JP5800464B2 - Ion conductive inorganic compound, method for synthesizing the same, and method for producing alkali metal ion secondary battery - Google Patents

Description

  The present invention mainly relates to a method for synthesizing an ion conductive inorganic compound used as a solid electrolyte of a secondary battery.

In recent years, as one of means for mitigating global warming, vehicles using electricity as a power source such as hybrid cars and electric cars have been widely used. For secondary batteries used as power sources for these vehicles, there is an increasing need for batteries with higher energy density for the purpose of extending the continuous travel distance. Accordingly, research institutes such as automobile manufacturers and battery manufacturers are energetically developing lithium-ion secondary batteries with high energy density.
At present, lithium ion secondary batteries mainly use organic electrolytes as electrolytes. However, the organic solvent, which is an electrolyte, has a low flash point and may ignite or burn. In addition, there is a risk of combustible gas generation in an overcharged state or a high temperature environment, and it is difficult to sufficiently ensure safety. Therefore, a solid battery using an inorganic solid electrolyte as an electrolyte has been proposed. Since the solid battery does not use the above-described flammable organic solvent, there is no possibility of causing problems such as liquid leakage or ignition, and the solid battery is excellent in safety.

JP2000-109360 JP2000-200621 JP2002-151142 JP2009-181807 JP-A-9-213366

H. Aono, E. Sugimoto, Y. Sadaoka, N. Inamura, and G. Adachi, J. Electrochem. Soc. 137, 1023-1027 (1990)

As one of lithium ion conductive inorganic solid electrolyte materials, lithium phosphate titanate LiTi ₂ (PO ₄ ) ₃ is disclosed in Patent Document 1 and Patent Document 2. Lithium phosphate titanate has a NASICON type structure and is expected to have high ionic conductivity. Non-Patent Document 1 describes Li _{1 + x} M _x Ti in which a part of Ti of lithium titanate phosphate is substituted with a trivalent metal element such as Al, Cr, Ga, Fe, Sc, Y, In, and La. It is disclosed that higher ionic conductivity can be obtained by using _2-x (PO ₄ ) ₃ .
Patent Document 1 discloses a method for producing LiTi ₂ (PO ₄ ) ₃ by a discharge plasma sintering method using H ₃ PO ₄ , Li ₃ PO ₄ , or H ₃ PO ₂ as a phosphorus source.
Patent Document 2 discloses a method for producing LiTi ₂ (PO ₄ ) ₃ by a discharge plasma sintering method using H ₃ PO ₄ and (NH ₄ ) ₂ HPO ₄ as a phosphorus source.
Patent Document 3 discloses that Li _{1 + a} X _a Ti _2-a (PO ₄ ) ₃ (X is Al, Sc, Pt) by a molten salt method using ammonium hydrogen phosphate or phosphoric acid pyrophosphate as a phosphoric acid source. A method for producing one kind selected from Y, La, In, Fe, Ga and Cr, 0 ≦ a <0.7) is disclosed.
In Patent Document 4, Li _{1 + x} M1 _x Ti _2-x (PO ₄ ) ₃ (by a laser absorption method or sputtering method using (NH ₄ ) ₂ HPO ₄ as a phosphoric acid source on a single crystal electrode layer. M1 discloses a method for producing one selected from Al, Sc, In, Fe, Cr, Ga, Y, and La, 0 ≦ x <2.0.

Conventionally, (NH ₄ ) ₃ PO ₄ , (NH ₄ ) ₂ HPO ₄ , (NH ₄ ) H are compounds containing phosphorus, nitrogen, and oxygen for the production of lithium phosphate titanate (LTP) and metal-substituted LTP. _{When 2} PO ₄ is used as a phosphorus source, there are problems that the yield of the target product is low and harmful gases are generated.
For example,
a.) When Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ is synthesized using (NH ₄ ) ₃ PO ₄ as a raw material, the reaction formula is
0.65Li ₂ CO ₃ +0.15 Al ₂ O ₃ + 1.7TiO ₂ +3 (NH ₄ ) ₃ PO ₄
→ Li _1.3 Ai _0.3 Ti _1.7 (PO ₄ ) ₃ + a ₁ NH ₃
+ b ₁ NO _x + c ₁ H ₂ O + d ₁ CO ₂
(A ₁ , b ₁ , c ₁ , d ₁ are all real numbers)
The theoretical yield is 59.3 wt%.
b.) When (NH ₄ ) ₂ HPO ₄ is used as a raw material and Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ is synthesized, the reaction formula is
0.65 Li ₂ CO ₃ +0.15 Al ₂ O ₃ + 1.7TiO ₂ +3 (NH ₄ ) ₂ HPO ₄
→ Li _1.3 Ai _0.3 Ti _1.7 (PO ₄ ) ₃ + a ₂ NH ₃
+ b ₂ NO _x + c ₂ H ₂ O + d ₂ CO ₂
(a ₂ , b ₂ , c ₂ , d ₂ are all real numbers)
The theoretical yield is 64.4 wt%.
b.) When Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ is synthesized using (NH ₄ ) H ₂ PO ₄ as a raw material, the reaction formula is
0.65Li ₂ CO ₃ + 0.15Al ₂ O ₃ + 1.7TiO ₂ +3 (NH ₄ ) H ₂ PO ₄
→ Li _1.3 Ai _0.3 Ti _1.7 (PO ₄ ) ₃ + a ₃ NH ₃ + b ₃ NO _x + c ₃ H ₂ O + d ₃ CO ₂
(a ₃ , b ₃ , c ₃ , d ₃ are all real numbers)
The theoretical yield is 70.5 wt%.
When producing LTP and metal-substituted LTP using these raw materials, the production yield is as low as 60 to 70 wt%, and the generation of harmful gases such as ammonia and nitrogen oxides is unavoidable. Since the processing cost is also high, there is a problem that the manufacturing cost becomes high.

