JP6197584B2 - Solid electrolyte, method for producing solid electrolyte, and lithium ion battery - Google Patents

Description

  The present invention relates to a solid electrolyte, a method for producing a solid electrolyte, and a lithium ion battery.

  Lithium batteries (including primary batteries and secondary batteries) are used as a power source for many electric devices including portable information devices. In particular, as a lithium battery that achieves both high energy density and safety, an all-solid-state lithium battery using a solid electrolyte for conducting lithium between the positive and negative electrodes has been proposed (see, for example, Patent Document 1).

  A solid electrolyte is attracting attention as a highly safe material because it can conduct lithium ions without using an organic electrolyte and does not cause electrolyte leakage or volatilization of the electrolyte due to driving heat generation.

  As solid electrolytes used in such all-solid-state lithium batteries, oxide-based solid electrolytes with high lithium ion conductivity, excellent insulating properties, and high chemical stability are widely known. As such an oxide, a material based on lithium lanthanum titanate has a high lithium ion conductivity that should be noted, and is expected to be applied to a battery.

  When such a solid electrolyte has a particulate shape (hereinafter sometimes referred to as solid electrolyte particles), it is often molded to a desired shape by compression molding. However, since the solid electrolyte particles are very hard, in the obtained molded product, the contact between the solid electrolyte particles is insufficient, the grain boundary resistance becomes high, and the lithium ion conductivity tends to be low.

  As a method of reducing the grain boundary resistance, a method is known in which particles are welded together by sintering at a high temperature of 1000 ° C. or higher after compression molding of solid electrolyte particles. However, in this method, the composition is likely to change due to high heat, and it is difficult to produce a solid electrolyte compact having desired physical properties.

Therefore, as a method for reducing the grain boundary resistance of the solid electrolyte, a method in which the surface of lithium lanthanum titanate particles is coated with SiO ₂ and then sintered at a high temperature has been studied (for example, see Patent Document 2). .

  On the other hand, as a method for forming a solid electrolyte, a synthetic system using a liquid phase material, particularly a sol-gel method may be employed. For example, lithium lanthanum titanate can be produced by the sol-gel method (see, for example, Patent Document 3).

JP 2009-215130 A Special table 2011-529243 gazette JP 2003-346895 A

However, the above method has the following problems. In the method of Patent Document 2, it is difficult to cover the surface of the solid electrolyte particles with SiO ₂ . In addition, by firing at a high temperature, lithium is volatilized from the obtained solid electrolyte or reacts with the material constituting the electrode, so that the composition may be shifted and a large amount of different phases may be formed. . If the firing temperature is lowered in order to suppress the formation of heterogeneous phases, the interface between the particles is not sufficiently sintered, and the grain boundary resistance cannot be reduced.

  In the method of Patent Document 3, since the product forms a uniform layer, it is difficult to control the structure of the solid electrolyte particles to be formed, and it is difficult to obtain desired physical properties.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing a solid electrolyte which reduces grain boundary resistance and shows high total ion conductivity. Another object of the present invention is to provide a method for producing a high-performance solid electrolyte exhibiting high total ion conductivity and a lithium ion battery having such a solid electrolyte.

In order to solve the above problems, one embodiment of the present invention is a method in which a plurality of first perovskite crystalline materials including at least a lithium atom and a metal atom having a crystal radius of 78 pm or more are used as a forming material. A region and a second region interposed between the plurality of first regions and made of an amorphous material containing lithium atoms and the metal atoms, and the abundance ratio of the metal atoms is A solid electrolyte gradually increasing from a first region toward the second region is provided.
In order to solve the above problems, according to one embodiment of the present invention, a plurality of first regions using a cubic perovskite crystalline material including at least a lithium atom and a tantalum atom as a forming material; A second region made of an amorphous material containing lithium atoms and tantalum atoms interposed between each of the regions, the abundance ratio of tantalum atoms from the first region to the second region A solid electrolyte that gradually increases toward

  According to this configuration, in the first region in which the number of metal atoms having a crystal radius of 78 pm or more is small, a cubic perovskite crystal phase is preferably exhibited, and in the second region in which the metal atom is relatively present, the cubic region is present. The crystal phase cannot be a perovskite crystal phase and becomes amorphous.

  In addition, the abundance ratio of the metal atoms does not change discontinuously, but changes continuously so that the boundary between the first region and the second region becomes unclear.

  Conventionally known solid electrolytes using solid oxide particles have a problem that the lithium ion conductivity is lowered due to the grain boundary resistance generated at the interface between the particles. However, in the solid electrolyte of the present embodiment, the “interface between particles” is unclear and does not exist due to having the above-described configuration.

