JP6735083B2 - Ion conductor and lithium battery - Google Patents

Description

The technology disclosed by the present specification relates to an ionic conductor.

In recent years, with the spread of electronic devices such as personal computers and mobile phones, the spread of electric vehicles, and the expansion of the use of natural energy such as sunlight and wind power, the demand for high-performance batteries has increased. Above all, it is expected to utilize an all-solid-state lithium-ion secondary battery in which all battery elements are solid. All-solid-state lithium-ion secondary batteries are safer than the conventional lithium-ion secondary batteries that use an organic electrolyte in which a lithium salt is dissolved in an organic solvent, because there is no risk of leakage or ignition of the organic electrolyte. In addition, since the exterior can be simplified, the energy density per unit mass or unit volume can be improved.

As the solid electrolyte used for the electrolyte layer or the electrode of the all-solid-state lithium ion secondary battery, for example, an oxide-based lithium ion conductor or a sulfide-based lithium ion conductor is used. The oxide-based lithium ion conductor has a high lithium ion conductivity (for example, 1.0×10 ⁻⁵ to 1.0×10 at 25° C. in the state of a sintered body that has been heat-treated at a high temperature of about 1000° C.). ^-3 S/cm), but the lithium ion conductivity is extremely low in the state where the unsintered powder is pressure-molded (for example, 1.0×10 ⁻⁷ S/cm or less at 25° C.). ). Therefore, the oxide-based lithium ion conductor requires a large amount of energy to obtain a high lithium ion conductivity, and at the same time, the degree of freedom in selecting materials such as electrodes when used as a battery form decreases.

On the other hand, the sulfide-based lithium ion conductor has a higher ionic conductivity than the oxide-based lithium ion conductor. This is because sulfide has a higher polarizability than oxide. Therefore, the sulfide-based lithium ion conductor has a high lithium ion conductivity within the particles. Further, since the sulfide-based lithium ion conductor is easily plastically deformed, the adhesion between particles is enhanced by simply applying pressure in a relatively low temperature range (for example, about 25° C. to 200° C.), and high lithium ion conductivity ( For example, it is 1.0×10 ^{−4 to} 1.0×10 ⁻² S/cm at 25° C.). However, the sulfide-based lithium ion conductor reacts with moisture in the atmosphere to generate hydrogen sulfide gas, which may be unfavorable in terms of safety.

Further, by mixing an oxide-based lithium ion conductor having a high lithium ion conductivity and a sulfide-based lithium ion conductor having a high lithium ion conductivity to produce a lithium ion conductor, it is possible to improve the safety and increase the lithium There is known a technique for achieving both improvement in ionic conductivity (see, for example, Patent Document 1).

U.S. Patent Application Publication No. 2015/0171463

The ionic conductor obtained by mixing the oxide-based lithium ion conductor and the sulfide-based lithium ion conductor as described above has a reduced content ratio of the sulfide-based lithium ion conductor, but also the sulfide-based lithium ion conductor. Since it contains an ionic conductor, there is room for improvement in terms of safety.

It should be noted that such a problem is not limited to the ionic conductor used in the electrolyte layer or the electrode of the all-solid-state lithium-ion secondary battery, but is common to ionic conductors having lithium ion conductivity in general.

This specification discloses a technique capable of solving the above-mentioned problems.

The technology disclosed in this specification can be implemented, for example, in the following modes.

(1) The ionic conductor disclosed in the present specification is an ionic conductor including a plurality of oxide-based lithium ion conductor particles, in which lithium halide is present between the two oxide-based lithium ion conductor particles. It is characterized by having an existing region. According to this ionic conductor, the safety is improved because it does not contain a sulfide-based lithium ion conductor, and because there is a region where lithium halide exists between the oxide-based lithium ion conductor particles. In addition, the adhesion between particles is improved and the lithium ion conductivity is improved.

(2) In the ionic conductor, the lithium halide may be lithium iodide. According to this ionic conductor, since there is a region where lithium iodide exists between the oxide-based lithium ion conductor particles, the adhesion between particles is improved and the lithium ion conductivity is improved.

(3) In the above-mentioned ionic conductor, as an index showing the degree of deviation of the distribution of the lithium halide in the ionic conductor, the abundance ratio of the oxide-based lithium ion conductor particles and the lithium halide in a fracture surface. The standard deviation value calculated from the above may be less than 0.6. According to this ionic conductor, the uneven distribution of the lithium halide in the ionic conductor is small and the lithium halide is evenly distributed, so the adhesion between particles is greatly improved and the lithium ion conductivity is greatly improved. To do.

(4) In the above ionic conductor, when the area ratio of the lithium halide on the fracture surface of the ionic conductor is Za and the area ratio of the lithium halide on the cut surface of the ionic conductor is Zb, Za It may be configured to satisfy the relation of >Zb. According to this ion conductor, there are many regions where lithium halide exists between the two particles of the oxide-based lithium ion conductor, the adhesion between particles is greatly improved, and the lithium ion conductivity is greatly improved. ..