On the other hand, diphosphorus pentoxide (P ₂ O ₅ ) can be used as a phosphorus source, and in this case, no toxic gas is generated as described above. However, diphosphorus pentoxide is highly hygroscopic and is a substance that easily absorbs moisture in the air and changes to phosphoric acid. Hypophosphorous acid (H ₃ PO ₂ ) and phosphorous acid (H ₃ PO ₃ ) are substances that are easily oxidized, and are unstable and difficult to handle substances that change into phosphoric acid by oxidation. Phosphoric acid (H ₃ PO ₄ ) is a liquid at room temperature, and it is difficult to accurately determine the phosphorus content in the liquid. When metal-substituted LTP (Li _{1 + x} M1 _x Ti _2-x (PO ₄ ) ₃ ) is used as the solid electrolyte of a lithium ion secondary battery, the lithium ion conductivity is set to the value x indicating the element content ratio. In order to obtain a solid electrolyte material that depends on sensitivity and obtains the best physical properties, it is necessary to quantify very accurately at the stage of mixing a lithium source, a metal source, and a phosphorus source. Therefore, there has been a problem that diphosphorus pentoxide and phosphoric acid are not preferable for producing a solid electrolyte material having excellent physical properties suitable for producing a high-performance battery. In addition to the problem that phosphoric acid is difficult to quantitate, there is a problem that the process becomes complicated because drying and separation of the solvent (water) are required after mixing with other substances. Furthermore, since it is an acidic solution, there have been problems such as causing a violent reaction depending on the substance to be mixed, and generating toxic fumes by heating.
Moreover, the pyrophosphoric acid phosphate described in patent document 3 is phosphoric acid and pyrophosphoric acid. Phosphoric acid (H ₃ PO ₄ ) has the above-described problems such as hygroscopicity. Pyrophosphate (H ₄ P ₂ O ₇ ) is an unstable substance in air containing normal water and becomes phosphoric acid when absorbed. Since it is hygroscopic and easily changes to phosphoric acid at room temperature, it has the same problem as phosphorus pentoxide.
Li ₃ PO ₄ is a substance that can be used as both a lithium source and a phosphorus source. However, Li ₃ PO ₄ is a substance with a large amount of Li in the element content ratio of Li and P. Therefore, in order to synthesize a substance having a high element content ratio of P, such as LTP and metal substitution type LTP, it is necessary to prepare and mix another phosphorus source. In some cases, there is a problem that a part of the raw material is excessively administered and it is not economical.
As described above, the problems in the method for synthesizing the lithium ion conductive inorganic solid electrolyte material have been described. In addition to the lithium, generally, in the synthesis of the alkali metal ion conductive inorganic solid electrolyte material, the raw material of the conventional phosphorus source is used. When used, there are the above-mentioned problems, and there is a need for a better phosphorus source material.

  An object of the present invention is to provide a method for synthesizing an ion conductive inorganic compound that can achieve high productivity and can suppress generation of harmful gases.

In the present invention (1), at least pyrophosphate is used as a phosphorus source, the chemical formula of the pyrophosphate is M1 _x P ₂ O ₇ (where x <2), and the chemical formula of the ion conductive inorganic compound is , A _{1 + y}
M2 _y M1 _2-y (PO ₄ ) ₃ (where A is an alkali metal element, M1 is a metal element selected from Ti and Sn, and M2 is a metal element selected from Al and Y) A synthetic method of an ion conductive inorganic compound, characterized in that it is an alkali metal phosphate compound represented by: Y ≦ 0.5 .

According to the present invention (1) to (3), in the production of inorganic compounds containing phosphorus, the generation of harmful gas such as ammonia gas and nitrogen oxide is minimized, and the scale of the harmful gas removal equipment The manufacturing cost can be reduced by reducing the size. In addition, the yield of the target inorganic compound can be improved. Furthermore, the content ratio of a plurality of elements constituting the inorganic compound can be accurately controlled, and an inorganic compound having excellent physical properties can be synthesized. In particular, by making _{x of} pyrophosphate M1 _x P ₂ O ₇ used for production less than 2, it is possible to synthesize an inorganic compound without using a phosphorus source by using only pyrophosphate as a phosphorus source. . Therefore, it is not necessary to additionally use a nitrogen compound raw material that generates harmful nitrogen gas as a phosphorus source.
According to the present invention (4), physical properties such as ionic conductivity can be improved by accurately controlling the content ratio of elements constituting the compound.
According to the present invention (5), by using a low-cost solid electrolyte material having high ion conductivity, a high-performance and low-cost all-solid-state secondary battery can be manufactured.

2 is X-ray diffraction data of an inorganic compound synthesized in Example 1. FIG. 3 is X-ray diffraction data of an inorganic compound synthesized in Example 5. FIG. 6 is an X-ray diffraction data of an inorganic compound synthesized in Comparative Example 5. FIG.

