JP2015204215A - Lithium ion-conducting solid electrolyte, manufacturing method thereof, and all-solid battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion-conducting solid electrolyte which is relatively high in ion conductivity, and small in variations of properties.SOLUTION: A lithium ion-conducting solid electrolyte comprises LiLaZrOparticles, and LiBOarranged in gaps between the LiLaZrOparticles; the LiLaZrOparticles are in surface contact with LiBO. The lithium ion-conducting solid electrolyte is manufactured by the steps of: mixing LiLaZrOpowder with 1-20 pts.mass of LiBOpowder having an average particle diameter of 0.05-10 μm to 100 pts.mass of the LiLaZrOpowder of a garnet type compound having an average particle diameter of 0.05-10 μm and lithium ion conductivity into a raw material mixture; pressing the raw material mixture into a predetermined shape; and performing a thermal treatment on the shaped resultant mixture at a temperature of 600-900°C in the atmosphere.

Description

  The present invention relates to an all-solid-state battery using a lithium-ion conductor such as a lithium-ion primary battery, a lithium-ion secondary battery, or a lithium-air battery, and a lithium-ion conductive solid electrolyte used in the all-solid battery and its production Regarding the method.

  In recent years, with the spread of small electronic devices and electric vehicles, lithium ion batteries having high energy density have attracted attention as power sources. However, since lithium ion batteries that are currently in practical use mainly use organic electrolytes composed of flammable organic solvents as electrolytes that serve as Li ion conductors, there is a risk of ignition when the batteries are short-circuited. There are concerns about sex. For this reason, the practical application of an all-solid battery using a nonflammable lithium ion conductive solid electrolyte as an electrolyte is expected.

  All solid state batteries can be broadly classified into thin film types and bulk types. In a thin film type all solid state battery, a good solid interface bonding between an electrode and an electrolyte is realized by laminating thin films using a vapor phase method. Such a thin-film type all-solid-state battery has already been put into practical use, and almost no capacity deterioration occurs even after 40,000 cycles of charge / discharge, so that the all-solid-state battery is essentially excellent in cycle life. Has been demonstrated.

  On the other hand, a bulk type all solid state battery manufactured by laminating fine particles has a feature that the battery capacity can be increased by introducing a large amount of an electrode active material into the electrode layer. However, it is not easy in nature to conduct ions as constituent particles at high speed in an inorganic solid having no fluidity. For this reason, the development of a solid electrolyte that has high ionic conductivity, including contact resistance between particles (grain boundary resistance), and that can easily form an interface with the electrode active material is desired for the practical application of bulk type solid state batteries. It is rare.

  Examples of the lithium ion conductive solid electrolyte capable of realizing such characteristics include an oxide solid electrolyte and a sulfide solid electrolyte. Of these, oxide-based solid electrolytes are ideal for applications such as the above-mentioned small electronic devices and electric vehicles because they can realize all-solid-state batteries with excellent chemical stability and high safety. It has been.

As oxide-based solid electrolytes, perovskite-type La _0.51 Li _0.34 TiO _2.94 , NASICON-type Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) _{3 and the} like are known. However, these oxide-based solid electrolytes have a drawback of low ionic conductivity in comparison with organic electrolytes as well as in comparison with sulfide-based solid electrolytes. For this reason, research and development for improving the ionic conductivity of the all-solid-state battery using the oxide-based solid electrolyte is being promoted.

For example, in Ramaswamy Murugan et al., “Fast Lithium Ion Conduction in Garnet-Tyape Li ₇ La ₃ Zr ₂ O ₁₂ ”, Angew. Chem. Int. Ed. 2007,46, 7778-7781, It has been proposed to use the compound Li ₇ La ₃ Zr ₂ O ₁₂ . However, particles made of Li ₇ La ₃ Zr ₂ O ₁₂ are hard particles although the ion conductivity as a bulk is as high as about 10 ⁻⁴ S / cm to 10 ⁻³ S / cm at room temperature. There is a problem that they can only make point contact with each other and the intergranular resistance increases.

With respect to this problem, in Japanese Patent No. 5234118, a garnet-type compound such as Li ₇ La ₃ Zr ₂ O ₁₂ is a main component, and the particle size is smaller than that of the garnet-type compound between the garnet-type compounds. And the solid electrolyte which has arrange | positioned the phosphoric acid group containing Li ion conductor which can be surface-contacted with a garnet-type compound is proposed. In such a solid electrolyte, the particles of the garnet-type compound can be brought into surface contact with each other via the phosphate group-containing Li ion conductor, so that it is considered that the intergranular resistance can be improved. However, in this document, the mixture of a hard garnet-type compound and a soft phosphate group-containing Li ion conductor is pressed at room temperature, and the phosphate group-containing Li ion conductor is plastically deformed as described above. A solid electrolyte having a structure is obtained. For this reason, the phosphate group-containing Li ion conductor at the time of pressing is not sufficiently softened, and cannot enter the voids existing between the particles of the garnet-type compound.

On the other hand, JP 2012-209256 A discloses, on an oxide basis, a first inorganic solid electrolyte having a transition metal content of less than 15% by mass, and a second inorganic solid electrolyte having a transition metal content of 15% by mass or more. Is described, followed by heat treatment at a temperature of 1100 ° C. or lower while being pressurized with a hydraulic press. In this document, LiPO ₃ is exemplified as the first inorganic solid electrolyte, and Li ₇ La ₃ Zr ₂ O ₁₂ is exemplified as the garnet-type compound as the second inorganic solid electrolyte. According to this manufacturing method, the softened first inorganic solid electrolyte is not only plastically deformed during heat treatment, but also can enter the voids between the particles of the second inorganic solid electrolyte, so that a solid electrolyte with fewer voids is formed. It is considered possible.