(5) In the above ionic conductor, the ratio of the area occupied by the oxide-based lithium ion conductor particles and the area occupied by the lithium halide-containing particles on at least one cut surface of the ionic conductor is Xa: When (100−Xa) is set, the configuration may satisfy 30≦Xa<100. When the ratio of the oxide-based lithium ion conductor particles and the particles containing lithium halide is within the above range, the lithium ion conductivity is greatly improved.

(6) In the ionic conductor, the ratio of the area occupied by the oxide-based lithium ion conductor particles and the area occupied by the lithium halide-containing particles on at least one cut surface of the ionic conductor is Xa: When (100−Xa), 38≦Xa≦97 may be satisfied. When the ratio of the oxide-based lithium ion conductor particles and the particles containing lithium halide is within the above range, the lithium ion conductivity is significantly improved.

(7) In the above ionic conductor, the lithium ion conductivity at 25° C. may be 1.0×10 ⁻⁵ S/cm or more. According to this ionic conductor, a high lithium ion conductivity can be secured at room temperature.

(8) In the ionic conductor, the oxide-based lithium ionic conductor is an ionic conductor having a garnet-type structure or a garnet-type similar structure containing at least Li, Zr, La, and O, and Li and M. (M is at least one of Ti, Zr and Ge) and an ionic conductor having a NASICON type structure containing at least P and O, and a perovskite type structure containing at least Li, Ti, La and O. It may be configured to be at least one kind of the ionic conductor having. That is, one kind of these ion conductors may be used, or a plurality of kinds thereof may be mixed and used. According to this ionic conductor, the adhesion between particles is improved and the lithium ion conductivity is improved.

The technology disclosed in the present specification can be realized in various forms, for example, in the form of an ionic conductor, a lithium battery including the ionic conductor, a manufacturing method thereof, and the like. It is possible.

It is explanatory drawing which shows roughly the cross-sectional structure of the all-solid-state lithium ion secondary battery 102 in this embodiment. It is explanatory drawing (SEM image of a fracture surface) which shows the structure of the lithium ion conductor LIC of this embodiment. It is explanatory drawing (SEM-EDS image of a fracture surface) which shows the structure of the lithium ion conductor LIC of this embodiment. It is a flowchart which shows the manufacturing method of the lithium ion conductor LIC of this embodiment. It is explanatory drawing which shows the structure of each sample in performance evaluation, and a performance evaluation result. It is explanatory drawing which shows the structure of each sample in performance evaluation, and a performance evaluation result. It is a graph which shows the measurement result of lithium ion conductivity Ci of each sample in performance evaluation. It is explanatory drawing (SEM image of a fracture surface) which shows the structure of the lithium ion conductor LIC which is not heat-processed. It is explanatory drawing (SEM-EDS image of a fracture surface) which shows the structure of the lithium ion conductor LIC which is not heat-processed. It is explanatory drawing (SEM image of a cut surface) which shows the structure of the lithium ion conductor LIC of this embodiment. It is explanatory drawing (SEM-EDS image of a cut surface) which shows the structure of the lithium ion conductor LIC of this embodiment.

A. Embodiment:
A-1. All solid state battery 102 configuration:
FIG. 1 is an explanatory view schematically showing a cross-sectional configuration of an all-solid-state lithium-ion secondary battery (hereinafter referred to as “all-solid-state battery”) 102 according to this embodiment. FIG. 1 shows XYZ axes that are orthogonal to each other for specifying a direction. In this specification, for convenience, the Z-axis positive direction is referred to as an upward direction, and the Z-axis negative direction is referred to as a downward direction.

The all-solid-state battery 102 includes a battery main body 110, a first current collecting member 154 arranged on one side (upper side) of the battery main body 110, and a second current collecting member 154 arranged on the other side (lower side) of the battery main body 110. Current collecting member 156. The first current collecting member 154 and the second current collecting member 156 are substantially flat plate-shaped members having conductivity, and for example, stainless steel, Ni (nickel), Ti (titanium), Fe (iron), Cu ( Copper), Al (aluminum), a conductive metal material selected from these alloys, a carbon material, or the like.

The battery body 110 is a secondary battery in which all battery elements are solid, and includes an electrolyte layer 112, a positive electrode layer 114 disposed on one side (upper side) of the electrolyte layer 112, and the other side of the electrolyte layer 112 ( And the negative electrode layer 116 disposed on the lower side).

The electrolyte layer 112 has a substantially flat plate shape and is composed of a lithium ion conductor LIC which is a solid electrolyte. The positive electrode layer 114 has a substantially flat plate shape and includes a positive electrode active material PAM and a lithium ion conductor LIC having the same configuration as the lithium ion conductor LIC included in the electrolyte layer 112. As the positive electrode active material PAM, for example, S (sulfur), TiS ₂ , LiCoO ₂ , LiMn ₂ O ₄ , LiFePO ₄ or the like is used. The negative electrode layer 116 has a substantially flat plate shape and includes a negative electrode active material NAM and a lithium ion conductor LIC having the same configuration as the lithium ion conductor LIC included in the electrolyte layer 112. As the negative electrode active material NAM, for example, Li metal, Li—Al alloy, Li ₄ Ti ₅ O ₁₂ , carbon, Si (silicon), SiO or the like is used. The positive electrode layer 114 and the negative electrode layer 116 may further contain a conductive additive (for example, conductive carbon, Ni, Pt (platinum), Ag (silver)).