The best mode of the present invention will be described below.
The inventors of the present invention conducted intensive studies to achieve the above object, and as a result of repeated experiments, the use of pyrophosphate (metal pyrophosphate) containing no nitrogen element as a phosphorus source generates harmful substances. It is possible to synthesize alkali metal ion-conducting inorganic compounds at a high yield without any control, and the content ratio of elements constituting the product can be accurately controlled. For example, physical properties such as ionic conductivity Has found that an excellent inorganic compound can be synthesized.

(Reaction formula and theoretical yield)
The reaction formulas and theoretical yields of typical ion conductive inorganic compound synthesis reactions according to the present invention will be described below with specific examples. However, the present invention is not limited to these specific examples. The comparative example is an explanation of a synthetic reaction of an ion conductive inorganic compound using a conventional phosphorus source. First, as a specific example, a case where only pyrophosphate is used as a phosphorus source will be described.
[Specific Example 1]
Reaction product: Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃
Reaction raw materials: lithium source (LiPO ₃ ), aluminum source (Al ₂ O ₃ ), titanium source (TiO ₂ ), titanium and phosphorus source (TiP ₂ O ₇ )
The reaction formula is
1.3LiPO ₃ + 0.15Al ₂ O ₃ + 0.85TiO ₂ + 0.85TiP ₂ O ₇
→ Li _1.3 Ai _0.3 Ti _1.7 (PO ₄ ) ₃
There is no gas generation and the theoretical yield is 100 wt%.
[Specific Example 2]
Reaction product: Li _1.3 Y _0.3 Ti _1.7 (PO ₄ ) ₃
Reaction raw materials: lithium source (Li ₂ CO ₃ ), yttrium source (Y ₂ O ₃ ), titanium source (TiO ₂ ), titanium and phosphorus source (TiP ₂ O ₇ )
The reaction formula is
0.65Li ₂ CO ₃ + 0.15Y ₂ O ₃ + 0.2TiO ₂ + 1.5TiP ₂ O ₇
→ Li _1.3 Y _0.3 Ti _1.7 (PO ₄ ) ₃
There is no gas generation and the theoretical yield is 100 wt%.
[Specific Example 3]
Reaction product: LiSn ₂ (PO ₄ ) ₃
Reaction raw materials: lithium source (LiPO ₃ ), tin source (SnO ₂ ), tin and phosphorus source (SnP ₂ O ₇ )
The reaction formula is
LiPO ₃ + SnO ₂ + SnP ₂ O ₇
→ LiSn ₂
(PO ₄ ) ₃
There is no gas generation and the theoretical yield is 100 wt%.
For comparison, the reaction formula and theoretical yield in the case of synthesizing Li _1.3 Y _0.3 Ti _1.7 (PO ₄ ) ₃ and LiSn ₂ (PO ₄ ) ₃ using ammonium dihydrogen phosphate are described below.
[Comparative Example 1]
Reaction product: Li _1.3 Y _0.3 Ti _1.7 (PO ₄ ) ₃
Reaction raw materials: lithium source (Li ₂ CO ₃ ), yttrium source (Y ₂ O ₃ ), titanium source (TiO ₂ ), phosphorus source (NH ₄ H ₂ PO ₄ )
The reaction formula is
0.65Li ₂ CO ₃ + 0.15Y ₂ O ₃ + 1.7TiO ₂ + 3NH ₄ H ₂ PO ₄
→ Li _1.3 Y _0.3 Ti _1.7 (PO ₄ ) ₃ + a ₄ NH3 + b ₄ Nox + c ₄ H2O + d ₄ CO2
(A ₄ , b ₄ , c ₄ , d ₄ are all real numbers)
Thus, ammonia gas, nitrogen oxide gas, and carbon dioxide gas are generated, and the theoretical yield is 71.4 wt%.
[Comparative Example 2]
Reaction product: LiSn ₂ (PO ₄ ) ₃
Reaction raw materials: lithium source (Li ₂ CO ₃ ), tin source (SnO ₂ ), phosphorus source (NH ₄ H ₂ PO ₄ )
The reaction formula is
0.5Li ₂ CO ₃ + 2.0SnO ₂ + 3NH ₄ H ₂ PO ₄
→ LiSn ₂ (PO ₄ ) ₃ + a ₅ NH3 + b ₅ Nox + c ₅ H2O + 0.5CO2
(A ₅ , b ₅ , c ₅ are all real numbers)
Then, ammonia gas, nitrogen oxide gas, and carbon dioxide gas are generated, and the theoretical yield is 77.4 wt%.
Thus, even when ammonium dihydrogen phosphate, which is considered to have the highest yield as an ammonium salt, is selected as the reaction raw material, it can be seen that nearly 30% of the reaction raw material is consumed as harmful gas or carbon dioxide gas. . This is because in any synthesis of lithium-phosphorus-metal compounds, the higher the proportion of ammonia molecules in the nitrogen-containing phosphate compound that can be a phosphorus source, the more ammonia gas or nitrogen oxides are present in the synthesis. This is because the amount produced is increased, resulting in a significant weight loss. This is a phenomenon that occurs in common regardless of the metal element constituting the target compound.