  Therefore, in the solid electrolyte according to one embodiment of the present invention, compared with a conventionally known solid electrolyte using solid oxide particles, the grain boundary resistance can be reduced, and the high total ionic conductivity is achieved. It can be set as the solid electrolyte which shows.

In one embodiment of the present invention, the crystalline material may be a composite oxide represented by a composition formula ABO ₃ . Here, in the composition formula, A and B are metal elements different from each other, A includes Li, and further includes one or more elements selected from the group consisting of La, Mg, and Ba, and B includes Ti, One or more elements selected from the group consisting of Ta, Zr, and Al.

  According to this configuration, high ion conductivity can be expected in the first region that is a cubic perovskite crystalline material, and a solid electrolyte that exhibits high total ion conductivity can be obtained.

In one embodiment of the present invention, the crystalline material may be Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16), and the metal atom may be Ta.

According to this configuration, the perovskite crystal having the characteristic formula Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) exhibits high ionic conductivity, and high bulk ionic conductivity can be expected. Further, the second region is preferably made amorphous by the effect of adding Ta, and the first region and the second region are combined, so that a high total ion conductivity can be obtained.

In one embodiment of the present invention, the mass ratio of Ta atoms contained in the entire solid electrolyte to Ti atoms contained in the entire solid electrolyte may be greater than 0 and less than or equal to 0.10.
According to this configuration, the total ionic conductivity can be improved as compared with a solid electrolyte not containing Ta atoms.

In one embodiment of the present invention, the amorphous structure may include at least Li, La, and Ta.
According to this configuration, suitable ion conductivity can be ensured also in the second region, and a solid electrolyte with improved total ion conductivity can be obtained.

Another embodiment of the present invention was obtained by removing a solvent from a solution in which a lithium compound, a lanthanum compound, a titanium compound, and a compound containing a metal atom having a crystal radius of 78 pm or more were dissolved and gelled. And a step of heat-treating the gel.
One embodiment of the present invention includes a step of gelling by removing a solvent from a solution in which a compound containing a lithium compound, a lanthanum compound, a titanium compound, and a tantalum atom is dissolved, and a step of heat-treating the obtained gel. A method for producing a solid electrolyte is provided.

  According to this method, the solution is placed on the surface of the desired material by any convenient means such as coating and impregnation, and gelation and heat treatment are performed, so that a solid having excellent lithium ion conductivity is easily formed on the surface of the desired material. An oxide can be formed.

  In one embodiment of the present invention, the compound containing a metal atom having a crystal radius of 78 pm or more is a tantalum compound, and the heat treatment step may be a manufacturing method in which a heat treatment temperature is 540 ° C. or higher and 800 ° C. or lower. .

  According to this method, when the heat treatment temperature is 540 ° C. or higher, a heterogeneous phase is hardly generated in the crystal grown by the heat treatment, and the crystal is likely to grow. Therefore, it becomes the 1st field where the crystal which has sufficient bulk ion conductivity grew.

  Further, when the heat treatment temperature is 800 ° C. or lower, crystallization hardly proceeds in the second region, and the second region is likely to be amorphous. Therefore, it is easy to obtain a structure in which the first region that is crystalline and the second region that is amorphous are combined, and it is easy to obtain a solid oxide with reduced grain boundary resistance.

Another embodiment of the present invention includes a positive electrode, a negative electrode, and a solid electrolyte layer sandwiched between the positive electrode and the negative electrode, and the solid electrolyte layer includes the above-described solid electrolyte as a forming material. I will provide a.
According to this configuration, the solid electrolyte layer has a high total ion conductivity and can be a lithium ion battery having high performance.

It is a schematic diagram of the solid electrolyte which concerns on this embodiment. It is a flowchart which shows the manufacturing method of the solid electrolyte which concerns on this embodiment. It is sectional drawing which shows the lithium ion battery of this embodiment. It is a photograph which shows the measurement result of an Example. It is a photograph which shows the measurement result of an Example. It is a photograph which shows the measurement result of an Example. It is a graph which shows the measurement result of an Example.

[Solid electrolyte]
Hereinafter, the solid electrolyte and the method for manufacturing the solid electrolyte according to the present embodiment will be described with reference to FIGS. In all the drawings below, the dimensions and ratios of the constituent elements are appropriately changed in order to make the drawings easy to see.

  FIG. 1 is a schematic diagram of a solid electrolyte according to this embodiment, and is a cross-sectional view at an arbitrary position of the solid electrolyte. As shown in the figure, the solid electrolyte of the present embodiment has a plurality of first regions AR1 made of a crystalline material and a second region AR2 made of an amorphous material.

  The first region AR1 is made of a cubic perovskite crystalline material containing lithium atoms and metal atoms having a crystal radius of 78 pm or more.

