Solid electrolyte ceramics and solid batteries

Abstract

The present invention provides a solid electrolyte ceramic having excellent ion conductivity and capable of more effectively suppressing increases in electronic conductivity caused by the operation of a solid battery. The present invention relates to a solid electrolyte ceramic containing at least Li (lithium), La (lanthanum), Bi (bismuth), and O (oxygen), having a garnet-type crystal structure, and further containing one or more transition metal elements selected from the group consisting of Co (cobalt), Ni (nickel), and Mn (manganese).

Description

Technical Field

[0001] The present invention relates to a solid electrolyte ceramic and a solid battery comprising the solid electrolyte ceramic. Background Art

[0002] In recent years, the demand for batteries as power sources for portable electronic devices such as mobile phones and portable personal computers has increased significantly. Development of sintered solid secondary batteries (so-called "solid batteries"), which use solid electrolytes as electrolytes and have other solid components, is underway for these applications.

[0003] A solid-state battery comprises a positive electrode layer, a negative electrode layer, and a solid electrolyte layer stacked between the positive electrode layer and the negative electrode layer. In particular, the solid electrolyte layer comprises a solid electrolyte ceramic, which is responsible for the conduction of ions between the positive electrode layer and the negative electrode layer. Solid electrolyte ceramics require higher ion conductivity and lower electronic conductivity. As such solid electrolyte ceramics, from the perspective of higher ion conductivity, attempts have been made to use ceramics formed by sintering a garnet-type solid electrolyte substituted with Bi (e.g., Patent Document 1 and Non-Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-050071

[0007] Non-patent literature

[0008] Non-patent document 1: Gao et al., Solid State Ionics, 181 (2010) 1415-1419. Summary of the Invention

[0009] Technical problem to be solved by the invention

[0010] The inventors of the present invention have discovered that solid-state batteries using the aforementioned conventional solid electrolyte ceramics suffer from the following problems. Specifically, conventional solid-state batteries using garnet-type solid electrolyte ceramics containing Bi easily generate impurities such as Li-Bi-O compounds at grain boundaries. These Li-Bi-O compounds are reduced during operation of the solid-state battery (i.e., during charge and discharge), increasing electronic conductivity. This increase in electronic conductivity can cause the solid-state battery to short-circuit and / or increase leakage current.

[0011] An object of the present invention is to provide a solid electrolyte ceramic having excellent ion conductivity and capable of more fully suppressing an increase in electron conductivity caused by the operation of a solid battery.

[0012] Solutions for solving technical problems

[0013] The present invention relates to a solid electrolyte ceramic having a garnet-type crystal structure.

[0014] The solid electrolyte ceramic contains at least Li (lithium), La (lanthanum), Bi (bismuth) and O (oxygen).

[0015] The solid electrolyte ceramic further contains one or more transition metal elements selected from the group consisting of Co (cobalt), Ni (nickel), and Mn (manganese).

[0016] Effects of the Invention

[0017] The solid electrolyte ceramic of the present invention has excellent ion conductivity and can more fully suppress an increase in electron conductivity caused by the operation of a solid battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 An enlarged schematic diagram of a solid electrolyte ceramic for explaining sintered particles constituting an example of the solid electrolyte ceramic of the present invention and their structure is shown.

[0019] Figure 2 The electron energy loss spectroscopic spectrum obtained by measuring the bulk particles in the solid electrolyte in the solid electrolyte single plate of Example 5A is shown. DETAILED DESCRIPTION

[0020] [Solid Electrolyte Ceramics]

[0021] The solid electrolyte ceramic of the present invention is composed of a sintered body formed by sintering solid electrolyte particles. The solid electrolyte ceramic of the present invention is a solid electrolyte ceramic containing at least Li (lithium), La (lanthanum), Bi (bismuth) and O (oxygen) and having a garnet-type crystal structure, and further contains one or more transition metal elements selected from the group consisting of Co (cobalt), Ni (nickel) and Mn (manganese) (hereinafter sometimes referred to as "predetermined transition metal elements"). In the present invention, the solid electrolyte ceramic containing Li (lithium), La (lanthanum), Bi (bismuth) and O (oxygen) and having a garnet-type crystal structure has excellent ion conductivity and can more fully suppress the increase in electronic conductivity by further containing the predetermined transition metal elements. In the case where such a solid electrolyte ceramic does not contain the predetermined transition metal elements, the increase in electronic conductivity cannot be fully suppressed. It should be noted that the solid electrolyte ceramic of the present invention is a ceramic composed of a solid electrolyte containing at least Li (lithium), La (lanthanum), Bi (bismuth) and O (oxygen) and having a garnet-type crystal structure, and may also contain other composite oxides or single oxides within the scope that does not impair the effects of the present invention. Furthermore, at least the sintered particles contained in the solid electrolyte ceramic as the main component of the present invention may have a garnet-type crystal structure.

[0022] The existence mode (or containing mode) of the predetermined transition metal element in the solid electrolyte ceramic of the present invention is not particularly limited, and it can exist in the crystal lattice or outside the crystal lattice. For example, the predetermined transition metal element can exist in the bulk, in the grain boundary, or in both in the solid electrolyte ceramic. As an example of the predetermined transition metal element existing in the bulk, in the solid electrolyte ceramic of the present invention, the predetermined transition metal element can also exist in the metal site (lattice site) constituting the garnet-type crystal structure. The metal site can be all metal sites, for example, it can be a Li site, a La site, a Bi site or two or more sites thereof. Since the solid electrolyte ceramic of the present invention is composed of a plurality of sintered particles, the predetermined transition metal element can also exist at the interface between two or more sintered particles.

[0023] The existence mode (or containing mode) of Bi (bismuth) in the solid electrolyte ceramic of the present invention is not particularly limited. For example, the predetermined Bi (bismuth) may be present in the bulk, in the grain boundaries, or in both in the solid electrolyte ceramic. From the perspective of insulation, it is preferred that Bi be present in the bulk. As an example of Bi being present in the bulk, in the solid electrolyte ceramic of the present invention, the Bi may also be present in the metal site (lattice site) constituting the garnet-type crystal structure. It may be present in the sintered particles in the solid electrolyte ceramic of the present invention, or it may be present on the surface thereof.

[0024] In the present invention, the predetermined transition metal and / or Bi (bismuth) may also be contained in a ceramic having a garnet-type crystal structure. Furthermore, the predetermined transition metal and / or Bi (bismuth) may also exist as a single oxide of the predetermined transition metal and / or Bi (bismuth). Furthermore, the predetermined transition metal and / or Bi (bismuth) may also exist as a composite oxide containing elements constituting the solid electrolyte ceramic. It should be noted that the oxide may also exist at the interface between sintered particles of the ceramic having a garnet-type crystal structure, which is the main component of the present invention.

[0025] Li (lithium) and La (lanthanum) in the solid electrolyte ceramic of the present invention can generally exist separately in the bulk. Specifically, as an example, in the solid electrolyte ceramic of the present invention, they can also exist at Li sites and La sites, which are metal sites (lattice sites) constituting a garnet-type crystal structure. In this case, a portion of Li (lithium) and La (lanthanum) can exist independently or as a composite oxide at the grain boundaries.

[0026] From the viewpoint of more fully suppressing an increase in electron conductivity, the transition metal element contained in the solid electrolyte ceramic of the present invention preferably contains Co.

[0027] The solid electrolyte ceramic of the present invention preferably has a chemical composition represented by the following general formula (I), and in this case, further contains the predetermined transition metal element as described above.

[0028] [Chemical Formula 1]

[0029] A α B β D γ O ω (I)

[0030] In formula (I), A is one or more elements selected from the group consisting of Li (lithium), Ga (gallium), Al (aluminum), Mg (magnesium), Zn (zinc), and Sc (scandium), and includes at least Li.

[0031] B is one or more elements selected from the group consisting of La (lanthanum), Ca (calcium), Sr (strontium), Ba (barium), and lanthanoid elements, and contains at least La. Examples of lanthanoid elements include Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium).

[0032] D represents one or more elements selected from the group consisting of transition elements capable of forming hexavalent coordination with oxygen and typical elements belonging to Groups 12 to 15. Examples of transition elements capable of forming hexavalent coordination with oxygen include Sc (scandium), Zr (zirconium), Ti (titanium), Ta (tantalum), Nb (niobium), Hf (hafnium), Mo (molybdenum), W (tungsten), and Te (tellurium). Examples of typical elements belonging to Groups 12 to 15 include In (indium), Ge (germanium), Sn (tin), Pb (lead), Sb (antimony), and Bi (bismuth). D contains at least Bi.

[0033] In formula (I), α, β, γ, and ω satisfy 5.0≤α≤8.0, 2.5≤β≤3.5, 1.5≤γ≤2.5, and 11≤ω≤13, respectively.

[0034] From the viewpoint of more fully suppressing an increase in electron conductivity, α preferably satisfies 5.5≤α≤7.0, more preferably satisfies 6.0≤α≤6.8, further preferably satisfies 6.2≤α≤6.8, and particularly preferably satisfies 6.2≤α≤6.6.

[0035] From the viewpoint of more fully suppressing an increase in electron conductivity, β preferably satisfies 2.5≤β≤3.3, more preferably satisfies 2.5≤β≤3.1, and still more preferably satisfies 2.8≤β≤3.0.

[0036] From the viewpoint of more fully suppressing an increase in electron conductivity, γ preferably satisfies 1.8≤γ≤2.5, more preferably satisfies 1.8≤γ≤2.3, and even more preferably satisfies 1.9≤γ≤2.3.

[0037] From the viewpoint of more fully suppressing an increase in electron conductivity, ω preferably satisfies 11≤ω≤12.5, and more preferably satisfies 11.5≤ω≤12.5.

[0038] The total content of the predetermined transition metal elements in the solid electrolyte ceramic of the present invention is usually determined by adding the content of B in the general formula (I) (for example, La and B in the general formula (II) described later) to the total content of the transition metal elements. 1 When the total number of ) is set to 100 mol%, it is more than 0 mol% and less than 3.50 mol% (for example, more than 0.01 mol% and less than 1.80 mol%), and from the viewpoint of more excellent ion conductivity and more sufficient suppression of the increase in electronic conductivity during operation, it is preferably more than 0 mol% and less than 1.20 mol% (for example, more than 0.01 mol% and less than 1.00 mol%), and more preferably more than 0 mol% and less than 0.25 mol% (for example, more than 0.01 mol% and less than 0.20 mol%).

[0039] The content of the predetermined transition metal element can be measured by performing inductively coupled plasma (ICP) emission spectrometry analysis (ICP analysis) of the solid electrolyte ceramic to obtain the average chemical composition of the material. Specifically, the average chemical composition can be obtained based on the ICP analysis, and the content of B in the general formula (I) (for example, La and B in the general formula (II) described later) can be used as the average chemical composition. 1 The contents of Co, Mn, and Ni can be determined by taking the total of the total of the Co, Mn, and Ni as 100 mol% as the ratio. Note that the contents can also be measured and calculated using ICP-AES (inductively coupled plasma optical emission spectrometry), LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry), TEM-EDX (energy dispersive X-ray spectroscopy), WDX (wavelength dispersive X-ray spectroscopy), and / or X-ray photoelectron spectroscopy (XPS).

