Solid Electrolyte and Lithium-Ion Batteries

Abstract

To provide a solid electrolyte capable of achieving high lithium ion conductivity by low temperature sintering at less than 900°C and a lithium ion battery using the same.SOLUTION: A solid electrolyte 1 has solid electrolyte particles 10 and a non-melting phase 11. The solid electrolyte particles 10 have garnet-type crystal structures and are composed of a lithium lanthanum zirconium composite oxide including an M3 element comprising at least one of Bi and Sb. The non-melting phase 11 is composed of a material with lithium ion conductivity lower than the lithium lanthanum zirconium composite oxide and exists on at least one of intragranular and intergranular portions of the solid electrolyte particles 10. A lithium ion battery 2 has the solid electrolyte 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte and a lithium-ion battery. [Background technology]

[0002] In recent years, lithium ion batteries (sometimes called all-solid-state batteries) that use a solid electrolyte as the electrolyte have become known. Known solid electrolytes used in lithium ion batteries include, for example, solid electrolytes having a garnet-type crystal structure containing Li, La, Zr, and O.

[0003] Prior Patent Document 1 discloses a solid electrolyte including a garnet-type crystalline first electrolyte made of lanthanum lithium zirconate doped with Al, Ga, etc., and an ion-conductive amorphous second electrolyte containing two elements selected from Nb, Ta, Sb, and Bi, and Li. This document describes the use of the solid electrolyte as a solid electrolyte layer, i.e., a separator layer, in a lithium-ion battery. This document also describes the solid electrolyte being obtained by performing a main firing process at a temperature of 900°C or higher but lower than 1000°C. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-168396 Summary of the Invention [Problem to be solved by the invention]

[0005] To increase the output of lithium-ion batteries, solid electrolytes are required to have high lithium-ion conductivity. However, the solid electrolyte of Patent Document 1 requires high-temperature sintering at 900°C or higher to reduce grain boundary resistance and ensure lithium-ion conductivity, resulting in significant energy loss. Furthermore, when the solid electrolyte is mixed with a positive electrode active material and sintered, heterogeneous phases are formed due to the high sintering temperature.

[0006] The present invention has been made in view of the above problems, and aims to provide a solid electrolyte that can achieve high lithium ion conductivity through low-temperature sintering at less than 900°C, and a lithium ion battery using the same. [Means for solving the problem]

[0007] One aspect of the present invention teeth, Ga solid electrolyte particles (10) made of a lithium-lanthanum-zirconium-based composite oxide having a net-type crystal structure and containing an M3 element consisting of at least one of Bi and Sb; a non-molten phase (11) made of a material having a lower lithium ion conductivity than the lithium-lanthanum-zirconium-based composite oxide and present at least either inside or between the solid electrolyte particles; a molten phase (12) including a Li-M3-O phase composed of a material containing Li, the M3 element, and O, and binding the solid electrolyte particles together; the non-melt phase is composed of a material containing Zr and O, The molten phase is crystalline. Ru, Solid electrolyte (1).

[0008] Another aspect of the present invention is a lithium ion battery (2) having the above solid electrolyte. [Effects of the Invention]

[0009] The solid electrolyte has the above-described structure, and therefore can achieve high lithium ion conductivity even when sintered at a low temperature of less than 900°C.

[0010] The lithium ion battery has the solid electrolyte, which is advantageous for achieving high power output.

[0011] In addition, the symbols in parentheses in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram schematically illustrating an example of the microstructure of the solid electrolyte of the first embodiment. [Figure 2] FIG. 2 is an explanatory view schematically showing another example (modification) of the microstructure of the solid electrolyte of the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an example of the lithium ion battery of the second embodiment. [Figure 4] FIG. 4 is an explanatory diagram showing the SEM-EDX analysis results of the solid electrolytes of Sample 2C, Sample 1, and Sample 2 obtained in Experimental Example 1, in which (a) is an SEM image of Sample 2C, (b) is a Zr element mapping image of Sample 2C, (c) is an SEM image of Sample 1, (d) is a Zr element mapping image of Sample 1, (e) is an SEM image of Sample 2, and (f) is a Zr element mapping image of Sample 2. [Figure 5] FIG. 5 is an explanatory diagram showing the results of SEM-EDX analysis of the solid electrolyte of Sample 4 obtained in Experimental Example 2, where (a) is an SEM image, (b) is a Zr element mapping image, and (c) is an Sb element mapping image. [Figure 6] FIG. 6 is an explanatory diagram showing the results of SEM-EDX analysis of the solid electrolyte of Sample 7 obtained in Experimental Example 2, in which (a) is an SEM image, (b) is a Zr element mapping image, (c) is an Sb element mapping image, and (d) is a B element mapping image. [Figure 7] FIG. 7 is a graph showing the relationship between the area ratio (%) of the non-molten phase (horizontal axis) and the lithium ion conductivity (S / cm) (vertical axis) obtained in Experimental Example 3. [Figure 8]FIG. 8 is a graph showing the relationship between the area ratio (%) of the Li-M3-O phase (horizontal axis) and the lithium ion conductivity (S / cm) (vertical axis) obtained in Experimental Example 4. [Figure 9] FIG. 9 is a graph showing the relationship between the area ratio (%) of the Li-M3-O phase (horizontal axis) and the relative density (%) (vertical axis) obtained in Experimental Example 4. [Figure 10] FIG. 10 is a graph showing the relationship between the area ratio (%) of the Li—BO phase (horizontal axis) and the lithium ion conductivity (S / cm) (vertical axis) obtained in Experimental Example 5. [Figure 11] FIG. 11 is a graph showing the relationship between the area ratio (%) of the Li—BO phase (horizontal axis) and the relative density (%) (vertical axis) obtained in Experimental Example 5. [Figure 12] FIG. 12 is a graph showing the results of measuring AC impedance obtained in Experimental Example 7 after bringing lithium metal into contact with the surface of the solid electrolyte and subjecting it to heat treatment at 190°C. DETAILED DESCRIPTION OF THE INVENTION

[0013] The solid electrolyte of this embodiment has a garnet-type crystal structure and includes solid electrolyte particles made of a lithium-lanthanum-zirconium-based composite oxide containing an M3 element consisting of at least one of Bi and Sb; The solid electrolyte particles are made of a material having a lower lithium ion conductivity than the lithium-lanthanum-zirconium-based composite oxide, and have a non-molten phase present at least either inside or between the particles.

[0014] The solid electrolyte of this embodiment has a non-molten phase. The non-molten phase is composed of a material with lower lithium ion conductivity than the lithium-lanthanum zirconium-based composite oxide constituting the solid electrolyte particles, and therefore has a different chemical potential from the lithium-lanthanum zirconium-based composite oxide constituting the solid electrolyte particles. In the solid electrolyte of this embodiment, the non-molten phase, which has a different chemical potential from the lithium-lanthanum zirconium-based composite oxide constituting the solid electrolyte particles, is dispersed at least intragranularly and / or intergranularly within the solid electrolyte particles. This increases the defect concentration locally, facilitating lithium ion hopping and improving lithium ion conductivity. Furthermore, in the solid electrolyte of this embodiment, the lithium-lanthanum zirconium-based composite oxide constituting the solid electrolyte particles contains an M3 element consisting of at least one of Bi and Sb. Therefore, the solid electrolyte of this embodiment can easily increase its density through low-temperature sintering below 900°C, which can contribute to increasing the number of interfaces between the solid electrolyte particles. Therefore, the solid electrolyte of this embodiment can achieve high lithium ion conductivity even when sintered at a low temperature below 900°C. The sintering temperature refers to the maximum temperature during the sintering of the solid electrolyte.

[0015] Furthermore, the lithium ion battery of this embodiment has the solid electrolyte of this embodiment, which is advantageous for achieving high output.

[0016] The solid electrolyte and lithium ion battery of the present embodiment will be described in detail below with reference to the drawings. Note that the solid electrolyte and lithium ion battery of the present embodiment are not limited to the following examples.

[0017] (Embodiment 1) The solid electrolyte of embodiment 1 will be described with reference to Figures 1 and 2. As illustrated in Figures 1 and 2, the solid electrolyte 1 of this embodiment has solid electrolyte particles 10 and a non-molten phase 11.

[0018] In the solid electrolyte 1, the solid electrolyte particles 10 are composed of a lithium-lanthanum zirconium-based composite oxide having a garnet-type crystal structure. The lithium-lanthanum zirconium-based composite oxide contains an M3 element consisting of at least one of Bi (bismuth) and Sb (antimony). The inclusion of the M3 element in the lithium-lanthanum zirconium-based composite oxide makes it easier to increase the density of the solid electrolyte 1 even when the sintering temperature during production of the solid electrolyte 1 is less than 900°C. The M3 element is preferably Sb, from the viewpoints of improving the sinterability of the solid electrolyte 1 at low temperatures and being highly effective in suppressing decomposition of the solid electrolyte 1 due to reactions caused by contact between the solid electrolyte 1 and lithium metal.

