JP2021190206A - Lithium ion conductor - Google Patents

Abstract

To provide a novel lithium ion conductor showing high conductivity at room temperature.SOLUTION: A lithium ion conductor has a composition represented by general formula: ALi6+s(X1-tZt)O6+δ (where KLi6BiO6 is excluded). In the general formula, A (positive monovalence) represents K and/or Rb, X (positive pentavalence) represents one or more elements selected from the group consisting of V, Nb, Ta, As, Sb and Bi, Z (positive tetravalence) represents one or more elements selected from the group consisting of Si, Ni, Se, Mn, Co, Ge, Cr, V, Fe, Rh, Ti, Pd, Ru, Ir, Pt, Re, Os, Mo, W, Nb, Ta, Sn, Hf, Zr, Tb, Pb, Pr and Ce, 0≤s<0.5 and 0≤t<0.5 are satisfied, and δ is a value that maintains electrical neutrality. In the lithium ion conductor, the ionic radiuses of constituent elements satisfy a predetermined relationships.SELECTED DRAWING: Figure 3

Description

The present invention relates to a lithium ion conductor, and more specifically, the general formula: Ali _{6 + s} (X _1-t Z _t ) O _{6 + δ} (where A is a monovalent metal element and X is a pentavalent metal). It relates to a novel lithium ion conductor composed of an oxide having a composition represented by an element (Z is a tetravalent metal element).

The lithium ion conductor is a solid electrolyte material that constitutes an all-solid-state lithium-ion battery. In order to increase the output of the battery, the solid electrolyte is required to have high conductivity. Currently, as a lithium ion conductor exhibiting high conductivity at room temperature, a sulfide such as _{Li 10 GeP 2 S 12 (LGPS} ) is known. However, sulfide has practical problems such as deterioration of characteristics due to decomposition of the material and generation of hydrogen sulfide.
On the other hand, many lithium ion conductors made of oxides that are more stable than sulfides have also been studied. However, the previously reported oxide has a conductivity of about 1 mS / cm @ room temperature at the maximum, and a material having a higher conductivity is desired.

In recent years, the technological development of materials informatics has been promoted worldwide as a means of accelerating the search for materials. Attempts have also been made to search for lithium-ion conductors using materials informatics techniques, and as a result, KLi ₆ BiO ₆ has recently been proposed as a promising material (Non-Patent Documents 1 and 2). Experimental verification has not yet been performed, but first-principles molecular dynamics calculations predict conductivity at 6 mS / cm @ room temperature. However, the predicted _{conductivity of KLi 6} BiO ₆ is lower than that of LGPS (10 mS / cm @ room temperature), and an oxide material having higher conductivity is desired.

Y.Zhang et al., Nature Comm. 10, 5260 (2019) X.He et al., Adv. Energy Mater., 1902078 (2019)

An object to be solved by the present invention is to provide a novel lithium ion conductor showing high conductivity at room temperature.

In order to solve the above problems, the lithium ion conductor according to the present invention has the following configurations.
(1) The lithium ion conductor has a composition represented by the following formula (1) ( _{excluding KLi 6} BiO ₆ ).
Ali _{6 + s} (X _1-t Z _t ) O _{6 + δ} … (1)
However,
A (+1 valence) is K and / or Rb,
X (+5 valence) is any one or more elements selected from the group consisting of V, Nb, Ta, As, Sb, and Bi.
Z (+4 valence) is Si, Ni, Se, Mn, Co, Ge, Cr, V, Fe, Rh, Ti, Pd, Ru, Ir, Pt, Re, Os, Mo, W, Nb, Ta, Sn. , Hf, Zr, Tb, Pb, Pr, and any one or more elements selected from the group consisting of Ce.
0≤s <0.5, 0≤t <0.5,
δ is a value that maintains electrical neutrality.
(2) The lithium ion conductor satisfies the following formulas (2) and (3).
｜ r _X1 −r _Xp ｜ × 100 / r _X1 ≦ 15… (2)
｜ r _X1 −r _zq ｜ × 100 / r _X1 ≦ 15… (3)
However,
r _X1, among the element X to occupy the X site, the ionic radius of at most 6 coordination high content elements X _1,
r _Xp is the ionic radius at the 6-coordination of the p-th (p ≧ 2) element X _{p other than the element X 1} among the elements X occupying the X site.
r _Zq is the ionic radius at the 6th coordination of the _qth (q ≧ 1) element Z q among the elements Z occupying the X site.
The "X site" means a site that can be occupied by the element X and the element Z in the crystal structure.