[0040] The Bi (bismuth) content is usually greater than 0 mol% and less than 50 mol% when the D content is set to 100 mol%. From the viewpoint of better ion conductivity and more sufficient suppression of the increase in electronic conductivity during operation, it is preferably greater than 0 mol% and less than 35 mol%, more preferably greater than 0.5 mol% and less than 20 mol%, and even more preferably greater than 2.5 mol% and less than 17.5 mol%.

[0041] The content of Bi can also be measured by performing inductively coupled plasma (ICP) emission spectrometry (ICP analysis) of the solid electrolyte ceramic to obtain the average chemical composition of the material, similarly to the content of the predetermined transition metal element. Specifically, the average chemical composition can be obtained based on the ICP analysis, and the average chemical composition can be used as the content of D in the general formula (I) (for example, Bi and D in the general formula (II) described later) 1 The Bi content can be determined by taking the total of the total Bi content (the total of the total Bi content) as 100 mol % to determine the Bi content. Note that the Bi content can also be measured and calculated using ICP-AES (inductively coupled plasma optical emission spectrometry), LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry), TEM-EDX (energy dispersive X-ray spectroscopy), WDX (wavelength dispersive X-ray spectroscopy), and / or X-ray photoelectron spectroscopy (XPS).

[0042] In the present invention, the solid electrolyte ceramic having a garnet-type crystal structure means that the solid electrolyte ceramic may have not only a "garnet-type crystal structure" but also a "garnet-type-like crystal structure". Specifically, the solid electrolyte ceramic of the present invention has a crystal structure that can be identified as a garnet-type or garnet-type-like crystal structure by a person skilled in the art in the field of solid batteries in X-ray diffraction. More specifically, the solid electrolyte ceramic of the present invention may exhibit one or more main peaks corresponding to the Miller index inherent to the so-called garnet-type crystal structure (diffraction pattern: ICDDCard No. 01-080-6142) in X-ray diffraction at a predetermined incident angle, or may also exhibit one or more main peaks corresponding to the Miller index inherent to the so-called garnet-type crystal structure as a garnet-type-like crystal structure with different incident angles (i.e., peak positions or diffraction angles) and intensity ratios (i.e., peak intensities or diffraction intensity ratios) due to composition differences. Representative diffraction patterns similar to the garnet-type crystal structure include, for example, ICD Card No. 00-045-0109, etc. It is sufficient that at least the sintered particles contained in the solid electrolyte ceramic as the main component of the present invention have a garnet-type crystal structure.

[0043] As a specific embodiment, the solid electrolyte ceramic of the present invention can have a chemical composition represented by the general formula (II). Specifically, the solid electrolyte ceramic can have a chemical composition represented by the general formula (II). It should be noted that in this case, the solid electrolyte ceramic of the present invention has a chemical composition represented by the general formula (II) and also contains a predetermined transition metal element as described above.

[0044] [Chemical Formula 2]

[0045] (Li p A 1 y )(La β-z B 1 z )(D 1 γ-x Bi x )O 12-δ (II)

[0046] In formula (II), A 1 Refers to the metal element that occupies the Li site in the garnet crystal structure. 1 It is an element corresponding to A in the general formula (I), and may be one or more elements selected from the group consisting of elements other than Li among the same elements as those exemplified as A. 1Typically, it is one or more elements selected from the group consisting of Ga (gallium), Al (aluminum), Mg (magnesium), Zn (zinc), and Sc (scandium). From the perspective of better ion conductivity and more sufficient suppression of the increase in electronic conductivity during operation, A 1 Preferably, it is one or more elements selected from the group consisting of Ga (gallium) and Al (aluminum), and more preferably, it is both Ga and Al.

[0047] In formula (II), B 1 Refers to the metal element that occupies the La site in the garnet crystal structure. 1 It is an element corresponding to B in the general formula (I), and may be one or more elements selected from the group consisting of elements other than La among the same elements as those exemplified as B. 1 Typically, it is one or more elements selected from the group consisting of Ca (calcium), Sr (strontium), Ba (barium), and lanthanoid elements.

[0048] In formula (II), D 1 Refers to a metal element that occupies a 6-coordinate site in a garnet-type crystal structure. An example of a 6-coordinate site in a garnet-type crystal structure is Li5La3Nb2O having a garnet-type crystal structure. 12 (ICD DCard No. 00-045-0109) in which Nb is present, Li7La3Zr2O 12 (ICD DCard No. 01-078-6708) in which Zr is present. 1 It is an element corresponding to D in the general formula (I), and may be one or more elements selected from the group consisting of elements other than Bi among the same elements as those exemplified as D. 1 Usually, it contains one or more elements selected from the group consisting of Zr (zirconium), Sn (tin), Sb (antimony), Ti (titanium), Ta (tantalum), Nb (niobium), Hf (hafnium), Mo (molybdenum), W (tungsten) and Te (tellurium). From the viewpoint of better ion conductivity and more sufficient suppression of the increase in electronic conductivity during operation, it is preferred to contain one or more elements selected from the group consisting of Zr (zirconium) and Ta (tantalum), more preferably to contain Zr (zirconium) and Ta (tantalum), and even more preferably to contain Zr (zirconium) and Ta (tantalum).

[0049] In formula (II), x satisfies 0<x≤1.00. From the viewpoint of more excellent ion conductivity and more sufficient suppression of the increase in electronic conductivity during operation, it preferably satisfies 0.01≤x≤0.70, more preferably satisfies 0.02≤x≤0.40, further preferably satisfies 0.05≤x≤0.40, and particularly preferably satisfies 0.05≤x≤0.35.

[0050] y satisfies 0≤y≤0.50. From the viewpoint of achieving better ion conductivity and more fully suppressing an increase in electronic conductivity during operation, y preferably satisfies 0≤y≤0.40, more preferably 0≤y≤0.30, further preferably 0≤y≤0.20, and particularly preferably 0.

[0051] β satisfies 2.5≤β≤3.3. From the viewpoint of achieving more excellent ion conductivity and more fully suppressing an increase in electron conductivity during operation, β is preferably 2.5≤β≤3.1, and more preferably 2.8≤β≤3.0.

[0052] z satisfies 0≤z≤2.00, preferably 0≤z≤1.00, more preferably 0≤z≤0.50, and even more preferably 0, from the viewpoint of achieving better ion conductivity and more fully suppressing an increase in electron conductivity during operation.

[0053] γ satisfies 1.5≤γ≤2.5. From the viewpoint of achieving better ion conductivity and more fully suppressing an increase in electronic conductivity during operation, γ preferably satisfies 1.8≤γ≤2.5, more preferably 1.8≤γ≤2.3, and still more preferably 1.9≤γ≤2.3.

[0054] In formula (II), p generally satisfies 6.0≤p≤7.0. From the viewpoint of achieving better ion conductivity and more adequately suppressing an increase in electronic conductivity during operation, it preferably satisfies 6.0≤p≤6.6, and more preferably satisfies 6.25≤p≤6.55.

[0055] a is A 1 For example, in the case of A 1 If the number of elements X with a valence of a+ is n1, the number of elements Y with a valence of b+ is n2, and the number of elements Z with a valence of c+ is n3, then A 1 The average valence is a value represented by (n1×a+n2×b+n3×c) / (n1+n2+n3).

[0056] b is B 1 For example, in the case of B 1 If the number of X elements with a valence of a+ is n1, the number of Y elements with a valence of b+ is n2, and the number of Z elements with a valence of c+ is n3, then B 1 The average price is the same as the above A 1 The same value as the average price.

[0057] c is D 1 For example, in D 1 If the number of elements X with a valence of a+ is n1, the number of elements Y with a valence of b+ is n2, and the number of elements Z with a valence of c+ is n3, D1 The average price is the same as the above A 1 The same value as the average price.

[0058] δ represents the amount of oxygen deficiency and can be 0. δ generally satisfies 0 ≤ δ < 1. The amount of oxygen deficiency δ cannot be quantitatively analyzed even with the latest equipment and can therefore be considered to be 0.

[0059] It should be noted that the molar ratio of each element in the chemical composition of the solid electrolyte ceramic of the present invention is not necessarily consistent with the molar ratio of each element in formula (II), and there is a tendency to deviate from it depending on the analysis method. However, as long as the composition deviation is not to the extent that the characteristics change, the effect of the present invention can be achieved.

[0060] In the present invention, the chemical composition of the solid electrolyte ceramic can be the composition of the entire ceramic material obtained using ICP (inductively coupled plasma method). ICP-AES (inductively coupled plasma emission spectrometry) and LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) can also be used to measure and calculate. In addition, the chemical composition can be measured and calculated using XPS analysis, or can be obtained using TEM-EDX (energy dispersive X-ray spectroscopy) and / or WDX (wavelength dispersive X-ray spectroscopy). In addition, the chemical composition can also be obtained by quantitatively analyzing (composition analysis) any 100 points of any 100 sintered particles and calculating their average value.

[0061] The content of the predetermined transition metal element (i.e., Co, Ni, Mn) in the solid electrolyte ceramic of the present invention [for example, the content of B in the general formula (I) (or the content of La and B in the general formula (II)] 1 The molar ratio when the total number of (the molar ratio when the total number of) is set to 100 mol% can be calculated by the following method. In the present invention, the chemical composition of the solid electrolyte ceramic can be obtained by performing ICP analysis (inductively coupled plasma analysis), LA-ICP-MS (laser ablation ICP mass spectrometry) analysis, etc. In addition, it can be measured and calculated using XPS analysis, or TEM-EDX (energy dispersive X-ray spectroscopy) or WDX (wavelength dispersive X-ray spectroscopy) can be used. In addition, the chemical composition can also be obtained by performing quantitative analysis (composition analysis) of any 100 points of each of any 100 sintered particles and calculating their average value.

[0062] For example, EDX or WDX analysis is to measure the cross section of the solid battery. The cross section of the solid battery refers to a cross section parallel to the stacking direction of the positive electrode layer, the solid electrolyte layer and the negative electrode layer. The cross section of the solid battery can be exposed by grinding after the solid battery is embedded in the resin. There is no particular limitation on the method of cross section grinding. After cutting with a cutting machine, grinding can be performed using grinding paper, chemical mechanical grinding, ion milling, etc. to expose the solid electrolyte layer. By quantitatively analyzing the exposed cross section (solid electrolyte layer) using EDX or WDX (wavelength dispersed fluorescent X-ray analysis device), the molar ratio of Co, Ni, and Mn relative to B can be calculated.

[0063] In TEM-EELS analysis, for example, the electrode layer or solid electrolyte layer of a solid battery is exfoliated using a FIB (focused ion beam) or similar technique, and then the solid electrolyte is analyzed using TEM-EELS (transmission microscopy-electron energy-loss spectroscopy). This allows the elements contained in B, as well as Co, Ni, and Mn, to be detected, and the molar ratios of Co, Ni, and Mn relative to B to be calculated.