A-2. Structure and manufacturing method of lithium ion conductor LIC:
The all-solid-state battery 102 of the present embodiment is characterized by a lithium ion conductor LIC which is a solid electrolyte used for the electrolyte layer 112, the positive electrode layer 114 and the negative electrode layer 116. The configuration and manufacturing method of the lithium ion conductor LIC will be described below. 2 and 3 are explanatory views showing the configuration of the lithium ion conductor LIC of this embodiment. FIG. 2 shows a SEM image (1000 times) of a fracture surface of a lithium ion conductor LIC (sample 12 described later), and FIG. 3 shows a lithium ion conductor LIC (described later) corresponding to FIG. A SEM-EDS image (elemental mapping image) (1000 times) of the fracture surface of Sample 12) is shown. In FIG. 3, La (lanthanum) is shown in blue, Zr (zirconium) is shown in red, and I (iodine) is shown in green. The lithium ion conductor LIC shown in FIGS. 2 and 3 is Sample 12 (see FIG. 5) in the performance evaluation described later.

As shown in FIGS. 2 and 3, the lithium ion conductor LIC of the present embodiment includes oxide-based lithium ion conductor particles 52 and lithium halide-containing particles 54. More specifically, the lithium ion conductor LIC has a region (region shown in FIGS. 2 and 3) in which the lithium halide-containing particles 54 are present between the oxide-based lithium ion conductor particles 52. That is, in the lithium ion conductor LIC of the present embodiment, the voids between the oxide-based lithium ion conductor particles 52 are filled with the lithium halide-containing particles 54.

The oxide-based lithium ion conductor particles 52 included in the lithium ion conductor LIC include, for example, an ion conductor (eg, Li ₇ La ₃ Zr ₂ O ₁₂ (hereinafter referred to as “LLZ”) or particles obtained by substituting Mg (magnesium) and Sr (strontium) for LLZ (hereinafter referred to as “LLZ-MgSr”) , Li and M (M is at least one of Ti, Zr and Ge (germanium)), P (phosphorus) and O having at least a NASICON type structure (for example, Li _1.5 Al). Any one of particles of _0.5 Ge _1.5 (PO ₄ ) ₃ (hereinafter referred to as “LAGP”) and particles of an ion conductor having a perovskite structure containing at least Li, Ti, La, and O. 1 It is a particle, or particles that are a mixture of at least two of these. Further, the lithium halide-containing particles 54 included in the lithium ion conductor LIC include, for example, LiI (lithium iodide) particles, LiBr (lithium bromide) particles, LiCl (lithium chloride) particles, and these halogenated particles. The particles are mainly composed of lithium (for example, lithium iodide glass). The main component means a component having a content rate of 50 w% or more. The examples shown in FIGS. 2 and 3 are examples in which particles of LLZ—MgSr are used as the oxide-based lithium ion conductor particles 52, and particles of LiI are used as the lithium halide-containing particles 54.

FIG. 4 is a flowchart showing a method for manufacturing the lithium ion conductor LIC of this embodiment. First, oxide-based lithium ion conductor powder and lithium halide powder are prepared (S110), and both prepared powders are mixed at a predetermined ratio (S120). After molding the obtained mixed powder, heat treatment (for example, 80° C., 17 hours) is performed on the mixed powder (S130). As a result, the lithium ion conductor LIC having the above-described configuration is obtained. The heat treatment temperature is preferably 60°C or higher and 459°C or lower, more preferably 70°C or higher and 300°C or lower, and further preferably 75°C or higher and 200°C or lower.

As described above, the lithium ion conductor LIC used in the all-solid-state battery 102 of the present embodiment has a region in which the lithium halide-containing particles 54 are present between the oxide-based lithium ion conductor particles 52. Since the oxide-based lithium ion conductor particles 52 are fused to each other by the lithium halide-containing particles 54, the adhesion between particles is high and the lithium ion conductivity is high (for example, 1.0×10 ^{− at} 25° C.). ⁵ S/cm or more). In addition, the lithium ion conductor LIC of the present embodiment has a high lithium ion conductivity only by performing heat treatment at a lower temperature without forming a sintered body by heat treatment at a relatively high temperature (for example, about 1000° C.). Therefore, the energy required for manufacturing can be reduced, and the positive electrode layer 114 and the negative electrode layer 116 are not subjected to a thermal load, so that the degree of freedom in selecting the material of the positive electrode layer 114 and the negative electrode layer 116 is improved. You can Further, the lithium ion conductor LIC of the present embodiment has high safety because it does not contain a sulfide-based lithium ion conductor that reacts with moisture in the air to generate hydrogen sulfide.

In general, the lithium ion conductivity (25° C.) of lithium halide is extremely low at about 1.0×10 ⁻⁷ S/cm. The inventor of the present application has found that by adding and mixing lithium halide having extremely low lithium ion conductivity to the oxide-based lithium ion conductor, it is possible to obtain the unpredictable effect that the lithium ion conductivity is significantly improved. I found it. In this respect, the invention of the present application can be said to be extremely difficult to conceive by a person skilled in the art.