[0019] Specific examples of the lithium-lanthanum-zirconium composite oxide constituting the solid electrolyte particles 10 include Li7La3Zr2O 12 Examples of the basic composition of LLZ (sometimes referred to as LLZ) include those in which at least a portion of Zr (zirconium) has been replaced with an M3 element consisting of at least one of Bi and Sb, and in addition, those in which a portion of Li (lithium) has been replaced with an M1 element consisting of at least one of Al (aluminum) and Ga (gallium), those in which a portion of La (lanthanum) has been replaced with an M2 element which is at least one element selected from the group consisting of Ca (calcium), Sr (strontium), Ba (barium), Mg (magnesium), Y (yttrium), and Rb (rubidium), those in which a portion of Zr has been replaced with an M4 element which is at least one element selected from the group consisting of Ta (tantalum), Nb (niobium), Ge (germanium), Te (tellurium), Sc (scandium), and Hf (hafnium), and combinations thereof.

[0020] The lithium-lanthanum-zirconium composite oxide constituting the solid electrolyte particles 10 is, more specifically, Li 7-3x+αy-z+βg (M1) x La 3-y (M2) y Zr 2-z-g (M3) z (M4)g O 12±δ It can be configured to have the composition. However, in the above composition, the M1 element is at least one of Al and Ga. The M2 element is at least one element selected from the group consisting of Ca, Sr, Ba, Mg, Y, and Rb. The M3 element is at least one of Bi and Sb. The M4 element is at least one element selected from the group consisting of Ta, Nb, Ge, Te, Sc, and Hf. α takes 0 ≦ α ≦ 2 depending on the valence of the M2 element. β takes -2 ≦ β ≦ 1 depending on the valence of the M4 element. x satisfies 0 ≦ x ≦ 0.4. y satisfies 0 < y ≦ 2.8. z satisfies 0 < z < 2. g satisfies 0 ≦ g < 2. δ is an oxygen non-stoichiometric amount. Note that the oxygen part in the above composition is "O 12 ", "O 12+δ ", "O 12-δ " can be any of them. When the lithium lanthanum zirconium-based composite oxide has the above composition, the above-described effects can be made certain.

[0021] In the above composition of the lithium lanthanum zirconium-based composite oxide, the M1 element can be Ga. According to this configuration, there are advantages such as being likely to improve lithium ion conductivity and relative density compared to the case where the M1 element is Al.

[0022] In the above composition of the lithium lanthanum zirconium-based composite oxide, x can preferably be 0. In this case (when the M1 element is not doped), compared with the case of 0 < x (when the M1 element is doped), it is easy to increase the lithium carrier concentration, and there are advantages such as it is easy to increase the lithium ion conductivity because there is no doped element in the lithium conduction path. In the case of 0 < x, from the viewpoint of stabilizing the space group having I-43d, which is a highly conductive crystal structure, x can preferably be 0.1 or more, more preferably 0.125 or more, and still more preferably 0.15 or more. Also, from the viewpoints of ensuring the lithium carrier concentration and reducing foreign elements in the lithium conduction path, x can preferably be 0.3 or less, more preferably 0.2 or less, and still more preferably 0.175 or less.

[0023] In the above composition of the lithium lanthanum zirconium-based composite oxide, the M2 element can preferably be Ca, Sr, Ba, etc. These can be used singly or in combination of two or more. When the M2 element is at least one selected from the group consisting of Ca, Sr, and Ba, sintering can proceed at a lower temperature compared with the case where the M2 element is Mg, Y, Rb, etc. Among the above M2 elements, Ca is particularly preferred.

[0024] In the above composition of the lithium lanthanum zirconium-based composite oxide, from the viewpoint of ensuring the lithium carrier concentration due to doping of the M1 element or M3 element, y can preferably be 0.01 or more, more preferably 0.02 or more. Also, from the viewpoint of avoiding the formation of heterogeneous phases exceeding the solid solubility limit, y can preferably be 0.5 or less, more preferably 0.4 or less, and still more preferably 0.3 or less.

[0025] In the above composition of the lithium lanthanum zirconium-based composite oxide, from the viewpoints of improving the sinterability of Solid Electrolyte 1 at a low temperature and having a large effect of suppressing the decomposition of Solid Electrolyte 1 due to the reaction caused by the contact between Solid Electrolyte 1 and lithium metal, the M3 element is preferably Sb.

[0026] In the above composition of the lithium lanthanum zirconium-based composite oxide, from the viewpoint of facilitating the securing of sinterability, etc., z can preferably be 0.1 or more, more preferably 0.2 or more, and still more preferably 0.5 or more. Also, from the viewpoint of not excessively reducing the lithium carrier concentration, etc., z can preferably be 1.5 or less, more preferably 1.0 or less, and still more preferably 0.8 or less.

[0027] In the above composition of the lithium lanthanum zirconium-based composite oxide, the M4 element is an element for adjusting the lithium carrier concentration and can be added as necessary. From the viewpoint of easily increasing the lithium carrier concentration, etc., preferably, Hf, Sc, Ge, etc. can be used. These can be used singly or in combination of two or more. Among these, particularly preferably, it is Sc.

[0028] In the above composition of the lithium lanthanum zirconium-based composite oxide, from the viewpoint of not reducing the lattice constant and sinterability, etc., g is preferably 0. For this, the following reasons are considered. From the viewpoint of the ionic radius, other than Sc, it causes a decrease in the lattice constant. Although the detailed reason is not clear, when Sc that does not cause a decrease in the lattice constant is introduced, the sinterability decreases. This is thought to be because, considering the bond strength between Sc - O and Zr - O, the bond strength of Sc - O is weaker, and thereby, the bond strength of Zr - O increases compared to the case where Sc is not doped, and atomic diffusion does not occur during sintering. Also, when 0 < g, g can preferably be 0.01 or more, more preferably 0.02 or more, and still more preferably 0.05 or more. In this case, there are advantages such as being able to increase the lithium carrier concentration reduced by the doping of the M3 element. Also, g can preferably be 0.15 or less, more preferably 0.14 or less, and still more preferably 0.1 or less. In this case, there are advantages such as being able to adjust the lithium carrier concentration while avoiding a decrease in resistance due to impurity generation by excessive doping of the M4 element.

[0029] In the above composition of the lithium-lanthanum zirconium-based composite oxide, α is 0≦α≦2 depending on the valence of the M2 element. Specifically, when M2 is an element with a valence of 2+, such as Ca, Sr, Ba, or Mg, α is 1. When M2 is an element with a valence of 1+, such as Rb, α is 2. When M2 is an element with a valence of 3+, such as Y, α is 0. In other words, when the valence of the M2 element is a, α takes the value of La valence (i.e., 3) - a. This is because in the lithium-lanthanum zirconium-based composite oxide, when La is 3, + Therefore, when an element with a different valence is selected as the M2 element, Li + This means that the value is increasing or decreasing.

[0030] In the above composition of the lithium-lanthanum zirconium-based composite oxide, β is −2≦β≦1 depending on the valence of the M4 element. Specifically, when the M4 element is an element with a valence of 6+, such as Te, β is −2. When the M4 element is an element with a valence of 5+, such as Ta, Nb, or Sb, β is −1. When the M4 element is an element with a valence of 4+, such as Ge or Hf, β is 0. When the M4 element is an element with a valence of 3+, such as Sc, β is 1. In other words, when the valence of the M4 element is b, β takes the value of Zr valence (i.e., 4) − b. This is because, in the lithium-lanthanum zirconium-based composite oxide, when Zr is 4, + Therefore, when an element with a different valence is selected as the M4 element, Li + This means that the value is increasing or decreasing.

[0031] When the lithium-lanthanum zirconium-based composite oxide has the above composition, the amount of Li contained in the solid electrolyte 1 can be greater than 7-3x+αy-z+βg, which represents the amount of Li in the above composition. Furthermore, the amount of M3 contained in the solid electrolyte 1 can be greater than 2, where the sum of 2-zg, which represents the amount of Zr in the above composition, and z, which represents the amount of M3 element in the above composition, is greater than 2. In these cases, the Li and M3 components do not fully enter the lithium-lanthanum zirconium-based composite oxide and segregate near the grain boundaries of the solid electrolyte particles 10. This acts as a liquid phase component, improving sinterability, enabling lithium ion conduction at the grain boundaries, and facilitating an increase in lithium ion conductivity. Another advantage is that it is easier to prevent the solid electrolyte particles 10 from becoming Li-deficient due to volatilization during production.

[0032] The above composition of the lithium-lanthanum zirconium-based composite oxide is a theoretical stoichiometric composition, but Li, in particular, is an element that is likely to volatilize at high temperatures during production of the solid electrolyte 1, causing compositional deviation. Therefore, in the above composition of the lithium-lanthanum zirconium-based composite oxide, the amount of Li determined by 7-3x+αy-z+βg can include a range of 0.85 to 1.2 times the value calculated by 7-3x+αy-z+βg.

[0033] In the solid electrolyte 1, the non-molten phase 11 is a phase that remains undissolved in the solid electrolyte 1 after sintering, and can be crystalline. The non-molten phase 11 can be, for example, a precipitate or a residual additive. The non-molten phase 11 is composed of a material having a lower lithium ion conductivity than the lithium lanthanum zirconium-based composite oxide that constitutes the solid electrolyte particle 10. The non-molten phase 11 may have a lower lithium ion conductivity than the lithium lanthanum zirconium-based composite oxide that constitutes the solid electrolyte particle 10, or may be insulating. Furthermore, one or more materials having a lower lithium ion conductivity than the lithium lanthanum zirconium-based composite oxide that constitutes the solid electrolyte particle 10 can be used alone or in combination. In this specification, the lithium ion conductivity is defined as a value at a temperature of 298 K.