[0064] In the electron energy loss spectroscopy (EELS spectrum) of the solid electrolyte ceramic (LLZ) of the present invention, as shown in FIG. Figure 2 As shown in the EELS spectrum of the present invention, the energy position of the Co L-end peak of the solid electrolyte ceramic (LLZ) is lower than the energy position of the Co L-end peak of LiCoO2 (LCO). In detail, the shift amplitude sw of these peaks (refer to Figure 2 ) is usually 0.1 to 3 eV, preferably 0.3 to 2 eV. Figure 2 The following shows the electron energy loss spectroscopic spectrum obtained by measuring the bulk particles in the solid electrolyte of the solid electrolyte single plate produced in the examples.

[0065] Specific examples of the chemical composition of the solid electrolyte ceramic of the present invention include the following chemical compositions: In the chemical compositions shown below, the transition metal element followed by a hyphen (-) indicates that it may exist in the bulk and / or in the grain boundaries as described above.

[0066] Li 6.3 La3(Zr 1.30 Ta 0.40 Bi 0.30 )O 12 -0.001Co

[0067] Li 6.3 La3(Zr 1.30 Ta 0.40 Bi<h2 style=";text-align:left;direction:ltr"> 0.30 <h2 style=";text-align:left;direction:ltr"> )O<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> -0.003Co<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0068] <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 6.3 <h2 style=";text-align:left;direction:ltr"> La3(Zr<h2 style=";text-align:left;direction:ltr"> 1.30 <h2 style=";text-align:left;direction:ltr"> Ta<h2 style=";text-align:left;direction:ltr"> 0.40 <h2 style=";text-align:left;direction:ltr"> Bi<h2 style=";text-align:left;direction:ltr"> 0.30 <h2 style=";text-align:left;direction:ltr"> )O<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> -0.005Co<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0069] <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 6.3 <h2 style=";text-align:left;direction:ltr"> La3(Zr<h2 style=";text-align:left;direction:ltr"> 1.30 <h2 style=";text-align:left;direction:ltr"> Ta<h2 style=";text-align:left;direction:ltr"> 0.40 <h2 style=";text-align:left;direction:ltr"> Bi<h2 style=";text-align:left;direction:ltr"> 0.30 <h2 style=";text-align:left;direction:ltr"> )O<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> -0.010Co<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0070] <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 6.3 <h2 style=";text-align:left;direction:ltr"> La3(Zr<h2 style=";text-align:left;direction:ltr"> 1.30 <h2 style=";text-align:left;direction:ltr"> Ta<h2 style=";text-align:left;direction:ltr"> 0.40 <h2 style=";text-align:left;direction:ltr"> Bi<h2 style=";text-align:left;direction:ltr"> 0.30 <h2 style=";text-align:left;direction:ltr"> )O<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> -0.025Co<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0071] <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 6.3 <h2 style=";text-align:left;direction:ltr"> La3(Zr<h2 style=";text-align:left;direction:ltr"> 1.30 <h2 style=";text-align:left;direction:ltr"> Ta<h2 style=";text-align:left;direction:ltr"> 0.40 <h2 style=";text-align:left;direction:ltr"> Bi<h2 style=";text-align:left;direction:ltr"> 0.30 <h2 style=";text-align:left;direction:ltr"> )O<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> -0.050Co<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0072] <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 6.3 <h2 style=";text-align:left;direction:ltr"> La3(Zr<h2 style=";text-align:left;direction:ltr"> 1.30 <h2 style=";text-align:left;direction:ltr"> Ta<h2 style=";text-align:left;direction:ltr"> 0.40 <h2 style=";text-align:left;direction:ltr"> Bi<h2 style=";text-align:left;direction:ltr"> 0.30 <h2 style=";text-align:left;direction:ltr"> )O<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> -0.001Mn<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0073] <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 6.3 <h2 style=";text-align:left;direction:ltr"> La3(Zr<h2 style=";text-align:left;direction:ltr"> 1.30 <h2 style=";text-align:left;direction:ltr"> Ta<h2 style=";text-align:left;direction:ltr"> 0.40 <h2 style=";text-align:left;direction:ltr"> Bi<h2 style=";text-align:left;direction:ltr"> 0.30 <h2 style=";text-align:left;direction:ltr"> )O<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> -0.005Mn<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0074] <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 6.3 <h2 style=";text-align:left;direction:ltr"> La3(Zr<h2 style=";text-align:left;direction:ltr"> 1.30 <h2 style=";text-align:left;direction:ltr"> Ta<h2 style=";text-align:left;direction:ltr"> 0.40 <h2 style=";text-align:left;direction:ltr"> Bi<h2 style=";text-align:left;direction:ltr"> 0.30 <h2 style=";text-align:left;direction:ltr"> )O<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> -0.010Mn<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0075] <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 6.3 <h2 style=";text-align:left;direction:ltr"> La3(Zr<h2 style=";text-align:left;direction:ltr"> 1.30 <h2 style=";text-align:left;direction:ltr"> Ta<h2 style=";text-align:left;direction:ltr"> 0.40 <h2 style=";text-align:left;direction:ltr"> Bi<h2 style=";text-align:left;direction:ltr"> 0.30 <h2 style=";text-align:left;direction:ltr"> )O<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> -0.001Ni<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0076] <h2 style=";text-align:left;direction:ltr"> Li<h2 style=";text-align:left;direction:ltr"> 6.3 <h2 style=";text-align:left;direction:ltr"> La3(Zr<h2 style=";text-align:left;direction:ltr"> 1.30 <h2 style=";text-align:left;direction:ltr"> Ta0.40 Bi 0.30 )O 12 -0.005Ni

[0077] Li 6.3 La3(Zr 1.30 Ta 0.40 Bi 0.30 )O 12 -0.010Ni

[0078] Li 6.3 La3(Zr 1.30 Ta 0.40 Bi 0.30 )O 12 -0.005Co-0.005Ni-0.005Mn

[0079] Li 6.5 La3(Zr 1.53 Ta 0.4 Bi 0.07 )O 12 -0.005Co

[0080] Li 6.5 La3(Zr 1.46 Ta 0.4 Bi 0.14 )O 12 -0.005Co

[0081] Li 6.3 La3(Zr 1.30 Ta 0.40 Bi 0.30 )O 12 -0.005Co

[0082] Li 6.1 La3(Zr 1.10 Ta 0.40 Bi 0.50 )O 12 -0.005Co

[0083] As long as the solid electrolyte ceramic of the present invention contains a predetermined transition metal element, Bi can be contained anywhere between the vicinity of the grain boundaries (described later) and the interior of the particles in each sintered particle constituting the solid electrolyte ceramic. Furthermore, the Bi concentration between the vicinity of the grain boundaries (described later) and the interior of the particles can be substantially uniform, or it can have a gradient. The solid electrolyte ceramics of the present invention involving the former and the latter can be referred to as "solid electrolyte ceramics with a uniform Bi concentration structure" and "solid electrolyte ceramics with a gradient Bi concentration structure," respectively.

[0084] Alternatively, in one embodiment of the present invention, the solid electrolyte ceramic of the present invention is a "Bi concentration gradient structure-type solid electrolyte ceramic" in which the Bi concentration has a gradient between the vicinity of the grain boundaries and the interior of each sintered particle, and contains the aforementioned predetermined transition metal element. It should be noted that the Bi concentration gradient structure-type solid electrolyte ceramic of the present invention preferably has a chemical composition represented by the aforementioned general formula (I) or (II) in the vicinity of the grain boundaries and throughout the interior of each sintered particle.

[0085] In each sintered particle constituting the Bi concentration gradient structure type solid electrolyte ceramic of the present invention, in detail, the Bi concentration near the grain boundary is higher than the Bi concentration inside the particle. More specifically, Figure 1 As shown, when the solid electrolyte ceramic 10 of the present invention is composed of a plurality of sintered particles 1, the Bi concentration in the grain boundary vicinity 3 close to the grain boundary 2 in each sintered particle 1 is higher than the Bi concentration in the particle interior 4 surrounded by the grain boundary vicinity 3. By providing the solid electrolyte ceramic of the present invention with such a Bi concentration gradient and simultaneously containing a predetermined transition metal element, the effect of containing the predetermined transition metal element in the present invention (particularly, the effect of suppressing an increase in electronic conductivity during operation) can be further fully exerted. Figure 1 An enlarged schematic diagram of a solid electrolyte ceramic is shown for explaining the sintered particles and their structure constituting the Bi concentration gradient structure type solid electrolyte ceramic of the present invention. Figure 1 In FIG, only three sintered particles 1 are shown, but generally, a large number of sintered particles exist around them, forming grain boundaries between adjacent sintered particles.

[0086] The grain boundary vicinity 3 refers to a region (i.e., a region near the grain boundary) within 50 nm of the grain boundary 2 (i.e., the distance from the grain boundary 2 to the particle interior 4). Therefore, the grain boundary vicinity 3 is arranged at the outer edge of the sintered particle (e.g., when observed in cross section) and surrounds the particle interior 4 described later.

[0087] The Bi concentration of the portion 3 near the grain boundary is the average Bi amount (x1) of the region near the grain boundary mentioned above. In this specification, the Bi concentration of the portion 3 near the grain boundary is obtained by performing a point analysis on 10 points of the portion 3 near the grain boundary using TEM-EDX (energy dispersive X-ray spectroscopy) and using their average value. In detail, for each of any 10 sintered particles, a composition analysis is performed by performing a point analysis on any 10 points of the portion 3 near the grain boundary to obtain a Bi / D ratio. The Bi amount x in the general formula (I) above is calculated from the Bi / D ratio, and its average value is used. It should be noted that the portion 3 near the grain boundary of a sintered particle forms a grain boundary 2 between them together with the portion 3 near the grain boundary of one or more adjacent sintered particles.

[0088] The particle interior 4 is a region whose distance from the grain boundary 2 (i.e., the distance from the grain boundary 2 to the particle interior 4) exceeds 50 nm. Specifically, the particle interior 4 is an inner region surrounded by the grain boundary vicinity 3 (eg, in cross-sectional view).

[0089] The Bi concentration within the particle interior 4 is the average Bi amount (x2) within the particle interior 4 described above. In this specification, the Bi concentration within the particle interior 4 is the average value obtained by performing a point analysis of 10 points within the particle interior 4 using TEM-EDX (energy dispersive X-ray spectroscopy). Specifically, for each of 10 arbitrary sintered particles, a composition analysis is performed by performing point analysis of 10 arbitrary points within the particle interior 4 to obtain the Bi / D ratio. The Bi amount x in the general formula (I) described above is calculated from the Bi / D ratio, and the average value is used.

[0090] In the solid electrolyte ceramic material having a garnet-type crystal structure of the present invention, Bi can occupy six coordination sites in the garnet-type crystal structure. In a preferred embodiment, when the Bi amount x is twice the molar ratio of Bi in such six coordination sites, the Bi amount x in the grain boundary vicinity 3 (referred to as "x1" in this specification) and the Bi amount x in the particle interior 4 (referred to as "x2" in this specification) satisfy the following relationship:

[0091] x2<x1.