A-3. Performance evaluation:
A plurality of samples (Samples 1 to 23) of the lithium ion conductor LIC were prepared, and the lithium ion conductivity Ci and the like of each sample were measured as performance evaluation. 5 and 6 are explanatory diagrams showing the configuration of each sample in the performance evaluation and the performance evaluation results, and FIG. 7 is a graph showing the measurement results of the lithium ion conductivity Ci of Samples 1 to 19 in the performance evaluation. .. The plot numbers (P1 to P19) in FIG. 7 correspond to the sample numbers (1 to 19) in FIG. 5, respectively. Note that some of the samples shown in FIG. 5 (samples 4 and 12) are also shown in FIG.

The materials used to make each sample are shown in FIGS. 5 and 6. In this performance evaluation, LLZ-MgSr was used as the oxide-based lithium ion conductor, and LiI was used as the lithium halide. 5 and 6, for each sample, oxide-based lithium ion conductor particles (specifically LLZ-MgSr particles) and lithium halide-containing particles (specifically LiI particles) on the cut surface. The ratio of the oxide-based lithium ion conductor particles to the total amount of the above (hereinafter, referred to as “oxide-based ratio X”) is shown. The ratio of the oxide-based lithium ion conductor particles, in the image analysis using the cut surface image described later, the area obtained from the area of the oxide-based lithium ion conductor particles and the area of the lithium halide-containing particles. It can be expressed as a percentage. Here, the ratio of the oxide-based lithium ion conductor particles and the lithium halide-containing particles is expressed as X:(100-X) using the oxide-based ratio X. Further, the oxide-based ratio X in the raw material stage is maintained at substantially the same value in the lithium ion conductor LIC manufactured through the mixing treatment and the heat treatment of the raw materials. The samples (Samples 1 and 9) in which the value of the oxide-based proportion X is 0 (zero)% are composed only of lithium halide-containing particles (LiI particles), and the value of the oxide-based proportion X is 100%. Samples (Samples 8, 16 and 19) are composed of only oxide-based lithium ion conductor particles (LLZ-MgSr particles).

Further, FIG. 5 shows a method of the mixing process (S120 in FIG. 4). As the mixing treatment, a mixing treatment using a mortar or a planetary ball mill was performed. It should be noted that the mixing process is not executed in the sample in which the value of the oxide system proportion X is 0 (zero)% or 100%. Further, in all the samples shown in FIG. 6, since the mixing process using the mortar was performed, the item “mixing process” is omitted in FIG. 6. Further, FIGS. 5 and 6 show the temperature and time of the heat treatment (S130 in FIG. 4). As the heat treatment, heat treatment was performed at 80° C. for 17 hours or 1100° C. for 4 hours. In addition, in Samples 1 to 8, 17, 20, and 21, the heat treatment is not performed.

As shown in FIGS. 5 and 6, Samples 1 to 8, 20, and 21 were produced without heat treatment, and are powders. The samples 1 to 8, 20, and 21 have different oxide-based proportions X from each other. On the other hand, Samples 9 to 16, 22, and 23 are heated products produced by performing heat treatment at 80° C. for 17 hours on powders having the same configurations as Samples 1 to 8, 20, and 21, respectively. Among the samples 1 to 16 and 20 to 23, the samples containing both LLZ-MgSr and LiI (samples 2 to 7, 10 to 15 and 20 to 23) are subjected to the mixing process using a mortar. ..

Sample 17 is the same as sample 4 except that the mixing treatment method is replaced with a planetary ball mill. Similarly, sample 18 is the same as sample 12 except that the mixing treatment method is a planetary ball mill. It has been replaced by the method used. In general, when the mixing process using the planetary ball mill is performed, the average particle size of the particles forming the lithium ion conductor LIC is smaller than that in the case of performing the mixing process using the mortar, and the particle size variation is small. Becomes smaller.

In addition, Sample 19 is a sintered body produced by subjecting LLZ-MgSr powder to heat treatment at 1100° C. for 4 hours. Hereinafter, the method for producing each sample will be described in detail.

_First, as a composition of _{Li 6.95 Mg 0.15 La 2.75 Sr 0.25} Zr 2.0 O 12, Li 2 CO 3, MgO, La (OH) 3, SrCO 3, and ZrO ₂ Weighed. At that time, in consideration of the volatilization of Li at the time of firing, Li ₂ CO ₃ was further added so as to be excessive by about 15 mol% in terms of element. This raw material was put into a nylon pot together with zirconia balls, and pulverized and mixed in a ball mill for 15 hours in an organic solvent. After mixing, the slurry was dried and calcined on a MgO plate at 1100° C. for 10 hours. The composition of the powder after calcination may deviate from the above composition to some extent. A binder was added to the powder after calcination, and the mixture was pulverized and mixed in a ball mill for 15 hours in an organic solvent. After mixing, the slurry was dried to obtain LLZ-MgSr powder.