(Method for producing ion-conductive inorganic compound)
Hereinafter, a method for producing an ion conductive inorganic compound according to an embodiment of the present invention will be described taking a method for producing a lithium ion conductive inorganic compound as an example. Needless to say, the manufacturing method described below is applicable not only to lithium but also to a method of manufacturing an inorganic compound having other alkali metal ion conductivity such as sodium.
Description will be made by taking the above-described specific example 1 as an example. First, a lithium source (LiPO ₃ ), an aluminum source (Al ₂ O ₃ ), a titanium source (TiO ₂ ), titanium and a phosphorus source (TiP ₂ O ₇ ) are mixed so as to have a predetermined weight ratio. Here, TiP ₂ O ₇ which is pyrophosphate is mixed as a phosphorus source. Then, dry pulverization / dispersion is performed with a lykai machine. Next, the powder obtained by the dispersion is molded with a pelleter, and then heated and fired, for example, in an air atmosphere to synthesize Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ . The heating conditions are preferably, for example, 600 to 1200 ° C. and 2 to 10 hours. In the implementation of this patent, it is desirable that the reaction raw material powder is sufficiently pulverized and mixed before the synthesis reaction is accelerated by heating. Making the reaction raw material fine has the effect of promoting an increase in the contact area between the reaction raw materials. By increasing the contact area between the reaction raw materials, element diffusion by heating at the time of synthesis is rapidly performed, and the target product can be obtained by heating in a shorter time. The reaction raw material powder is pulverized and dispersed by dry pulverization using a reiki machine, dry vibration mill, etc., pot mill, bead mill, etc. The reaction raw material mixed powder can be obtained. The effect of the present invention is attributed to minimizing the amount of nitrogen-containing phosphorus compound that causes generation of harmful gas as a reaction raw material. Even when the dispersion method is used, the effect is exhibited.

The chemical formula of the ion conductive inorganic compound that can obtain excellent effects such as yield improvement by applying the technique of the present invention is that the alkali metal element is A, the metal element is M1, and the metal element substituting M1 is M2.
A _{1 + y} M2 _y M1 _2-y (PO ₄ ) ₃
It can be expressed as. However, M1 is a metal element selected from Ti, Hf, Ge, Sn, Zr, Si, V, Nb, and M2 is Al, Sc,
It is a metal element selected from In, Fe, Cr, Ga, Y, and La.
As a phosphorus supply source for synthesizing the above ion conductive inorganic compound, it is preferable to use pyrophosphate. Unlike pyrophosphate described in Patent Document 3, pyrophosphate is a substance that is solid at room temperature, where pyrophosphate and metal are combined and neutralized. Since pyrophosphate is a neutralized solid unlike phosphoric acid or pyrophosphoric acid, it has low reactivity and low hygroscopicity at room temperature and is easy to handle. The chemical formula of such pyrophosphate is
M1 _x P ₂ O ₇ x <2
It can be expressed as.

(Differences in the effect of the invention depending on the element content ratio of the ion conductive inorganic compound)
The method for synthesizing an ion conductive inorganic compound using pyrophosphate as a phosphorus source of the present invention is based on the element ratio of M1 and P in the chemical formula A _{1 + y} M2 _y M1 _2-y (PO ₄ ) ₃ , that is, 2 When -y: 3 is smaller than 1: 2 = 0.5, which is the element ratio of M1 and P in the chemical formula M1P ₂ O ₇ of pyrophosphate (when y ≥ 0.5), all phosphorus sources can be covered with pyrophosphoric acid Therefore, it is not necessary to mix a phosphorus source such as an ammonium phosphate compound as a raw material, so that no harmful gas is generated, and the effects of the present invention can be sufficiently obtained.
On the other hand, when y <0.5, it is necessary to use a phosphorus source in addition to pyrophosphate. However, when a pyrophosphate is used in combination with a conventional phosphorus source as a part of the reaction raw material, it is possible to obtain effects such as reduction in the amount of harmful gas generated and improvement in yield. Hereinafter, the reaction formula and the theoretical yield will be described in the case where y = 0.5, but pyrophosphate and ammonium dihydrogen phosphate are used as the phosphorus source.
[Comparative Example 3]
When Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ was synthesized using only NH ₄ H ₂ PO ₄ as the phosphorus source,
The reaction formula is
0. 75Li ₂ CO ₃ + 0.25Al ₂ O ₃ + 1.5TiO ₂ + 3NH ₄ H ₂ PO ₄
→ Li _1.5 Al _0.5 Ti
_1.5 (PO ₄ ) ₃ + GAS
Then, ammonia gas, nitrogen oxide gas, and carbon dioxide gas are generated, and the theoretical yield is 69.7 wt%.
[Specific Example 4]
On the other hand, when Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ was synthesized using TiP ₂ O ₇ as the phosphorus source,
The reaction formula is
0.75Li ₂ CO ₃ + 0.25Al ₂ O ₃ + 1.5TiP ₂ O ₇
→ Li _1.5 Al _0.5 Ti _1.5
(PO ₄ ) ₃
No harmful gas such as ammonia gas and nitrogen oxide gas is generated, and the theoretical yield is 92.0 wt%.