[0092] It should be noted that the 6-coordinate site in the garnet-type crystal structure referred to in the present invention refers to, for example, the site occupied by D in the chemical composition of the general formula (I). In other specific examples, the 6-coordinate site in the garnet-type crystal structure refers to, for example, Li5La3Nb2O having a garnet-type crystal structure. 12 The site occupied by Nb in (ICDDCardNo.00-045-0109) is also a garnet-type crystal structure Li7La3Zr2O 12 (ICDD Card No. 01-078-6708) The site occupied by Zr.

[0093] From the viewpoint of achieving superior ion conductivity and more adequately suppressing an increase in electronic conductivity during operation, the Bi amount x1 in the grain boundary vicinity 3 and the Bi amount x2 in the particle interior 4 preferably satisfy the relationship of the following embodiment p1, more preferably satisfy the relationship of the following embodiment p2, further preferably satisfy the relationship of the following embodiment p3, and particularly preferably satisfy the relationship of the following embodiment p4:

[0094] Implementation method p1:

[0095] 0<x1≤0.80; and

[0096] 0≤x2≤0.30.

[0097] Implementation method p2:

[0098] 0.20≤x1≤0.60; and

[0099] 0.01≤x2≤0.25.

[0100] Implementation method p3:

[0101] 0.30≤x1≤0.50; and

[0102] 0.05≤x2≤0.20.

[0103] Implementation method p4:

[0104] 0.35≤x1≤0.45; and

[0105] 0.08≤x2≤0.16.

[0106] From the viewpoint of achieving superior ion conductivity and more fully suppressing an increase in electronic conductivity during operation, the Bi amount x1 in the grain boundary vicinity 3 and the Bi amount x2 in the particle interior 4 preferably satisfy the relationship of the following embodiment q1, more preferably satisfy the relationship of the following embodiment q2, further preferably satisfy the relationship of the following embodiment q3, and particularly preferably satisfy the relationship of the following embodiment q4:

[0107] Implementation method q1:

[0108] 0.01≤x1-x2.

[0109] Implementation method q2:

[0110] 0.01≤x1-x2≤0.50.

[0111] Implementation method q3:

[0112] 0.10≤x1-x2≤0.40.

[0113] Implementation method q4:

[0114] 0.15≤x1-x2≤0.35.

[0115] The average particle size of the sintered particles constituting the solid electrolyte ceramic is usually greater than 100 nm and less than 100 μm, particularly greater than 200 nm and less than 10 μm.

[0116] The average particle size of the sintered particles is the average particle size of the sintered particles whose outer edges are defined by the grain boundaries.

[0117] In this specification, the average particle size of sintered particles is the average value of 100 random particles obtained by analyzing the particles using a TEM image and image analysis software (for example, "Azokun" (manufactured by Asahi Kasei Engineering Corporation)) and calculating the equivalent circle diameter.

[0118] [Method for producing solid electrolyte ceramics]

[0119] The solid electrolyte ceramic with a uniform Bi concentration structure of the present invention can be obtained by mixing a compound containing a predetermined metal element (i.e., a starting material) with water and then drying and heat-treating (e.g., at least calcining). The compound containing the predetermined metal element is generally a mixture of compounds containing a metal element selected from the group consisting of Li (lithium), La (lanthanum), Bi (bismuth), and a predetermined transition metal element. Examples of the compound containing the predetermined metal element (i.e., the starting material) include lithium hydroxide monohydrate LiOH·H2O, lanthanum hydroxide La(OH)3, zirconium oxide ZrO2, tantalum oxide Ta2O5, bismuth oxide Bi2O3, cobalt oxide Co3O4, alkaline nickel carbonate hydrate NiCO3·2Ni(OH)2·4H2O, and manganese carbonate MnCO3. The mixing ratio of the compound containing the predetermined metal element can be any ratio as long as the solid electrolyte ceramic of the present invention has a predetermined chemical composition after heat treatment. The heat treatment temperature is generally above 500°C and below 1200°C, preferably above 600°C and below 1000°C. The heat treatment time is usually 10 minutes to 1440 minutes, particularly 60 minutes to 600 minutes.

[0120] The Bi concentration gradient structure type solid electrolyte ceramic of the present invention can be obtained by heat treating (for example, at least sintering) in a state where a Bi-containing solid electrolyte layer as a shell layer exists around the Bi-free solid electrolyte particles as core particles. In detail, it can be obtained by causing Bi to diffuse from the shell layer to the core particles. In more detail, a solution in which the core particles and the shell forming material are dissolved is prepared and the two are mixed. Thereafter, the solvent is evaporated and heat treated to obtain solid electrolyte particles covered with a shell layer on the core particles. In addition, the solid electrolyte ceramic of the present invention can be obtained by heat treating the solid electrolyte particles covered with the shell layer. In addition, the above-mentioned manufacturing method is an example of obtaining the Bi concentration gradient structure type solid electrolyte ceramic material of the present invention, and it can also be produced by other manufacturing methods.

[0121] The core particles are Bi-free solid electrolyte particles, for example, particles composed of a solid electrolyte having a garnet-type crystal structure that does not contain Bi. As long as the Bi concentration gradient structure type solid electrolyte ceramic of the present invention can be obtained, the core particles can also use a solid electrolyte having a garnet-type crystal structure that contains Bi. The solid electrolyte used as the core particle, for example, except that x is in the range of 0≤x<1.0, can be the same material as the solid electrolyte having the chemical composition represented by the above-mentioned general formula (II). x is preferably in the same range as x2 in the above-mentioned embodiments p1 to p4. It should be noted that the core particles can be manufactured by the same method as the Bi concentration uniform structure type solid electrolyte ceramic of the present invention.

[0122] The chemical composition of the solid electrolyte constituting the core particles is not particularly limited. For example, the solid electrolyte ceramic of the present invention may have a chemical composition represented by the general formula (I) or (II) as a whole.

[0123] The average particle size of the core particles is usually more than 50 nm and 100 μm or less, particularly 100 nm or more and 10 μm or less.

[0124] In this specification, the average particle size of the core particles is a value measured by the same measuring method as that of the average particle size of the sintered particles.

[0125] The shell layer-forming material is a material used to form a Bi-containing solid electrolyte layer serving as the shell layer, and is, for example, a material mixture used to form a layer composed of a Bi-containing solid electrolyte having a garnet-type crystal structure. The mixing ratio in this material mixture is sufficient as long as the shell layer and the solid electrolyte ceramic of the present invention have a predetermined chemical composition after sintering. The Bi-containing solid electrolyte serving as the shell layer can be, for example, the same material as the solid electrolyte having the average chemical composition represented by the aforementioned general formula (II), except that x is within the same range as x1 in the aforementioned embodiments p1 to p4.

[0126] The chemical composition of the solid electrolyte constituting the shell layer is not particularly limited. For example, the solid electrolyte ceramic of the present invention may have a chemical composition represented by the general formula (I) or (II) as a whole.

[0127] The average thickness of the shell layer is usually more than 10 nm and 10 μm or less, and particularly not less than 20 nm and not more than 1 μm.

[0128] In this specification, the average film thickness of the shell layer can be calculated by performing TEM measurement on the core particle having the shell layer, measuring the film thickness of the shell layer at 20 arbitrary locations, and averaging the measured values.

[0129] The content of the shell layer forming material in the slurry is not particularly limited as long as the solid electrolyte ceramic of the present invention can be obtained. For example, it can be 1 mol% to 70 mol%, particularly 10 mol% to 50 mol%, relative to 100 mol% of the core particles.

[0130] The solvent is not particularly limited as long as it can dissolve the shell layer forming material. For example, a solvent that can be used in the manufacture of a positive electrode layer, a negative electrode layer, or a solid electrolyte layer in the field of solid batteries is used. As the solvent, a solvent that can be used with a binder described later is generally used. Examples of such solvents include alcohols such as 2-methoxyethanol.

[0131] The sintering conditions for forming the shell layer are not particularly limited as long as the Bi concentration gradient structure type solid electrolyte ceramic of the present invention can be obtained. For example, if the sintering conditions are too strong, the amount of Bi inside the particles becomes too high, and the Bi concentration gradient structure type solid electrolyte ceramic of the present invention cannot be obtained. In addition, for example, when the sintering conditions are too weak, elemental diffusion of Bi from the shell layer to the core particle does not occur, and the Bi concentration gradient structure type solid electrolyte ceramic of the present invention cannot be obtained. The sintering temperature can be, for example, 600°C or higher and 1100°C or lower, in particular 700°C or higher and 950°C or lower. The sintering time can be, for example, 10 minutes or higher and 1440 minutes or lower, in particular 60 minutes or higher and 600 minutes or lower.

[0132] As the sintering aid that can be included in the Bi concentration uniform structure type and Bi concentration gradient structure type solid electrolyte ceramic of the present invention, all sintering aids known in the field of solid batteries can be used. Such a sintering aid preferably contains at least Li (lithium), B (boron) and O (oxygen), and the molar ratio of Li to B (Li / B) is 2.0 or more. Specific examples of such a sintering aid include Li3BO3, (Li 2.7 Al 0.3 )BO3、Li 2.8 (B 0.8 C 0.2 )O3, LiBO2.

[0133] In particular, when the Bi concentration gradient structure type solid electrolyte ceramic of the present invention contains a sintering aid, from the perspective of Bi element diffusion, the less the content of the sintering aid, the better. The volume ratio relative to the garnet-type solid electrolyte is preferably greater than 0% and less than 10%, and particularly preferably greater than 0% and less than 5%.

[0134] [Solid-state battery]

[0135] The term "solid-state battery" as used in this specification refers broadly to a battery whose constituent elements (especially the electrolyte layer) are composed of solids, and narrowly to an "all-solid-state battery" whose constituent elements (especially all constituent elements) are composed of solids. The term "solid-state battery" as used in this specification includes so-called "secondary batteries" that can be repeatedly charged and discharged, and "primary batteries" that can only be discharged. "Solid-state battery" is preferably a "secondary battery." The term "secondary battery" is not overly restrictive in its name and may also include electrochemical devices such as "power storage devices," for example.

[0136] The solid battery of the present invention includes a positive electrode layer, a negative electrode layer and a solid electrolyte layer, and generally has a stacked structure in which the positive electrode layer and the negative electrode layer are stacked via a solid electrolyte layer. The positive electrode layer and the negative electrode layer can be stacked in two or more layers respectively as long as they have a solid electrolyte layer between them. The solid electrolyte layer is in contact with the positive electrode layer and the negative electrode layer and is sandwiched by them. It is also possible that the positive electrode layer and the solid electrolyte layer form a sintered body that is sintered together, and / or the negative electrode layer and the solid electrolyte layer form a sintered body that is sintered together. The so-called integral sintering of sintered bodies refers to the joining of two or more adjacent or contacting components (especially layers) by sintering. Here, the two or more components (especially layers) are all sintered bodies, but can also be sintered as a whole.