  Here, examples of the “metal atom having an atom crystal radius of 78 pm or more” include Ta, Mo, W, Nb, and Hf.

The crystalline material forming the first region AR1 is preferably a composite oxide represented by the composition formula ABO ₃ . Here, A and B are metal elements different from each other, A includes Li, and further includes one or more elements selected from the group consisting of La, Mg, and Ba, and B is Ti, Ta And one or more elements selected from the group consisting of Zr, Al.
Such a crystalline material can be expected to have high ion conductivity in the first region AR1, and can be a solid electrolyte exhibiting high total ion conductivity.

  The second region AR2 is a region interposed between the first regions AR1, and is made of an amorphous material containing lithium atoms and the above metal atoms.

  The solid electrolyte of the present embodiment is preferably composed of the first region AR1 and the second region AR2.

  The “metal atom having an atom crystal radius of 78 pm or more” included in the second region AR2 has an abundance continuously increasing from the first region AR1 toward the second region AR2. When the metal atoms are present in such a ratio, the first region AR1 having a small number of metal atoms preferably exhibits a cubic perovskite crystal phase, and the second region has a relatively large amount of the metal atoms. AR2 cannot be a cubic perovskite type crystal phase but is amorphous.

  Further, the boundary between the first region AR1 and the second region AR2 becomes unclear because the abundance ratio of the metal atoms does not change discontinuously but changes continuously.

  Conventionally known solid electrolytes using solid oxide particles have a problem that the lithium ion conductivity is lowered due to the grain boundary resistance generated at the interface between the particles. However, in the solid electrolyte of the present embodiment, the “interface between particles” is unclear and does not exist due to having the above-described configuration. Therefore, in the solid electrolyte of this embodiment, the grain boundary resistance can be reduced as compared with a conventionally known solid electrolyte using solid oxide particles.

  The state in which the “metal atom having an atomic crystal radius of 78 pm or more” continuously changes and gradually increases from the first region AR1 to the second region AR2 is shown in the cross section of the obtained solid electrolyte. It can be confirmed by measuring by X-ray diffraction (XRD) and examining the distribution of the metal atoms.

As the solid electrolyte of the present embodiment, for example, a crystalline composition that is Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) can be suitably used. An example of “a metal atom having an atom crystal radius of 78 pm or more” is Ta.

In such a solid electrolyte, a perovskite crystal having the characteristic formula Li _3x La _{2 / 3-x} TiO ₃ (0 <x <0.16) exhibits high ionic conductivity, and high bulk ionic conductivity can be expected. Further, the second region is preferably made amorphous by the effect of adding Ta, and the first region and the second region are combined, so that a high total ion conductivity can be obtained.

  When the “metal atom having an atomic crystal radius of 78 pm or more” is Ta, the ratio of the amount of Ta atoms contained in the entire solid electrolyte to Ti atoms contained in the entire solid electrolyte is more than 0 and 0.10 or less. And preferred. When the amount ratio of Ta atoms is included in this range, the total ion conductivity can be improved as compared with a solid electrolyte not containing Ta atoms. If the amount ratio of Ta atoms exceeds 0.10, formation of a heterogeneous phase is prioritized and the ionic conductivity is lowered.

The substance amount ratio of Ta atoms to Ti atoms is more preferably 0.01 or more, and further preferably 0.02 or more. Further, the mass ratio of Ta atoms to Ti atoms is more preferably 0.08 or less, and further preferably 0.06 or less. These upper limit value and lower limit value can be arbitrarily combined.
Most preferably, the mass ratio of Ta atoms to Ti atoms is 0.04.

  At this time, the amorphous material preferably contains at least Li, La and Ta. When the amorphous material contains Li, Ta, and La, a suitable lithium ion conductivity can be ensured even in the amorphous second region, and a solid electrolyte with improved total ion conductivity can be obtained.

Conventionally, LiLaTiO ₃ containing Ta in the crystal phase is known, but the known substance has low lithium ion conductivity and cannot be employed as a solid electrolyte. On the other hand, the solid electrolyte of the present embodiment has higher lithium ion conductivity than the above-described conventional materials, and is suitable as a solid electrolyte.

[Method for producing solid electrolyte]
FIG. 2 is a flowchart showing a method for manufacturing a solid electrolyte according to the present embodiment. Hereinafter, description will be made with reference to FIG. 1 and using the reference numerals shown in FIG.

  The method for producing a solid electrolyte of this embodiment includes (1) a step of gelling by removing a solvent from a solution in which a lithium compound, a lanthanum compound, a titanium compound, and a compound containing a metal atom having a crystal radius of 78 pm or more are dissolved. And (2) a step of heat-treating the obtained gel.