(Method for producing lithium ion secondary battery)
Hereinafter, a method for producing a lithium ion secondary battery using the lithium ion conductive inorganic compound of the present invention as a solid electrolyte material will be described using a specific example. The method for producing a lithium ion secondary battery according to the present invention is described below. It is not limited to these specific examples. The secondary battery manufacturing method using the method for manufacturing an ion conductive compound of the present invention is not limited to a lithium ion secondary battery, and can be applied to an alkali metal ion secondary battery other than lithium and has an excellent effect of the invention. It goes without saying that can be obtained.
As a first specific example of the production method, there is a production method of a multilayer all solid-state lithium ion secondary battery including the following steps (1) to (5).
Step (1): A positive electrode paste containing a metal powder and a positive electrode active material, a negative electrode paste containing a metal powder and a negative electrode active material, and a solid electrolyte paste containing a solid electrolyte powder are prepared.
Step (2): A solid electrolyte paste is applied onto a PET substrate and dried to produce a solid electrolyte sheet. Hereinafter, the green sheet is simply referred to as a sheet. Next, a positive electrode paste is applied on the solid electrolyte sheet and dried to prepare a positive electrode sheet. Moreover, a negative electrode paste is apply | coated and dried on a solid electrolyte sheet, and a negative electrode sheet is produced.
Step (3): The positive electrode unit in which the solid electrolyte sheet and the positive electrode sheet are laminated is peeled from the PET substrate. Further, the negative electrode unit in which the solid electrolyte sheet and the negative electrode sheet are laminated is peeled from the PET substrate. Next, a positive electrode unit and a negative electrode unit are alternately laminated, and a laminate in which a positive electrode sheet and a negative electrode sheet are alternately laminated via a solid electrolyte sheet is produced. At this time, as necessary, the positive electrode unit and the negative electrode unit are aligned and laminated so that the negative electrode sheet is not exposed on one side surface of the laminate and the positive electrode sheet is not exposed on the other side surface.
Step (4): The laminate is pressure-bonded and fired to produce a sintered laminate.
Step (5): On the side surface of the laminate, a positive electrode terminal is formed so as to be connected to the positive electrode layer, and a negative electrode terminal is formed so as to be connected to the negative electrode layer. The electrode terminal (extraction electrode) can be formed, for example, by applying an extraction electrode paste to each side surface of the battery and then baking it at a temperature of 500 to 900 ° C. Although not shown, a protective layer is formed on the outermost part of the laminated body as necessary to complete the battery.

As a second specific example of the production method, there is a production method of a multilayer all solid-state lithium ion secondary battery including the following steps (1 ′) to (5 ′).
Step (1 ′): A positive electrode paste containing a positive electrode active material, a negative electrode paste containing a negative electrode active material, and a solid electrolyte paste containing a solid electrolyte powder are prepared.
Step (2 ′): A solid electrolyte paste, a positive electrode paste, a positive electrode current collector paste, and a positive electrode paste are applied in this order on a PET base material, and after drying in some cases, the base material is peeled off and the positive electrode unit After applying the paste in the order of solid electrolyte paste, negative electrode paste, negative electrode current collector paste, and negative electrode paste on the substrate, and optionally drying it, the substrate is peeled off to produce a negative electrode unit .
Step (3 ′): A positive electrode unit and a negative electrode unit are alternately laminated, and a laminate in which a positive electrode sheet and a negative electrode sheet are alternately laminated via a solid electrolyte sheet is produced. At this time, as necessary, the positive electrode unit and the negative electrode unit are aligned and laminated so that the negative electrode sheet is not exposed on one side surface of the laminate and the positive electrode sheet is not exposed on the other side surface.
Step (4 ′): The laminate is pressed and fired to produce a sintered laminate.
Step (5 ′): A positive electrode terminal is formed on the side surface of the laminate so as to be connected to the positive electrode layer, and a negative electrode terminal is formed so as to be connected to the negative electrode layer. The electrode terminal (extraction electrode) can be formed, for example, by applying an extraction electrode paste to each side surface of the battery and then baking it at a temperature of 500 to 900 ° C. Although not shown, a protective layer is formed on the outermost part of the laminated body as necessary to complete the battery.

As a third specific example of the production method, there is a production method of a multilayer all solid-state lithium ion secondary battery including the following steps (i) to (iii).
Step (i): A positive electrode paste containing a metal powder and a positive electrode active material, a negative electrode paste containing a metal powder and a negative electrode active material, and a solid electrolyte paste containing a lithium ion conductive inorganic substance powder are prepared.
Step (ii): A positive electrode paste, a solid electrolyte paste, a negative electrode paste, and a solid electrolyte paste are applied and dried in this order to produce a laminate composed of green sheets. At this time, if necessary, alignment is performed so that the negative electrode sheet is not exposed on one side surface of the laminate and the positive electrode sheet is not exposed on the other side surface.
Step (iii): If necessary, the substrate used for producing the green sheet is peeled off, and the laminate is pressure-fired to produce a sintered laminate.
Step (iv): A positive electrode terminal is formed on the side surface of the laminate so as to be connected to the positive electrode layer, and a negative electrode terminal is formed so as to be connected to the negative electrode layer. If necessary, a protective layer is formed on the outermost part of the laminate to complete the battery.