For samples 2 to 7, 20, and 21, the prepared LLZ-MgSr powder and lithium iodide powder (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) were used according to the oxide system proportion X of each sample. The ingredients were blended in the above blending ratio, and pulverized and mixed in a mortar for 15 minutes to obtain a mixed powder. It should be noted that the samples 1 and 8 do not carry out the mixing process because a single powder is used. With respect to Samples 1 to 8, 20, and 21, the mixed powder (or simple substance powder) was placed in a cylindrical insulating container having a diameter of 10 mm, and pressed together with a stainless current collector at 360 MPa with a pressing machine to obtain a green compact. With respect to each of the obtained green compacts (Samples 1 to 8, 20, and 21), the lithium ion conductivity Ci at 25° C. was measured by an AC impedance method (using Solartron 1470E and 1255B).

Further, for Samples 9 to 16, 22, and 23, a green compact was prepared in the same manner as in Samples 1 to 8, 20, and 21, and then the green compact was fixed again at 50 MPa and sealed in an Ar (argon) atmosphere. It was put in a glass container and heat-treated at 80° C. for 17 hours in a high temperature tank (PU-1KPH manufactured by ESPEC) in the atmosphere to obtain a heated product. Each of the obtained heated products (Samples 9 to 16, 22, 23) was cooled to 25° C., and the lithium ion conductivity Ci was measured in the same manner as in Samples 1 to 8, 20, 21.

For sample 17, the prepared LLZ-MgSr powder and lithium iodide powder (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) were mixed in a mixing ratio according to the oxide ratio X. A 45 cc zirconia pot and 40 g of Φ4 mm balls were pulverized and mixed in a planetary ball mill at 40 rpm for 3 hours to obtain a mixed powder. Thereafter, similarly to Samples 1 to 8, 20, and 21, a green compact was obtained from the mixed powder, and the lithium ion conductivity Ci was measured for the obtained green compact (Sample 17). For sample 18, after obtaining a green compact in the same manner as in sample 17, heat treatment is performed in the same manner as in samples 9 to 16, 22, 23 to obtain a heated product, and the obtained heated product (sample 18) As a target, the lithium ion conductivity Ci was measured.

For sample 19, the prepared LLZ-MgSr powder was press-molded with a mold having a diameter of 12 mm to a thickness of about 1.5 mm, and a cold isostatic press (CIP) was used. Then, a hydrostatic pressure of 1.5 t/cm ² was applied to obtain a molded body. The obtained molded body was covered with a calcined powder having the same composition as that of the molded body, and heat-treated at 1100° C. for 4 hours in a nitrogen atmosphere to obtain a sintered body. When this sintered body was pulverized and the main crystal phase was identified by XRD, the crystal structure of this sintered body was an LLZ cubic crystal with a high ionic conductivity Ci. Both surfaces of the sintered body were polished and gold vapor deposition was performed to obtain a measurement sample. The lithium ion conductivity Ci was measured for the obtained measurement sample (Sample 19) as in Samples 1 to 8.

Further, in Samples 4, 12, and 20 to 23 shown in FIG. 6, oxide-based ionic conductor particles having a fracture surface as an index showing the degree of deviation of the distribution of lithium halide in the lithium ionic conductor LIC. The standard deviation σ was calculated from the ratio of existence with lithium halide. In the present specification, the fracture surface refers to a cross section that appears when an external force is applied to the sample to break it, and is a cross section that is a cross section processed by polishing, ion beam, or the like, and is not a cut surface. The standard deviation σ calculated from the abundance ratio of the oxide-based ionic conductor particles on the fractured surface and the lithium halide as the above index can be obtained by the following method. First, the fracture surface of the sample is subjected to elemental analysis by SEM-EDS measurement, and among the elements constituting the oxide-based lithium ion conductor, the representative element X is selected from the elements excluding the element contained in lithium halide and the oxygen element. Also, the halogen element Y of lithium halide is selected. In the sample shown in FIG. 6, La (lanthanum) is selected as the representative element X (hereinafter, simply referred to as “element X”) that constitutes the oxide-based lithium ion conductor, and the halogen element Y of lithium halide (hereinafter referred to as “element X”) is selected. , (Referred to simply as “element Y”), I (iodine) was selected. Next, the ratio Y/X of the element Y to the element X in the fracture surface is calculated. Here, the ratio Y/X is calculated at nine or more points in the sample. It should be noted that selection of 9 or more locations may be random. Further, an average value is calculated for the calculated ratios Y/X at nine or more locations. The ratio Y/X calculated at nine or more locations is divided by the average value, and the standard deviation σ with respect to the average value is calculated for this divided value (9 points or more).

When the deviation of the distribution of lithium halide in the lithium ion conductor LIC is sufficiently small, the standard deviation σ is less than 0.6. When the deviation of the distribution of lithium halide in the lithium ion conductor LIC is extremely small, the standard deviation σ is less than 0.4. Therefore, when the standard deviation σ is less than 0.6, the deviation of the distribution of lithium halide is sufficiently small and the lithium ion conductivity Ci is greatly improved, which is preferable. Further, when the standard deviation σ is less than 0.4, the deviation of the distribution of lithium halide is extremely small, and the lithium ion conductivity Ci is extremely improved, which is more preferable.