[0034] The non-molten phase 11 is present at least either within the grains or between the grains (grain boundaries) of the solid electrolyte particles 10. Fig. 1 shows an example in which the non-molten phase 11 is present between the grains of the solid electrolyte particles 10. Fig. 2 shows an example in which the non-molten phase 11 is present both within the grains and between the grains of the non-molten phase 11.

[0035] The non-molten phase 11 is preferably present at least between the particles of the solid electrolyte particles 10. This configuration offers the following advantages when the solid electrolyte 1 is used as the electrolyte of a lithium-ion battery. When lithium metal is used in the negative electrode of a lithium-ion battery, the garnet-type solid electrolyte usually reacts with the lithium metal of the negative electrode, causing the solid electrolyte to decompose. In contrast, when the non-molten phase 11 is present at least between the particles of the solid electrolyte particles 10, the non-molten phase 11 protects the solid electrolyte particles 10, thereby suppressing the reaction between the solid electrolyte 1 and the lithium metal of the negative electrode. Therefore, in this case, decomposition of the solid electrolyte 1 due to contact with the lithium metal of the negative electrode can be suppressed. Therefore, in this case, it becomes easier to use lithium metal in the negative electrode of a lithium-ion battery, making it possible to obtain a high-capacity lithium-ion battery. In this case, if non-molten phase 11 is a precipitate that precipitates during firing of solid electrolyte 1, decomposition of solid electrolyte 1 due to contact with lithium metal of the negative electrode can be suppressed by non-molten phase 11 that is self-formed between particles of solid electrolyte particles 10, even without adding non-molten phase 11 separately as a raw material.

[0036] The material constituting the non-melted phase 11 is preferably an insulating material (insulator). In this case, the defect concentration in the solid electrolyte 1 is increased, and lithium ion conductivity is likely to be improved. The insulating material is preferably a material containing Zr and O. In this case, the improvement in lithium ion conductivity can be ensured. In this case, the solid electrolyte 1 is produced by sintering, at a low temperature of less than 900°C, raw material powders including a solid electrolyte powder made of, for example, a lithium lanthanum zirconium-based composite oxide having the above-mentioned composition, a lithium lanthanum zirconium-based composite oxide having an excess composition in which the amount of Li and M3 is excessive compared to the stoichiometric ratio of the lithium lanthanum zirconium-based composite oxide having the above-mentioned composition, or a lithium lanthanum zirconium-based composite oxide having an excess composition in which the amount of Li or the amount of Li and M3 is excessive compared to the stoichiometric ratio of the lithium lanthanum zirconium-based composite oxide having the above-mentioned composition and containing B (boron). Examples of materials containing Zr and O that constitute an insulator include compounds containing Zr and O (Zr-O compounds such as ZrO2), compounds containing Zr, an M3 element, and O (Zr-M3-O compounds), compounds containing Zr, an M3 element, C, and O (Zr-M3-CO compounds), compounds containing Zr, C, and O (Zr-CO compounds), compounds containing Li, Zr, and O (Li-Zr-O compounds such as Li2ZrO3), compounds containing Li, Zr, an M3 element, and O (Li-Zr-M3-O compounds), compounds containing Li, Zr, an M3 element, C, and O (Li-Zr-CO compounds), and compounds containing Li, Zr, C, and O (Li-Zr-CO compounds). These may be contained alone or in combination.

[0037] The area ratio of the non-molten phase 11 can be set to 1% or more and 10% or less. In this case, the effect of improving the lithium ion conductivity of the solid electrolyte 1 can be enhanced, which is advantageous for increasing the output of the lithium ion battery. From the viewpoint of improving the lithium ion conductivity of the solid electrolyte 1, the area ratio of the non-molten phase 11 can be set to preferably 1.2% or more, more preferably 1.4% or more, even more preferably 1.6% or more, and still more preferably 1.8% or more. From the viewpoint of improving the lithium ion conductivity of the solid electrolyte 1, the area ratio of the non-molten phase 11 can be set to preferably 9.5% or less, more preferably 9% or less, even more preferably 8.5% or less, and still more preferably 8% or less.

[0038] The non-molten phase 11 can be in the form of particles. The particle diameter of the non-molten phase 11 can be configured to be smaller than the particle diameter of the solid electrolyte particles 10. The non-molten phase 11 is configured from a material having a lower lithium ion conductivity than the lithium lanthanum zirconium-based composite oxide that constitutes the solid electrolyte particles 10. Therefore, with this configuration, it is easier to suppress a decrease in the lithium ion conductivity of the solid electrolyte 1. In particular, when the material that constitutes the non-molten phase 11 is an insulating material, the effect of adopting this configuration can be enhanced.

[0039] The area ratio of the non-molten phase 11, the particle size of the non-molten phase 11, the particle size of the solid electrolyte particles 10, etc. can be measured by a combination of scanning electron microscope (SEM) observation of a cross section of the solid electrolyte 1, EDX analysis (energy dispersive X-ray analysis), image analysis, etc. Details will be described in the experimental examples.

[0040] The solid electrolyte 1 may further have a molten phase 12 that bonds the solid electrolyte particles 10 together. The molten phase 12 is a phase that becomes a liquid phase during sintering and then solidifies. , conclusion It is crystalline do.The molten phase 12 may include a Li-M3-O phase composed of a material containing Li, an M3 element, and O. Because Li-M3-O phases, such as the Li-Bi-O phase and the Li-Sb-O phase, are Li oxides with low melting points, they become liquid at low temperatures, facilitating sintering of the solid electrolyte, thereby improving the density of the solid electrolyte 1. Therefore, this configuration improves the lithium ion conductivity of the solid electrolyte 1. When the lithium-lanthanum zirconium-based composite oxide constituting the solid electrolyte particles contains Bi as the M3 element, the Li-M3-O phase can be a Li-Bi-O phase. When the lithium-lanthanum zirconium-based composite oxide contains Sb as the M3 element, the Li-M3-O phase can be a Li-Sb-O phase.

[0041] Specifically, the molten phase 12 can be present so as to fill the gaps (pores) between the solid electrolyte particles 10, as exemplified in Figures 1 and 2. The molten phase 12 may be present throughout the solid electrolyte 1, or may be present in only a partial region of the solid electrolyte 1.

[0042] When the solid electrolyte 1 has a molten phase 12 containing a Li-M3-O phase, the solid electrolyte 1 preferably has a non-molten phase 11 composed of a material containing Zr and O. In this case, element exchange is likely to occur between the M3 element (Bi or Sb) of the Li-M3-O phase contained in the molten phase 12 and the Zr contained in the non-molten phase 11. As described above, the Li-M3-O phase is a Li oxide with a low melting point. Therefore, in this case, sintering of the solid electrolyte can proceed at a lower temperature, which makes it easier to improve the density and lithium ion conductivity of the solid electrolyte 1.

[0043] In addition to the Li-M3-O phase, the molten phase 12 may further contain a Li-BO phase composed of a material containing Li, B (boron), and O. When the amount of the Li-M3-O phase contained in the molten phase 12 is too little or too much, the lithium ion conductivity tends to decrease. When the molten phase 12 contains the Li-BO phase, it is possible to suppress a decrease in lithium ion conductivity caused by an insufficient or excessive amount of the Li-M3-O phase.

[0044] The area ratio of the Li-M3-O phase can be set to 5% or more and 35% or less. In this case, the effect of improving the lithium ion conductivity of the solid electrolyte 1 can be enhanced, which is advantageous for increasing the output of lithium ion batteries. From the viewpoint of improving the lithium ion conductivity of the solid electrolyte 1, the area ratio of the Li-M3-O phase can be set to preferably 6% or more, more preferably 7% or more, and even more preferably 8% or more. From the viewpoint of improving the lithium ion conductivity of the solid electrolyte 1, the area ratio of the Li-M3-O phase can be set to preferably 34% or less, more preferably 33% or less, even more preferably 32% or less, and even more preferably 31% or less.

[0045] The area ratio of the Li-BO phase can be 1% or more and 12.5% ​​or less. In this case, the effect of suppressing a decrease in lithium ion conductivity due to an insufficient or excessive Li-M3-O phase can be ensured. From the viewpoint of improving the lithium ion conductivity of the solid electrolyte 1, the area ratio of the Li-BO phase can be preferably 1.2% or more, more preferably 1.4% or more, and even more preferably 1.6% or more. From the viewpoint of improving the lithium ion conductivity of the solid electrolyte 1, the area ratio of the Li-BO phase can be preferably 12% or less, more preferably 11.5% or less, even more preferably 11% or less, and even more preferably 10.5% or less.

[0046] The area ratios of the Li-MO phase and the Li-BO phase can be measured by combining scanning electron microscope (SEM) observation of a cross section of the solid electrolyte 1, EDX analysis (energy dispersive X-ray analysis), image analysis, etc. Details will be described in the Experimental Examples.

[0047] The solid electrolyte 1 can be configured such that the M3 element contained in the lithium-lanthanum-zirconium-based composite oxide constituting the solid electrolyte particles 10 is Sb, and a resistance component different from the resistance component derived from the solid electrolyte particles 10 is detected in AC impedance measurement after bringing lithium metal into contact with the surface of the solid electrolyte 1 and subjecting it to heat treatment at 190°C.

[0048] This configuration can suppress decomposition of the solid electrolyte 1 due to contact with lithium metal. Furthermore, the solid electrolyte 1 has high lithium ion conductivity. Therefore, this configuration allows lithium metal to be used in the negative electrode bonded to the solid electrolyte 1, that is, lithium metal can be used as the negative electrode active material, making it possible to construct a lithium ion battery with high capacity and in which decomposition of the solid electrolyte 1 is suppressed.

