrite short-circuiting. The density of the ceramic material can be calculated, for example, by measuring the weight and volume of the pellet. For example, in the case of a cylindrical pellet, after measuring the weight, the diameter of the pellet was measured several times with a micrometer to obtain an average value, and the thickness was also measured with a micrometer at several places as an average value. It is preferable that the volume is calculated from a numerical value, and the density is measured from each value or measured by a method that can obtain an accuracy and accuracy equivalent to or higher than that. The ceramic material of the present invention preferably has a 4-point bending strength measured in accordance with JIS R1601 (2008) of 70 MPa or more, more preferably 100 MPa or more.

  The lithium ion conductivity of the ceramic material of the present invention is preferably 0.70 mS / cm or more, more preferably 0.80 mS / cm or more, more preferably 0.880 mS / cm or more, and still more preferably 0. 890 mS / cm or more. The lithium ion conductivity is preferably measured by, for example, an AC impedance method or a method that can obtain the same accuracy and accuracy.

  The ceramic material of the present invention is used as a solid electrolyte material for various applications by utilizing its conductivity and denseness. For example, it can be used for a lithium battery such as a lithium secondary battery and various gas sensor materials such as SOx, NOx, carbon dioxide gas and oxygen, but is particularly preferably used as a solid electrolyte of an all-solid lithium secondary battery. For example, the electrolyte solution on the positive electrode side and the negative electrode side can be completely separated by overlaying or replacing the ceramic material according to the present invention on the separator portion of a normal lithium ion secondary battery using the electrolyte solution. In addition, even in a battery using sulfur as a positive electrode (for example, a LiS battery in combination with negative electrode lithium), at least a part of the separator is replaced with the ceramic material according to the present invention to completely separate the positive and negative electrode electrolytes, Battery capacity reduction due to elution of the positive electrode polysulfide into the electrolyte can be avoided or suppressed. Furthermore, even in an air secondary battery such as a lithium-air battery, the use of an organic electrolyte can be avoided or suppressed by replacing at least a part of the liquid electrolyte with the ceramic material according to the present invention, and at the same time the battery structure is simplified. It is possible to suppress side reactions caused by the organic electrolyte.

  As described above, batteries that are expected to be applied with the ceramic material targeted by the present invention include all-solid-state batteries and current lithium ions, including lithium-air batteries and lithium-sulfur batteries that are assumed to use lithium metal for the negative electrode. Various types of batteries can be mentioned up to the battery, and these are collectively referred to as a lithium battery in this specification. In any of these batteries, as a means for essentially preventing a dendrite short circuit, it is considered effective to use a dense solid electrolyte made of ceramics as a partition between positive and negative electrodes. In this regard, in the past, secondary batteries using lithium metal as the negative electrode have frequently suffered short-circuit accidents between the positive and negative electrodes due to dendrite (resin-like crystal) precipitates. When a dendrite short-circuit occurs, current has concentrated in the short-circuited part, causing excessive heat generation, leading to a thermal runaway of the battery, resulting in an accident that generates heat and ignites.Currently, batteries using lithium metal as the negative electrode are not for primary batteries In not used. Under such circumstances, the ceramic material which is the subject of the present invention has an advantage that the various types of batteries can be used as secondary batteries by essentially preventing this dendrite short circuit. Therefore, according to a preferred aspect of the present invention, there is provided a lithium battery, particularly preferably a lithium secondary battery, comprising a positive electrode, a negative electrode, and a solid electrolyte made of a ceramic material provided between the positive electrode and the negative electrode. Is preferably made of lithium metal or a lithium alloy.

Manufacturing Method The solid electrolyte ceramic material according to the present invention as described above can be manufactured by the following procedure. First, a raw material powder is prepared that includes main constituent elements that are Li, La, and Zr in a mixing ratio capable of giving a garnet-type or garnet-like crystal structure, and a substitution element that contains Bi and optionally Ta or Nb. . Next, the raw material powder is fired in one step or in multiple steps, and an oxide sintered body having a garnet-type or garnet-type similar crystal structure composed of the main constituent elements partially substituted with substitution elements is synthesized as a ceramic material. To do. Then, Al and / or Mg is added as an additional element as desired in the step of preparing the raw material powder and / or the synthesis step. Hereinafter, these steps will be specifically described.