  Here, a description will be given on the assumption that a solid electrolyte is formed using Ta as a compound containing a metal atom having a crystal radius of 78 pm or more.

[1. Step of gelling]
First, as “(1) gelation step” (step S1), a solution in which a lithium compound, a lanthanum compound, a titanium compound, and a tantalum compound are dissolved is obtained (step S11). In the following description, the solution prepared in step S11 is referred to as “precursor solution”.

Examples of the lithium compound include inorganic salts such as LiOH, LiF, LiBr, LiCl, LiNO ₃ , Li ₂ SO ₄ ;
Such as lithium formate (LiHCOO), lithium acetate (LiCH ₃ COO), LiC ₂ H ₃ O ₃ , lithium citrate (Li ₃ C ₆ H ₅ O ₇ ), LiC ₇ H ₅ O ₂ , LiC ₁₈ H ₃₅ O ₂ Organic acid salt;
Organolithium compounds such as methyl lithium (CH ₃ Li), butyl lithium (LiC ₄ H ₉ ), phenyl lithium (C ₆ H ₅ Li);
Lithium alkoxides such as lithium methoxide (LiOCH ₃ ), lithium ethoxide (LiOC ₂ H ₅ ), lithium propoxide (LiOC ₃ H ₇ );
And so on.

  The alkoxy group constituting the lithium alkoxide may be linear or branched.

Examples of the lanthanum compound include inorganic salts, organic acid salts, organic lanthanum compounds, diketone complexes, and metal alkoxides. As the anion constituting the inorganic salt and the organic acid salt, the organic group constituting the organic lanthanum compound, and the alkoxy group constituting the metal alkoxide, those similar to those exemplified in the above lithium compound can be used.
As a ligand constituting the diketone complex, a β-diketone such as 2,4-pentanedione can be used.

Examples of the titanium compound include tantalum inorganic salts, organic acid salts, complexes, metal alkoxides, and the like. As the anion constituting the inorganic salt and the organic acid salt, the organic group constituting the organic lanthanum compound, and the alkoxy group constituting the metal alkoxide, those similar to those exemplified in the above lithium compound can be used.
As the ligand constituting the complex, a β-diketone such as 2,4-pentanedione can be used.

Examples of the tantalum compound include tantalum inorganic salts, organic acid salts, complexes, metal alkoxides, and the like. As the anion constituting the inorganic salt and the organic acid salt, the organic group constituting the organic lanthanum compound, and the alkoxy group constituting the metal alkoxide, those similar to those exemplified in the above lithium compound can be used.
As the ligand constituting the complex, a β-diketone such as 2,4-pentanedione can be used.

  As a solvent that can be used for the precursor solution, a polar solvent that dissolves each of the above-described compounds can be used, and examples thereof include alcohols such as n-butanol and organic acids such as propionic acid.

Here, LiCH ₃ COO as the lithium compound, lanthanum acetate as the lanthanum compound (La (CH ₃ COO) ₃ ), tetraisopropoxy titanium (Ti (OC ₃ H ₇ ) ₄ ) tantalum compound as the titanium compound, pentaethoxy Description will be made using tantalum (Ta (OC ₂ H ₅ ) ₅ ).

Next, as “(1) gelation step” (step S1), the solvent is removed from the precursor solution to cause gelation (step S12).
For example, a transparent gel can be obtained by heating the precursor solution to 140 ° C. and holding it for 1 hour.
Note that this step may be performed continuously with the next heat treatment step.

[2. Heat treatment process]
Next, the obtained gel is heat-treated to obtain a solid oxide (step S2).

  By performing heat treatment, lithium atoms, lanthanum atoms, and titanium atoms contained in the gel form cubic perovskite crystals. At the same time, the tantalum atoms contained in the gel are unevenly distributed in the region where the crystal is not grown while being excluded from the region where the cubic perovskite crystal is formed.

  That is, a cubic perovskite crystal grows at the crystal growth location because tantalum atoms are not taken in. On the other hand, since tantalum atoms are concentrated around the crystal growth site, it becomes gradually difficult to form a cubic perovskite crystal, resulting in an amorphous region.

  In this manner, a solid electrolyte having the crystalline first region AR1 and the amorphous second region AR2 interposed between the first regions AR1 is obtained.

  The heat treatment temperature is preferably 540 ° C. or higher and 800 ° C. or lower. For example, the obtained gel is heat-treated by heating at 540 ° C. for 1 hour.

  When the heat treatment temperature is 540 ° C. or higher, a heterogeneous phase is hardly generated in the crystal grown by the heat treatment, and the crystal is likely to grow. Therefore, the first region AR1 in which a crystal having sufficient bulk ion conductivity is grown is obtained.