[0049] Specifically, the resistance component originating from the solid electrolyte particles 10 is the intra-particle resistance and the grain boundary resistance originating from the solid electrolyte particles 10 detected in the AC impedance measurement. The resistance component different from the resistance component originating from the solid electrolyte particles 10 is a resistance component that appears in a lower frequency range than the frequency range of the resistance component originating from the solid electrolyte particles 10 detected in the AC impedance measurement.

[0050] The solid electrolyte 1 can be produced by, for example, the first to third production methods described below, but is not limited to these.

[0051] First, we will explain the first manufacturing method of the solid electrolyte 1. The first manufacturing method is a method in which a mixed raw material powder containing a first solid electrolyte powder composed of a lithium-lanthanum-zirconium-based composite oxide having the above composition, a Li-M3-O powder containing Li, the above M3 element, and O, and, as necessary, a Li-BO powder containing Li, B, and O is used as a starting raw material powder, the starting raw material powder is molded, and the resulting molded body is sintered at a sintering temperature of less than 900°C.

[0052] In synthesizing the first solid electrolyte powder, for example, the Li source, M1 source, La source, M2 source, Zr source, M3 source, and M4 source are weighed out so as to obtain the lithium-lanthanum-zirconium composite oxide having the above-mentioned composition. When synthesizing by solid-state reaction, each raw material can be prepared in the form of an oxide, hydroxide, carbonate, or the like. When synthesizing by wet synthesis, each raw material can be prepared in the form of a nitrate, or the like. Next, the predetermined raw materials are pulverized and mixed using a planetary ball mill or the like containing an organic solvent such as ethanol and zirconia balls. Next, the resulting material is dried and sieved to separate the zirconia balls, and then placed in an alumina crucible or the like and fired at 700°C to 950°C in an air atmosphere. Next, the resulting material is pulverized using a uniaxial ball mill or the like containing an organic solvent such as ethanol and zirconia balls, dried, and then sieved to separate the zirconia balls. This allows the synthesis of the first solid electrolyte powder.

[0053] Examples of Li-M3-O powders that can be used include LiBiO2 powder and Li7SbO6 powder. When the M3 element of the first solid electrolyte powder is Bi, LiBiO2 powder can be used. When the M3 element of the first solid electrolyte powder is Sb, Li7SbO6 powder can be used. For example, the Li-M3-O powder is prepared by weighing out the Li and M3 source materials to achieve the desired Li-M3-O powder composition. The materials can be synthesized, for example, by solid-state reactions and prepared in the form of oxides, hydroxides, carbonates, or the like. The materials are then pulverized and mixed using a planetary ball mill or similar device containing an organic solvent such as ethanol and zirconia balls. The resulting material is then dried and sieved to separate it from the zirconia balls. The mixture is then placed in an alumina crucible or similar device and fired at 600°C to 900°C in an argon or air atmosphere. The resulting material is then pulverized using a uniaxial ball mill containing zirconia balls and an organic solvent such as ethanol, dried, and sieved to separate the zirconia balls, resulting in the synthesis of Li-MO powder.

[0054] Li-BO powder can be, for example, Li3BO3 powder. For Li-BO powder, for example, the Li and B raw materials are weighed to achieve the desired Li-BO powder composition. The raw materials can be synthesized, for example, by solid-state reaction and can be prepared in the form of oxide, hydroxide, carbonate, or the like. Next, the predetermined raw materials are pulverized and mixed using a planetary ball mill or the like containing zirconia balls and an organic solvent such as ethanol. The resulting material is then dried and sieved to separate the zirconia balls. The resulting material is then placed in an alumina crucible and fired at 500°C to 600°C in an inert gas atmosphere such as argon. The resulting material is then pulverized using a uniaxial ball mill or the like containing zirconia balls and an organic solvent such as ethanol, dried, and sieved to separate the zirconia balls. This allows the synthesis of Li-BO powder.

[0055] The sintering temperature during production of the solid electrolyte 1 can be preferably 890°C or lower, more preferably 870°C or lower, even more preferably 860°C or lower, and even more preferably 850°C or lower. From the viewpoint of sintering acceleration, the sintering temperature during production of the solid electrolyte 1 can be preferably 640°C or higher, more preferably 690°C or higher, even more preferably 720°C or higher, and even more preferably 730°C or higher. The sintering time can be 2 to 72 hours. Additives such as binders and pore formers can be added to the starting material powder as needed. Examples of methods for forming the compact include known powder compacting and slurry casting. The compact can also be composed of multiple layers.

[0056] According to the first manufacturing method, a solid electrolyte 1 can be obtained in which non-molten phases 11 made of a material containing Zr and O are precipitated between and within solid electrolyte particles 10 made of a lithium-lanthanum-zirconium-based composite oxide. When the starting raw material powder contains Li-M3-O powder or Li-BO powder, these are converted into a liquid phase during sintering, and a solid electrolyte 1 can be obtained in which the solid electrolyte particles are bound together by a molten phase containing the Li-M3-O phase or Li-BO phase.

[0057] Next, a second method for producing the solid electrolyte 1 will be described. The second method uses a mixed starting powder material, which is a second solid electrolyte powder synthesized by charging the raw materials so that the amounts of Li and M3 are in excess compared to the stoichiometric ratio of the lithium-lanthanum-zirconium-based composite oxide having the above composition, and, if necessary, a Li-BO powder containing Li, B, and O. The starting powder material is molded, and the resulting molded body is sintered at a sintering temperature of less than 900°C. In other words, in the second method, the starting powder material does not contain Li-M3-O powder. The second method is similar to the first method except for the different starting powder material, and only the differences will be described.

[0058] In the second manufacturing method, a second solid electrolyte powder is synthesized. Specifically, the second solid electrolyte powder can be composed of a lithium-lanthanum-zirconium-based composite oxide having an excess composition in which the amount of Li and the amount of M3 are in excess compared to the stoichiometric ratio of the lithium-lanthanum-zirconium-based composite oxide having the above composition.

[0059] In synthesizing the second solid electrolyte powder, for example, the Li source, M1 source, La source, M2 source, Zr source, M3 source, and M4 source are weighed so that the amount of Li and M3 is in excess compared to the stoichiometric ratio of the lithium-lanthanum-zirconium composite oxide having the above composition. When synthesized by solid-state reaction, each raw material can be prepared in the form of an oxide, hydroxide, carbonate, etc., while when synthesized by wet synthesis, it can be prepared in the form of a nitrate, etc. Next, the predetermined raw materials are pulverized and mixed using a planetary ball mill or the like containing an organic solvent such as ethanol and zirconia balls. The resulting material is then dried and sieved to separate the zirconia balls, and placed in an alumina crucible or the like and fired at 700°C to 950°C in an air atmosphere. The resulting material is then pulverized using a uniaxial ball mill or the like containing an organic solvent such as ethanol and zirconia balls, dried, and sieved to separate the zirconia balls. This allows the second solid electrolyte powder to be synthesized.

[0060] The second manufacturing method can provide a solid electrolyte 1 in which non-molten phases 11 composed of a material containing Zr and O are precipitated between and within solid electrolyte particles 10 composed of a lithium-lanthanum-zirconium-based composite oxide. Furthermore, during sintering, a liquid phase of Li-M3-O is generated from the second solid electrolyte powder contained in the starting material powder. Therefore, the second manufacturing method can provide a solid electrolyte 1 including regions where the solid electrolyte particles are bonded together by a molten phase containing the Li-M3-O phase. If the starting material powder contains Li-BO powder, this powder becomes liquid during sintering. Therefore, in this case, a solid electrolyte 1 can be provided in which the solid electrolyte particles are bonded together by a molten phase containing the Li-M3-O phase and the Li-BO phase.

[0061] Next, a third manufacturing method for the solid electrolyte 1 will be described. The third manufacturing method uses a mixed raw material powder as a starting raw material powder, which includes a third solid electrolyte powder synthesized so that the amount of Li, or the amount of Li and M3, is in excess compared to the stoichiometric ratio of the lithium-lanthanum-zirconium-based composite oxide having the above composition, and also contains B, and optionally a Li-M3-O powder containing Li, M3, and O. This starting raw material powder is molded, and the resulting molded body is sintered at a sintering temperature of less than 900°C. In other words, in the third manufacturing method, the starting raw material powder does not contain Li-BO powder. The third manufacturing method is similar to the first manufacturing method except for the different starting raw material powder, so only the differences will be described.

[0062] In the third manufacturing method, a third solid electrolyte powder is synthesized. Specifically, the third solid electrolyte powder has an excess composition in which the amount of Li, or the amount of Li and M3, is excess compared to the stoichiometric ratio of the lithium-lanthanum-zirconium-based composite oxide having the above composition, and can be composed of a lithium-lanthanum-zirconium-based composite oxide containing the element B.