[0137] The solid electrolyte ceramic of the present invention is useful as a solid electrolyte for a solid-state battery. Therefore, the solid-state battery of the present invention includes the solid electrolyte ceramic of the present invention as a solid electrolyte. Specifically, the solid electrolyte ceramic of the present invention is included as a solid electrolyte in at least one layer selected from the group consisting of a positive electrode layer, a negative electrode layer, and a solid electrolyte layer. From the perspective of achieving superior ion conductivity in the solid electrolyte layer and more effectively suppressing an increase in electronic conductivity during operation, the solid electrolyte ceramic of the present invention is preferably included at least in the solid electrolyte layer.

[0138] (Positive electrode layer)

[0139] In the solid battery of the present invention, the positive electrode layer is not particularly limited. For example, the positive electrode layer contains a positive electrode active material and may further contain the solid electrolyte ceramic of the present invention. By containing the solid electrolyte ceramic of the present invention in the positive electrode layer, short circuit of the solid battery can be suppressed. The positive electrode layer may have the form of a sintered body containing positive electrode active material particles. The positive electrode layer may be a layer capable of intercalating and deintercalating ions (particularly lithium ions).

[0140] There is no particular limitation on the positive electrode active material, and the positive electrode active materials known in the field of solid batteries can be used. As the positive electrode active material, for example, lithium-containing phosphate compound particles having a NASICON structure, lithium-containing phosphate compound particles having an olivine structure, lithium-containing layered oxide particles, lithium-containing oxide particles having a spinel structure, etc. can be listed. As specific examples of lithium-containing phosphate compounds with a NASICON structure that are preferably used, Li3V2(PO4)3 and the like can be listed. As specific examples of lithium-containing phosphate compounds with an olivine structure that are preferably used, Li3Fe2(PO4)3, LiMnPO4 and the like can be listed. As specific examples of lithium-containing layered oxide particles that are preferably used, LiCoO2, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 As specific examples of lithium-containing oxides with a spinel structure preferably used, LiMn2O4, LiNi 0.5 Mn 1.5 O4、Li4Ti5O 12 From the viewpoint of reactivity when co-sintered with the garnet-type solid electrolyte used in the present invention, it is more preferable to use LiCoO2, LiCo 1 / 3 Ni 1 / 3Mn 1 / 3 It should be noted that only one of these positive electrode active material particles may be used, or a mixture of multiple types may be used.

[0141] The positive electrode active material having a NASICON structure in the positive electrode layer means that the positive electrode active material (especially its particles) has a NASICON crystal structure, which in a broad sense means a crystal structure that can be identified as a NASICON crystal structure by those skilled in the art in the field of solid batteries. In a narrow sense, the positive electrode active material having a NASICON structure in the positive electrode layer means that the positive electrode active material (especially its particles) shows one or more main peaks corresponding to the Miller index inherent to the so-called NASICON crystal structure in X-ray diffraction at a predetermined angle of incidence. As the preferred positive electrode active material having a NASICON structure, the compounds exemplified above can be listed.

[0142] The positive electrode active material having an olivine-type structure in the positive electrode layer means that the positive electrode active material (especially its particles) has an olivine-type crystal structure, which in a broad sense refers to a crystal structure that can be identified as an olivine-type crystal structure by those skilled in the art in the field of solid-state batteries. In a narrow sense, the positive electrode active material having an olivine-type structure in the positive electrode layer means that the positive electrode active material (especially its particles) shows one or more main peaks corresponding to the Miller index inherent in the so-called olivine-type crystal structure in X-ray diffraction at a predetermined angle of incidence. As the preferred positive electrode active material having an olivine-type structure, the compounds exemplified above can be listed.

[0143] The positive electrode active material having a spinel structure in the positive electrode layer means that the positive electrode active material (especially its particles) has a spinel crystal structure, and in a broad sense, refers to a crystal structure that can be identified as a spinel crystal structure by those skilled in the art in the field of solid batteries. In a narrow sense, the positive electrode active material having a spinel structure in the positive electrode layer means that the positive electrode active material (especially its particles) shows one or more main peaks corresponding to the Miller index inherent in the so-called spinel crystal structure in X-ray diffraction at a predetermined angle of incidence. As the preferred positive electrode active material with a spinel structure, the compounds exemplified above can be listed.

[0144] The chemical composition of the positive electrode active material may also be an average chemical composition. The average chemical composition of the positive electrode active material refers to the average value of the chemical composition of the positive electrode active material in the thickness direction of the positive electrode layer. The average chemical composition of the positive electrode active material can be analyzed and measured by breaking the solid battery and using SEM-EDX (energy dispersive X-ray spectroscopy) to perform composition analysis using EDX in the entire field of view in the thickness direction of the positive electrode layer.

[0145] The positive electrode active material can be produced, for example, by the following method or can be obtained as a commercial product. When producing the positive electrode active material, first, a raw material compound containing a predetermined metal atom is weighed so that the chemical composition becomes a predetermined chemical composition, and water is added and mixed to obtain a slurry. Next, the slurry is dried, pre-calcined at 700°C to 1000°C for 1 hour to 30 hours, and then pulverized to obtain the positive electrode active material.

[0146] The chemical composition and crystal structure of the positive electrode active material in the positive electrode layer generally change due to element diffusion during sintering. Alternatively, the positive electrode active material may have the above-mentioned chemical composition and crystal structure in a solid battery after the negative electrode layer and the solid electrolyte layer are sintered together.

[0147] The average particle size of the positive electrode active material is not particularly limited, and may be, for example, 0.01 μm or more and 10 μm or less, and preferably 0.05 μm or more and 4 μm or less.

[0148] The average particle size of the positive electrode active material can be determined by, for example, randomly selecting 10 or more and 100 or less particles from a SEM image and simply averaging their particle sizes (arithmetic mean).

[0149] The particle size is the diameter of a spherical particle assuming a perfectly spherical particle shape. This particle size can be determined, for example, by cutting a cross section of a solid-state battery, taking an SEM image of the cross section, and calculating the particle's cross-sectional area S using image analysis software (e.g., "Azokun" (manufactured by Asahi Kasei Engineering Corporation)). The particle diameter R can then be calculated using the following formula.

[0150] [Mathematical formula 1]

[0151] R=2×(S / π) 1 / 2

[0152] It should be noted that the average particle size of the positive electrode active material in the positive electrode layer can be automatically measured by identifying the positive electrode active material according to its composition during the measurement of the above-mentioned average chemical composition.

[0153] The average particle size of the positive electrode active material in the positive electrode layer generally changes due to sintering during the manufacturing process of the solid battery. The positive electrode active material may have the above average particle size in the solid battery after the negative electrode layer and the solid electrolyte layer are sintered together.

[0154] The volume ratio of the positive electrode active material in the positive electrode layer is not particularly limited, and may be, for example, 30% or more and 90% or less, and particularly 40% or more and 70% or less.

[0155] The positive electrode layer may contain the solid electrolyte ceramic of the present invention as a solid electrolyte, and / or may contain a solid electrolyte other than the solid electrolyte ceramic of the present invention.

[0156] The positive electrode layer may further contain a sintering aid and / or a conductive material.

[0157] When the positive electrode layer includes the solid electrolyte ceramic of the present invention, the volume ratio of the solid electrolyte ceramic of the present invention can generally be 20% to 60%, and particularly 30% to 45%.

[0158] As the sintering aid in the positive electrode layer, the same compounds as the sintering aid that can be contained in the solid electrolyte ceramic can be used.

[0159] The volume ratio of the sintering aid in the positive electrode layer is not particularly limited, but is preferably, for example, 0.1% to 20%, and more preferably 1% to 10%.

[0160] The conductive material in the positive electrode layer can be any conductive material known in the field of solid-state batteries. Preferred conductive materials include, for example, metal materials such as Ag (silver), Au (gold), Pd (palladium), Pt (platinum), Cu (copper), Sn (tin), and Ni (nickel); and carbon materials such as carbon nanotubes such as acetylene black, Ketjen Black, Super P (registered trademark), and VGCF (registered trademark). The shape of the carbon material is not particularly limited, and any shape such as spherical, plate-like, or fibrous can be used.

[0161] The volume ratio of the conductive material in the positive electrode layer is not particularly limited, but is preferably, for example, 10% to 50%, and more preferably 20% to 40%.

[0162] The thickness of the positive electrode layer is usually 0.1 to 30 μm, for example, preferably 1 to 20 μm. The thickness of the positive electrode layer is the average value of thicknesses measured at arbitrary 10 locations in the SEM image.

[0163] The porosity in the positive electrode layer is not particularly limited, but is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0164] The porosity of the positive electrode layer was measured using a SEM image of a cross-section processed by FIB.

[0165] The positive electrode layer is a layer that can be called a “positive electrode active material layer.” The positive electrode layer may include a so-called positive electrode current collector or a positive electrode current collecting layer.

[0166] (Negative electrode layer)

[0167] In the solid battery of the present invention, the negative electrode layer is not particularly limited. For example, the negative electrode layer contains a negative electrode active material and may further contain the solid electrolyte ceramic of the present invention. By containing the solid electrolyte ceramic of the present invention in the negative electrode layer, short circuiting of the solid battery can be suppressed. The negative electrode layer may have the form of a sintered body containing negative electrode active material particles. The negative electrode layer may be a layer capable of intercalating and deintercalating ions (particularly lithium ions).

[0168] The negative electrode active material is not particularly limited, and any negative electrode active material known in the field of solid batteries can be used. Examples of the negative electrode active material include carbon materials such as graphite, graphite-lithium compounds, lithium metal, lithium alloy particles, phosphate compounds having a NASICON structure, Li-containing oxides having a spinel structure, and β-type lithium-containing oxides. II -Li3VO4 type structure, γ II-Li3VO4 type structure oxides, etc. The negative electrode active material is preferably lithium metal, II -Li3VO4 type structure, γ II -Li3VO4 type Li-containing oxide.

[0169] In the negative electrode layer, the oxide has β II -Li3VO4 type structure means that the oxide (especially its particles) has β II -Li3VO4 type crystal structure, in a broad sense, refers to a structure that can be identified as β by those skilled in the art in the field of solid state batteries II -Li3VO4 type crystal structure. In a narrow sense, the oxide in the negative electrode layer has β II -Li3VO4 type structure means that the oxide (especially its particles) shows the same as the so-called β-type structure in X-ray diffraction at a predetermined incident angle. II -Li3VO4 type crystal structure has one or more main peaks corresponding to the Miller index. II -Li3VO4 type Li-containing oxides include Li3VO4.

[0170] In the negative electrode layer, the oxide has γ II -Li3VO4 type structure means that the oxide (especially its particles) has γ II -Li3VO4 type crystal structure, in a broad sense, refers to a structure that can be identified as γ-Li3VO4 by those skilled in the art in the field of solid-state batteries. II -Li3VO4 type crystal structure. In a narrow sense, the oxide in the negative electrode layer has γ II -Li3VO4 type structure means that the oxide (especially its particles) shows the same as the so-called γ-ray diffraction at a predetermined incident angle (x axis) in X-ray diffraction. II -Li3VO4 type crystal structure has one or more main peaks corresponding to the Miller index. II -Li3VO4 type Li-containing oxides, including Li 3.2 V 0.8 Si 0.2 O4.