  Further, when the heat treatment temperature is 800 ° C. or lower, crystallization hardly proceeds in the second region AR2, and the second region AR2 tends to be amorphous. Therefore, it is easy to obtain a structure in which the first region AR1 that is crystalline and the second region AR2 that is amorphous are combined, and it is easy to obtain a solid oxide with reduced grain boundary resistance.

  In the method for producing a solid oxide according to the present embodiment, as described above, the precursor solution is gelled and heat-treated to suitably have the crystalline first region AR1 and the amorphous second region AR2. Solid oxides can be produced. Therefore, for example, the precursor solution can be placed on the surface of the desired material by any convenient means such as coating or impregnation, and gelation and heat treatment can be easily performed on the surface of the desired material for solid oxidation with excellent lithium ion conductivity. Things can be formed.

  According to the solid electrolyte having the above-described configuration, it is possible to provide a solid electrolyte that reduces the grain boundary resistance and exhibits high total ion conductivity.

  Moreover, according to the manufacturing method of the solid electrolyte of the above structures, the high performance solid electrolyte which shows high total ion conductivity can be manufactured easily.

When a metal other than Ta is used as the “metal atom having an atom crystal radius of 78 pm or more”, the “compound containing a metal atom having an atom crystal radius of 78 pm or more” is a metal having an atom crystal radius of 78 pm or more. And inorganic salts, organic acid salts, organic lanthanum compounds, diketone complexes, metal alkoxides, and the like. As the anion constituting the inorganic salt and the organic acid salt, the organic group constituting the organic lanthanum compound, and the alkoxy group constituting the metal alkoxide, those similar to those exemplified in the above lithium compound can be used.
As a ligand constituting the diketone complex, a β-diketone such as 2,4-pentanedione can be used.

[Lithium ion battery]
Next, the lithium ion battery of this embodiment will be described. FIG. 3 is a cross-sectional view showing the lithium ion battery of this embodiment.

  A lithium ion battery 100 shown in FIG. 3 has a configuration in which a current collector 1, an active material layer 2, a solid electrolyte layer 3, and an electrode 4 are laminated in this order. The solid electrolyte layer 3 uses the above-described solid electrolyte as a forming material.

  As a material for forming the current collector 1, copper (Cu), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), One metal selected from the group consisting of germanium (Ge), indium (In), gold (Au), platinum (Pt), silver (Ag) and palladium (Pd), or selected from this group Examples include alloys containing two or more metal elements.

  As the shape of the current collector 1, a plate shape, a foil shape, a net shape, or the like can be adopted. The surface of the current collector 1 may be smooth or uneven.

  The active material layer 2 is formed of different materials depending on whether the current collector 1 is used on the positive electrode side or the negative electrode side in the lithium ion battery 100.

  In the case where the current collector 1 is used on the positive electrode side, as the material for forming the active material layer 2, a substance usually known as a positive electrode active material can be used. Examples of such a substance include lithium double oxide.

Examples of the lithium double oxide include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₃ , LiFePO ₄ , Li ₂ FeP ₂ O ₇ , LiMnPO ₄ , LiFeBO ₃ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ CuO ₂ , LiFeF ₃ , Li ₂ FeSiO ₄ , Li ₂ MnSiO _{4 and the} like. Further, solid solutions in which some atoms in the crystals of these lithium double oxides are substituted with other transition metals, typical metals, alkali metals, alkali rare earths, lanthanoids, chalcogenides, halogens, etc. can also be used as the positive electrode active material. .

  When the current collector 1 is used on the negative electrode side, as the material for forming the active material layer 2, a substance that is usually known as a negative electrode active material can be used.

As the negative electrode active material, a silicon - manganese alloy (Si-Mn), silicon - cobalt alloy (Si-Co), silicon - nickel alloy (Si-Ni), niobium pentoxide _{(Nb 2 O} 5), vanadium pentoxide ( Oxidation with addition of V ₂ O ₅ ), titanium oxide (TiO ₂ ), indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), tin oxide (SnO ₂ ), nickel oxide (NiO), tin (Sn) Indium (ITO), zinc oxide (AZO) to which aluminum (Al) is added, zinc oxide (GZO) to which gallium (Ga) is added, tin oxide (ATO) to which antimony (Sb) is added, fluorine (F ) Added tin oxide (FTO), a carbon material, a substance in which lithium ions are inserted between carbon material layers, an anatase phase of TiO ₂ , Li ₄ Ti ₅ O _{1 2} , Li ₂ Ti ₃ O _{7 and} other lithium double oxides, Li metal and the like.

  When the current collector 1 is used on the positive electrode side, the electrode 4 is a negative electrode. In this case, aluminum can be selected as the material for forming the current collector 1, and lithium can be selected as the material for forming the electrode 4.