[0063] In the synthesis of the third solid electrolyte powder, for example, the Li source, M1 source, La source, M2 source, Zr source, M3 source, M4 source, and B source are weighed out so that the amount of Li or the amount of Li and M3 is in excess compared to the stoichiometric ratio of the lithium-lanthanum-zirconium-based composite oxide having the above composition, and the desired amount of Li-BO compound is added. When synthesized by solid-state reaction, each raw material can be prepared in the form of an oxide, hydroxide, carbonate, etc., or when synthesized by wet synthesis, it can be prepared in the form of a nitrate, etc. Next, the predetermined raw materials are pulverized and mixed using a planetary ball mill or the like containing an organic solvent such as ethanol and zirconia balls. The resulting material is then dried and sieved to separate it from the zirconia balls, and then placed in an alumina crucible or the like and fired in an air atmosphere at 700°C to 950°C. The resulting material is then pulverized using a uniaxial ball mill containing zirconia balls and an organic solvent such as ethanol, dried, and sieved to separate the zirconia balls, thereby synthesizing the third solid electrolyte powder.

[0064] According to the third manufacturing method, a solid electrolyte 1 can be obtained in which a non-molten phase 11 composed of a material containing Zr and O is precipitated between, within, and between solid electrolyte particles 10 composed of a lithium-lanthanum-zirconium-based composite oxide. Furthermore, during sintering, a liquid phase of Li-BO phase is produced from the third solid electrolyte powder contained in the starting material powder. If the amount of M3 is excessive, a Li-M3-O phase is also produced from the third solid electrolyte powder. Therefore, according to the third manufacturing method, a solid electrolyte 1 can be obtained in which the solid electrolyte particles are bonded together by the Li-BO phase or a molten phase containing the Li-M3-O phase and the Li-BO phase.

[0065] (Embodiment 2) The lithium-ion battery of embodiment 2 will be described with reference to Fig. 3. Note that, among the symbols used in embodiment 2 and subsequent embodiments, the same symbols as those used in the previous embodiments represent the same components as those in the previous embodiments, unless otherwise specified.

[0066] As illustrated in FIG. 3, the lithium ion battery 2 of this embodiment is a so-called all-solid-state battery (sometimes called an all-solid-state lithium ion secondary battery), and has the solid electrolyte 1 of Embodiment 1 as an electrolyte.

[0067] Specifically, the lithium-ion battery 2 includes a cell 20 and a current collecting layer 3. FIG. 3 illustrates a lithium-ion battery 2 in which the cell 20 is sandwiched between a pair of current collecting layers 3. Although not shown, the lithium-ion battery 2 may include a plurality of cells 20 and have a stacked structure in which the plurality of cells 20 are stacked with the current collecting layers 3 interposed therebetween (a stacked structure in which the cells 20 and the current collecting layers 3 are alternately stacked). Specifically, the cell 20 includes a layered solid electrolyte 1, a positive electrode layer 21 provided on one side of the solid electrolyte 1, and a negative electrode layer 22 provided on the other side of the solid electrolyte 1. The layered solid electrolyte 1 functions as a separator layer. The layered solid electrolyte 1, the positive electrode layer 21, and the negative electrode layer 22 can be integrated by firing. That is, the positive electrode layer 21 and the negative electrode layer 22 can all be bonded to the layered solid electrolyte 1. The current collecting layer 3 can be integrated with the positive electrode layer 21 or the negative electrode layer 22 by firing. That is, the current collecting layer 3 can be bonded to the positive electrode layer 21 or the negative electrode layer 22.

[0068] The positive electrode layer 21 can be configured to include, for example, a positive electrode active material (not shown) containing Li and a solid electrolyte (not shown) in the positive electrode layer that exhibits lithium ion conductivity. The positive electrode active material is a material that can release lithium ions when the lithium ion battery 2 is charged and can take in lithium ions when the lithium ion battery 2 is discharged. Examples of the positive electrode active material include lithium cobalt oxide (lithium cobalt oxide) such as LiCoO2, LiNi x Mn y Co zExamples of the solid electrolyte in the positive electrode layer include a composite oxide of Li and a transition metal, such as lithium nickel manganese cobalt oxide (lithium nickel manganese cobalt oxide) such as O2 (x + y + z = 1), lithium manganese oxide (lithium manganese oxide) such as LiMn2O4, and lithium iron phosphate such as LiFePO4. These may be used alone or in combination of two or more. Examples of the solid electrolyte in the positive electrode layer include a solid electrolyte composed of a known lithium lanthanum zirconium composite oxide having a garnet-type crystal structure, and the solid electrolyte 1 of embodiment 1.

[0069] The negative electrode layer 22 can be composed of, for example, a negative electrode active material (not shown) containing Li, or can be composed of a negative electrode active material containing Li and a negative electrode solid electrolyte (not shown) exhibiting lithium ion conductivity. Examples of the negative electrode active material include lithium metal, lithium alloys, and lithium compounds such as lithium-containing composite oxides. These can be used alone or in combination. Lithium metal is preferably used as the negative electrode active material because it can increase the potential difference and provide a high-capacity lithium-ion battery 2. Examples of the negative electrode solid electrolyte include a solid electrolyte composed of a known lithium-lanthanum-zirconium-based composite oxide having a garnet-type crystal structure, such as the solid electrolyte 1 of embodiment 1. In the lithium-ion battery 2 of this embodiment, the solid electrolyte in the positive electrode layer and the solid electrolyte in the negative electrode layer can be composed of the solid electrolyte 1 of embodiment 1.

[0070] Examples of materials constituting the current collecting layer 3 include nickel, stainless steel, carbon, conductive glass, gold, lithium metal, and mixtures of these materials with insulating glass. The current collecting layer 3 on the positive electrode layer 21 side and the current collecting layer 3 on the negative electrode layer 22 side may be made of the same material or different materials.

[0071] The lithium ion battery 2 of this embodiment is advantageous for achieving high output because it uses the solid electrolyte 1 of this embodiment 1. In particular, when the M3 element of the solid electrolyte 1 is Sb and lithium metal is used as the negative electrode active material of the negative electrode layer 22, it is possible to configure a lithium ion battery that has a high capacity and high durability in which decomposition of the solid electrolyte 1 is suppressed.

[0072] In the lithium ion battery 2, only the positive electrode layer 21 may use the solid electrolyte 1 as the solid electrolyte in the positive electrode layer, only the separator layer may use the solid electrolyte 1, or only the negative electrode layer 22 may use the solid electrolyte 1 as the solid electrolyte in the negative electrode layer. In the lithium ion battery 2, the positive electrode layer 21 and the separator layer may use the solid electrolyte 1, or the negative electrode layer 22 and the separator layer may use the solid electrolyte 1, or the positive electrode layer 21, the separator layer, and the negative electrode layer 22 may use the solid electrolyte 1.

[0073] (Experimental Example 1) <Preparation of solid electrolyte> According to the first manufacturing method described above, solid electrolytes of Samples 1, 2, 1C, and 2C were prepared.

[0074] -Sample 1- The Li source was LiOH(HO), the La source was La(OH), the M source was CaCO, the Zr source was ZrO, and the M source was BiO. Each raw material was a lithium-lanthanum-zirconium-based composite oxide (specifically, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Bi 0.6 O 12) were weighed to obtain a composition of the raw materials. Next, each raw material was crushed and mixed using a planetary ball mill or the like containing ethanol and zirconia balls. Next, the obtained material was dried, sieved to separate the zirconia balls, and placed in an alumina crucible and fired at 900°C for 12 hours in an air atmosphere. Next, the obtained material was crushed for 10 hours using a uniaxial ball mill or the like containing ethanol and zirconia balls, dried, and then sieved to separate the zirconia balls. As a result, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Bi 0.6 O 12 A solid electrolyte powder composed of the above was synthesized. Li2ZrO3 powder was also synthesized as a non-molten phase material. Specifically, LiOH(H2O) and ZrO2 were prepared. Each raw material was weighed to achieve the Li2ZrO3 composition. Next, each raw material was crushed and mixed using a planetary ball mill or similar device containing ethanol and zirconia balls. The resulting material was then dried and sieved to separate the zirconia balls. It was then placed in an alumina crucible and fired at 600°C for 12 hours in an air atmosphere. The resulting material was then crushed for 10 hours using a uniaxial ball mill or similar device containing ethanol and zirconia balls, dried, and sieved to separate the zirconia balls. This resulted in the synthesis of Li2ZrO3 powder.

[0075] Next, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Bi 0.6 O 12 A mixed raw material powder was prepared by adding 1.5 wt% of Li2ZrO3 powder to a solid electrolyte powder composed of the above and mixing them in a mortar. This mixed raw material powder was compacted into a layer at 98 MPa, and the resulting compact was sintered for 5 hours at a sintering temperature of 850°C shown in Table 1. This produced the solid electrolyte of Sample 1 (thickness: 1000 μm).

[0076] -Sample 2- The Li source was LiOH(H2O), the La source was La(OH)3, the M2 source was CaCO3, the Zr source was ZrO2, and the M3 source was Sb2O3. Each raw material was a lithium-lanthanum-zirconium-based composite oxide (specifically, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 ) were weighed to obtain a composition of the raw materials. Next, each raw material was crushed and mixed using a planetary ball mill or the like containing ethanol and zirconia balls. Next, the obtained material was dried, sieved to separate the zirconia balls, and placed in an alumina crucible and fired at 900°C for 12 hours in an air atmosphere. Next, the obtained material was crushed for 10 hours using a uniaxial ball mill or the like containing ethanol and zirconia balls, dried, and then sieved to separate the zirconia balls. As a result, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 A solid electrolyte powder composed of the above was synthesized.