For samples 4, 12, 20 to 23 shown in FIG. 6, the lithium halide area ratio (%), which is the area ratio of lithium halide in the cross section (broken surface and cut surface) of the lithium ion conductor LIC, was calculated. did. The lithium halide area ratio on the fracture surface of the lithium ion conductor LIC is represented by Za, and the lithium halide area ratio on the cut surface of the lithium ion conductor LIC is represented by Zb. Here, the fracture surface has the same meaning as the above-mentioned fracture surface. Further, in the present specification, the cut surface refers to a cross section processed by polishing, ion beam, or the like, and is a cross section different from the above fracture surface. The cut surface can be obtained by, for example, the cross section polisher method (CP method) or the like. Further, the lithium halide area ratio Za at the fracture surface and the lithium halide area ratio Zb at the cut surface can be obtained by element mapping by SEM-EDS.

When the lithium ion conductor LIC satisfies the relationship (Za>Zb) that the lithium halide area ratio Za at the fracture surface is greater than the lithium halide area ratio Zb at the cut surface, the lithium ion conductivity Ci is significantly improved. preferable. Further, when the relationship that the ratio of the lithium halide area ratio Za at the fracture surface to the lithium halide area ratio Zb at the cut surface is larger than 1.3 ((Za/Zb)>1.3), the lithium ion conductivity is increased. It is more preferable because Ci is further improved. The fact that the lithium ion conductor LIC satisfies Za>Zb means that there are many regions where lithium halide particles are present between the oxide-based lithium ion conductor particles. That is, it can be said that there are many regions where the oxide-based lithium ion conductor particles are covered with the lithium halide particles. The reason that can be said in this way is that the fracture surface is a cross section obtained by fracture due to an external force, and therefore fracture occurs between the oxide-based lithium ion conductor particles. That is, in a form in which there are many regions in which lithium halide particles are present between oxide-based lithium ion conductor particles, many lithium halide particles are exposed. On the other hand, the cut surface is a polished surface or a cross section processed by an ion beam or the like, so that the oxide-based lithium ion conductor particles are also cut and the internal structure of the oxide-based lithium ion conductor particles is exposed. Become. As a result, the exposed surface of the oxide-based lithium ion conductor particles is higher in the cut surface than in the fracture surface. However, in the form in which there is no region where the lithium halide particles are present between the oxide-based lithium ion conductor particles, the lithium halide area ratio Za at the fracture surface is compared with the lithium halide area ratio Zb at the cut surface. However, the difference hardly appears (that is, Za≈Zb (Za and Zb are almost equal)). Therefore, when the lithium halide area ratio in the fractured surface is Za and the lithium halide area ratio in the cut surface is Zb, the relationship of Za>Zb is satisfied, so that the halogen compounds are oxidized between the oxide-based lithium ion conductor particles. It can be said that there are many regions where lithium particles exist.

(Measurement result)
As shown in FIGS. 5 and 7, Samples 10 to 15 exhibited higher lithium ion conductivity Ci than Samples 2 to 7. Therefore, it can be said that when the mixed powder of LLZ-MgSr and LiI is heat-treated at about 80° C., the lithium ion conductivity Ci increases. It is considered that this is because LiI is fused by the heat treatment and the LiI fills the voids between the LLZ-MgSr particles, and the adhesion between the particles is increased.

8 and 9 are explanatory views showing the configuration of the lithium ion conductor LIC on which the heat treatment is not performed. FIG. 8 shows a SEM image (1000 times) of the fracture surface of Sample 4, and FIG. 9 shows an SEM-EDS image (elemental mapping image) of the fracture surface of Sample 4 corresponding to FIG. Times) are shown. In FIG. 9, La (lanthanum) is shown in blue, Zr (zirconium) is shown in red, and I (iodine) is shown in green. As shown in FIGS. 8 and 9, in the lithium ion conductor LIC (Sample 4) in which the heat treatment is not performed, the particles 52 of the oxide-based lithium ion conductor (specifically, LLZ-MgSr) are provided. Although there is a portion where the lithium halide (specifically, LiI)-containing particles 54 exist, since the degree of dispersion of LiI is small, the adhesion between particles is relatively low. Therefore, in sample 4, the lithium ion conductivity Ci is relatively low. On the other hand, as shown in FIG. 2 and FIG. 3 described above, in the lithium ion conductor LIC (Sample 12) that has been subjected to the heat treatment, the degree of dispersion of LiI is high and the adhesion between particles is high, so The ionic conductivity Ci is relatively high.

It should be noted that FIG. 7 shows a part of a third-order approximation curve AC derived from the plots (P9 to P16) of Samples 9 to 16. Based on this approximate curve AC, if the oxide system proportion X is 30% or more and less than 100% (30≦X<100), the lithium ion conductivity Ci is approximately 1.0×10 ⁻⁵ S/cm or more. Can be said to be preferable because Further, when the oxide system ratio X is 38% or more and 97% or less (38≦X≦97), it is equal to or more than that of the sample 19 which is a sintered body of LLZ-MgSr, and is approximately 1.0×10 ^−3. It can be said that it is more preferable because a lithium ion conductivity Ci of S/cm or more can be obtained.