(1) Preparation of raw material powder First, the main constituent elements Li, La and Zr, substitution element Bi, and optionally Ta or Nb, and optionally added at a blending ratio capable of giving a garnet-type or garnet-like crystal structure. A raw material powder containing Al and / or Mg as an element, that is, a pulverized powder of a raw material for firing is prepared. These constituent metal elements may be contained in the firing raw material as a Li component, a La component, a Zr component, a Bi component, a Ta component or Nb component as required, and an Al component and / or Mg component as desired. Although the ceramic material of the present invention contains O, O may be contained as a constituent element in a compound of these constituent metal elements. These various raw material components can be in any form such as various metal salts such as metal oxides, metal hydroxides, and metal carbonates containing the respective metal elements, and are not particularly limited. For example, Li ₂ CO ₃ or LiOH is used as the Li component, La (OH) ₃ or La ₂ O ₃ is used as the La component, ZrO ₂ is used as the Zr component, and Bi ₂ O ₃ is used as the Bi component. It is possible to use Ta ₂ O ₅ as the Ta component and Nb ₂ O ₅ as the Nb component.

  The raw material powder can contain main constituent elements Li, La, Zr and a substitution element to such an extent that an LLZ crystal structure can be obtained by solid phase reaction or the like. Li component, La component, and Zr component + substitution element component (ie Bi component and optionally Ta component or Nb component) are 7: 3: 2 or a composition close to the composition ratio according to the stoichiometric composition of LLZ. Can be used. When considering the disappearance of the Li component due to the volatilization of Li during heat treatment, the Li component includes an amount slightly increased (for example, about 10%) from the molar ratio equivalent amount based on the stoichiometry of Li in LLZ. The La component and the Zr component can be contained in amounts corresponding to the LLZ molar ratio, respectively. For example, it can mix | blend so that the molar ratio of Li: La: (Zr + Bi + Ta + Nb) may be 7.7: 3: 2.

The Bi component, the Ta component, and the Nb component can be in any form such as a metal oxide, a metal hydroxide, and a metal carbonate containing the respective metal components, and are not particularly limited. Examples of Bi components include bismuth oxide (Bi ₂ O ₃ ), bismuth hyponitrite (Bi ₅ O (OH) ₉ (NO ₃ ) ₄ ), bismuth carbonate oxide (Bi ₂ (CO ₃ ) O ₂ ), hydroxide Bismuth (Bi (OH) ₃ ) etc. are mentioned. Examples of the Nb component include niobium alkoxide containing Nb ₂ O ₅ , NbCl ₅ , Nb, propoxyniobium and the like. Examples of the Ta component include Ta ₂ O ₅ , TaCl ₅ , Ta, tantalum alkoxide containing tantalum ethoxide, and the like.

Al may be added when preparing the raw material powder. That is, the raw material powder can contain Al-containing powder. The Al component can be in any form such as a metal oxide containing Al, a metal hydroxide, a metal nitrate, a metal organic substance, or a simple metal, and is not particularly limited. Examples of Al _{component, Al 2 O 3, Al (} NO 3) 3 · 9H 2 O, Al (OH) 3, Al, aluminum acetylacetonate, aluminum triethoxide, aluminum butoxide, aluminum propoxide, aluminum methoxide Aluminum chloride, aluminum chloride hexahydrate, diethyl aluminum chloride, aluminum oleate, aluminum acetate n hydrate, aluminum oxalate, aluminum bromide hexahydrate, aluminum stearate, triethyl aluminum, trimethyl aluminum, tri Examples include isobutylaluminum, aluminum sulfate, and aluminum iodide. The addition of Al is preferably performed so that the oxide sintered body contains Al in an amount of 0.01 to 1% by mass, and more preferably 0.05 to 1.2% by mass. In this case, the molar ratio of Al / La in the oxide sintered body is preferably 0.008 or more and 0.12 or less, more preferably 0.10 or less.

Mg may be added when preparing the raw material powder. That is, the raw material powder can contain Mg-containing powder. The Mg component can be in any form such as a metal oxide containing Mg, a metal hydroxide, a metal nitrate, a metal organic substance, or a simple metal, and is not particularly limited. Examples of Mg _{component, MgO, MgO 2, Mg (} OH) 2, MgCl 2, MgBr 2, MgI 2, MgH 2, MgB 2, Mg 3 N 2, MgCO 3, Mg (NO 3) 2, MgClO 4 Mg (CH ₃ COO) ₂ , C ₁₄ H ₁₀ MgO ₄ , Mg (CH ₃ (CH ₂ ) ₁₆ COO) _{2 and the} like. Mg is preferably added so that the oxide sintered body contains Mg in an amount of 0.01 to 1% by mass, and more preferably 0.05 to 0.30% by mass.