Such a lithium ion battery 100 can be manufactured as follows.
First, by preparing a current collector 1 having an active material layer 2 formed on the surface, applying the above precursor solution to the surface of the active material layer 2, and performing gelation and heat treatment of the precursor solution, The solid electrolyte layer 3 excellent in lithium ion conductivity is easily formed on the surface of the active material layer 2.

  At this time, the heat treatment temperature for obtaining the solid electrolyte layer 3 is preferably 540 ° C. or higher and 800 ° C. or lower as described above. When the heat treatment is performed in such a temperature range, the material constituting the active material layer 2 and the solid oxide generated by the heat treatment do not react to form a different phase, and a desired solid electrolyte layer can be easily formed. Can do.

  Next, the electrode 4 is formed on the surface of the solid electrolyte layer 3. Thereby, the lithium ion battery 100 can be manufactured easily.

  As other methods for manufacturing the lithium ion battery 100, a member having a solid electrolyte layer formed on the surface of the active material layer 2 and a member having a solid electrolyte layer formed on the surface of the electrode 4 are manufactured. The solid electrolyte layers of the members may be bonded together.

  According to such a lithium ion battery, the total ion conductivity of the solid electrolyte layer is high, and a lithium ion battery having high performance can be obtained.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

  In the above embodiment, the oxide particles of the present invention have been described as being used as a material for forming a solid electrolyte layer of a lithium ion battery. However, the present invention is not limited thereto, and for example, used as a material for forming a solid electrolyte layer of a lithium air battery. It is also possible.

[Example]
EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1
A precursor solution was prepared by preparing a solution of (a) a lithium compound, (b) a solution of a lanthanum compound, (c) a solution of a titanium compound, and (d) a solution of a tantalum compound.

(A): Propionic acid solution of LiCH ₃ COO (0.36 mol / kg) 2 g
(B): La (CH ₃ COO) ₃ · 1.5H ₂ O in propionic acid solution (0.27 mol / kg) 4 g
(C): tetraisopropoxy _{n-C 4 H} 9 OH titanium solution (1.0 mol / kg)
_{(D): n-C 4} H 9 OH solution pentaethoxytantalum (1.0 mol / kg)

  At this time, the mass ratio of (c) to (d) is (c) :( d) = 100: 4, and the total amount of (c) and (d) is weighed to 2 g. The total amount of body solution was 8 g. That is, the mass ratio of Ta atoms to Ti atoms is 0.04.

  Subsequently, the obtained precursor solution was dried at 140 ° C. for 1 hour to obtain a transparent gel.

  Subsequently, the obtained gel was baked at 540 ° C. for 1 hour to obtain a transparent product. The product obtained corresponds to the solid oxide of the invention.

 After the obtained product was pulverized, 100 mg of the pulverized product was filled in a pellet die having an inner diameter of 10 mm and pressed at a pressure of 624 MPa to obtain tablet-type pellets having a thickness of 0.5 mm. The obtained pellets were fired at 700 ° C. for 14 hours in an air atmosphere to obtain a solid electrolyte compact.

(Example 2)
Example 1 except that the mass ratio of (c) to (d) is (c) :( d) = 100: 1, that is, the mass ratio of Ta atoms to Ti atoms is set to 0.01. Similarly, a solid oxide and a molded body of the solid oxide were obtained.

(Example 3)
Example 1 except that the mass ratio of (c) to (d) is (c) :( d) = 100: 2, that is, the mass ratio of Ta atoms to Ti atoms is 0.02. Similarly, a solid oxide and a molded body of the solid oxide were obtained.

Example 4
Example 1 except that the mass ratio of (c) to (d) was (c) :( d) = 100: 6, that is, the mass ratio of Ta atoms to Ti atoms was 0.06. Similarly, a solid oxide and a molded body of the solid oxide were obtained.

(Example 5)
Example 1 except that the mass ratio of (c) to (d) is (c) :( d) = 100: 8, that is, the mass ratio of Ta atoms to Ti atoms is 0.08. Similarly, a solid oxide and a molded body of the solid oxide were obtained.

(Example 6)
Example 1 except that the mass ratio of (c) to (d) was (c) :( d) = 100: 10, that is, the mass ratio of Ta atoms to Ti atoms was 0.10. Similarly, a solid oxide and a molded body of the solid oxide were obtained.

(Comparative Example 1)
The mass ratio of (c) to (d) is (c) :( d) = 100: 0, that is, the same as in Example 1, except that Ta atoms are not included. A molded body of was obtained.