The oxide having the composition represented by the formula (1) exhibits high conductivity at room temperature. This is because all the oxides having the composition represented by the formula (1) are
(A) In the presence of excess lithium, lithium ions diffuse to connect the sites present in the crystal, and
(B) Since the diffusion barrier (E _mig ) of lithium ions is lower than that of KLi ₆ BiO _6,
it is conceivable that.

This is the conductivity of a conventional lithium-ion conductor. It is a list of elements selected as substitution elements for KLi ₆ (Ta / Bi) O _6. It is a figure which shows the conductivity of various oxides obtained from the first-principles molecular dynamics calculation. It is a figure which shows the diffusion locus of lithium ion obtained from the first-principles molecular dynamics calculation. It is a figure which shows the change of energy along the diffusion path of lithium ion. It is a figure which shows the conductivity of the oxide which changed the amount of excess lithium and the oxide which was doped with excess lithium and Zr at the same time, which was obtained from the first-principles molecular dynamics calculation.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Lithium-ion conductor]
The lithium ion conductor according to the present invention is made of an oxide having the following constitution.

[1.1. Crystal structure]
The lithium ion conductor according to the present invention has a crystal structure belonging to the space group R3_m (No. 166) or a crystal structure similar thereto.
The "crystal structure similar to the space group R3_m" is not strictly a crystal structure belonging to the space group R3_m, but refers to a crystal structure that can be equated with this. In the crystal structure belonging to the space group R3_m, Li is usually located at the 18f site and the 9d site is empty (see FIG. 4). Ion conduction occurs when excess lithium ions enter all or part of this empty 9d site. Strictly speaking, the crystal structure in which excess lithium ions are contained in the 9d site is not a "crystal structure belonging to the space group R3_m", but in the present application, this is treated as a "crystal structure similar to the space group R3_m".

[1.2. composition]
The lithium ion conductor according to the present invention has a composition represented by the following formula (1) ( _{excluding KLi 6} BiO ₆ ).
Ali _{6 + s} (X _1-t Z _t ) O _{6 + δ} … (1)
However,
A (+1 valence) is K and / or Rb,
X (+5 valence) is any one or more elements selected from the group consisting of V, Nb, Ta, As, Sb, and Bi.
Z (+4 valence) is Si, Ni, Se, Mn, Co, Ge, Cr, V, Fe, Rh, Ti, Pd, Ru, Ir, Pt, Re, Os, Mo, W, Nb, Ta, Sn. , Hf, Zr, Tb, Pb, Pr, and any one or more elements selected from the group consisting of Ce.
0≤s <0.5, 0≤t <0.5,
δ is a value that maintains electrical neutrality.

[1.2.1. Element A]
Element A is an element located at the 3b site of the crystal structure belonging to the space group R3_m. In the present invention, the element A is a monovalent metal element and is composed of K or Rb. All of these elements can occupy 3b sites, and all of the oxides containing these elements show relatively high ionic conductivity, so that they are suitable as element A. The lithium ion conductor may contain either K or Rb, or may contain both.

[1.2.2. Li]
As described above, in the crystal structure belonging to the space group R3_m, Li is usually located at the 18f site and the 9d site is empty. It is considered that ion conduction occurs when excess lithium ions enter all or part of this empty 9d site.

[12.3. Element X]
The element X is an element located at the 3a site (six-coordinated seats) (hereinafter, also simply referred to as “X site”) of the crystal structure belonging to the space group R3_m. In the present invention, the element X is a pentavalent metal element and is composed of V, Nb, Ta, As, Sb, or Bi. All of these elements can occupy 3a sites, and all of the oxides containing these elements show relatively high ionic conductivity, so that they are suitable as the element X.
The lithium ion conductor may contain any one of these elements X, or may contain two or more of them. When the lithium ion conductor contains two or more kinds of elements X, their ionic radii must satisfy the conditions described later.

