WO2023032294A1

WO2023032294A1 - Solid electrolyte, all-solid-state battery, method for manufacturing solid electrolyte, and method for manufacturing all-solid-state battery

Info

Publication number: WO2023032294A1
Application number: PCT/JP2022/011205
Authority: WO
Inventors: 伊藤大悟; 織茂洋子
Original assignee: 太陽誘電株式会社
Priority date: 2021-08-30
Filing date: 2022-03-14
Publication date: 2023-03-09
Also published as: JP2023033898A

Abstract

This solid electrolyte is characterized by being represented by the compositional formula Li_1+yTa_2-xM_xPO₈, where x satisfies 0<x<0.5, M is an element having a lower valence than Ta, and when the valence of M is defined as A, y=(5-A)x.　

Description

Solid electrolyte, all-solid battery, method for producing solid electrolyte, and method for producing all-solid battery

The present invention relates to a solid electrolyte, an all-solid battery, a method for producing a solid electrolyte, and a method for producing an all-solid battery.

In recent years, secondary batteries have been used in various fields. A secondary battery using an electrolytic solution has problems such as leakage of the electrolytic solution. Therefore, development of an all-solid-state battery in which a solid electrolyte is provided and other components are also solid is being developed.

Various types of solid electrolytes are known, including sulfides, which have high ionic conductivity at room temperature, and oxides, which are more stable in the atmosphere, as well as polymers and hydrides. Oxide-based solid electrolytes are advantageous over other compound systems in terms of high stability and safety in the atmosphere. Therefore, the biggest problem is that it is necessary to sinter the particles to lower the interfacial resistance.

As oxide-based solid electrolytes having relatively high ion conductivity, garnet type such as Li-La-Zr-O system, perovskite type such as Li-La-Ti-O system, Li-Al-Ti-P-O system and Li--Al--Ge--P--O system NASICON type and the like are widely known. In addition, recently reported Li--Ta--P--O compounds (for example, LiTa ₂ PO ₈ in Non-Patent Document 1) are also reported to exhibit high ionic conductivity. Although they have high ionic conductivity, they are mechanically hard and generally require high firing temperatures.

On the other hand, as materials suitable for firing at low temperatures, Li-Ge-O-based LISICON type, Li-Si-O-based, Li-BO-based, Li-SO-based, Li-PO-based and glass-ceramic systems in which these are combined have been disclosed (see Patent Documents 1 and 2, for example).

JP-A-2000-26135 JP 2019-46559 A

LiTa ₂ PO ₈ described in Non-Patent Document 1 exhibits a high ionic conductivity of 2.5×10 ⁻⁴ S/cm at room temperature, but has a high sintering temperature of 1050° C., and is expected to form an all-solid-state battery. As a result, interdiffusion reactions occur with most of the active materials during firing, making it extremely difficult to use.

On the other hand, the glass-ceramics disclosed in Patent Documents 1 and 2 can be sintered at relatively low temperatures, but have the problem of low ionic conductivity.

Although it is possible to obtain a solid electrolyte sintered body with a certain degree of ionic conductivity at a relatively low temperature by combining these, the ionic conductivity is lower than that of the high ionic conductor LiTa ₂ PO ₈ alone. . In addition, it is possible to sinter at a lower temperature by increasing the amount of Li, but if the amount of Li is excessive, the crystal structure of LiTa ₂ PO ₈ is difficult to maintain and a secondary phase is generated. Ionic conductivity decreases.

The present invention has been made in view of the above problems, and aims to provide a solid electrolyte exhibiting high ionic conductivity and capable of being fired at a low temperature, an all-solid battery, a method for producing a solid electrolyte, and a method for producing an all-solid battery. aim.

The solid electrolyte according to the present invention is represented by a composition formula of Li _1+y Ta _2-x M _x PO ₈ , where x satisfies 0<x<0.5, and M is an element with a lower valence than Ta. and y=(5−A)x, where A is the valence of M.

In the above solid electrolyte, M may be at least one of Zr, Ti, Ge, Hf, Sn, Y, B, Al, and Ga.

In the above solid electrolyte, x may satisfy 0<x≦0.3.

It may be confirmed from the results of XRD measurement that the solid electrolyte has a crystal structure belonging to a monoclinic system.