  Each of the above components can be used without particular limitation as long as it is industrially produced and available, but preferably has a purity of 95% or more, and more preferably has a purity of 98% or more. It is. Moreover, it is preferable that the water | moisture content in each component is 1% or less, and you may dry as needed.

  In the preparation of the raw material for firing, a known raw material powder preparation method in ceramic powder synthesis can be appropriately employed. For example, the raw materials for firing can be uniformly mixed by putting them into a reiki machine or an appropriate ball mill. The preparation conditions of such a raw material for firing are appropriately determined according to the subsequent synthesis step. That is, a raw material for firing containing all the raw material components necessary for the ceramic material of the present invention may be prepared at once, or a part of the raw material components (for example, Li component, La component, Zr component, Bi) First, a raw material for firing containing a component, Ta component, Nb component, Al component, and Mg component) is prepared, and the fired powder (temporary) of the raw material for firing is prepared immediately before the synthesis step. The final component for firing may be obtained by adding the remaining components and the remaining amount (for example, the total amount of Al component and / or Mg component or a part thereof) to (baked powder).

(2) Synthesis process The raw material powder is fired in one or multiple stages, and an oxide sintered body having a garnet-type or garnet-like crystal structure composed of at least Li, La, Zr, Bi, and O is a ceramic. Synthesized as a material. In this synthesis step, Al and / or Mg may be added.

  In at least one stage of this synthesis process, firing is performed in a firing container made of an Mg-containing material (hereinafter referred to as a firing sheath) filled with raw material powder, and Mg is diffused from this container to add Mg. It is particularly preferred that Thereby, the occurrence of uneven composition can be effectively suppressed, and defects such as uneven firing, cracks, vacancies, abnormal grain growth, and the like can be more effectively prevented. The Mg-containing material is not particularly limited as long as it is a material that contains Mg so that it can diffuse into the sintered body as it is fired, but MgO is preferred. However, as described above, when Mg-containing powder is added to the raw material powder, it is not essential to use a fired sheath made of Mg-containing material. In that case, a fired sheath made of other materials such as alumina is used. May be. Further, in the aspect in which Mg is diffused from the fired sheath, addition of the Mg-containing powder to the raw material powder may also be performed. In any case, the addition of Mg as an additional element other than the substitution element is preferably performed so that the oxide sintered body contains Mg in an amount of 0.01 to 1% by mass, and more preferably, 0.8%. It is 05-0.30 mass%.

  The firing atmosphere in the synthesis step may be an oxidizing atmosphere containing oxygen or an inert atmosphere made of an inert gas such as Ar, and is not particularly limited. By synthesizing the ceramic material in an inert gas atmosphere, it becomes easier to obtain a higher density, and it is an element that tends to be lost during synthesis with respect to La (an element that is difficult to lose during synthesis) in the raw material for firing. ) The ratio of the number of moles of Li is easily maintained even in the sintered body. When heat treatment is performed in an inert gas atmosphere, the raw material is preferably a powder containing an O component such as an oxide. Moreover, even when the ceramic material is synthesized in an oxidizing atmosphere, high density and ionic conductivity can be realized. Therefore, it is preferable to perform the second baking step in an inert gas atmosphere or an oxidizing atmosphere in the first baking step and the second baking step described later. Examples of the inert gas species include one or more selected from helium (He), argon (Ar), and nitrogen (N), preferably Ar. The firing temperature for synthesis is not particularly limited, but is preferably 800 ° C. or higher, and more preferably 850 ° C. or higher and 1250 ° C. or lower. Examples of the oxidizing atmosphere include an air atmosphere and an oxygen atmosphere, but an oxygen atmosphere is preferable, and an oxygen atmosphere of about 100% oxygen is more preferable.

  According to a preferred embodiment of the present invention, the synthesis step includes a first firing step of firing the raw material powder described above to obtain a precursor powder, and pulverizing and firing the obtained precursor powder to obtain an oxide sintered body. A second firing step. By such a combination of firing steps, an LLZ crystal structure is easily obtained. In this embodiment, when the above-described addition by diffusion of Mg is performed, it is preferably performed in the second firing step. In this case, in the firing container (firing sheath) made of the Mg-containing material filled with the precursor powder. And adding Mg by diffusing Mg from this container.