(Comparative Example 2)
Example 1 except that the mass ratio of (c) and (d) is (c) :( d) = 100: 20, that is, the mass ratio of Ta atoms to Ti atoms is 0.20. Similarly, a solid oxide and a molded body of the solid oxide were obtained.

(Comparative Example 3)
Example 1 except that the mass ratio of (c) to (d) is (c) :( d) = 100: 40, that is, the mass ratio of Ta atoms to Ti atoms is 0.40. Similarly, a solid oxide and a molded body of the solid oxide were obtained.

(Identification of crystal structure)
About the obtained product, the crystal phase was identified by X-ray analysis using a powder X diffraction device MRD (manufactured by Philips). When the crystal phase was identified based on the XRD diffraction pattern, a cubic perovskite crystal phase could be confirmed. In addition, when the mass ratio of Ta atoms to Ti atoms was 0.04 or more, it was confirmed that an unidentifiable heterogeneous peak appeared in the vicinity of a diffraction angle of 25 to 30 °.

(Observation of crystal structure)
Thin pieces were prepared from the obtained solid electrolyte compact, and the obtained thin pieces were observed using a transmission electron microscope (CM200, manufactured by Philips).

  4 and 5 are photographs showing the observation results of the solid electrolyte molded body by an energy filter type transmission electron microscope. FIG. 4 shows the result of observing the molded body of the Ta-undoped sample of Comparative Example 1, and FIG. 5 shows the result of observing the molded body of the Ta-added sample of Example 1. Each figure (a) is a micrograph of each, and each figure (b) is an electron beam diffraction pattern in the entire field of view of each photograph.

  As a result of the observation, as shown in FIG. 4A, a clear fine particle structure was developed in the sample to which Ta was not added, and the crystallites were in point contact. In FIG. 4A, the white area shown by the symbol α is a portion where no fine particles are present and the substrate used at the time of measurement is exposed.

  On the other hand, as shown in FIG. 5A, in the sample to which Ta is added, a region (reference symbol γ) in which no lattice stripe can be confirmed around a black region (indicated by reference symbol β) in which the lattice stripe indicating the crystal phase can be confirmed. It was found that there is. Further, in FIG. 5A, it is found that the entire drawing is colored black, and the region β is blacker than the region γ. Further, there is no clear boundary between the region β and the region γ, and the black density gradually changes in the figure.

  Further, according to the electron diffraction pattern in each field of view, as shown in FIG. 4B, a clear diffraction pattern was obtained in the sample with no Ta added, as shown in FIG. 5B. In addition, a halo pattern indicating the presence of amorphous was confirmed in the Ta-added sample.

  From these facts, it was confirmed that the Ta-added sample of Example 1 was crystalline and amorphous.

  6 shows the observation results for the Ta-added sample of Example 1. FIG. FIG. 6A is a HAADF-STEM (High Angle Annular Dark-Field Scanning Transmission Electron Microscopy) image including an amorphous region (corresponding to the region γ in FIG. 5A), and FIG. These are Ta mapping data by the energy dispersive X-ray-spectral-analysis in the same visual field as Fig.6 (a).

  In FIG. 6A, the crystalline region (region β in FIG. 5A) is shown in white, and the amorphous region (region γ in FIG. 5A) is shown in black. In FIG. 6B, the abundance of Ta is indicated by white-black brightness, and the closer to white, the more Ta is present.

  As shown in FIG. 6, the amorphous region shown in black in FIG. 6A has more white dots in FIG. 6B, and the amorphous region has a larger amount of Ta. I understand. Further, Ta can be confirmed in the entire visual field. Further, it can be seen that the Ta abundance gradually changes between the crystalline region and the amorphous region.

  From the above, the Ta-added sample of Example 1 has a crystalline region and an amorphous region, and both the crystalline region and the amorphous region contain Ta. It is confirmed that the abundance of Ta is larger in the amorphous region than in the crystalline region, and the Ta abundance gradually changes between the crystalline region and the amorphous region. did it.

(Ion conductivity measurement)
A Pt electrode was formed on the surface of the obtained solid electrolyte compact by sputtering, and ion conductivity was analyzed using an AC impedance analyzer (1620 type, manufactured by Solartron).

  FIG. 7 is a graph showing the results of measuring ionic conductivity for the molded bodies of Examples 1 to 6 and Comparative Examples 1 to 3. The horizontal axis represents the mass ratio of Ta atoms to Ti atoms, and the vertical axis represents ionic conductivity (unit: S / cm).

  As a result of the measurement, when the mass ratio of Ta atoms to Ti atoms is 0.01 to 0.10 (Examples 1 to 6), the total ionic conductivity is improved as compared with the Ta-free product (Comparative Example 1) Was confirmed. However, it was found that when the mass ratio of Ta atoms to Ti atoms exceeds 0.10, the total ionic conductivity is lower than that of the Ta-free product (Comparative Examples 2 and 3). This is presumed to reflect the generation of a heterogeneous phase based on the result of the above-mentioned XRD.