In the above solid electrolyte, the average particle size may be 0.2 μm or more and 20 μm or less.

An all-solid-state battery according to the present invention includes a solid electrolyte layer containing the solid electrolyte as a main component; and a second electrode that contains a substance and is formed on a second main surface of the solid electrolyte layer that faces the first main surface.

In the above all-solid-state battery, a plurality of units may be stacked, with the solid electrolyte layer, the first electrode, and the second electrode forming one unit.

In the all-solid-state battery, one of the first electrode and the second electrode may contain a positive electrode active material, and the other may contain a negative electrode active material.

In the method for producing a solid electrolyte according to the present invention, a composition of Li _1+y Ta _2-x M _x PO ₈ is prepared from a raw material containing Li, Ta, P, and M, which is an element with a lower valence than Ta. Synthesize at 1100 ° C. or less an oxide-type solid electrolyte represented by the formula that satisfies the relationship 0<x<0.5 and has y = (5-A) x where A is the valence of M. characterized by

The method for producing an all-solid-state battery according to the present invention is represented by a composition formula of Li _1+y Ta _2-x M _x PO ₈ , satisfies the relationship 0<x<0.5, and M has a lower valence than Ta. A green sheet containing a solid electrolyte powder that is an element and y=(5−A) when the valence of M is A; and a first electrode layer formed on the first main surface of the green sheet preparing a laminate having a paste coating and a second electrode layer paste coating formed on the second main surface of the green sheet; and firing the laminate. It is characterized by

In the method for manufacturing an all-solid-state battery, the firing temperature in the firing step may be 500°C or higher and 900°C or lower.

According to the present invention, it is possible to provide a solid electrolyte that exhibits high ion conductivity and that can be fired at a low temperature, an all-solid battery, a method for producing a solid electrolyte, and a method for producing an all-solid battery.

(a) is a schematic cross-sectional view showing the basic structure of an all-solid-state battery, and (b) is a schematic cross-sectional view of a solid electrolyte layer. 1 is a schematic cross-sectional view of an all-solid-state battery according to an embodiment; FIG. FIG. 4 is a schematic cross-sectional view of another all-solid-state battery; It is a figure which illustrates the flow of the manufacturing method of an all-solid-state battery. (a) and (b) are figures which illustrate a lamination process. FIG. 10 is a diagram illustrating the flow of another method for manufacturing an all-solid-state battery;

Embodiments will be described below with reference to the drawings.

(embodiment)
FIG. 1(a) is a schematic cross-sectional view showing the basic structure of an all-solid-state battery 100. FIG. As illustrated in FIG. 1( a ), the all-solid battery 100 has a structure in which a solid electrolyte layer 30 is sandwiched between a first electrode 10 and a second electrode 20 . The first electrode 10 is formed on the first main surface of the solid electrolyte layer 30 and has a structure in which the first electrode layer 11 and the first current collector layer 12 are laminated. A first electrode layer 11 is provided. The second electrode 20 is formed on the second main surface of the solid electrolyte layer 30, has a structure in which a second electrode layer 21 and a second current collector layer 22 are laminated, and is provided on the solid electrolyte layer 30 side. A second electrode layer 21 is provided.

When using the all-solid-state battery 100 as a secondary battery, one of the first electrode 10 and the second electrode 20 is used as a positive electrode, and the other is used as a negative electrode. In this embodiment, as an example, the first electrode 10 is used as a positive electrode, and the second electrode 20 is used as a negative electrode.

The solid electrolyte layer 30 is mainly composed of a solid electrolyte having ionic conductivity. As illustrated in FIG. 1B, the solid electrolyte layer 30 has a structure containing a plurality of solid electrolyte particles 31 as a main component ceramic. For example, LiTa ₂ PO ₈ may be used as the solid electrolyte particles 31 . This LiTa ₂ PO ₈ exhibits a high ionic conductivity of 2.5×10 ⁻⁴ S/cm at room temperature. However, the sintering temperature of LiTa ₂ PO ₈ is as high as 1050°C. Therefore, LiTa ₂ PO ₈ is very difficult to use because it causes an interdiffusion reaction with most of the active materials during firing of the all-solid-state battery.