[0171] The chemical composition of the negative electrode active material may be an average chemical composition. The average chemical composition of the negative electrode active material refers to the average chemical composition of the negative electrode active material in the thickness direction of the negative electrode layer. The average chemical composition of the negative electrode active material can be analyzed and measured by fracturing the solid-state battery and performing composition analysis using SEM-EDX (energy dispersive X-ray spectroscopy) in the field of view of the entire thickness direction of the negative electrode layer using EDX.

[0172] The negative electrode active material can be produced by, for example, the same method as that for the positive electrode active material, or can be obtained as a commercial product.

[0173] The chemical composition and crystal structure of the negative electrode active material in the negative electrode layer typically vary due to elemental diffusion during sintering during the solid battery manufacturing process. Alternatively, the negative electrode active material may have the aforementioned average chemical composition and crystal structure in the solid battery after the positive electrode layer and solid electrolyte layer are sintered together.

[0174] The volume ratio of the negative electrode active material in the negative electrode layer is not particularly limited, but is preferably 50% or more (particularly 50% or more and 99% or less), more preferably 70% or more and 95% or less, and even more preferably 80% or more and 90% or less, for example.

[0175] The negative electrode layer may contain the solid electrolyte ceramic of the present invention as a solid electrolyte, and / or may contain a solid electrolyte other than the solid electrolyte ceramic of the present invention.

[0176] The negative electrode layer may further contain a sintering aid and / or a conductive material.

[0177] When the negative electrode layer includes the solid electrolyte ceramic of the present invention, the volume ratio of the solid electrolyte ceramic of the present invention can generally be 20% to 60%, particularly 30% to 45%.

[0178] As the sintering aid in the negative electrode layer, the same compound as the sintering aid in the positive electrode layer can be used.

[0179] As the conductive material in the negative electrode layer, the same compound as the conductive material in the positive electrode layer can be used.

[0180] The thickness of the negative electrode layer is usually 0.1 to 30 μm, preferably 1 to 20 μm. The thickness of the negative electrode layer is the average value of thicknesses measured at arbitrary 10 locations in the SEM image.

[0181] The porosity in the negative electrode layer is not particularly limited, but is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0182] The porosity of the negative electrode layer was measured using the same method as that for the porosity of the positive electrode layer.

[0183] The negative electrode layer is a layer that can be called a “negative electrode active material layer.” The negative electrode layer may include a so-called negative electrode current collector or a negative electrode current collecting layer.

[0184] (Solid electrolyte layer)

[0185] In the solid battery of the present invention, the solid electrolyte layer preferably includes the above-mentioned solid electrolyte ceramic of the present invention from the viewpoint of achieving more excellent ion conductivity and more fully suppressing an increase in electron conductivity during operation.

[0186] The volume ratio of the solid electrolyte ceramic of the present invention in the solid electrolyte layer is not particularly limited. From the viewpoint of achieving better ion conductivity and more fully suppressing the increase in electronic conductivity during operation, it is preferably 10% or more and 100% or less, more preferably 20% or more and 100% or less, and even more preferably 30% or more and 100% or less.

[0187] When the solid electrolyte layer comprises the solid electrolyte ceramic of the present invention, it is sufficient that the solid electrolyte ceramic of the present invention having the chemical composition described above is present at least in the central portion of the thickness direction of the solid electrolyte layer (particularly at least 5 points, preferably at least 8 points, and more preferably at least 10 points out of any 10 points). This is because the solid electrolyte layer is sandwiched between the positive electrode layer and the negative electrode layer, and sintering during the solid battery manufacturing process may cause element diffusion from the positive electrode layer and the negative electrode layer into the solid electrolyte layer and / or element diffusion from the solid electrolyte layer into the positive electrode layer and the negative electrode layer.

[0188] The solid electrolyte layer may contain, in addition to the garnet-type solid electrolyte ceramic of the present invention, one or more materials selected from a solid electrolyte composed of at least Li, Zr, and O, a solid electrolyte having a γ-Li3VO4 structure, and an oxide glass-ceramic lithium ion conductor. An example of a solid electrolyte composed of at least Li, Zr, and O is Li2ZrO3.

[0189] Examples of the solid electrolyte having a γ-Li 3 VO 4 structure include a solid electrolyte having an average chemical composition represented by the following general formula (III).

[0190] [Chemical Formula 3]

[0191] (Li [3-ax+(5-c)(1-y) ]A x )(B y D 1-y )O4 (III)

[0192] In formula (III), A is one or more elements selected from the group consisting of Na, K, Mg, Ca, Al, Ga, Zn, Fe, Cr, and Co.

[0193] B is one or more elements selected from the group consisting of V and P.

[0194] D is one or more elements selected from the group consisting of Zn, Al, Ga, Si, Ge, Sn, As, Ti, Mo, W, Fe, Cr, and Co.

[0195] x satisfies 0≤x≤1.0, in particular, 0≤x≤0.2.

[0196] y satisfies 0≤y≤1.0, in particular, 0.20≤y≤0.50.

[0197] a is the average valence of A. For example, when n1 elements X with a valence of a+, n2 elements Y with a valence of b+, and n3 elements Z with a valence of c+ are considered as A, the average valence of A is represented by (n1×a+n2×b+n3×c) / (n1+n2+n3).

[0198] c is the average valence of D. For example, when D is considered to include n1 elements X with a valence of a+, n2 elements Y with a valence of b+, and n3 elements Z with a valence of c+, the average valence of D is the same as the average valence of A described above.

[0199] As specific examples of solid electrolytes having a γ-Li3VO4 structure, for example, Li 3.2 (V 0.8 Si 0.2 )O4、Li 3.5 (V 0.5 Ge 0.5 )O4、Li 3.4 (P 0.6 Si 0.4 )O4、Li 3.5 (P 0.5 Ge 0.5 )O4, etc.

[0200] As the oxide glass ceramic-based lithium ion conductor, for example, a phosphate compound containing lithium, aluminum, and titanium as constituent elements (LATP) and a phosphate compound containing lithium, aluminum, and germanium as constituent elements (LAGP) can be used.

[0201] The solid electrolyte layer may contain, in addition to the solid electrolyte, for example, a sintering aid and the like.

[0202] As the sintering aid in the solid electrolyte layer, the same compound as the sintering aid in the positive electrode layer can be used.

[0203] The volume ratio of the sintering aid in the solid electrolyte layer is not particularly limited, but is preferably 0% to 20%, more preferably 1% to 10%, from the viewpoint of achieving better ion conductivity and more adequately suppressing an increase in electronic conductivity during operation.

[0204] The thickness of the solid electrolyte layer is generally 0.1 to 30 μm, and preferably 1 to 20 μm from the viewpoint of better ion conductivity and more sufficient suppression of an increase in electronic conductivity during operation. The thickness of the solid electrolyte layer is the average value of thicknesses measured at arbitrary 10 locations in the SEM image.

[0205] The porosity in the solid electrolyte layer is not particularly limited, but is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less from the viewpoint of achieving superior ion conductivity and more adequately suppressing an increase in electronic conductivity during operation.

[0206] The porosity of the solid electrolyte layer was measured using the same method as that for the porosity of the positive electrode layer.

[0207] [Method for manufacturing solid-state batteries]

[0208] Solid-state batteries can be produced, for example, by a so-called green sheet method, a printing method, or a method combining these methods.

[0209] The green film method will be described.

[0210] First, a paste is prepared by mixing a solvent, a binder, and other ingredients with the positive electrode active material. This paste is applied to a sheet and dried to form a first green sheet, which will form the positive electrode layer. This first green sheet may contain a solid electrolyte, a conductive material, and / or a sintering aid.

[0211] A paste is prepared by mixing a suitable solvent, binder, and other ingredients with the negative electrode active material. This paste is applied to a sheet and dried to form a second green sheet for the negative electrode layer. The second green sheet may contain a solid electrolyte, a conductive material, and / or a sintering aid.

[0212] A paste is prepared by appropriately mixing a solvent, a binder, etc. with a solid electrolyte. This paste is applied and dried to produce a third green sheet for forming the solid electrolyte layer. The third green sheet may contain a sintering aid, etc.

[0213] The solvent used to prepare the first to third green sheets is not particularly limited; for example, any solvent that can be used to produce positive electrode layers, negative electrode layers, or solid electrolyte layers in the field of solid-state batteries can be used. Typically, a solvent that can be used with the binder described below is used. Examples of such solvents include alcohols such as 2-propanol.

[0214] The binder used to prepare the first to third green sheets is not particularly limited. For example, a binder that can be used to prepare positive electrode layers, negative electrode layers, or solid electrolyte layers in the field of solid batteries can be used. Examples of such binders include butyral resins and acrylic resins.

[0215] Next, the first to third green sheets are stacked as appropriate to produce a laminate. The produced laminate may be pressed. Preferred pressing methods include hydrostatic pressing.

[0216] Thereafter, the stacked body is sintered at, for example, 600 to 800° C. to obtain a solid battery.

[0217] The printing method will be described.

[0218] The printing method is the same as the green sheet method except for the following matters.

[0219] Ink for each layer is prepared having the same composition as that of the paste for obtaining each layer of the green sheet, except that the blending amounts of the solvent and the resin are adjusted to amounts suitable for use as ink.

[0220] Print and stack using ink for each layer to create a laminate.

[0221] Hereinafter, the present invention will be described in more detail based on specific examples. However, the present invention is not limited to the following examples and can be implemented with appropriate modifications within the scope of the present invention.

[0222] Example

[0223] <Experimental Example 1: Bi-Concentration Uniform Structure-Type Solid Electrolyte Ceramic>

[0224] <Examples 1A to 14A, 1B to 3B, 1C to 4C, and Comparative Example 1>

[0225] [Manufacturing of solid electrolyte ceramics]

[0226] The raw materials used were lithium hydroxide monohydrate LiOH·H2O, lanthanum hydroxide La(OH)3, zirconium oxide ZrO2, tantalum oxide Ta2O5, bismuth oxide Bi2O3, cobalt oxide Co3O4, basic nickel carbonate hydrate NiCO3·2Ni(OH)2·4H2O, and manganese carbonate MnCO3.

[0227] Each starting material was weighed so that the chemical composition became the chemical composition shown in Table 1, Table 2, or Table 3.

[0228] Water was added, the mixture was sealed in a polyethylene polymer tank, and the mixture was rotated at 150 rpm on a tank stand for 16 hours to mix the raw materials.

[0229] Furthermore, in consideration of Li deficiency during sintering, lithium hydroxide monohydrate LiOH·H 2 O was added in an excess amount of 3 wt % as a Li source relative to the target composition.

[0230] The obtained slurry was evaporated and dried, and then pre-calcined at 900° C. for 5 hours in O 2 to obtain the target phase.

[0231] A toluene-acetone mixed solvent was added to the calcined powder obtained and the powder was pulverized in a planetary ball mill for 12 hours. ICP analysis of the pulverized powder confirmed that there was no compositional variation. The average particle size of the pulverized powder at this time was 150 nm.

[0232] [Manufacturing of solid electrolyte single sheets]

[0233] As a sample for evaluating the solid electrolyte ceramic, a solid electrolyte single plate was produced by the following method.

[0234] The obtained pulverized powder was kneaded with a butyral resin, alcohol, and a binder to produce a slurry.