(Reactivity with positive electrode active material)
1 g of LiCoO ₂ powder (Sigma-Aldrich) was mixed with 2 g of the precursor solution of Example 1 and baked at 700 ° C. for 14 hours in an air atmosphere. Then, a different phase by XRD and surface scanning electron microscope The presence or absence of generation was confirmed. As a result, no heterogeneous formation was observed in any analysis.

(Comparative Example 4)
0.035 g of polyacrylic acid powder (Sigma-Aldrich) is added to 1 g of Li _0.35 La _0.55 TiO ₃ powder (high-purity chemistry) with an average particle size of 4 μm and mixed well in an agate bowl, and 100 mg of the mixture Was filled into a pellet die having an inner diameter of 10 mm, and tableted with a pressure of 624 MPa.

 This was sintered at 700 ° C. for 14 hours in an air atmosphere to obtain a solid electrolyte compact.

When the ionic conductivity of the obtained molded product was measured by the above-described method, it was found that the total ionic conductivity was extremely low as 3.4 × 10 ⁻⁸ S / cm. As a result of the identification analysis of the impedance spectrum, it was found that most of the resistance of the sintered body was the grain boundary resistance.

(Comparative Example 5)
A solid oxide compact was obtained in the same manner as in Comparative Example 4 except that the sintering temperature was 1000 ° C.

About the obtained molded object, when the ionic conductivity was measured by the above-mentioned method, the total ionic conductivity was 7 * 10 < ^-5 > S / cm.

Next, in order to confirm the reactivity with the positive electrode active material, 2 g of LiCoO ₂ powder (Sigma-Aldrich) and 1 g of Li _0.35 La _0.55 TiO ₃ powder (high purity chemistry) were mixed at 1000 ° C. Baked for 8 hours.

  Using the obtained powder, observation by XRD and a transmission electron microscope was performed.

As a result of observation by XRD, a result indicating that Co atoms diffused into a tetragonal perovskite crystal of Li _0.35 La _0.55 TiO ₃ as a crystal phase was obtained.
As a result of observation with a transmission electron microscope, it was found that heterogeneous crystals in which Li _0.35 La _0.55 TiO ₃ and a Co compound were complexed in a mosaic shape were formed.

From the above results, it was found that, when firing at a high temperature in order to ensure the ionic conductivity of the Li _0.35 La _0.55 TiO ₃ powder, the positive electrode active material reacts to generate a heterogeneous phase.

  From the above results, it was confirmed that the present invention is useful.

DESCRIPTION OF SYMBOLS 1 ... Current collector, 2 ... Active material layer, 3 ... Solid electrolyte layer, 4 ... Electrode, 100 ... Lithium ion battery, AR1 ... 1st area | region, AR2 ... 2nd area | region

Claims (8)

A plurality of first regions made of a cubic perovskite-type crystalline material containing at least lithium atoms and tantalum atoms;
A second region that is interposed between each of the plurality of first regions and is made of an amorphous material containing lithium atoms and tantalum atoms, and
The solid electrolyte in which the abundance ratio of tantalum atoms gradually increases from the first region toward the second region. The solid electrolyte according to claim 1, wherein the crystalline is a composite oxide represented by a composition formula ABO ₃ .
(In the formula, A and B are metal elements different from each other, A includes Li, and further includes one or more elements selected from the group consisting of La, Mg, and Ba, and B includes Ti, Ta, and Zr. , One or more elements selected from the group consisting of Al.) The _{crystalline, Li 3x La 2 / 3x TiO} 3 (0 <x <0.16) a solid electrolyte according to claim 2.   4. The solid electrolyte according to claim 3, wherein a substance amount ratio of Ta atoms contained in the whole solid electrolyte to Ti atoms contained in the whole solid electrolyte is more than 0 and 0.10 or less.   The solid electrolyte according to claim 3 or 4, wherein the amorphous material includes at least Li, La, and Ta. Removing a solvent from a solution in which a compound containing a lithium compound, a lanthanum compound, a titanium compound and a tantalum atom is dissolved, and gelling;
And a step of heat-treating the obtained gel. A step of pre-Symbol heat treatment method for producing a solid electrolyte according to claim 6 heat treatment temperature of 800 ° C. or less 540 ° C. or higher. A positive electrode, a negative electrode, and a solid electrolyte layer sandwiched between the positive electrode and the negative electrode,
The said solid electrolyte layer is a lithium ion battery which uses the solid electrolyte of any one of Claim 1 to 5 as a forming material.