Therefore, it is conceivable to combine LiTa ₂ PO ₈ and glass ceramics containing Li to obtain a solid electrolyte sintered body having a certain degree of ionic conductivity at a relatively low temperature. However, the ionic conductivity of the solid electrolyte layer 30 in this case is lower than the ionic conductivity of the high ionic conductor LiTa ₂ PO ₈ alone. _In addition, by increasing the amount of Li, it is possible to sinter at a _low temperature. decreases.

Therefore, in the present embodiment, a solid electrolyte represented by a composition formula of Li _1+x Ta _2-x M _x PO ₈ is used as the solid electrolyte particles 31 . M is a metal element with a valence lower than that of pentavalent Ta. In the above composition, part of the pentavalent Ta is substituted with a metal element having a low valence such as tetravalent or trivalent, and the amount of Li for charge compensation is increased according to the substitution amount of Ta. Therefore, the crystal structure of LiTa ₂ PO ₈ is maintained and the generation of secondary phases is suppressed. Thereby, good ionic conductivity can be obtained. Furthermore, the sintering temperature can be lowered by increasing the amount of Li. From the above, it becomes possible to exhibit high ionic conductivity and to perform low-temperature firing. In order to increase the amount of Li, x satisfies the relationship 0<x. Also, if x is too large, the amount of secondary phases increases, so x satisfies the relationship of x<0.5. M is, for example, at least one of Zr, Ti, Ge, Hf, Sn, Y, B, Al and Ga.

In the composition of Li _1+x Ta _2−x M _x PO ₈ , x preferably satisfies the relationship of 0.02≦x, more preferably 0.05≦x, from the viewpoint of increasing the amount of Li. preferable. From the viewpoint of suppressing the secondary phase amount, x preferably satisfies the relationship of x≦0.4, and more preferably satisfies the relationship of x≦0.3.

It is preferable to confirm that the solid electrolyte particles 31 have a crystal structure belonging to a monoclinic system as a result of XRD (X-ray diffraction) measurement. In addition, "confirmed by XRD measurement that it belongs to a monoclinic crystal structure" means that the main peak is observed at least at 25.2 ° to 25.7 ° in XRD measurement using Cu Kα as a radiation source. , and subpeaks of diffraction peak intensity of 30% to 70% of the main peak intensity in the three ranges of 20.2 ° to 20.7 °, 24.6 ° to 25.1 ° and 34.6 ° to 35.1 ° is observed.

In the solid electrolyte layer 30, if the average grain diameter of the solid electrolyte particles 31 is small, there is a risk of reduced ionic conductivity. Therefore, it is preferable to set a lower limit for the average grain diameter of the solid electrolyte particles 31 . For example, the average grain diameter of the solid electrolyte particles 31 is preferably 0.3 μm or more, more preferably 0.6 μm or more, and even more preferably 1.2 μm or more.

In the solid electrolyte layer 30, if the average grain diameter of the solid electrolyte particles 31 is large, there is a risk of deterioration in sinterability. Therefore, it is preferable to set an upper limit for the average grain diameter of the solid electrolyte particles 31 . For example, the average grain diameter of the solid electrolyte particles 31 is preferably 22 μm or less, more preferably 12 μm or less, and even more preferably 6 μm or less.

The average grain diameter of the solid electrolyte particles 31 is obtained by measuring the horizontal or vertical Ferret diameter of 50 solid electrolyte particles 31 specified by EDS mapping in the cross section of the solid electrolyte layer 30, and averaging the diameter. It can be measured by giving a value.

The thickness of the solid electrolyte layer 30 is, for example, in the range of 1 μm to 30 μm, in the range of 2 μm to 25 μm, and in the range of 5 μm to 20 μm.

The positive electrode active material of the first electrode 10 is not particularly limited, but LiCoPO ₄ , Li ₂ CoP ₂ O ₇ , Li ₆ Co ₅ (P ₂ O ₇ ) ₄ and the like can be mentioned. Regarding the negative electrode active material of the second electrode 20, prior art in secondary batteries can be referred to as appropriate. compounds such as

In the production of the first electrode layer 11 and the second electrode layer 21, in addition to these electrode active materials, a solid electrolyte having ionic conductivity, a conductive material (conductive aid) such as carbon or metal, and the like are further added. may For these members, an electrode layer paste can be obtained by uniformly dispersing a binder and a plasticizer in water or an organic solvent. Examples of the metal of the conductive aid include Pd, Ni, Cu, Fe, and alloys containing these.