(Differences from similar prior art)
In Patent Document 5, in paragraph [0049], a negative electrode of a lithium ion secondary battery is prepared by dry-mixing and baking tin monoxide, tin pyrophosphate, diboron trioxide, potassium carbonate, magnesium oxide, and germanium dioxide. An example of synthesizing the material SnGe _0.1 B _0.5 P _0.58 Mg _0.1 K _0.1 O _3.35 is disclosed. It is similar to the technique according to the present invention in that an inorganic compound is synthesized using tin pyrophosphate, which is a pyrophosphate.
However, since tin pyrophosphate described in Patent Document 5 is Sn ₂ P ₂ O ₇ and the ratio of Sn and P is equal, when synthesizing a compound such as LiSn ₂ (PO ₄ ) ₃ , a phosphorus source is used. It will be insufficient, and it is necessary to prepare and mix another phosphorus source.
Non-Patent Document 1 describes that the ionic conductivity of LTP was improved by mixing LTP with Li ₄ P ₂ O ₇ which is a pyrophosphate as a binder and then baking. However, Non-Patent Document 1 describes that LTP was synthesized using (NH ₄ ) ₂ HPO ₄ as a raw material, and pyrophosphates were not used for the purpose of preventing the generation of nitrogenous harmful gases.

Hereinafter, the present invention will be described in detail using Examples and Comparative Examples. However, the present invention is not limited to these examples.
(Example)
In the examples, metal element-substituted LTP was synthesized using pyrophosphate as a phosphorus source of the reaction raw material.
(Example 1)
Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ was synthesized using Li ₂ CO ₃ as the lithium source and TiP ₂ O ₇ which is pyrophosphate as the phosphorus source. First, Li ₂ CO ₃ , Al ₂ O ₃ , TiO ₂ , and TiP ₂ O ₇ are mixed so that the weight ratio is 0.65: 0.15: 0.2: 1.5, and then dry pulverization / dispersion is performed for 1 hour with a lykai machine I did it. Next, the powder obtained by dispersion was molded into a diameter of 40 mmφ and a height of about 10 mm with a pelleter, and the weight of the molded body was measured. After measuring the weight, it was placed on a platinum setter with a known weight and baked at 800 ° C. for 4 hours in an air atmosphere to synthesize Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ . After firing, the sample is taken out and weighed together with the platinum setter to determine the weight before the reaction and the weight after the reaction, and the weight of the molded body after the firing reaction is divided by the weight before the reaction. Was calculated. In addition, the gas generated during the firing process was collected, and the presence or absence of generation of ammonia gas was examined with an ammonia gas detector tube. The synthesized inorganic compound was identified with an X-ray diffractometer. As a result, as shown in FIG. 1, the production of Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ was confirmed. Generation of ammonia gas was not observed, and the yield was 91.2%.

(Example 2)
Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ was synthesized using LiPO ₃ as the lithium source and TiP ₂ O ₇ which is pyrophosphate as the phosphorus source. First, LiPO ₃ , Al ₂ O ₃ , TiO ₂ , and TiP ₂ O ₇ were mixed so that the weight ratio was 1.3: 0.15: 0.85: 0.85, and then dry pulverization / dispersion was performed for 1 hour with a lykai machine. . Next, the powder obtained by dispersion was molded into a diameter of 40 mmφ and a height of about 10 mm with a pelleter, and the weight of the molded body was measured. After measuring the weight, it was placed on a platinum setter with a known weight and baked for 4 hours at a temperature of 800 ° C. in an air atmosphere to synthesize Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ . After firing, the sample is taken out and weighed together with the platinum setter to determine the weight before the reaction and the weight after the reaction, and the weight of the molded body after the firing reaction is divided by the weight before the reaction. Was calculated. In addition, the gas generated during the firing process was collected, and the presence or absence of generation of ammonia gas was examined with an ammonia gas detector tube. The synthesized inorganic compound was identified with an X-ray diffractometer. As a result, formation of Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ was confirmed. Generation of ammonia gas was not observed, and the yield was 97.9%.

(Example 3)
Li _1.3 Y _0.3 Ti _1.7 (PO ₄ ) ₃ was synthesized using Li ₂ CO ₃ as the lithium source and TiP ₂ O ₇ which is pyrophosphate as the phosphorus source. First, Li ₂ CO ₃ , Y ₂ O ₃ , TiO ₂ , and TiP ₂ O ₇ are mixed so that the weight ratio is 0.65: 0.15: 0.2: 1.5, and then dry pulverization and dispersion is performed for 1 hour in a lykai machine. I did it. Next, the powder obtained by dispersion was molded into a diameter of 40 mmφ and a height of about 10 mm with a pelleter, and the weight of the molded body was measured. After measuring the weight, it was placed on a platinum setter with a known weight and baked at 800 ° C. for 4 hours in an air atmosphere to synthesize Li _1.3 Y _0.3 Ti _1.7 (PO ₄ ) ₃ . After firing, the sample is taken out and weighed together with the platinum setter to determine the weight before the reaction and the weight after the reaction, and the weight of the molded body after the firing reaction is divided by the weight before the reaction. Was calculated. In addition, the gas generated during the firing process was collected, and the presence or absence of generation of ammonia gas was examined with an ammonia gas detector tube. The synthesized inorganic compound was identified with an X-ray diffractometer. As a result, formation of Li _1.3 Y _0.3 Ti _1.7 (PO ₄ ) ₃ was confirmed. Generation of ammonia gas was not observed, and the yield was 91.1%.