[12.4. Element Z]
The element Z is a dopant that replaces the element X. In the present invention, the element Z is a tetravalent metal element, Si, Ni, Se, Mn, Co, Ge, Cr, V, Fe, Rh, Ti, Pd, Ru, Ir, Pt, Re, Os. , Mo, W, Nb, Ta, Sn, Hf, Zr, Tb, Pb, Pr, or Ce. Substituting the pentavalent element X with the tetravalent element Z facilitates the introduction of excess lithium ions into the 9d site in order to maintain electrical neutrality. As a result, the oxide containing the element Z may exhibit higher conductivity than the oxide containing no element Z.
The lithium ion conductor may contain any one of these elements Z, or may contain two or more of them. When the lithium ion conductor contains the element Z, the ionic radius of the element Z needs to satisfy the conditions described later.
In the present invention, the term "metal element" also includes metalloids such as Si and Ge.

[1.2.5. s]
s correlates with the number of lithium ions occupying 9d sites. Formally, the lithium ion conductor according to the present invention exhibits relatively high conductivity even when s is zero. In general, as s increases, the number of lithium ions occupying 9d sites increases, and the conductivity may increase. As shown in the examples, s is preferably 0.125 or more, more preferably 0.33 or more.
On the other hand, if s becomes too large, the charge neutral condition cannot be maintained, and phase separation or Li precipitation may occur. Therefore, s needs to be less than 0.5.

[1.2.6. t]
t represents the amount of element Z that replaces element X. The lithium ion conductor according to the present invention exhibits relatively high conductivity even when it does not contain the element Z. That is, t may be zero. However, when t is zero, it may be difficult to introduce excess lithium (ie, s> 0). On the other hand, when t is larger than zero, the introduction of excess lithium is relatively easy, and the larger t, the higher the conductivity. As shown in the examples, t is preferably 0.125 or more, more preferably 0.33 or more.
On the other hand, if t becomes too large, all of the elements Z may not replace the element X and may precipitate as a different phase. Therefore, t needs to be less than 0.5.

[1.2.7. δ]
When the dopant (element Z) is not included, δ is ideally zero. However, in practice, excess lithium ions may enter the 9d site even when the dopant is not included. Further, when a dopant (element Z) having a valence lower than that of element X is added, excess lithium ions usually enter the 9d site so that electrical neutrality is maintained. In the case of the oxide represented by the formula (1), it can be formally expressed as 2δ = s-t. δ is −0.25 ≦ δ ≦ + 0.25 from the upper limit of s and t.

[1.2.8. Ionic radius]
The lithium ion conductor according to the present invention satisfies the following formulas (2) and (3).
｜ r _X1 −r _Xp ｜ × 100 / r _X1 ≦ 15… (2)
｜ r _X1 −r _zq ｜ × 100 / r _X1 ≦ 15… (3)
However,
r _X1, among the element X to occupy the X site, the ionic radius of at most 6 coordination high content elements X _1,
r _Xp is the ionic radius at the 6-coordination of the p-th (p ≧ 2) element X _{p other than the element X 1} among the elements X occupying the X site.
r _Zq is the ionic radius at the 6th coordination of the _qth (q ≧ 1) element Z q among the elements Z occupying the X site.
The "X site" means a site that can be occupied by the element X and the element Z in the crystal structure.

The element X ₁ represents the element having the highest content among the elements X occupying the X site. When there are a plurality of elements X having the highest content, the element X ₁ represents the element X 1 having the largest ionic radius.
Element X _p and the element Z _q satisfying Equation (2) and (3) both ionic radius close to the element X _1, it is possible to replace the element X _1. Further, since the element Z _q has a smaller valence than the element X, when the element Z _q is doped, excess lithium ions are introduced into the 9d site. Therefore, the material containing the element Z _q, which may exhibit high conductivity as compared with the material containing no elements Z _q.