  The first firing step is a step of obtaining a precursor powder for easily forming an LLZ crystal structure in the second firing step by performing thermal decomposition of at least a Li component, a La component, a Zr component, and a Bi component. . The precursor powder may already have an LLZ crystal structure. The firing temperature is preferably 850 ° C. or higher and 1150 ° C. or lower. The first baking step may include a step of heating at a lower heating temperature and a step of heating at a higher heating temperature within the above temperature range. By providing such a heating step, a more uniform ceramic powder can be obtained, and a high-quality sintered body can be obtained by the second firing step. When carrying out the first firing step in such a plurality of steps, it is preferable to knead and pulverize after completion of each firing step by using a reiki machine, a ball mill, a vibration mill or the like. Further, it is desirable that the pulverization method is dry. By doing so, a more uniform LLZ phase can be obtained by the second firing step. And addition of Mg may be performed by adding Mg containing powder to a precursor powder at the time of a grinding | pulverization, or before and after that.

  The first firing step may be performed in an oxidizing atmosphere such as the air, or may be performed in an inert atmosphere, and it is preferable that an atmosphere according to the raw material is appropriately selected. Considering thermal decomposition, an oxidizing atmosphere is preferable. Further, the first baking step is preferably composed of heat treatment of 850 ° C. or higher and 1150 ° C. or lower once to twice, and heat treatment step of 900 ° C. or higher and 1000 ° C. or lower (more preferably about 950 ° C.) twice. More preferably, it is comprised. In this case, it is preferable that the first baking step is performed for 15 hours to 25 hours in total as the total heating time at the maximum temperature set as the heating temperature as a whole.

  The firing raw material used in the first firing step may not contain an Al component and / or a Mg component. In this case, if necessary, in the second firing step, an Al component and / or an Mg component may be added and fired. The addition of the Al component and / or Mg component may be performed by addition of Al-containing powder and / or Mg-containing powder, or may be performed by diffusion of Al and / or Mg from a fired sheath or setter. .

  The firing raw material used in the first firing step may include an Al component and / or a Mg component. In this case, since the precursor powder containing Al and / or Mg can be obtained, it is not necessary to separately add the Al component and / or Mg component to the precursor powder in the subsequent second firing step. That is, since Al and / or Mg are inherent in the precursor powder, the second firing step is performed in the presence of Al and / or Mg. The firing raw material used in the first firing step includes a part of the necessary amount of the Al component and / or Mg component, and the remaining Al component and / or Mg component is added to the precursor powder in the second firing step. You may make it add. The addition of the Al component and / or Mg component may be performed by addition of Al-containing powder and / or Mg-containing powder, or may be performed by diffusion of Al and / or Mg from the fired sheath.

  The second baking step is preferably a step of heating the precursor powder obtained in the first baking step at a temperature of 950 ° C. to 1250 ° C. According to the second firing step, the precursor powder obtained in the first firing step can be fired to finally obtain a ceramic material having an LLZ crystal structure that is a composite oxide. The heating time at the heating temperature in the second firing step is preferably about 18 hours or more and 50 hours or less. When the time is shorter than 18 hours, the formation of the LLZ ceramics is not sufficient. When the time is longer than 50 hours, it becomes easy to react with the setter via the filling powder, and the crystal growth is not able to maintain the strength as a sample. Because. Preferably, it is 30 hours or more. The second baking step may be performed in an inert gas atmosphere or in an oxidizing atmosphere.

  The second firing step is preferably performed after forming a molded body containing the precursor powder. For example, a precursor powder or a powder obtained by adding an Al component or Mg component to a precursor powder is pressure-molded using a known press technique and can be used as a desired three-dimensional shape (for example, as a solid electrolyte or separator for a secondary battery) It is preferable to carry out after forming a molded body having a suitable shape and size). By using a molded body, a solid phase reaction is promoted, and a sintered body can be easily obtained. In addition, you may implement separately a sintering process at the temperature similar to the heating temperature in a 2nd baking process by using the ceramic powder obtained by the 2nd baking process as a molded object after a 2nd baking process. When the precursor powder compact is fired and sintered in the second firing step, the compact is preferably embedded in the same powder. By doing so, the loss of Li can be suppressed and the change in the composition before and after the second firing step can be suppressed. Moreover, the curvature at the time of baking of a sintered compact can be prevented by pressing a molded object with a setter from the upper and lower sides of a filling powder as needed. On the other hand, when the temperature is lowered by using LiOH as the Li raw material in the second firing step, the precursor powder compact can be sintered without being embedded in the same powder. This is because the loss of Li is relatively suppressed by lowering the temperature of the second firing step.