[0077] Next, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 A mixed raw material powder was prepared by adding 1.5 wt% of Li2ZrO3 powder to a solid electrolyte powder composed of the above and mixing them in a mortar. This mixed raw material powder was compacted into a layer at 98 MPa, and the resulting compact was sintered for 5 hours at a sintering temperature of 850°C shown in Table 1. This produced the solid electrolyte of Sample 2 (thickness 1000 μm).

[0078] -Sample 1C- In the preparation of sample 1, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Bi 0.6 O 12The solid electrolyte of Sample 1C was prepared in the same manner as above, except that only the solid electrolyte powder composed of the above was compressed and sintered.

[0079] -Sample 2C- In the preparation of sample 2, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 The solid electrolyte of Sample 2C was produced in the same manner as above, except that only the solid electrolyte powder composed of the above was compressed and sintered.

[0080] <Microstructural observation of solid electrolyte> -Non-molten phase- The resin-embedded solid electrolyte sample was processed with a cross-section polisher (CP) under cryo-conditions to expose a cross section along the thickness direction. Next, elemental mapping was obtained by SEM-EDX analysis of the cross section of the solid electrolyte. Specifically, the cross section of the solid electrolyte was observed using a field emission scanning electron microscope (FE-SEM) (Hitachi High-Tech Corporation, "S-4800"). Furthermore, EDX analysis (energy dispersive X-ray analysis, Bruker AXS, "QUANTAX Flat QUAD System Xflash5060FQ") was performed on the SEM-observed portion to obtain elemental mapping. In this experimental example, the non-melted phase was composed of a material containing Zr and O, so the Zr elemental mapping image was used to calculate the area ratio and particle size of the non-melted phase.

[0081] Specifically, image analysis software (ImageJ, manufactured by the National Institutes of Health, USA) was used to import the Zr elemental mapping data. The contrast was then adjusted as necessary to focus on areas with high Zr brightness. A histogram of brightness was then created, and the number of voxels corresponding to the bright areas and the total number of voxels were calculated. The area fraction (%) of the non-molten phase was calculated using the formula: (number of voxels corresponding to the bright areas) / (total number of voxels) × 100 × relative density / 100. The relative density (%) was calculated using the volume and weight of the solid electrolyte sample, the specific gravity of the material, and the material mixing ratio. Note that voids can be excluded by multiplying the relative density as described above.

[0082] In addition, the particle size of the bright areas of the Zr element mapping image was measured with an n number of 20, and the average value of the obtained particle size measurements was calculated as the particle size of the non-molten phase. The particle size of the solid electrolyte was calculated using the image analysis software (ImageJ) mentioned above. The relationship between the particle size of the solid electrolyte and the particle size of the non-molten phase was then determined. The basic operations for particle size analysis using ImageJ were performed according to the procedures detailed at https: / / www.nims.go.jp / tem / download / Image_J.pdf.

[0083] -Li-BO phase- The area fraction of the Li-BO phase was calculated for each solid electrolyte. In this experimental example, the area where B was detected in the SEM-EDX analysis described above was considered to be the Li-BO phase, and the area fraction of the Li-BO phase was calculated in the same manner as for calculating the area fraction of the molten phase. Specifically, because B is not doped into the lithium-lanthanum-zirconium composite oxide, B is not detected inside the solid electrolyte particles. However, the detection sensitivity of B, a light element, is low in EDX. Therefore, after confirming the location of B using EDX, the contrast portion corresponding to the Li-BO phase was extracted by comparing it with the SEM backscattered electron image. Since the Li-BO phase is composed of light elements, it appears the darkest. Then, analysis was performed using image analysis software in the same manner as for calculating the area fraction of the molten phase, and the area fraction of the Li-BO phase was calculated.

[0084] -Li-M3-O phase- The area fraction of the Li-M3-O phase was calculated for each solid electrolyte. In this experimental example, the Li-M3-O phase was either the Li-Sb-O phase or the Li-Bi-O phase. The calculation of the area fraction of the Li-M3-O phase was similar to the calculation of the area fraction of the Li-BO phase described above. Specifically, since the M3 element is also present inside the lithium-lanthanum-zirconium-based composite oxide, it is detected between and within the solid electrolyte particles. Therefore, EDX was used to identify the molten phase where the M3 element was detected, and the contrast corresponding to the Li-M3-O phase was extracted by comparing it with the backscattered electron image of the SEM. Due to the weight of the constituent elements, the Li-M3-O phase appears brighter than the Li-BO phase and darker than the lithium-lanthanum-zirconium-based composite oxide. Then, similar to the calculation of the area fraction of the molten phase, image analysis software was used to calculate the area fraction of the Li-M3-O phase.

[0085] <Measurement of lithium ion conductivity and relative density of solid electrolyte> The lithium ion conductivity (S / cm) and relative density (%) at 298 K were measured for each solid electrolyte. The lithium ion conductivity of the solid electrolyte was measured using an impedance analyzer (Keysight, "E4990A"), with Au sputtered layers formed to a thickness of 500 nm or more on both sides of the solid electrolyte as electrodes. The relative density was calculated using the volume and weight of the sample, the specific gravity of the material, and the mixing ratio of the material. The specific gravity of the material was measured using a Shimadzu "AccuPyc 1340-1CC."

[0086] The composition, manufacturing conditions, and measurement results of the solid electrolyte of each sample are summarized in Table 1. FIG. 4 shows the SEM-EDX analysis results of the solid electrolytes of Sample 2C, Sample 1, and Sample 2.

[0087] [Table 1]

[0088] Table 1 and Figure 4 reveal the following. As shown in Figures 4(a) and (b), the solid electrolyte of Sample 2C did not exhibit any non-molten phases within or between the solid electrolyte particles. Although not shown, the solid electrolyte of Sample 1C exhibited similar results. In contrast, as can be seen from a comparison of Figures 4(c) and 4(d) and a comparison of Figures 4(e) and 4(f), the solid electrolytes of Samples 1 and 2 exhibited particulate non-molten phases within or between the solid electrolyte particles. The Zr element mapping images in Figures 4(d) and 4(f) reveal that the non-molten phase (corresponding to the bright granular areas in Figures 4(d) and 4(f)) was composed of a material containing Zr and O, specifically, Li2ZrO3. The material comprising this non-molten phase is an insulating material with lower lithium ion conductivity than the lithium-lanthanum-zirconium-based composite oxide comprising the solid electrolyte particles. The particle size of the non-molten phase was smaller than that of the solid electrolyte particles. In the solid electrolytes of Samples 1 and 2, gaps (pores) between the solid electrolyte particles were observed, but the molten phase binding the solid electrolyte particles together was not observed within the observation range.

[0089] As shown in Table 1, the solid electrolytes of Samples 1C and 2C had low lithium ion conductivity due to the absence of a non-molten phase at least either within or between the solid electrolyte particles having a specific composition. In contrast, the solid electrolytes of Samples 1 and 2 had a non-molten phase at least either within or between the solid electrolyte particles having a specific composition, and thus were able to achieve high lithium ion conductivity even with low-temperature sintering below 900°C.

[0090] (Experimental Example 2) <Preparation of solid electrolyte> According to the first manufacturing method described above, the solid electrolytes of Samples 3 to 6 were produced. Furthermore, the solid electrolytes of Samples 3C and 4C were produced by a conventional manufacturing method in which the sintering temperature exceeds 900°C.

[0091] -Sample 3 to Sample 6- The solid electrolyte was prepared in the same manner as in Sample 2 of Experimental Example 1. 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 A solid electrolyte powder composed of the above was synthesized.

[0092] In addition, Li7SbO6 powder was synthesized as Li-M3-O powder in the same manner as in the preparation of the solid electrolyte of Sample 2 in Experimental Example 1.

[0093] In addition, Li7SbO6 powder was synthesized as Li-M3-O powder. Specifically, a Li source: LiOH(H2O) and an M3 source: Sb2O3 were prepared. Each raw material was weighed to achieve the composition Li7SbO6. Next, each raw material was crushed and mixed using a planetary ball mill or similar device containing ethanol and zirconia balls. The resulting material was then dried and sieved to separate the zirconia balls, and placed in an alumina crucible where it was fired at 850°C for 24 hours in an air atmosphere. Next, the resulting material was crushed for 12 hours using a uniaxial ball mill or similar device containing ethanol and zirconia balls, dried, and then sieved to separate the zirconia balls. This resulted in the synthesis of Li7SbO6 powder.

[0094] In addition, Li3BO3 powder was synthesized as Li-BO powder. Specifically, a Li source: LiOH(H2O) and a B source: B2O3 were prepared. Each raw material was weighed to achieve the composition of Li3BO3. Next, each raw material was crushed and mixed using a planetary ball mill or the like containing ethanol and zirconia balls. Next, the obtained material was dried and sieved to separate the zirconia balls, and then placed in an alumina crucible and fired at 510°C for 6 hours in an Ar atmosphere. Next, the obtained material was crushed for 12 hours using a uniaxial ball mill or the like containing ethanol and zirconia balls, dried, and then sieved to separate the zirconia balls. In this way, Li3BO3 powder was synthesized.

[0095] Next, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 A mixed raw material powder was prepared by adding 2% by weight of Li7SbO6 powder to a solid electrolyte powder composed of the above and mixing them in a mortar. This mixed raw material powder was compacted into a layer at 98 MPa, and the resulting compact was sintered at a sintering temperature of 850°C shown in Table 2 for 5 hours to prepare the solid electrolyte of Sample 3. Similarly, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12A mixed raw material powder was prepared by adding 2 wt% of Li7SbO6 powder to a solid electrolyte powder composed of the above and mixing them in a mortar. This mixed raw material powder was compacted into a layer at 98 MPa, and the resulting compact was sintered at a sintering temperature of 800°C (Table 2) for 5 hours to prepare the solid electrolyte of Sample 4.