The ionic radius of each element is described in, for example, References 1 and 2 below.
[Reference 1] http://pmsl.planet.sci.kobe-u.ac.jp/~seto/?page_id=51
[Reference 2] Shannon et al., Acta A 32 (1976) 751

In order to replace element X ₁ with element X _p and / or element Z _{q , both element X p} and element Z _q have an ionic radius difference of 15% or less from _{element X 1} at the 6-coordination. Some are preferred (see Hume Rosalie's Law, References 3-6). The ionic radius difference is preferably 12% or less, more preferably 10% or less.
[Reference 3] W. Hume-Rothery and HM Powell, Z. Krist., 91 (1935) 23
[Reference 4] W. Hume-Rothery, Atomic Theory for Students of Metallurgy, The Institute of Metals, London, 1969 (fifth reprint)
[Reference 5] W. Hume-Rothery, RW Smallman and CW Hawoth, The Structure of Metals and Alloys, The Institute of Metals, London, 1969
[Reference 6] http://ja.wikipedia.org/wiki/ Hume Rosalie's Law

For example, if the element X ₁ is V ⁵⁺ (r _X1 = 0.53),
(A) Elements X _p (p ≧ 2) include, for example, As ⁵⁺ (r _X2 = 0.46), Sb ⁵⁺ (r _X3 = 0.6), and the like.
(B) Elements Z _q (q ≧ 1) include, for example, Ni ⁴⁺ (r _Z1 = 0.48), Se ⁴⁺ (r _Z2 = 0.50), Mn ⁴⁺ (r _Z3 = 0.53). ), Co ⁴⁺ (r _Z4 = 0.53), Ge ⁴⁺ (r _Z5 = 0.53), Cr ⁴⁺ (r _Z6 = 0.55), V ⁴⁺ (r _Z7 = 0.58), Fe ⁴⁺ (r _Z8 = 0.585), Rh ⁴⁺ (r _Z9 = 0.60), Ti ⁴⁺ (r _Z10 = 0.605), Pd ⁴⁺ (r _Z11 = 0.615), Ru ^{4 +} (R _Z12 = 0.62) and so on.
Table 1 below shows an example of a combination of elements.

[1.3. Concrete example]
The lithium ion conductor according to the present invention is particularly preferably one having the following composition.
[1.3.1. Specific Example 1: K-based oxide]
The first specific example comprises KLi ₆ VO ₆ , KLi ₆ NbO ₆ , KLi ₆ TaO ₆ , KLi ₆ AsO ₆ , or KLi ₆ SbO ₆ . Hereinafter, these are also collectively referred to as "K-based oxide".
Among the compositions represented by the formula (1), the K-based compound has advantages such as high ionic conductivity and thermodynamic stability. Among them, KLi ₆ NbO ₆ , KLi ₆ TaO ₆ , and KLi ₆ SbO ₆ have advantages such as low toxicity and small bandgap, so that electron conduction is unlikely to occur.

[1.3.2. Specific Example 2: Rb-based oxide]
The second specific example comprises RbLi ₆ VO ₆ , RbLi ₆ NbO ₆ , RbLi ₆ TaO ₆ , RbLi ₆ AsO ₆ , RbLi ₆ SbO ₆ , or RbLi ₆ BiO ₆ . Hereinafter, these are also collectively referred to as “Rb-based oxide”.
Among the compositions represented by the formula (1), the Rb-based compound has advantages such as high ionic conductivity and thermodynamic stability. Among them, RbLi ₆ NbO ₆ , RbLi ₆ TaO ₆ , and RbLi ₆ SbO ₆ have advantages such as low toxicity and small bandgap, so that electron conduction is unlikely to occur.

[1.3.3. Specific Example 3: KZ-based oxide]
The third specific example comprises a KLi ₆ BiO ₆ or a K-based oxide in which a part of X (+5 valence) is replaced with Z (+4 valence). Hereinafter, these are also collectively referred to as "KZ-based oxide". The element Z preferably satisfies the above-mentioned formula (3).
Among the compositions represented by the formula (1), the KZ-based oxide has advantages such as high ionic conductivity and thermodynamic stability.

[1.3.4. Specific Example 4: Rb-Z-based oxide]
The fourth specific example comprises a part of X (+5 valence) contained in the Rb-based oxide substituted with Z (+4 valence). Hereinafter, these are also collectively referred to as "Rb-Z-based oxide". The element Z preferably satisfies the above-mentioned formula (3).
Among the compositions represented by the formula (1), the Rb-Z-based compound has advantages such as high ionic conductivity and thermodynamic stability.