[0235] The slurry was sheet-formed onto a PET film using a doctor blade method to produce a sheet. The sheets were stacked until the thickness reached 200 μm and then cut into 10 mm x 10 mm squares. After removing the binder at 400°C, the sheets were pressurized and sintered at 950°C and 100 MPa for 300 minutes to produce a solid electrolyte single plate. The porosity of the solid electrolyte single plate was less than 10%, confirming that the sintering was sufficient. The surface of the resulting sintered body was polished to obtain a garnet solid electrolyte substrate.

[0236] [Crystal structure of solid electrolyte single plate]

[0237] In all the examples and comparative examples, X-ray diffraction analysis of the solid electrolyte single plate confirmed that an X-ray diffraction pattern attributable to a garnet-type crystal structure was obtained (ICD DCard No. 00-045-0109).

[0238] [Chemical composition of solid electrolyte single plate]

[0239] ICP-AES analysis of the solid electrolyte single plate was performed to obtain the average chemical composition of the solid electrolyte single plate. The Co, Mn, and Ni contents in the average chemical composition of the entire solid electrolyte single plate were calculated as the ratio when the B content in the garnet-type crystal structure of the general formula (I) (for example, the total of La and B in the general formula (II)) was taken as 100 mol%.

[0240] In Example 2A, quantitative analysis was also performed using LA-ICP-MS, and similar results were confirmed.

[0241] In Examples 4A, 5A, 13A, and 14A, quantitative analysis using WDX confirmed equivalent results.

[0242] [Electron conductivity measurement (before and after storage test)]

[0243] An Au electrode was sputtered onto one side of the resulting single plate to serve as the working electrode. Lithium metal with the same surface area as the Au electrode was bonded to the other side. Finally, the cell was sealed in a 2035-size coin battery to serve as an evaluation cell. All of the above operations were performed in a dry room with a dew point below -40°C.

[0244] A voltage of 2 V relative to Li was applied to the working electrode at room temperature, and the transient current was observed. The current flowing after 10 hours of voltage application was read as the leakage current before the storage test. It should be noted that the leakage current value before the storage test was confirmed to be approximately 1×10 -10 ~6×10 -7 S / cm. The battery cell was then stored at 90°C for approximately one month, and the above test was repeated. The leakage current after the storage test was read. The electron conductivity was calculated from the leakage current using the following formula.

[0245] Electron conductivity = (I / V) × (L / A)

[0246] (I: leakage current, V: applied voltage, L: solid electrolyte single plate thickness, A: electrode area)

[0247] The electron conductivity after the storage test was evaluated according to the following criteria.

[0248] ◎: Electronic conductivity <1.0×10 -8 S / cm (excellent);

[0249] ○:1.0×10 -8 S / cm≤Electronic conductivity<1.0×10 -7 S / cm (good);

[0250] △: 1.0×10 -7 S / cm≤Electronic conductivity<1.0×10 -6 S / cm (ok) (no problem in practice);

[0251] ×: 1.0×10 -6 S / cm ≤ electron conductivity (not possible) (problematic in practice).

[0252] [Ionic conductivity measurement]

[0253] Gold (Au) layers, serving as current collector layers, were formed on both sides of the solid electrolyte sheet by sputtering, and then sandwiched and secured with SUS current collectors. The ionic conductivity of each solid electrolyte tablet was evaluated by AC impedance measurement at room temperature (25°C) within a frequency range of 0.1 Hz to 10 MHz (±50 mV).

[0254] ◎:5.0×10 -4 S / cm≤ ionic conductivity (excellent);

[0255] ○:1.0×10 -4 S / cm≤ ion conductivity<5.0×10- 4 S / cm (good);

[0256] △: 5.0×10 -5 S / cm≤ionic conductivity<1.0×10 -4 S / cm (ok) (no problem in practice);

[0257] ×: Ionic conductivity <5.0×10 -5 S / cm (not possible) (problematic in practice).

[0258]

[0259]

[0260]

[0261] The following can be seen from Table 1.

[0262] Comparative Example 1 shows that the electronic conductivity of the Bi-substituted garnet-type solid electrolyte increases dramatically when subjected to a storage test at 90°C with Li attached. This is presumably because the Bi-substituted garnet-type solid electrolyte readily forms Li-Bi-O compounds as a heterogeneous phase at the grain boundaries, and these Li-Bi-O compounds are reduced by Li, thereby exhibiting electronic conductivity.

[0263] Comparison of Comparative Example 1 with Examples 1A to 12A shows that the electronic conductivity after the storage test is significantly reduced by Bi-substituted garnet-type solid electrolytes containing one or more transition metal elements selected from Co, Mn, and Ni. This is believed to be because Bi-substituted garnet-type solid electrolytes containing one or more transition metal elements selected from Co, Mn, and Ni can suppress the formation of Li-Bi-O compounds, which are the main cause of electronic conductivity.

[0264] From the above, it can be seen that by replacing the garnet-type solid electrolyte with Bi and containing one or more transition metal elements selected from Co, Mn and Ni, an all-solid-state battery with low leakage current even at high temperatures can be constructed.

[0265] Comparison of Examples 1A to 6A shows that the leakage current after the storage test also changes depending on the Co content. It can be seen that the Co content is preferably greater than 0 mol% and less than 1.20 mol%, and more preferably greater than 0 mol% and less than 0.25 mol%. In other words, it can be seen that even with excessive Co content, electronic conductivity increases. This is believed to be because, while increasing the Co content suppresses the formation of Li-Bi-O compounds, excessively increasing the Co content results in the formation of a Li-La-Co-O-based heterogeneous phase with electronic conductivity.

[0266] From the measurement of electronic conductivity before storage, if the amount of Co added is too large, the electronic conductivity before storage becomes higher. Therefore, when the total content of transition metal elements is set to 100 mol%, it is preferably greater than 0 mol% and less than 1.20 mol%, more preferably greater than 0 mol% and less than 0.50 mol% (for example, greater than 0.01 mol% and less than 0.50 mol%), and further preferably greater than 0 mol% and less than 0.25 mol% (for example, greater than 0.01 mol% and less than 0.20 mol%).

[0267] Comparison of Examples 4A to 12A shows that, among Ni, Mn, and Co, the effect of reducing the electronic conductivity is particularly significant when the Bi-substituted garnet-type solid electrolyte contains Co.

[0268] The following can be seen from Table 2.

[0269] From Examples 3A and 1B to 3B, it can be seen that the amount of Bi substitution in the garnet-type solid electrolyte affects the electronic conductivity after the storage test. From the perspective of the decrease in electronic conductivity after the storage test, it can be seen that a smaller amount of Bi substitution is preferred. It can be seen that the electronic conductivity is greatly increased in Example 3B. This is believed to be because if the amount of Bi substitution in the garnet-type solid electrolyte is too large, not only will Li-Bi-O compounds be easily generated, but the garnet-type solid electrolyte itself will be easily reduced and decomposed.

[0270] The following can be seen from Table 3.

[0271] As can be seen from Examples 1C to 4C, the effects of the present invention can be obtained even when γ in the general formula (I) has various values.

[0272] <Experimental Example 2: Bi Concentration Uniform Structure Type and Bi Concentration Gradient Structure Type Solid Electrolyte Ceramics>

[0273] <Example 1D and Comparative Example 2>

[0274] Except for weighing the starting materials so that the chemical composition becomes the chemical composition of Table 3, the same method as Example 1A was used to manufacture Bi concentration uniform structure solid electrolyte ceramics and solid electrolyte single plates, evaluate the crystal structure and chemical composition of the solid electrolyte single plates, and measure the electronic conductivity and ionic conductivity.

[0275] In these Examples and Comparative Examples, X-ray diffraction of the solid electrolyte single plate confirmed that an X-ray diffraction pattern attributable to a garnet-type crystal structure was obtained (ICD DCard No. 00-045-0109).

[0276] <Example 2D and Comparative Example 3>

[0277] Except for using a Bi concentration gradient structure solid electrolyte ceramic manufactured by the following method, the same method as Example 1A was used to manufacture a solid electrolyte single plate, evaluate the crystal structure and chemical composition of the solid electrolyte single plate, and measure the electronic conductivity and ionic conductivity.

[0278] In these examples and comparative examples, X-ray diffraction analysis of the solid electrolyte single plate confirmed that the ceramic single plate produced an X-ray diffraction pattern attributable to a garnet-type crystal structure (ICD DCard No. 00-045-0109). Furthermore, TEM-EDX analysis confirmed a Bi concentration gradient structure.

[0279] [Manufacturing of a solid electrolyte ceramic with a Bi concentration gradient structure]

[0280] Core particles and shell layers for manufacturing a solid electrolyte ceramic having a Bi concentration gradient structure were manufactured.

[0281] (Manufacturing of Core Particles)

[0282] As core particles, garnet-type solid electrolyte powder was produced as follows.

[0283] The raw materials used were lithium hydroxide monohydrate LiOH·H2O, lanthanum hydroxide La(OH)3, zirconium oxide ZrO2, tantalum oxide Ta2O5, bismuth oxide Bi2O3, and cobalt oxide Co3O4.

[0284] Weigh the raw materials so that the chemical composition is Li 6.6 La3(Zr 1.6 Ta 0.4 )O 12 , in Example 2D, Li 6.6 La3(Zr1.6 Ta0 .4 )O 12 The raw materials were mixed by adding water to a 100ml polyethylene polymer tank and rotating it on a tank stand at 150 rpm for 16 hours. Furthermore, lithium hydroxide monohydrate (LiOH·H2O) was added as a lithium source in an amount exceeding the target composition by 3 wt% to account for lithium deficiency during sintering.

[0285] The obtained slurry was evaporated and dried, and then calcined at 900° C. for 5 hours to obtain the target phase.

[0286] A mixed solvent of toluene and acetone was added to the obtained calcined powder, and the mixture was pulverized using a planetary ball mill for 6 hours.

[0287] The pulverized powder was dried to prepare a solid electrolyte powder. ICP analysis of the powder confirmed no compositional deviation. The average particle size of the core particles at this time was 150 nm.

[0288] In the examples and comparative examples, the primary particle size of the material was not changed, and the structure and composition were controlled by the composition, molar ratio, and calcination time of the core phase and the shell phase.

[0289] (Production of a powder in which core particles are covered with a shell layer)

[0290] A powder in which core particles were covered with a garnet-type solid electrolyte as a shell layer was produced as follows.

[0291] The raw materials used were lithium nitrate LiNO3, lanthanum nitrate hexahydrate La(NO3)3·6H2O, bismuth nitrate pentahydrate Bi(NO3)3·5H2O, zirconium (IV) isopropoxide Zr(OC3H7)4, tantalum (V) ethoxide Ta(OC2H5)5, cobalt nitrate hexahydrate Co(NO3)2·6H2O, and ethyl acetoacetate. The materials were weighed so that the Li 6.0 La3(Zr 1.0 Ta 0.4 Bi 0.6 )O 12 , in Example 2D, Li 6.0 La3(Zr 1.0 Ta 0.4 Bi 0.6 )O 12-0.0050Co chemical composition. In addition, ethyl acetoacetate was weighed so as to be 4 times the molar amount relative to each alkoxide. First, each alkoxide and ethyl acetoacetate were placed in a glass container and stirred for 30 minutes using a stirring plate (as solution A). Next, each nitrate and 2-methoxyethanol were placed in a glass container to dissolve the nitrate (as solution B). A uniform solution C was prepared by adding solution A little by little to solution B. After mixing the predetermined core particles into solution C, the mixture was mixed for 5 hours using a stirring plate, and then the solvent was evaporated at 100°C. By heat treating the obtained dry powder at 700°C for 5 hours, a garnet-type solid electrolyte powder having a shell layer on the core particles was obtained.