Example 4
LiSn ₂ (PO ₄ ) ₃ was synthesized using Li ₂ CO ₃ as the lithium source and SnP ₂ O ₇ which is pyrophosphate as the phosphorus source. First, Li ₂ CO ₃ , SnO ₂ , and SnP ₂ O ₇ were mixed so that the weight ratio was 0.5: 0.5: 1.5, and then dry pulverization / dispersion was performed for 1 hour in a lycra machine. Next, the powder obtained by dispersion was molded into a diameter of 40 mmφ and a height of about 10 mm with a pelleter, and the weight of the molded body was measured. After the weight measurement, it was placed on a platinum setter with a known weight and baked at 1000 ° C. for 4 hours in an air atmosphere to synthesize LiSn ₂ (PO ₄ ) ₃ . After firing, the sample is taken out and weighed together with the platinum setter to determine the weight before the reaction and the weight after the reaction, and the weight of the molded body after the firing reaction is divided by the weight before the reaction. Was calculated. In addition, the gas generated during the firing process was collected, and the presence or absence of generation of ammonia gas was examined with an ammonia gas detector tube. The synthesized inorganic compound was identified with an X-ray diffractometer. As a result, production of LiSn ₂ (PO ₄ ) ₃ was confirmed. Generation of ammonia gas was not observed, and the yield was 94.8%.

(Example 5)
Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ was synthesized using Li ₂ CO ₃ as the lithium source and TiP ₂ O ₇ which is pyrophosphate as the phosphorus source. First, Li ₂ CO ₃ , Al ₂ O ₃ , and TiP ₂ O ₇ were mixed so that the weight ratio was 0.75: 0.25: 1.5, and then dry pulverization and dispersion were performed for 1 hour in a likai machine. Next, the powder obtained by dispersion was molded into a diameter of 40 mmφ and a height of about 10 mm with a pelleter, and the weight of the molded body was measured. After the weight measurement, it was placed on a platinum setter with a known weight and baked at a temperature of 800 ° C. for 4 hours in an air atmosphere to synthesize Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ . After firing, the sample is taken out and weighed together with the platinum setter to determine the weight before the reaction and the weight after the reaction, and the weight of the molded body after the firing reaction is divided by the weight before the reaction. Was calculated. In addition, the gas generated during the firing process was collected, and the presence or absence of generation of ammonia gas was examined with an ammonia gas detector tube. The synthesized inorganic compound was identified with an X-ray diffractometer. As a result, generation of Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ was confirmed as shown in FIG. Generation of ammonia gas was not observed, and the yield was 90.6%.

(Comparative example)
In the comparative example, the metal element substitution type LTP was synthesized using only NH ₄ H ₂ PO ₄ without using pyrophosphate as the phosphorus source of the reaction raw material.
(Comparative Example 1)
Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ was synthesized using Li ₂ CO ₃ as the lithium source and NH ₄ H ₂ PO ₄ as the phosphorus source. First, after mixing Li ₂ CO ₃ , Al ₂ O ₃ , TiO ₂ , NH ₄ H ₂ PO _{4 so} that the weight ratio is 0.65: 0.15: 1.7: 3, dry pulverization / dispersion is performed with a lykai machine. For 1 hour. Next, the powder obtained by the dispersion was molded into a diameter of 40 mmφ and a height of about 10 mm with a pelleter. After calcining at 900 ° C in an air atmosphere and pulverizing again, the pulverized powder was molded into a diameter of 40mmφ and a height of about 10mm with a pelleter, and the molded body was heated at 1100 ° C for 4 hours in an air atmosphere. Firing was performed. The weight was measured before and after each firing, and the yield was calculated by dividing the weight of the molded body after the firing reaction by the weight before the reaction. In addition, the gas generated during the firing process was collected, and the presence or absence of generation of ammonia gas was examined with an ammonia gas detector tube. The synthesized inorganic compound was identified with an X-ray diffractometer. As a result, formation of Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ was confirmed. Generation of ammonia gas was confirmed, and the yield was 61.5%.

(Comparative Example 2)
Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ was synthesized using LiPO ₃ as the lithium source and NH ₄ H ₂ PO ₄ as the phosphorus source. First, LiPO ₃ , Al ₂ O ₃ , TiO ₂ , and NH ₄ H ₂ PO ₄ are mixed so that the weight ratio is 1.3: 0.15: 1.7: 1.7, and then dry pulverization and dispersion for 1 hour with a lycra machine I did it. Next, the powder obtained by the dispersion was molded into a diameter of 40 mmφ and a height of about 10 mm with a pelleter. After calcining at 900 ° C in an air atmosphere and pulverizing again, the pulverized powder was molded into a diameter of 40mmφ and a height of about 10mm with a pelleter, and the molded body was heated at 1100 ° C for 4 hours in an air atmosphere. Firing was performed. The weight was measured before and after each firing, and the yield was calculated by dividing the weight of the molded body after the firing reaction by the weight before the reaction. In addition, the gas generated during the firing process was collected, and the presence or absence of generation of ammonia gas was examined with an ammonia gas detector tube. The synthesized inorganic compound was identified with an X-ray diffractometer. As a result, formation of Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ was confirmed. Generation of ammonia gas was confirmed, and the yield was 73.6%.