In addition, the sample 18 exhibited a higher lithium ion conductivity Ci than the sample 12. Therefore, it can be said that when the mixing process using the planetary ball mill is performed, the lithium ion conductivity Ci becomes higher than when the mixing process using the mortar is performed. When the mixing process using the planetary ball mill is performed, the average particle size of the particles forming the lithium ion conductor LIC is smaller than that when performing the mixing process using the mortar, and the variation in the particle size is small. Therefore, it is considered that the lithium ion conductivity Ci becomes high due to at least one of them. The average particle diameter of the oxide-based lithium ion conductor particles of Sample 12 was 14.8 μm, and the average particle diameter of the oxide-based lithium ion conductor particles of Sample 18 was 3.1 μm.

Further, as shown in FIG. 6, in Samples 4, 20, and 21 which were not subjected to the heat treatment, the above-mentioned standard deviation σ was 0.6 or more. That is, it can be said that in these samples, the uneven distribution of lithium halide is relatively large. Therefore, in these samples, the lithium ion conductivity Ci showed a relatively low value. On the other hand, in the samples 12, 22, and 23 that were subjected to the heat treatment, the above-mentioned standard deviation σ was less than 0.6. That is, it can be said that in these samples, the uneven distribution of the lithium halide distribution is relatively small. Therefore, in these samples, the lithium ion conductivity Ci showed a relatively high value. From this result, it can be said that the value of the standard deviation σ is preferably less than 0.6.

Further, as shown in FIG. 6, in Sample 4 in which the heat treatment was not performed, the lithium halide area ratio Za in the fracture surface was the same value as the lithium halide area ratio Zb in the cut surface (Za=Zb). That is, in this sample, it can be said that the area where the lithium halide particles are present between the oxide-based lithium ion conductor particles is small or does not exist. Therefore, in this sample, the lithium ion conductivity Ci showed a relatively low value. On the other hand, in Samples 12, 22, and 23 that were subjected to the heat treatment, the lithium halide area ratio Za at the fracture surface was larger than the lithium halide area ratio Zb at the cut surface (Za>Zb). That is, in these samples, it can be said that there are many regions where the lithium halide particles are present between the oxide-based lithium ion conductor particles. Therefore, in these samples, the lithium ion conductivity Ci showed a relatively high value. From this result, it can be said that it is preferable to satisfy the relationship of Za>Zb.

10 and 11 are explanatory views showing the configuration of the lithium ion conductor LIC of this embodiment. FIG. 10 shows a SEM image (1000 times) of the cut surface of the sample 12, and FIG. 11 shows a SEM-EDS image (elemental mapping image) (1000) of the cut surface of the sample 12 corresponding to FIG. Times) are shown. In FIG. 11, La (lanthanum) is shown in blue, Zr (zirconium) is shown in red, and I (iodine) is shown in green. As shown in FIGS. 10 and 11, in the cross section of the lithium ion conductor LIC, the lithium halide area ratio (Zb) is smaller than that in the fracture surface of the lithium ion conductor LIC shown in FIGS. 2 and 3. Has become.

A sample (oxide-based ratio X=50%) using an oxide-based lithium ion conductor obtained by substituting Al for LLZ (hereinafter referred to as “LLZ-Al”), and The lithium ion conductivity Ci was similarly measured for a sample using LAGP as the oxide lithium ion conductor (oxide ratio X=50%). The conditions (oxide ratio X, mixing treatment method, heat treatment conditions) other than the materials used for these samples are the same as those of the sample 12. As a result of the measurement, even in the samples using LLZ-Al or LAGP as these oxide-based lithium ion conductors, it is as high as 4.4×10 ⁻⁴ S/cm and 1.2×10 ⁻⁴ S/cm. It was confirmed that the lithium ion conductivity Ci was exhibited.

The oxide-based proportion X in the lithium ion conductor LIC can be measured by the following method. When the lithium ion conductor LIC is a particle, the particle is embedded in a resin or the like and fixed, and thereafter, a cut surface of the particle is obtained by polishing, a cross section polisher method (CP method) or the like. The area ratio of the oxide-based lithium ion conductor is calculated by performing SEM-EDS analysis on this cut surface and determining the ratio of the “element X” described above. Next, assuming that the whole is 100%, a value obtained by subtracting the area ratio of the oxide-based lithium ion conductor from 100% is taken as the area ratio of lithium halide. When the lithium ion conductor LIC is a bulk body, the cut surface of the bulk body is obtained by polishing, cross section polisher method (CP method) or the like for this bulk body. The area ratio of the oxide-based lithium ion conductor is calculated by performing SEM-EDS analysis on this cut surface and determining the ratio of the “element X” described above. Next, assuming that the whole is 100%, a value obtained by subtracting the area ratio of the oxide-based lithium ion conductor from 100% is taken as the area ratio of lithium halide. In the case of a bulk body in which the lithium ion conductor LIC is used by being mixed with another material (for example, when it is used as an electrode material), the mixed substances are identified by crystal structure analysis by XRD. Next, the cut surface of the bulk body is obtained by polishing or the cross section polisher method (CP method) for this bulk body. SEM-EDS analysis is performed on this cut surface, and together with the result of XRD, the lithium ion conductor LIC and other materials are separated. Then, with respect to the portion of the lithium ion conductor LIC, the ratio of the “element X” described above is calculated from the result of the elemental analysis by SEM-EDS, and is set as the area ratio of the oxide-based lithium ion conductor. Next, assuming that the entire portion of the lithium ion conductor LIC is 100%, a value obtained by subtracting the area ratio of the oxide-based lithium ion conductor from 100% is taken as the area ratio of lithium halide. That is, in such a case, the proportion occupied by other materials (for example, the electrode active material, the conductive auxiliary agent, etc.) is excluded.