[0292] In addition, only Solution C was dried and then heat-treated at 700° C. for 5 hours to obtain a shell layer powder.

[0293] XRD analysis of the shell layer powder confirmed that a garnet-type solid electrolyte monomer was obtained. In addition, ICP analysis confirmed that the powder had no compositional deviation in the shell layer.

[0294] [Measurement]

[0295] (Bi content near grain boundaries (x1))

[0296] After processing the solid electrolyte sheet into a thin sheet using FIB processing, quantitative analysis (composition analysis) was performed using TEM-EDX (energy dispersive X-ray spectroscopy). EDX was used to analyze 20 points in the vicinity of the grain boundaries of each of the ten sintered particles. This yielded the Bi / D ratio in the vicinity of the grain boundaries. The Bi amount x in formula (I) was calculated from the Bi / D ratio in the vicinity of the grain boundaries, and this was taken as the Bi amount (x1) in the vicinity of the grain boundaries.

[0297] (Amount of Bi inside the particle (x2))

[0298] After processing the solid electrolyte sheet into a thin sheet using FIB processing, quantitative analysis (compositional analysis) was performed using TEM-EDX (energy dispersive X-ray spectroscopy). EDX was used to analyze 20 points within each of 10 random sintered particles. This yielded the Bi / D ratio within the particles. The Bi content x in equation (I) was calculated from the Bi / D ratio within the particles, and this was used as the Bi content (x2) near the grain boundaries.

[0299]

[0300] The following can be seen from Table 3.

[0301] Although the same average chemical composition is present in Comparative Examples 2 and 3, the electronic conductivity after the storage test of the garnet-type solid electrolyte in which the Bi substitution amount increases near the grain boundary is shown in Comparative Example 3. According to the comparison between Comparative Examples 2 and 3 and the comparison between Example 1D and Example 2D, in the solid electrolyte in which the Bi substitution amount increases near the grain boundary, the electronic conductivity after the storage test increases compared to the solid electrolyte in which Bi is uniformly dissolved. It can be considered that this is because the Bi substitution amount near the grain boundary increases, making it easier to form a Li-Bi-O system heterogeneous phase at the grain boundary. From the comparison between Comparative Example 3 and Example 2D, it can be seen that by containing Co in the solid electrolyte, the electronic conductivity after the storage test is significantly improved even in the garnet-type solid electrolyte in which the Bi substitution amount increases near the grain boundary. In addition, it can be seen that in the garnet-type solid electrolyte in which the Bi substitution amount increases near the grain boundary (Example 2D), the effect of containing Co is particularly large compared to the solid electrolyte in which Bi is uniformly dissolved (Comparative Example 2, Example 1D). This shows that the effect of the present invention is particularly effective for a garnet-type solid electrolyte in which the Bi substitution amount increases near the grain boundary.

[0302] (TEM-EELS measurement)

[0303] The solid electrolyte used in Example 5A and lithium cobalt oxide LiCoO2 were weighed so as to have a volume ratio of 1:1 to prepare a mixed powder.

[0304] The obtained mixed powder was kneaded with butyral resin, alcohol, and a binder to produce a slurry.

[0305] The slurry was formed into a sheet on a PET film using a doctor blade method to obtain a positive electrode sheet.

[0306] The solid electrolyte sheets prepared in the same manner as in Example 5A were stacked to a thickness of 200 μm to form a solid electrolyte stack. The positive electrode sheets prepared above were stacked to a thickness of 30 μm to form a positive electrode stack. The obtained solid electrolyte stack and the positive electrode stack were stacked and then pressed together to form a positive electrode / solid electrolyte sheet stack. The sheets were cut into square shapes of 10 mm × 10 mm in size, and after removing the binder at 400°C, they were pressure-sintered at 800°C at a pressure of 100 MPa for 120 minutes to form a positive electrode / solid electrolyte co-fired body. Li metal was attached to the surface of the obtained positive electrode / solid electrolyte co-fired body opposite to the positive electrode, thereby producing a positive electrode half-cell.

[0307] The positive electrode layer of the prepared positive electrode half-cell was peeled by FIB processing, and EELS measurement of the solid electrolyte particles in the positive electrode layer was performed using TEM (JEOL - JEM-ARM200FNEOARMex) and EELS (Gatan ContinuumER). The EELS spectrum obtained by measuring the bulk particles in the solid electrolyte is as follows: Figure 2 As shown. The peak from the L end of Co was detected, which shows that Co is contained in the solid electrolyte particles. In addition, it can be seen that its peak position (LLZ) is observed on the low energy side compared with the peak position of LiCoO2 (lithium cobalt oxide) (LCO) of the reference material. Regarding Example 5A, the offset width sw (reference) of the peak position of the Co L end of the solid electrolyte ceramic (LLZ) of the present invention and the peak position of the Co L end of LiCoO2 (LCO) is Figure 2 ) is 0.9eV.

[0308] As a quantitative method, the first differential peak intensity of the obtained EELS spectrum was used. Specifically, the maximum value I was read from the peaks at the Co L end and LaM end in the first differential spectrum. max and minimum value I min , their difference (I max -I min ) as the peak intensity, and the Co / La ratio was calculated by dividing the peak intensity at the L end of Co by the peak intensity at the M end of La. In this way, EELS measurements were performed at five arbitrary points within the solid electrolyte particle, and the Co / La ratios were calculated for each. These values ​​were averaged to obtain the Co / La ratio. The result showed that the Co / La ratio was 0.8%, which was approximately the same as the value measured by ICP.

[0309] Industrial applicability

[0310] The solid battery including the solid electrolyte ceramic of the present invention can be applied to various fields where batteries or power storage are expected to be used. Although this is merely an example, the solid battery according to one embodiment of the present invention can be applied to the field of electronic devices. The solid battery involved in one embodiment of the present invention can also be applied to the following fields: electrical, information and communication fields using mobile devices, etc. (for example, electrical and electronic equipment fields or mobile equipment fields including small electronic devices such as portable phones, smart phones, smart watches, laptops, digital cameras, activity meters, ARM computers, electronic paper, wearable devices, RFID tags, card-type electronic currency, smart watches, etc.); household and small industrial uses (for example, the fields of power tools, golf carts, household, nursing and industrial robots); large industrial uses (for example, the fields of forklifts, elevators, and port cranes); transportation system fields (for example, hybrid vehicles, electric vehicles, buses, trams, electric bicycles, electric motorcycles, etc.); power system uses (for example, various power generation, load regulators, smart grids, general household installation type storage systems, etc.); medical uses (medical equipment fields such as headphones and hearing aids); pharmaceutical uses (dosage management systems, etc.); and IoT fields; space and deep sea uses (for example, space probes, submersible research vessels, etc.), etc.

Claims

1. A solid electrolyte ceramic having a garnet crystal structure, The solid electrolyte ceramic contains at least Li (lithium), La (lanthanum), Bi (bismuth) and O (oxygen). The solid electrolyte ceramic further contains one or more transition metal elements selected from the group consisting of Co (cobalt), Ni (nickel), and Mn (manganese). The solid electrolyte ceramic further contains element D, wherein the element D is one or more elements selected from the group consisting of transition elements capable of forming hexacoordinates with oxygen and typical elements belonging to Groups 12 to 15, and contains at least Bi (bismuth), wherein the content of Bi (bismuth) is greater than 0 mol% and less than 25 mol% when the content of the element D is 100 mol%. The Bi concentration in the vicinity of the grain boundary is higher than the Bi concentration in the interior of the particle.

2. The solid electrolyte ceramic according to claim 1, wherein The solid electrolyte ceramic has a chemical composition represented by the following general formula (I), and further contains one or more transition metal elements: In formula (I), A is one or more elements selected from the group consisting of Li (lithium), Ga (gallium), Al (aluminum), Mg (magnesium), Zn (zinc), and Sc (scandium), and includes at least Li (lithium); B is one or more elements selected from the group consisting of Ca (calcium), Sr (strontium), Ba (barium), and lanthanoid elements, and includes at least La (lanthanum); D is the element D and contains at least Bi (bismuth); α satisfies 5.0≤α≤8.0; β satisfies 2.5≤β≤3.5; γ satisfies 1.5≤γ≤2.5; ω satisfies 11≤ω≤13.

3. The solid electrolyte ceramic according to claim 2, wherein When the B content is 100 mol %, the total content of the one or more transition metal elements is more than 0 mol % and 3.50 mol % or less.

4. The solid electrolyte ceramic according to claim 2, wherein When the B content is 100 mol %, the total content of the one or more transition metal elements is more than 0 mol % and 1.20 mol % or less.

5. The solid electrolyte ceramic according to claim 2, wherein When the B content is 100 mol %, the total content of the one or more transition metal elements is more than 0 mol % and 0.25 mol % or less.

6. The solid electrolyte ceramic according to any one of claims 1 to 5, wherein The one or more transition metal elements contain Co.

7. The solid electrolyte ceramic according to any one of claims 1 to 5, wherein Regarding Bi, when the amount x is twice the molar ratio of Bi in D in the garnet-type crystal structure, the amount x of Bi near the grain boundary (i.e., x1) and the amount x inside the particle (i.e., x2) satisfy the following relationship: x2<x1.

8. The solid electrolyte ceramic according to claim 7, wherein The Bi amount x1 near the grain boundary and the Bi amount x2 inside the particle satisfy the following relationship: 0<x1≤0.80; and 0≤x2≤0.30。 9. The solid electrolyte ceramic according to claim 7, wherein The Bi amount x1 near the grain boundary and the Bi amount x2 inside the particle satisfy the following relationship: 0.01≤x1-x2.

10. The solid electrolyte ceramic according to any one of claims 1 to 5, wherein In the electron energy loss spectrum of the solid electrolyte ceramic, the peak position of the Co L end is lower than the peak position of the CoL end of LiCoO 2 .

11. A solid battery, A solid electrolyte ceramic comprising the solid electrolyte ceramic according to any one of claims 1 to 10.

12. The solid battery according to claim 11, wherein The solid battery includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer stacked between the positive electrode layer and the negative electrode layer. The positive electrode layer and the negative electrode layer are layers capable of inserting and extracting lithium ions.

13. The solid battery according to claim 12, wherein The solid electrolyte layer, the positive electrode layer, and the negative electrode layer are integrally sintered to form a sintered body.

14. The solid state battery according to any one of claims 11 to 13, wherein The solid electrolyte ceramic is contained in a solid electrolyte layer of the solid battery.

Images