[0096] Also, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 A mixed raw material powder was prepared by adding 2 wt% of Li7SbO6 powder and 4.75 wt% of Li3BO3 powder to a solid electrolyte powder composed of the above. The mixture was then mixed in a mortar. This mixed raw material powder was compacted into a layer at 98 MPa, and the resulting compact was sintered at 750°C for 5 hours as shown in Table 2 to prepare the solid electrolyte of Sample 5. Similarly, Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 A mixed raw material powder was prepared by adding 2 wt% of Li7SbO6 powder and 9.5 wt% of Li3BO3 powder to a solid electrolyte powder composed of the above. This mixed raw material powder was compacted into a layer at 98 MPa, and the resulting compact was sintered at 750°C for 5 hours as shown in Table 2 to prepare the solid electrolyte of Sample 6.

[0097] -Sample 3C, Sample 4C- In the preparation of the solid electrolyte of Sample 2 in Experimental Example 1, Li was prepared in the same manner as in the preparation of the solid electrolyte of Sample 2 except that the M2 source was not used and Ga2O3 as the M1 source and Nb2O5 as the M4 source were added. 5.45 Ga 0.5 La3Zr 1.95 Sb 0.025 Nb 0.025 O 12 In addition, in the same manner as in the solid electrolytes of Samples 3 to 6, Li7SbO6 powder was synthesized as the Li-M3-O powder, and Li3BO3 powder was synthesized as the Li-BO powder.

[0098] Li 6.5 Ga 0.15 La3Zr 1.95 Sb 0.025 Nb 0.025 O 12 A mixed raw material powder was prepared by adding 2% by weight of Li7SbO6 powder to a solid electrolyte powder composed of the above and mixing them in a mortar. This mixed raw material powder was compacted into a layer at 98 MPa, and the resulting compact was sintered at 900°C for 5 hours as shown in Table 2 to prepare the solid electrolyte of sample 3C. 6.5 Ga 0.15 La3Zr 1.95 Sb 0.025 Nb 0.025 O 12 A mixed raw material powder was prepared by adding 2 wt% of Li7SbO6 powder and 3 wt% of Li3BO3 powder to a solid electrolyte powder composed of the above. This mixed raw material powder was compacted into a layer at 98 MPa, and the resulting compact was sintered at 900°C for 5 hours, as shown in Table 2, to prepare the solid electrolyte of sample 4C.

[0099] The microstructure of the solid electrolyte of each sample was observed, and the lithium ion conductivity and relative density were measured in the same manner as in Experimental Example 1. Table 2 summarizes the composition, manufacturing conditions, and measurement results of the solid electrolyte of each sample. Figure 5 shows the SEM-EDX analysis results of the solid electrolyte of Sample 4. Figure 6 shows the SEM-EDX analysis results of the solid electrolyte of Sample 6.

[0100] [Table 2]

[0101] Table 2, Figures 5, and 6 reveal the following. Comparing the solid electrolytes of Samples 3, 4, and 3C, we find that the solid electrolytes of Samples 3 and 4 maintain high lithium-ion conductivity even when sintered at low temperatures below 900°C. Similarly, comparing the solid electrolytes of Samples 5, 6, and 4C, we find that the solid electrolytes of Samples 5 and 6 maintain high lithium-ion conductivity even when sintered at low temperatures below 900°C. This is because the solid electrolytes of Samples 3 to 6 have a non-molten phase, as shown in Figures 5(b), 6(b), and Table 2, whereas the solid electrolytes of Samples 3C and 4C do not, as shown in Table 2. Furthermore, in the solid electrolytes of Samples 3 to 6, regions where a molten phase was formed were observed, filling the gaps between the solid electrolyte particles, as shown in Figures 5(a) and 6(a). In the solid electrolytes of samples 3 and 4, which contained Li-MO powder but not Li-BO powder, it was confirmed that the molten phase contained the Li-MO phase (here, the amorphous Li-Sb-O phase) as shown in Figures 5(a) and 5(c).In the solid electrolytes of samples 5 and 6, which contained both Li-MO powder and Li-BO powder, it was confirmed that the molten phase contained the Li-MO phase (here, the amorphous Li-Sb-O phase) and the Li-BO phase as shown in Figures 6(a), 6(c), and 6(d).

[0102] (Experimental Example 3) <Preparation of solid electrolyte> According to the first manufacturing method described above, solid electrolytes of Samples 7 to 14 were prepared.

[0103] -Sample 7 to Sample 14- The solid electrolytes of Samples 7 to 14 were prepared in the same manner as in the preparation of the solid electrolytes of Samples 5 and 6 in Experimental Example 2. These solid electrolytes had solid electrolyte particles made of a lithium-lanthanum zirconium-based composite oxide containing Sb as the M3 element, a non-molten phase made of Zr and O, and a molten phase containing the Li-Sb-O phase and the Li-BO phase. In this experiment, ZrO2 powder was mixed with the synthesized lithium-lanthanum zirconium-based composite oxide, and the area proportion of the non-molten phase was changed by changing the mixture ratio and the ZrO2 particle size.

[0104] In the same manner as in Experimental Example 1, the microstructure of the solid electrolyte of each sample was observed, and the lithium ion conductivity and relative density were measured. Table 3 shows the composition, manufacturing conditions, and measurement results of the solid electrolyte of each sample. In addition, Figure 7 shows the relationship between the area ratio (%) of the non-molten phase and the lithium ion conductivity (S / cm).

[0105] [Table 3]

[0106] Table 3 and FIG. 7 reveal the following. As shown in Table 3 and FIG. 7, when the area ratio of the non-molten phase 11 is in the range of 1% or more and 10% or less, the effect of improving the lithium ion conductivity can be enhanced. Therefore, in this case, it can be said that a solid electrolyte advantageous for increasing the output of a lithium ion battery can be obtained. Furthermore, when the solid electrolytes of Samples 7 to 13 are compared with the solid electrolyte of Sample 14, it can be seen that by configuring the particle size of the non-molten phase to be smaller than the particle size of the solid electrolyte particles, it is easier to suppress the decrease in the lithium ion conductivity of the solid electrolyte. In particular, when the material constituting the non-molten phase 11 is an insulating material, it can be said that the effect of adopting this configuration can be enhanced.

[0107] (Experimental Example 4) <Preparation of solid electrolyte> According to the first manufacturing method described above, solid electrolytes of Samples 15 to 20 were produced.

[0108] -Sample 15 to Sample 20- In the same manner as in the preparation of the solid electrolytes of Samples 5 and 6 in Experimental Example 2, the solid electrolytes of Samples 15 to 20 were prepared, each having solid electrolyte particles composed of a lithium-lanthanum-zirconium-based composite oxide containing Sb as the M3 element, a non-molten phase composed of Zr and O, and a molten phase containing the Li-M3-O phase (Li-Sb-O phase in this Experimental Example) and Li-BO phase. In this Experimental Example, the area proportion of the Li-M3-O phase in the molten phase was changed by changing the proportion of the Li7SbO6 powder mixed.

[0109] The microstructure of the solid electrolyte of each sample was observed, and the lithium ion conductivity and relative density were measured in the same manner as in Experimental Example 1. Table 4 summarizes the composition, manufacturing conditions, and measurement results of the solid electrolyte of each sample. Figure 8 shows the relationship between the area percentage (%) of the Li-M3-O phase and the lithium ion conductivity (S / cm). Figure 9 shows the relationship between the area percentage (%) of the Li-M3-O phase and the relative density (%).

[0110] [Table 4]

[0111] Table 4, Figures 8 and 9 reveal the following. As shown in Table 4 and Figure 8, when the area ratio of the Li-M3-O phase is in the range of 5% or more and 35% or less, the effect of improving lithium ion conductivity can be enhanced. This is thought to be because, as shown in Table 4 and Figure 9, when the area ratio of the Li-M3-O phase is in the above-mentioned specific range, the liquid phase wets and spreads during sintering, making it easier for the solid electrolyte particles to be closely packed, promoting densification and improving the relative density.

[0112] (Experimental Example 5) <Preparation of solid electrolyte> According to the first manufacturing method described above, solid electrolytes of Samples 21 to 25 were prepared.

[0113] -Samples 21 to 25- In the same manner as in the preparation of the solid electrolytes of Samples 5 and 6 in Experimental Example 2, the solid electrolytes of Samples 21 to 25 were prepared, each having solid electrolyte particles composed of a lithium-lanthanum-zirconium-based composite oxide containing Sb as the M3 element, a non-molten phase composed of Zr and O, and a molten phase containing the Li-M3-O phase (Li-Sb-O phase in this Experimental Example) and the Li-BO phase. In this Experimental Example, the area proportion of the Li-BO phase in the molten phase was changed by changing the proportion of the Li3BO3 powder to be mixed.

[0114] The microstructure of the solid electrolyte of each sample was observed, and the lithium ion conductivity and relative density were measured in the same manner as in Experimental Example 1. Table 5 summarizes the composition, manufacturing conditions, and measurement results of the solid electrolyte of each sample. Figure 10 shows the relationship between the area percentage (%) of the Li-BO phase and the lithium ion conductivity (S / cm). Figure 11 shows the relationship between the area percentage (%) of the Li-BO phase and the relative density (%).