The first current collector layer 12 and the second current collector layer 22 are mainly composed of a conductive material. For example, metal, carbon, or the like can be used as the conductive material of the first current collector layer 12 and the second current collector layer 22 .

FIG. 2 is a schematic cross-sectional view of a stacked all-solid-state battery 100a in which a plurality of battery units are stacked. The all-solid-state battery 100a includes a laminated chip 60 having a substantially rectangular parallelepiped shape. In the laminated chip 60, the first external electrode 40a and the second external electrode 40b are provided so as to be in contact with two side surfaces of the four surfaces other than the top surface and the bottom surface of the stacking direction end. The two side surfaces may be two adjacent side surfaces or two side surfaces facing each other. In the present embodiment, the first external electrode 40a and the second external electrode 40b are provided so as to be in contact with two side surfaces (hereinafter referred to as two end surfaces) facing each other.

In the following description, those having the same composition range, the same thickness range, and the same particle size distribution range as the all-solid-state battery 100 are denoted by the same reference numerals, and detailed description thereof is omitted.

In the all-solid-state battery 100a, a plurality of first collector layers 12 and a plurality of second collector layers 22 are alternately laminated. Edges of the plurality of first current collector layers 12 are exposed on the first end face of the laminated chip 60 and are not exposed on the second end face. Edges of the plurality of second current collector layers 22 are exposed on the second end surface of the laminated chip 60 and are not exposed on the first end surface. Thereby, the first current collector layer 12 and the second current collector layer 22 are alternately connected to the first external electrode 40a and the second external electrode 40b.

A first electrode layer 11 is laminated on the first collector layer 12 . A solid electrolyte layer 30 is laminated on the first electrode layer 11 . The solid electrolyte layer 30 extends from the first external electrode 40a to the second external electrode 40b. A second electrode layer 21 is laminated on the solid electrolyte layer 30 . A second collector layer 22 is laminated on the second electrode layer 21 . Another second electrode layer 21 is laminated on the second collector layer 22 . Another solid electrolyte layer 30 is laminated on the second electrode layer 21 . The solid electrolyte layer 30 extends from the first external electrode 40a to the second external electrode 40b. A first electrode layer 11 is laminated on the solid electrolyte layer 30 . These stacking units are repeated in the all-solid-state battery 100a. Accordingly, the all-solid-state battery 100a has a structure in which a plurality of battery units are stacked.

The first current collector layer 12 and the two first electrode layers 11 sandwiching it are regarded as one electrode, and the second current collector layer 22 and the two second electrode layers 21 sandwiching it are regarded as one electrode. Considering one electrode, the laminated chip 60 can be said to have a structure in which a plurality of internal electrodes and a plurality of solid electrolyte layers are alternately laminated.

The all-solid-state battery 100a does not have to have a collector layer. For example, as illustrated in FIG. 3, the first current collector layer 12 and the second current collector layer 22 may not be provided. In this case, only the first electrode layer 11 constitutes the first electrode 10 , and only the second electrode layer 21 constitutes the second electrode 20 .

Next, a method for manufacturing the all-solid-state battery 100a illustrated in FIG. 2 will be described. FIG. 4 is a diagram illustrating the flow of the method for manufacturing the all-solid-state battery 100a.

(Ceramic raw material powder preparation process)
First, a solid electrolyte powder for obtaining the above-described solid electrolyte particles 31 is prepared.
The raw material powder of the solid electrolyte particles 31 represented by the composition formula of Li _1+x Ta _2-x M _x PO ₈ is, for example, Li, Ta, P, and M, which is a metal element with a lower valence than Ta. is synthesized by a solid-phase synthesis method from a raw material containing For example, Li ₃ PO ₄ , Ta ₂ O ₅ , NH ₄ H ₂ PO ₄ and an oxide of M are mixed in a predetermined molar ratio and heat-treated at about 900° C. in air. If M is trivalent, the _oxide of M is _M2O3 . If M is tetravalent, the oxide of M is _MO2 . After the obtained reactant is ground and mixed, the main heat treatment is performed again at 1100° C. or less. The obtained powder is pulverized to a desired particle size with a wet ball mill.