[1.4. Band gap]
In the present invention, the "band gap" means a value calculated by using the HSE (Heyd Scuseria Ernzerhof) method.
If the bandgap becomes too small, electron / hole conduction becomes dominant rather than ionic conduction. Therefore, the band gap is preferably 2 eV or more. The band gap is preferably 3 eV or more, more preferably 4 eV or more.

[1.5. shape]
The shape of the lithium ion conductor according to the present invention is not particularly limited, and the optimum shape can be selected according to the intended purpose. Specifically, the lithium ion conductor according to the present invention may be used in a bulk state, or may be used in a powder, nanoparticles, or thin film state.

[2. Method for manufacturing lithium-ion conductor]
The lithium ion conductor according to the present invention can be produced by various methods.
For example, bulk lithium-ion conductors
(A) The raw materials are mixed so as to have a predetermined composition, and the raw materials are mixed.
(B) The raw material mixture is calcined under predetermined conditions and then calcined.
(C) It can be produced by appropriately crushing the calcined powder and then molding and sintering the calcined powder.
The production conditions are not particularly limited, and it is preferable to select the optimum conditions according to the desired composition.
The same applies to the case of producing a lithium ion conductor of powder, nanoparticles, or a thin film, and the lithium ion conductor can be produced by a known method.

[3. Action]
FIG. 1 shows the conductivity of a conventional lithium ion conductor. Currently, as a lithium ion conductor exhibiting high conductivity at room temperature, a sulfide such as _{Li 10 GeP 2 S 12 (LGPS} ) is known. However, sulfide has practical problems such as deterioration of characteristics due to decomposition of the material and generation of hydrogen sulfide.
On the other hand, many lithium ion conductors made of oxides that are more stable than sulfides have also been studied. However, all of the previously reported oxides have insufficient ionic conductivity.

On the other hand, the oxide represented by the formula (1) has a higher _{conductivity obtained by first-principles molecular dynamics calculation than that of KLi 6} BiO _{6, which is a previously reported material.} This is because all the oxides having the composition represented by the formula (1) are
(A) In the presence of excess lithium, lithium ions diffuse to connect the sites present in the crystal, and
(B) Since the diffusion barrier (E _mig ) of lithium ions is lower than that of KLi ₆ BiO _6,
it is conceivable that.

[1. Introduction]
In recent years, the inventors of the present application have developed a unique method for evaluating lithium ion conductivity at high speed (Reference 7). Using this technique, all oxide materials registered in the Inorganic Crystal Structure Database (ICSD) were screened. As a result, KLi ₆ TaO ₆ , KLi ₆ IrO ₆ , and KLi ₆ BiO ₆ were found as materials having high predicted conductivity. These are materials that have already been synthesized and whose crystal structure has been clarified (References 8 to 10).
[Reference 7] A. France-Lanord et al., Sci. Rep. 9, 15123 (2019)
[Reference 8] KLi6TaO6: W. Scheld et al., ZAAC 619, 337 (1993)
[Reference 9] KLi6IrO6: P. Kroeshell et al., ZAAC 619, 537 (1986)
[Reference 10] KLi6BiO6: R. Hubenthal et al., Acta Chem. Scandinavia 45, 805 (1991)

Among these, KLi ₆ BiO ₆ has already been disclosed in Non-Patent Documents 1 and 2 as being promising as a lithium ion conductor as described above. On the other hand, KLi ₆ IrO ₆ was excluded from the candidates as an ionic conductor because it had a zero bandgap and was found to be metallic.
Therefore, _{elemental substitution was performed on KLi 6} (Ta / Bi) O ₆ to search for a new material showing high conductivity. FIG. 2 shows a list of elements selected as substitution elements for _{KLi 6} (Ta / Bi) O _6.