[0115] [Table 5]

[0116] Table 5, Figures 10 and 11 reveal the following. As shown in Table 5 and Figure 10, when the area ratio of the Li-BO phase is in the range of 1% to 12.5%, it is possible to suppress a decrease in lithium ion conductivity due to an insufficient or excessive Li-M3-O phase. This is thought to be because, as shown in Table 5 and Figure 11, when the area ratio of the Li-BO phase is in the above-mentioned specific range, the liquid phase wets and spreads during sintering, making it easier for the solid electrolyte particles to be closely packed, promoting densification and improving the relative density. .

[0117] (Experimental Example 6) <Preparation of solid electrolyte> The solid electrolyte of Sample 26 was prepared according to the above-mentioned third manufacturing method, and the solid electrolyte of Sample 27 was prepared according to the above-mentioned first manufacturing method.

[0118] -Sample 26- The Li source was LiOH(H2O), the La source was La(OH)3, the M2 source was CaCO3, the Zr source was ZrO2, the M3 source was Sb2O3, and the B source was B2O3. 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 Each raw material was weighed to give a composition of +4.75 wt% Li3BO3. Next, each raw material was crushed and mixed using a planetary ball mill or the like containing ethanol and zirconia balls. Next, the obtained material was dried, sieved to separate the zirconia balls, placed in an alumina crucible, and fired at 900°C for 12 hours in an air atmosphere. Next, the obtained material was crushed for 10 hours using a uniaxial ball mill or the like containing ethanol and zirconia balls, dried, and then sieved to separate the zirconia balls. This resulted in Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 A solid electrolyte powder containing B element and having an excess composition in which the amount of Li is in excess compared to the stoichiometric ratio was synthesized.

[0119] Similarly to the solid electrolytes of Samples 3 to 6, Li7SbO6 powder was synthesized as Li-M3-O powder.

[0120] A mixed raw material powder was prepared by adding 2 wt% of Li7SbO6 powder to the solid electrolyte powder prepared above and mixing them in a mortar. This mixed raw material powder was compacted into a layer at 98 MPa, and the resulting compact was sintered at 750°C for 5 hours as shown in Table 2 to prepare the solid electrolyte of Sample 26.

[0121] -Sample 27- In the same manner as in the preparation of the solid electrolytes of Samples 5 and 6 in Experimental Example 2, a solid electrolyte of Sample 27 was prepared, which had solid electrolyte particles made of a lithium-lanthanum-zirconium-based composite oxide containing Sb as the M3 element, a non-molten phase made of Zr and O, and a molten phase containing a Li-Sb-O phase and a Li-BO phase. -Sample 28- The Li source was LiOH(H2O), the La source was La(OH)3, the M2 source was CaCO3, the Zr source was ZrO2, the M3 source was Sb2O3, and the B source was B2O3. 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 Each raw material was weighed to give a composition of +2 wt% Li7SbO6. Next, each raw material was crushed and mixed using a planetary ball mill or the like containing ethanol and zirconia balls. Next, the obtained material was dried, sieved to separate the zirconia balls, placed in an alumina crucible, and fired at 900°C for 12 hours in an air atmosphere. Next, the obtained material was crushed for 10 hours using a uniaxial ball mill or the like containing ethanol and zirconia balls, dried, and then sieved to separate the zirconia balls. This resulted in Li 6.5 La 2.9 Ca 0.1 Zr 1.4 Sb 0.6 O 12 A solid electrolyte powder was synthesized having an excess composition in which the amount of Li and Sb was excessive compared to the stoichiometric ratio. To the solid electrolyte powder prepared above, 4.75 wt% of Li3BO3 powder was added and mixed in a mortar to prepare a mixed raw material powder. This mixed raw material powder was compacted into a layer at 98 MPa, and the resulting compact was sintered at 750°C for 5 hours as shown in Table 2 to prepare the solid electrolyte of Sample 28.

[0122] The microstructure of the solid electrolyte of each sample was observed and the lithium ion conductivity and relative density were measured in the same manner as in Experimental Example 1. Table 6 shows the composition, manufacturing conditions, measurement results, etc. of the solid electrolyte of each sample.

[0123] [Table 6]

[0124] Table 6 reveals the following. As shown in Table 6, the solid electrolytes of Samples 26 to 28 all achieved high lithium ion conductivity through low-temperature sintering at less than 900°C. Furthermore, the molten phase of the solid electrolyte of Sample 26 contained a Li-BO phase. In Sample 26, Li3BO3 dissolved from the material constituting the solid electrolyte powder during sintering, thereby improving sinterability.

[0125] (Experimental Example 7) Of the samples produced in Experimental Examples 1 to 6 described above, a solid electrolyte of Sample 23 was prepared. In each of the prepared solid electrolyte samples, the M3 element contained in the lithium-lanthanum-zirconium-based composite oxide constituting the solid electrolyte particles was Sb.

[0126] A Li electrode was formed by contacting one surface of the solid electrolyte with lithium metal and heat-treating it at 190°C. An Au electrode was formed on the other surface of the solid electrolyte. The solid electrolyte was then placed in a sealed holder under an argon atmosphere, and AC impedance measurements were performed. An impedance analyzer (Keysight, "E4990A") was used for the AC impedance measurements, with the measurement temperature at 298K and the frequency range from 20 to 190°C. 8 In addition, for the AC impedance measurement, after the initial measurement, the sample was stored in an environment of 100°C, and the same measurement was performed after 5 days, 10 days, and 30 days.

[0127] The results of the AC impedance measurement are shown in Figure 12. As a result, a resistance component A different from the intra-grain resistance and grain boundary resistance originating from the solid electrolyte particles 10 was detected in the solid electrolyte of each sample. This resistance component A was observed in a lower frequency range than the frequency range of the resistance component originating from the solid electrolyte particles 10.

[0128] The solid electrolyte has high lithium ion conductivity and can suppress decomposition of the solid electrolyte due to contact with lithium metal. Therefore, the solid electrolyte can be used to form a negative electrode bonded to the solid electrolyte, that is, to use lithium metal as the negative electrode active material, thereby enabling the construction of a lithium ion battery with high capacity and suppressed decomposition of the solid electrolyte.

[0129] The present invention is not limited to the above-described embodiments and experimental examples, and various modifications are possible without departing from the spirit of the present invention. Furthermore, the configurations shown in the embodiments and experimental examples can be combined in any manner. [Explanation of symbols]

[0130] 1 Solid electrolyte 10 Solid electrolyte particles 11 Non-molten phase 2. Lithium-ion battery

Claims

1. Solid electrolyte particles (10) having a garnet-type crystal structure and made of a lithium-lanthanum-zirconium-based composite oxide containing an M3 element consisting of at least one of Bi and Sb; a non-molten phase (11) made of a material having a lower lithium ion conductivity than the lithium-lanthanum-zirconium-based composite oxide and present at least either inside or between the solid electrolyte particles; a molten phase (12) that includes a Li-M3-O phase composed of a material containing Li, the M3 element, and O, and that binds the solid electrolyte particles together; the non-melt phase is composed of a material containing Zr and O, The melt phase is crystalline. Solid electrolyte (1).

2. The material constituting the non-melt phase is an insulating material. The solid electrolyte according to claim 1 .

3. The molten phase includes a Li—B—O phase composed of a material containing Li, B, and O. The solid electrolyte according to claim 1 or 2.

4. The area ratio of the non-molten phase is 1% or more and 10% or less. The solid electrolyte according to any one of claims 1 to 3.

5. the particle size of the non-molten phase is smaller than the particle size of the solid electrolyte particles; The solid electrolyte according to any one of claims 1 to 4.

6. The area ratio of the Li-M3-O phase is 5% or more and 35% or less. The solid electrolyte according to any one of claims 1 to 5.

7. The area ratio of the Li—B—O phase is 1% or more and 12.5% ​​or less, The solid electrolyte according to claim 3.

8. The lithium-lanthanum-zirconium composite oxide is Li ７－３ｘ＋αｙ－ｚ＋βｇ (M1) ｘ La ３－ｙ (M2) ｙ Zr ２－ｚ－ｇ (M3) ｚ (M4) ｇ O １２±δ having a composition of The solid electrolyte according to any one of claims 1 to 7. In the above composition, the M1 element is at least one of Al and Ga, The M2 element is at least one element selected from the group consisting of Ca, Sr, Ba, Mg, Y, and Rb, The M3 element is at least one of Bi and Sb, The M4 element is at least one element selected from the group consisting of Ta, Nb, Ge, Te, Sc, and Hf, 0≦α≦2 depending on the valence of the M2 element, and −2≦β≦1 depending on the valence of the M4 element, satisfying 0≦x≦0.4, 0<y≦2.8, 0<z<2, and 0≦g<2; δ is the oxygen non-stoichiometry.

9. The M3 element is Sb, In the measurement of AC impedance after bringing lithium metal into contact with the surface of the solid electrolyte and heat-treating it at 190°C, a resistance component different from the resistance component derived from the solid electrolyte particles is detected; The solid electrolyte according to any one of claims 1 to 8.

10. The non-melt phase is a non-melt phase (excluding a phase formed by Li 2 ZrO 3 particles). The solid electrolyte according to any one of claims 1 to 9.

11. A lithium-ion battery (2) comprising a solid electrolyte according to any one of claims 1 to 10.

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