  In order to carry out the second firing step in the presence of Al and / or Mg, as already explained, the first firing step is carried out using the firing raw material containing the Al component and / or the Mg component. In addition to the form in which the obtained precursor powder is used as it is in the second firing step, the first firing step is performed using a raw material for firing that does not contain an Al component and / or an Mg component, and the obtained precursor powder is made of Al. The form which adds and mixes a component and / or Mg component, and implements a 2nd baking process, and also the form which implements a 2nd baking process using the baking sheath containing Al and / or Mg are mentioned. In order to perform the second firing step in the presence of Al and / or Mg, any of these forms may be used, or these forms may be appropriately combined.

  Through the synthesis process as described above, the ceramic material of the present invention can be obtained as an oxide sintered body.

  The present invention is more specifically described by the following examples.

Example 1 : Production and Evaluation of Oxide Sintered Body Using Ar Atmosphere in the Second Firing Process As raw material components for preparing a raw material for firing, lithium hydroxide (Kanto Chemical Co., Ltd.), lanthanum hydroxide (Shin-Etsu) Chemical Industry Co., Ltd.), zirconium oxide (Tosoh Corporation), tantalum oxide and bismuth oxide were prepared. These powders were weighed and blended so as to have the composition shown in Table 1, and γ-Al ₂ O ₃ was added in an amount of 0.025 in terms of the molar ratio of Al to the garnet composition formula. And mixed to obtain a raw material for firing. In addition, the composition shown in Table 1 is a preparation composition, and is included in a larger amount than the target composition in consideration of loss of Li during firing. Therefore, although the charged composition is a composition that does not satisfy the charge compensation of the garnet-type crystal structure, it is understood that a composition that satisfies the charge compensation is obtained after firing due to loss of Li and / or oxygen deficiency. It should be noted that elements other than Li have substantially no loss during firing, and are basically retained after firing at the composition ratio shown in Table 1.

  In the first firing step, the firing raw material is placed in a magnesia crucible and heated at 600 ° C./hour in the air, and held at 950 ° C. for samples 1 to 7 and 900 ° C. for sample 8. Firing was performed under the conditions for a total of 20 hours.

  As a 2nd baking process, the powder obtained by the 1st baking process and a cobblestone were mixed, and it grind | pulverized for 3 hours using the vibration mill, and the pulverized powder corresponding to the samples 1-8 of Table 1 was obtained. After sieving this pulverized powder, the obtained powder was press-molded at about 100 MPa using a mold to obtain a molded body having a desired shape. The obtained molded body was placed on a magnesia setter, and the setter was put in a magnesia sheath and heated at 200 ° C./hour in an Ar atmosphere. Was obtained by holding at 1050 ° C. for 36 hours, from which samples 1 to 8 of 10 mm square × thickness 1 mm or diameter 12 mm × thickness 1 mm were obtained. In the case of using an Ar atmosphere, the inside of a furnace having a capacity of about 3 L was evacuated in advance, and then Ar gas having a purity of 99.99% or more was allowed to flow through the electric furnace at 1 L / min.

  After polishing the upper and lower surfaces of Samples 1 to 8, various evaluations and measurements shown below were performed.

When the X-ray diffraction measurement of the structural evaluation samples 1 to 8 was performed, the X-ray diffraction file No. of CSD (Cambridge Structural Database) was obtained. A crystal structure similar to 422259 (Li ₇ La ₃ Zr ₂ O ₁₂ ) was obtained. From this, it was confirmed that all the obtained samples have the characteristics of the LLZ crystal structure.

Electrodes were formed on both surfaces of a sample for measuring lithium ion conductivity by Au sputtering, and then introduced into a glove box in an Ar atmosphere and incorporated into a CR2032 coin cell. The coin cell is taken out into the atmosphere, and AC impedance measurement is performed at a frequency of 0.1 Hz to 1 MHz and a voltage of 10 mV using a Solartron electrochemical measurement system (potentiometer / galvano stud, frequency response analyzer), and the lithium ion conductivity is measured. Calculated. As a result, the lithium ion conductivity of each sample was as shown in Table 1. Samples 1-7 according to the present invention showed higher conductivity than comparative sample 8.

Density measurement After measuring the weight of samples 1 to 8, the length or diameter and thickness of each side of samples 1 to 8 were measured several times using a micrometer, and the average value was calculated. The volume of 8 was calculated and the density was calculated. As a result, the density of each sample was as shown in Table 1. Samples 1 to 8 all showed high sintered body density.