B. Modification:
The technology disclosed in this specification is not limited to the above-described embodiment, and can be modified into various forms without departing from the gist thereof, and the following modifications are possible, for example.

In the above-described embodiment, the lithium ion conductor LIC having the above-described configuration is included in all of the electrolyte layer 112, the positive electrode layer 114, and the negative electrode layer 116. However, the lithium-ion conductor LIC having the above-described configuration does not include the electrolyte layer 112. It may be contained in at least one of the positive electrode layer 114 and the negative electrode layer 116, and any one of the electrolyte layer 112, the positive electrode layer 114, and the negative electrode layer 116 may have a lithium ion conductor LIC (for example, sulfide) having another structure. System lithium ion conductor or oxide system lithium ion conductor) may be included. Further, an intermediate layer is provided between the electrolyte layer 112 and the positive electrode layer 114, or between the electrolyte layer 112 and the negative electrode layer 116, or both of them, and only the intermediate layer has the above-described lithium ion conductor LIC. May be included. The lithium ion conductor LIC having the above-described configuration may be included in all of the intermediate layer, the electrolyte layer 112, the positive electrode layer 114, and the negative electrode layer 116.

In addition, the material forming each member in the above embodiment is merely an example, and each member may be formed of another material.

Further, although the lithium ion conductor LIC used in the all-solid-state battery 102 has been described as an example in the above embodiment, the present invention uses a lithium-ion conductive solid electrolyte such as a lithium air battery or a lithium flow battery. It is also applicable to the lithium ion conductor LIC used for the lithium battery and the lithium ion conductor LIC used for other than the lithium battery.

52: Oxide-based lithium ion conductor particles 54: Lithium halide-containing particles 102: All-solid-state lithium ion secondary battery 110: Battery body 112: Electrolyte layer 114: Positive electrode layer 116: Negative electrode layer 154: Current collecting member 156: Collection Electrical member

Claims (8)

In an ionic conductor comprising a plurality of oxide-based lithium ion conductor particles,
A region in which lithium halide is present between the two oxide-based lithium ion conductor particles,
When the area ratio of the lithium halide on the fracture surface of the ionic conductor is Za and the area ratio of the lithium halide on the cut surface of the ionic conductor is Zb, the relation Za>Zb is satisfied. Ion conductor. The ionic conductor according to claim 1, wherein
The ionic conductor, wherein the lithium halide is lithium iodide. The ionic conductor according to claim 1 or 2, wherein
The value of the standard deviation calculated from the abundance ratios of the oxide-based lithium ion conductor particles and the lithium halide on the fracture surface is 0 as an index showing the degree of deviation of the distribution of the lithium halide in the ionic conductor. Ion conductor characterized by being less than 0.6. The ion conductor according to any one of claims 1 to 3,
When the ratio of the area occupied by the oxide-based lithium ion conductor particles and the area occupied by the particles containing lithium halide is Xa:(100-Xa) on at least one cut surface of the ionic conductor, An ionic conductor, which satisfies 30≦Xa<100. The ionic conductor according to claim 4, wherein
When the ratio of the area occupied by the oxide-based lithium ion conductor particles and the area occupied by the particles containing lithium halide is Xa:(100-Xa) on at least one cut surface of the ionic conductor, An ionic conductor, which satisfies 38≦Xa≦97. The ionic conductor according to any one of claims 1 to 5, wherein:
An ionic conductor having a lithium ion conductivity of 1.0×10 ⁻⁵ S/cm or more at 25° C. The ionic conductor according to any one of claims 1 to 6, wherein:
The oxide-based lithium ion conductor is an ionic conductor having a garnet type structure or a garnet type similar structure containing at least Li, Zr, La and O, and Li and M (M is Ti, Zr or Ge). At least one of the above), an ionic conductor having a NASICON type structure containing at least P and O, and an ionic conductor having a perovskite type structure containing at least Li, Ti, La and O. An ionic conductor characterized by being one type. In a lithium battery including a solid electrolyte layer, a positive electrode, and a negative electrode,
At least one of the said solid electrolyte layer, the said positive electrode, and the said negative electrode contains the ionic conductor in any one of Claim 1-7, The lithium battery characterized by the above-mentioned.