(Comparative Example 3)
Li _1.3 Y _0.3 Ti _1.7 (PO ₄ ) ₃ was synthesized using Li ₂ CO ₃ as the lithium source and NH ₄ H ₂ PO ₄ as the phosphorus source. First, Li ₂ CO ₃ , Y ₂ O ₃ , TiO ₂ , NH ₄ H ₂ PO ₄ were mixed so that the weight ratio was 0.65: 0.15: 1.7: 3, and then dry pulverized and dispersed with a likai machine. For 1 hour. Next, the powder obtained by the dispersion was molded into a diameter of 40 mmφ and a height of about 10 mm with a pelleter. After calcining at 900 ° C in an air atmosphere and pulverizing again, the pulverized powder was molded into a diameter of 40mmφ and a height of about 10mm with a pelleter, and the molded body was heated at 1100 ° C for 4 hours in an air atmosphere. Firing was performed. The weight was measured before and after each firing, and the yield was calculated by dividing the weight of the molded body after the firing reaction by the weight before the reaction. In addition, the gas generated during the firing process was collected, and the presence or absence of generation of ammonia gas was examined with an ammonia gas detector tube. The synthesized inorganic compound was identified with an X-ray diffractometer. As a result, formation of Li _1.3 Y _0.3 Ti _1.7 (PO ₄ ) ₃ was confirmed. Generation of ammonia gas was confirmed, and the yield was 61.0%.

(Comparative Example 4)
LiSn ₂ (PO ₄ ) ₃ was synthesized using Li ₂ CO ₃ as the lithium source and NH ₄ H ₂ PO ₄ as the phosphorus source. First, Li ₂ CO ₃ , SnO ₂ , and NH ₄ H ₂ PO ₄ were mixed so that the weight ratio was 0.5: 2: 3, and then dry pulverization and dispersion were carried out for 1 hour in a lykai machine. Next, the powder obtained by the dispersion was molded into a diameter of 40 mmφ and a height of about 10 mm with a pelleter. After calcining at 900 ° C in an air atmosphere and pulverizing again, the pulverized powder was molded into a diameter of 40mmφ and a height of about 10mm with a pelleter, and the molded body was heated at 1100 ° C for 4 hours in an air atmosphere. Firing was performed. The weight was measured before and after each firing, and the yield was calculated by dividing the weight of the molded body after the firing reaction by the weight before the reaction. In addition, the gas generated during the firing process was collected, and the presence or absence of generation of ammonia gas was examined with an ammonia gas detector tube. The synthesized inorganic compound was identified with an X-ray diffractometer. As a result, production of LiSn ₂ (PO ₄ ) ₃ was confirmed. Generation of ammonia gas was confirmed, and the yield was 69.0%.

(Comparative Example 5)
Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ was synthesized using Li ₂ CO ₃ as the lithium source and NH ₄ H ₂ PO ₄ as the phosphorus source. First, Li ₂ CO ₃ , Al ₂ O ₃ , TiO ₂ , NH ₄ H ₂ PO ₄ are mixed so that the weight ratio is 0.75: 0.25: 1: 3, and then dry pulverized and dispersed with a lykai machine. For 1 hour. Next, the powder obtained by the dispersion was molded into a diameter of 40 mmφ and a height of about 10 mm with a pelleter. After calcining at 900 ° C in an air atmosphere and pulverizing again, the pulverized powder was molded into a diameter of 40mmφ and a height of about 10mm with a pelleter, and the molded body was heated at 1100 ° C for 4 hours in an air atmosphere. Firing was performed. The weight was measured before and after each firing, and the yield was calculated by dividing the weight of the molded body after the firing reaction by the weight before the reaction. In addition, the gas generated during the firing process was collected, and the presence or absence of generation of ammonia gas was examined with an ammonia gas detector tube. The synthesized inorganic compound was identified with an X-ray diffractometer. As a result, generation of Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ was confirmed as shown in FIG. Generation of ammonia gas was confirmed, and the yield was 59.9%.

(Test results)
In Examples 1 to 5, generation of ammonia gas was not observed, and the yield of metal substitution LTP was as high as 90% or more. On the other hand, in the comparative example using only NH ₄ H ₂ PO ₄ without using pyrophosphate as the phosphorus source, generation of ammonia gas was confirmed in all syntheses. The yield of the comparative example was as low as 60 to 70%. In some comparative examples, the sample pellets swelled and the original shape was not retained. This is considered to occur due to a large amount of gas such as ammonia. A large amount of substances other than the target product is generated, which causes the yield to decrease. Moreover, it has confirmed from the result of the X-ray diffraction measurement that the compound of any of an Example and a comparative example was a target product.

  As described above in detail, the present invention mainly enables improvement of physical properties and reduction of manufacturing cost of an ion conductive inorganic compound suitable for manufacturing all solid state secondary batteries. Will contribute greatly.

Claims (1)

At least pyrophosphate is used as a phosphorus source, and the chemical formula of pyrophosphate is M1 _x P ₂ O ₇ (where x <2),
The chemical formula of the ion conductive inorganic compound is A _{1 + y} M2 _y M1 _2-y (PO ₄ ) ₃
(However, A is an alkali metal element, M1 is a metal element selected from Ti and Sn,
M2 is a metal element selected from Al and Y. A method of synthesizing an ion-conductive inorganic compound, wherein the compound is an alkali metal phosphate compound represented by Y ≦ 0.5.

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