When searching for materials, materials that satisfy the following conditions were selected as candidates.
(1) The material has a low production energy ΔHf of the compound based on the oxide raw material of the constituent element, and has high dynamic stability without soft mode vibration from the calculation of lattice vibration.
(2) First-principles The lithium ion conductivity at room temperature determined by molecular dynamics calculation is higher than _{that of the previously reported KLi 6} BiO _{6. In Non-Patent Document 2, the conductivity of KLi 6} BiO ₆ predicted by first-principles molecular dynamics calculation at room temperature is 5.7 mS / cm, which is a calculated value (4 mS / cm) by the inventors of the present application. Since it almost matched with, the reliability of the method is mutually confirmed.
_{(3) The material has a band gap (E g} ) of 2 eV or more calculated by the HSE method with high calculation accuracy. The material that satisfies this condition is likely to be an ionic conductor rather than a material that conducts electrons / holes.

[2. result]
[2.1. Conductivity at room temperature]
Table 2 shows a novel oxide-based lithium ion conductor found by first-principles molecular dynamics calculation, in which the amount of excess lithium (s) is 1/8 = 0.125, but at room temperature (300K). ) Shows the predicted value σ of the conductivity. In Table 2,
"V" represents the volume per atom
"E _g (PBE)" represents the bandgap calculated using the PBE correlation potential.
"E _g (HSE)" represents the bandgap calculated by the HSE method.
"E _mig (Li ⁺ )" represents the diffusion barrier of lithium ions.
"E _a" represents the activation energy determined from first principles molecular dynamics calculation (FPMD).
In addition, FIG. 3 shows the conductivity of various oxides obtained from the first-principles molecular dynamics calculation.

The following can be seen from Table 2 and FIG.
(1) Among the materials shown in Table 2, all _{the materials other than KLi 6} BiO ₆ (hereinafter, these are collectively referred to as “proposal materials”) have higher conductivity than _{KLi 6} BiO _6.
(2) All band gaps are 2 eV or more. In particular, the bandgap _{of the proposed materials other than KLi 6} BiO ₆ and RbLi ₆ BiO ₆ is 3 eV or more, and electron conduction is unlikely to occur.
(3) Among the proposed materials, the material of A = K has higher conductivity than the material of A = Rb. However, when using it for an application device, it is necessary to select the material in consideration of the usage conditions and the combination with the electrode material.

[2.2. Ion conduction path]
First-principles Molecular dynamics calculations have identified the diffusion pathways of lithium ions. FIG. 4 shows the diffusion locus of lithium ions obtained from the first-principles molecular dynamics calculation. In FIG. 4, the shaded area represents the diffusion path of lithium ions. From FIG. 4, it was clarified that the lithium atom diffuses so as to connect the sites (18f site and 9d site) existing in the crystal in the presence of excess lithium.
FIG. 5 shows the change in energy along the diffusion path of lithium ions. The proposed materials shown in Table 2 show high conductivity because the diffusion barrier (E _mig ) value is _{smaller than the KLi 6} BiO ₆ value (0.13 eV) and the energy change associated with the diffusion of lithium ions is small. it is conceivable that.

From the above, it was understood why the proposed material has high ionic conductivity in the presence of excess lithium. That is, the _{reason why Ali 6} XO ₆ exhibits high conductivity is that the change in potential energy felt by lithium ions is small and lithium ions can be easily diffused.
Further, the proposed material having X-sites such as Ta and Nb shows higher ionic conductivity than the proposed material having X-sites of Bi. It is considered that this is because the ionic radius of Ta, Nb, etc. is smaller than that of Bi, so that the connectivity of the diffusion path of lithium ions is enhanced and the diffusion barrier is reduced.

[2.3. Effect of dopant]
General formula: Appropriate doping is required to stabilize excess lithium in the proposed material represented by _{Ali 6} XO _6. The proposed material containing the dopant Z is represented by the general formula: Ali _{6 + s} (X _1-t Z _t ) O _{6 + δ} , but the dopant Z was selected according to the well-known Hume Rosalie's law.

FIG. 6 shows the conduction of an oxide in which the amount of excess lithium is changed and an oxide in which excess lithium and Zr are simultaneously doped (in the case of t = s = 0.125) obtained from the first-principles molecular dynamics calculation. Indicates the degree. In FIG. 6, “X%, Y / Z” is contained in the unit cell due to excessive introduction of (YZ) lithium ions into the unit cell composed of Z Li atoms before doping. When the number of Li atoms becomes Y, it means that the amount of lithium ions increases by X%. A relationship of X = (Y−Z) × 100 / Z holds between X, Y, and Z.