If the average particle size of the obtained raw material powder is large, it becomes difficult to make the solid electrolyte layer 30 thin and smooth. Therefore, it is preferable to set an upper limit for the average particle size of the raw material powder. For example, the average particle size of the raw material powder is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. If the average particle size of the raw material powder to be obtained is small, it becomes difficult to handle, and there is a risk of causing aggregation of the particles. Therefore, it is preferable to set a lower limit for the average particle size of the raw material powder. For example, the average particle size of the raw material powder is preferably 0.2 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more.

(Solid electrolyte green sheet manufacturing process)
Next, the obtained powder is uniformly dispersed in an aqueous solvent or an organic solvent together with a binder, a dispersant, a plasticizer, etc., and wet pulverized to obtain a solid electrolyte slurry having a desired average particle size. get At this time, a bead mill, a wet jet mill, various kneaders, a high-pressure homogenizer, or the like can be used, and it is preferable to use a bead mill from the viewpoint of being able to simultaneously adjust the particle size distribution and disperse. A binder is added to the obtained solid electrolyte slurry to obtain a solid electrolyte paste. By applying the obtained solid electrolyte paste, a solid electrolyte green sheet can be produced. The coating method is not particularly limited, and a slot die method, a reverse coating method, a gravure coating method, a bar coating method, a doctor blade method, or the like can be used. The particle size distribution after wet pulverization can be measured, for example, using a laser diffraction measurement device using a laser diffraction scattering method.

(Internal electrode paste preparation process)
Next, an internal electrode paste for producing the above-described first electrode layer 11 and second electrode layer 21 is produced. For example, an internal electrode paste can be obtained by uniformly dispersing a conductive aid, an electrode active material, a solid electrolyte material, a binder, a plasticizer, and the like in water or an organic solvent. As the solid electrolyte material, the solid electrolyte paste described above may be used. Pd, Ni, Cu, Fe, alloys containing these, various carbon materials, and the like may further be used as conductive aids. When the compositions of the first electrode layer 11 and the second electrode layer 21 are different, each internal electrode paste may be prepared separately.

(Current collector paste preparation step)
Next, a current collector paste for manufacturing the above-described first current collector layer 12 and second current collector layer 22 is prepared. For example, a current collector paste can be obtained by uniformly dispersing Pd powder, carbon black, plate-like graphite carbon, a binder, a dispersant, a plasticizer, and the like in water or an organic solvent.

(External electrode paste preparation process)
Next, an external electrode paste for producing the first external electrode 40a and the second external electrode 40b is prepared. For example, an external electrode paste can be obtained by uniformly dispersing a conductive material, an electrode active material, a solid electrolyte, a binder, a plasticizer, and the like in water or an organic solvent.

(Lamination process)
As illustrated in FIG. 5A, on one surface of a solid electrolyte green sheet 51, an internal electrode paste 52, a current collector paste 53, and an internal electrode paste 52 are printed. A reverse pattern 54 is printed on a region of the solid electrolyte green sheet 51 where the internal electrode paste 52 and the current collector paste 53 are not printed. As the reverse pattern 54, the same one as the solid electrolyte green sheet 51 can be used. A laminate is obtained by stacking a plurality of solid electrolyte green sheets 51 alternately after printing, and crimping a cover sheet 55 in which a plurality of solid electrolyte green sheets are bonded together from above and below in the stacking direction. In this case, a substantially rectangular parallelepiped laminate is obtained so that pairs of the internal electrode paste 52 and the current collector paste 53 are alternately exposed on the two end surfaces of the laminate. Next, as exemplified in FIG. 5B, an external electrode paste 56 is applied to each of the two end faces by a dipping method or the like and dried. Thereby, a molding for forming the all-solid-state battery 100a is obtained.

(Baking process)
Next, the obtained laminate is fired. The firing conditions include, without particular limitation, an oxidizing atmosphere or a non-oxidizing atmosphere and a maximum temperature of preferably 500°C to 900°C, more preferably 600°C to 800°C. A step of holding below the maximum temperature in an oxidizing atmosphere may be provided to sufficiently remove the binder until the maximum temperature is reached. In order to reduce process costs, it is desirable to bake at as low a temperature as possible. After firing, reoxidation treatment may be performed. Through the above steps, the all-solid-state battery 100a is produced.