Example 2: Production and evaluation of oxide sintered body using oxygen atmosphere in second firing step As raw material components for preparing raw materials for firing, lithium hydroxide (Kanto Chemical Co., Ltd.), lanthanum hydroxide (Shin-Etsu) Chemical Industry Co., Ltd.), zirconium oxide (Tosoh Corporation), tantalum oxide and bismuth oxide were prepared. These powders are weighed and blended so as to have the composition shown in Table 2, and further γ-Al ₂ O ₃ is an amount (samples 9 to 11) in which the molar ratio of Al to the garnet composition formula is 0.1 or An amount (sample 12) of 0.025 in terms of the molar ratio of Al was added and mixed with a lyker machine to obtain a firing raw material. In addition, the composition shown in Table 2 is a charged composition, and is included in a larger amount than the target composition in consideration of loss of Li during firing. Therefore, although the charged composition is a composition that does not satisfy the charge compensation of the garnet-type crystal structure, it is understood that a composition that satisfies the charge compensation is obtained after firing due to loss of Li and / or oxygen deficiency. It should be noted that elements other than Li have virtually no loss during firing, and are basically retained after firing at the composition ratio shown in Table 2.

  As a first firing step, the firing raw material is put in a magnesia crucible and heated at 600 ° C./hour in an air atmosphere, and the conditions of holding at 950 ° C. for samples 9 to 11 and 900 ° C. for sample 12 Then, baking was performed for a total of 20 hours.

  As a 2nd baking process, the powder obtained by the 1st baking process and cobblestone were mixed, and it grind | pulverized for 3 hours using the vibration mill, and the pulverized powder corresponding to the samples 9-12 of Table 2 was obtained. After sieving this pulverized powder, the obtained powder was press-molded at about 100 MPa using a mold to obtain a molded body having a desired shape. The obtained molded body was placed on a magnesia setter, and the setter was put in a magnesia sheath and heated at 200 ° C./hour in an oxygen atmosphere of about 100% oxygen. At 1030 ° C., the sample 12 was held at 1050 ° C. for 36 hours to obtain a sintered body, from which samples 9 to 12 of 10 mm square × thickness 1 mm or diameter 12 mm × thickness 1 mm were obtained. In the case of using an oxygen atmosphere, the inside of a furnace having a capacity of about 3 L was evacuated in advance, and then an oxygen gas having a purity of 99.99% or more was flowed into the electric furnace at 1 L / min.

  After polishing the upper and lower surfaces of Samples 9 to 12, various evaluations and measurements were performed in the same manner as in Example 1. The results are as shown in Table 2. A relatively high density and lithium ion conductivity were obtained in any sample except for the sample 12 containing no Bi.

Claims (12)

A solid electrolyte ceramic material having lithium ion conductivity,
Ceramics comprising the ceramic material comprising an oxide sintered body having a garnet-type or garnet-type similar crystal structure containing a main constituent element of Li, La, Zr and O and a substitution element containing at least Bi material.   The ceramic material according to claim 1, wherein the substitution element further contains Ta or Nb.   The ceramic material according to claim 1 or 2, wherein the substitution element partially substitutes Zr of the crystal structure.   The ceramic material according to claim 3, wherein the amount of partial substitution of Zr by the substitution element is 5 to 30 mol% with respect to the total number of moles of elements constituting the Zr site. The crystal structure has the general formula:
Li _7-xy La ₃ (Zr _{2 -xy} , M _x , Bi _y ) O _12-δ
(In the formula, 0 ≦ x <0.6, 0.03 ≦ y ≦ 0.6, 0.1 ≦ x + y ≦ 0.6, M includes Ta or Nb, and δ indicates the amount of oxygen deficiency. Can be 0)
The ceramic material as described in any one of Claims 1-4 containing the composition represented by these.   The ceramic material according to claim 1, wherein the oxide sintered body contains Al as an additive element.   The ceramic material according to claim 6, wherein a molar ratio of Al / La in the oxide sintered body is 0.008 or more and 0.12 or less.   The ceramic material according to claim 1, wherein the oxide sintered body further contains Mg as an additive element.   The ceramic material according to any one of claims 1 to 8, which is used as a solid electrolyte for a lithium battery. The ceramic material according to any one of claims 1 to 9, wherein the lithium ion conductivity of the ceramic material is 0.70 mS / cm or more. Comprising a positive electrode, a negative electrode, and said positive electrode and is disposed between the negative electrode made of a ceramic material according to any one of claims 1-10 solid electrolyte, a lithium battery. The lithium battery according to claim 11 , wherein the negative electrode is made of lithium metal or a lithium alloy.