From FIG. 6, the following can be seen.
(1) KLi ₆ TaO ₆ and KLi _{6 + s} conductivity at room temperature of _{(Ta 1-t Zr t)} O 6 , the value of KLi ₆ BiO ₆ (estimated Conductivity: 4 mS / cm @ RT) higher than.
(2) The higher the concentration of excess lithium, the higher the conductivity of _{KLi 6} TaO _6.
(3) KLi _{6 + s} conductivity at room temperature of _{(Ta 1-t Zr t)} O 6 is lower than that of KLi ₆ TaO _6. It is considered that this is because Zr of Tasite reduces the mobility as an impurity of ionic conduction. However, its conductivity is 5 mS / cm, which is higher than the conductivity (4 mS / cm, see Table 2) in which only the same amount of excess lithium is introduced into the _{known material: KLi 6} BiO _6. Further, when the Bisite is doped with the element Z at the same time, it is considered that the higher the concentration of excess lithium, the higher the conductivity, as _{in the case of KLi 6} TaO _6.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

The lithium ion conductor according to the present invention can be used as a solid electrolyte material for a lithium ion battery or the like.

Claims (5)

A lithium ion conductor having the following configurations.
(1) The lithium ion conductor has a composition represented by the following formula (1) ( _{excluding KLi 6} BiO ₆ ).
Ali _{6 + s} (X _1-t Z _t ) O _{6 + δ} … (1)
However,
A (+1 valence) is K and / or Rb,
X (+5 valence) is any one or more elements selected from the group consisting of V, Nb, Ta, As, Sb, and Bi.
Z (+4 valence) is Si, Ni, Se, Mn, Co, Ge, Cr, V, Fe, Rh, Ti, Pd, Ru, Ir, Pt, Re, Os, Mo, W, Nb, Ta, Sn. , Hf, Zr, Tb, Pb, Pr, and any one or more elements selected from the group consisting of Ce.
0≤s <0.5, 0≤t <0.5,
δ is a value that maintains electrical neutrality.
(2) The lithium ion conductor satisfies the following formulas (2) and (3).
｜ r _X1 −r _Xp ｜ × 100 / r _X1 ≦ 15… (2)
｜ r _X1 −r _zq ｜ × 100 / r _X1 ≦ 15… (3)
However,
r _X1, among the element X to occupy the X site, the ionic radius of at most 6 coordination high content elements X _1,
r _Xp is the ionic radius at the 6-coordination of the p-th (p ≧ 2) element X _{p other than the element X 1} among the elements X occupying the X site.
r _Zq is the ionic radius at the 6th coordination of the _qth (q ≧ 1) element Z q among the elements Z occupying the X site.
The "X site" means a site that can be occupied by the element X and the element Z in the crystal structure. The lithium ion conductor according to claim 1, which has a crystal structure belonging to the space group R3_m or a crystal structure similar thereto. The lithium ion conductor according to claim 1 or 2, wherein the bandgap calculated by using the HSE method is 2 eV or more. (A) K-based oxide consisting of _{KLi 6} VO ₆ , KLi ₆ NbO ₆ , KLi ₆ TaO ₆ , KLi ₆ AsO ₆ , or KLi ₆ SbO _6,
(B) Rb-based oxide consisting of _{RbLi 6} VO ₆ , RbLi ₆ NbO ₆ , RbLi ₆ TaO ₆ , RbLi ₆ AsO ₆ , RbLi ₆ SbO ₆ , or RbLi ₆ BiO _6.
(C) KLi ₆ BiO ₆ or a KZ-based oxide in which a part of the X (+5 valence) contained in the K-based oxide is replaced with the Z (+4 valence), or a KZ-based oxide.
(D) Any one of claims 1 to 3 containing an Rb—Z-based oxide in which a part of the X (+5 valence) contained in the Rb-based oxide is replaced with the Z (+4 valence). Lithium ion conductor according to. The lithium ion conductor according to any one of claims 1 to 4, which is used as a bulk, powder, nanoparticles, or thin film.

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