For the all-solid-state battery 100a illustrated in FIG. 2, the step of applying the current collector paste 53 in the step of FIG. 5(a) may be omitted.

Note that the first external electrode 40a and the second external electrode 40b may be baked after the baking process. FIG. 6 is a flowchart illustrating the manufacturing method in this case. For example, the external electrode paste 56 is not applied in the stacking process, and the external electrode paste 56 is applied to the two end faces of the laminated chip 60 obtained in the firing process and baked. Thereby, the first external electrode 40a and the second external electrode 40b can be formed.

According to this embodiment, the solid electrolyte represented by the composition formula of Li _1+x Ta _2-x M _x PO ₈ is used as the raw material powder synthesized for the solid electrolyte particles 31 . M is a metal element with a valence lower than that of pentavalent Ta. A part of the pentavalent Ta is substituted with a metal element having a low valence such as tetravalent or trivalent, and the amount of Li for charge compensation is increased according to the substitution amount of Ta. Therefore, the crystal structure of LiTa ₂ PO ₈ is maintained and the generation of secondary phases is suppressed. Thereby, good ionic conductivity can be obtained. Furthermore, the sintering temperature can be lowered by increasing the amount of Li. From the above, it is possible to exhibit high ion conductivity and to perform low-temperature firing.

All-solid-state batteries were produced according to the embodiments, and their characteristics were investigated.

(Example 1)
Li _1+x Ta _2-x Zr _x PO ₈ in which part of Ta in crystalline LiTa ₂ PO ₈ was replaced with Zr was synthesized by a solid-phase synthesis method. First, the starting materials Li ₃ PO ₄ , Ta ₂ O ₅ , ZrO ₂ and NH ₄ H ₂ PO ₄ were ground and mixed so that x=0.1, heat-treated at 900° C. in the air, and then ground. After the crushing treatment, it was synthesized by heat treatment at 1050° C. again. From the results of XRD measurement of the synthetic powder, it was confirmed that the main phase was a monoclinic crystal phase similar to LiTa ₂ PO ₈ . Synthetic powder is dispersed in a mixed solvent of ethanol and toluene, and organic binder is mixed well to prepare a slurry. This slurry is spread on a PET film that has been subjected to surface release treatment with a doctor blade, and then heated and dried to form a green sheet. got Forty green sheets were laminated and pressure-bonded, and the small pieces were sintered at various temperatures in the atmosphere to be degreased and sintered. Au electrodes were formed on both sides of the sintered body by Au sputtering, and ion conductivity (total conductivity σ) was evaluated at 25° C. by an AC impedance method. The highest densification temperature was 950° C. and σ was 5.3×10 ⁻⁵ S/cm.

(Example 2)
Synthetic powder and sintered pellets were obtained in the same manner as in Example 1, except that x=0.2 in the composition of Li _1+x Ta _2-x Zr _x PO ₈ . From the results of XRD measurement of the synthetic powder, it was confirmed that the main phase was a monoclinic crystal phase similar to LiTa ₂ PO ₈ . The maximum densification temperature was 950° C. and σ was 4.5×10 ⁻⁵ S/cm.

(Example 3)
Synthetic powder and sintered pellets were obtained in the same manner as in Example 1, except that x=0.3 in the composition of Li _1+x Ta _2-x Zr _x PO ₈ . From the results of XRD measurement of the synthetic powder, a mixed phase of a monoclinic crystal phase and a secondary phase similar to LiTa ₂ PO ₈ was confirmed. The highest densification temperature was 900° C. and σ was 3.2×10 ⁻⁵ S/cm.

(Comparative example 1)
A synthetic powder and a sintered pellet were obtained in the same manner as in Example 1, except that x=0.5 in the composition of Li _1+x Ta _2-x Zr _x PO ₈ . As a result of the XRD measurement of the synthetic powder, in addition to the monoclinic crystal phase similar to LiTa ₂ PO ₈ , many diffraction peaks attributed to secondary phases were observed. The highest densification temperature was 900° C. and σ was 8.5×10 ⁻⁶ S/cm.

(Comparative example 2)
Synthetic powder and sintered pellets were obtained _in the same manner as in Example 1, except that crystalline _LiTa2PO8 _was synthesized using _Li3PO4 _, _Ta2O5 , _ZrO2 , and _NH4H2PO4 _as starting materials _. rice field. From the results of XRD measurement of the synthetic powder, it was confirmed that the monoclinic crystal phase was the main phase. The highest densification temperature was 1050° C. and σ was 6.2×10 ⁻⁵ S/cm.

Table 1 shows the results of Examples 1 to 3 and Comparative Examples 1 and 2.

Regarding the sinterability, if the most densified temperature (densification temperature) was 950°C or less, it was judged to be acceptable, and if it exceeded 950°C, it was judged to be unsatisfactory. Regarding the ionic conductivity, if the ionic conductivity is 1.0 × 10 ^-5 S / cm or more, it is judged to be passed "○", and if it is less than 1.0 × 10 ^-5 S / cm, it is judged to be unsatisfactory "× ” was determined. When both the sinterability and the ionic conductivity were determined to be acceptable, the comprehensive evaluation was made as "good". When at least one of the sinterability and ionic conductivity was judged to be unacceptable, the overall judgment was set as unacceptable "x".

In all of Examples 1 to 3, the comprehensive judgment was acceptable. This is represented by a composition formula of Li _1+x Ta _2−x M _x PO ₈ , where x satisfies 0<x<0.5, and M is a metal element with a lower valence than Ta. This is probably because it was used as the main component ceramic of the electrolyte layer 30 . In Comparative Example 1, the ionic conductivity was rejected. It is considered that this is because the value of x was too large and the amount of secondary phases increased. In Comparative Example 2, the sinterability was rejected. It is considered that this is because the sintering temperature became high because the amount of Li was not increased.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention described in the scope of claims. Change is possible.

Claims

Represented by the composition formula Li 1+y Ta 2-x M x PO 8 ,
x satisfies 0<x<0.5,
M is an element with a lower valence than Ta,
A solid electrolyte characterized in that y=(5−A)x, where A is the valence of M.
The solid electrolyte according to claim 1, wherein M is at least one of Zr, Ti, Ge, Hf, Sn, Y, B, Al and Ga.
3. The solid electrolyte according to claim 1, wherein x satisfies 0<x≦0.3.
The solid electrolyte according to any one of claims 1 to 3, characterized in that it is confirmed to have a crystal structure belonging to a monoclinic system as a result of XRD measurement.
The solid electrolyte according to any one of claims 1 to 4, characterized in that the average particle size is 0.2 µm or more and 20 µm or less.
A solid electrolyte layer containing the solid electrolyte according to any one of claims 1 to 5 as a main component;
a first electrode including an electrode active material and formed on the first main surface of the solid electrolyte layer;
and a second electrode that includes an electrode active material and is formed on a second main surface of the solid electrolyte layer that faces the first main surface.
7. The all-solid-state battery according to claim 6, wherein the solid electrolyte layer, the first electrode, and the second electrode are used as one unit, and a plurality of the units are stacked.
The all-solid-state battery according to claim 6 or 7, wherein one of the first electrode and the second electrode contains a positive electrode active material, and the other contains a negative electrode active material.
A raw material containing Li, Ta, P, and M, which is an element with a lower valence than Ta, is represented by a composition formula of Li 1+y Ta 2-x M x PO 8 , where 0<x<0. A method for producing a solid electrolyte, characterized by synthesizing at 1100° C. or less an oxide-type solid electrolyte that satisfies the relationship of 5 and y=(5−A)x where A is the valence of M. .
Represented by the composition formula Li 1+y Ta 2-x M x PO 8 , satisfying the relationship 0<x<0.5, M being an element with a lower valence than Ta, and the valence of M being A a green sheet containing a solid electrolyte powder where y=(5−A), a first electrode layer paste coating material formed on a first main surface of the green sheet, and a second main surface of the green sheet; a step of preparing a laminate having a second electrode layer paste coating formed on the surface;
and a sintering step of sintering the laminate.
11. The method for manufacturing an all-solid-state battery according to claim 10, wherein the firing temperature in the firing step is 500[deg.] C. or higher and 900[deg.] C. or lower.