  By the way, in order to improve the ionic conductivity of the solid electrolyte, in addition to improving the ionic conductivity as a bulk, the solid electrolyte layer in the case of configuring an all-solid battery may be thinned to about several tens of μm. It becomes important. This is because the thicker the solid electrolyte layer, the greater the resistance to lithium ion conduction. However, in Japanese Patent Application Laid-Open No. 2012-209256, since the solid electrolyte is compacted, it is difficult to form a solid electrolyte layer having a thickness of about several tens of μm by the technique described in this document.

In order to reduce the thickness of the solid electrolyte layer, it is effective to form the solid electrolyte layer after pasting the solid electrolyte. For example, Japanese Patent Laid-Open No. 2013-37992 discloses that 33% by volume to 50% by volume of a crystalline lithium ion conductive material made of Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ or the like is added to a flux made of Li ₃ BO ₃ or the like. In addition, a solid electrolyte formed into a paste is described by adding a binder and kneading the mixture. In this solid electrolyte, since the base material is formed by melting the flux during heat treatment, the lithium ion conductive material and the base material can be in surface contact, and there are almost no voids inside. Conceivable. In addition, according to this document, Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ has higher lithium ion conductivity and lower activation energy than Li ₇ La ₃ Zr ₂ O _12. It is said that output characteristics can be improved in an all-solid-state battery using a battery. However, this solid electrolyte has a low content of lithium ion conductive material, and in addition to forming a base material by solidifying the molten flux, the lithium ion conductive material is made uniform. Since it is difficult to disperse in ionic conductivity, there is a problem that characteristics such as ionic conductivity tend to vary.

Japanese Patent No. 5234118 JP 2012-209256 A JP 2013-37992 A

Ramaswamy Murugan et al., “Fast Lithium Ion Conduction in Garnet-Tyape Li7La3Zr2O12”, Angew. Chem. Int. Ed. 2007,46, 7778-7781

  An object of the present invention is to provide a lithium ion conductive solid electrolyte having a relatively high ionic conductivity and having small variations in characteristics including the ionic conductivity. Another object of the present invention is to provide a production method capable of easily mass-producing such a lithium ion conductive solid electrolyte. Furthermore, this invention aims at providing the all-solid-state battery using this lithium ion conductive solid electrolyte.

The lithium ion conductive solid electrolyte of the present invention is a lithium ion conductive electrolyte containing Li ₇ La ₃ Zr ₂ O ₁₂ , which is a garnet-type compound having lithium ion conductivity, and Li ₃ BO ₃ .

In particular, the lithium ion conductive solid electrolyte of the present invention, is 100 parts by weight and the content of the _{Li 7 La 3 Zr 2 O 12} , the Li ₃ BO ₃ 1 part by weight to 20 parts by weight, preferably 1 part by mass to 10 parts by mass, more preferably 2 parts by mass to 5 parts by mass, and the Li ₃ BO ₃ is disposed in the space between the particles composed of the Li ₇ La ₃ Zr ₂ O ₁₂ , and The particles made of Li ₇ La ₃ Zr ₂ O ₁₂ and the Li ₃ BO _{3 are in} surface contact.

The average particle diameter of the particles made of Li ₇ La ₃ Zr ₂ O ₁₂ is preferably 0.05 μm to 10 μm, and more preferably 0.1 μm to 5 μm.

In the lithium ion conductive solid electrolyte of the present invention, the ion conductivity measured by the impedance method is 2.0 × 10 ⁻⁷ S / cm or more, and 1.0 × 10 ⁻⁶ S / cm or more. It is preferably 5.0 × 10 ⁻⁶ S / cm or more.

The method of manufacturing a lithium ion conductive solid electrolyte of the present invention, Li ₇ against La ₃ Zr ₂ O ₁₂ powder 100 parts by weight of Li ₃ BO ₃ powder and 1 part by mass to 20 parts by weight, preferably 1 part by mass to 10 parts by mass, more preferably 2 parts by mass to 5 parts by mass are mixed to obtain a raw material mixture, a molding process for pressure-molding the raw material mixture to obtain a molded body, and the molded body in the atmosphere. A heat treatment step of heat treatment at a temperature of 600 ° C to 900 ° C, preferably 600 ° C to 800 ° C, more preferably 650 ° C to 750 ° C.

The average particle diameter of the Li ₇ La ₃ Zr ₂ O ₁₂ powder is preferably 0.05 μm to 10 μm, more preferably 0.1 μm to 5 μm, and 0.5 μm to 1.5 μm. Further preferred.

The average particle size of the Li ₃ BO ₃ powder is preferably 0.05 μm to 10 μm, and more preferably 0.1 μm to 5 μm.

  Moreover, the all-solid-state battery of this invention is equipped with the positive electrode, the negative electrode, and the solid electrolyte, The said lithium ion conductive solid electrolyte is used as said solid electrolyte, It is characterized by the above-mentioned.

  According to the present invention, it is possible to provide a lithium ion conductive solid electrolyte that has a relatively high ionic conductivity and has small variations in characteristics including the ionic conductivity. Further, according to the present invention, it is possible to provide a production method capable of easily mass-producing this lithium ion conductive solid electrolyte. Furthermore, according to this invention, the all-solid-state battery using this lithium ion conductive solid electrolyte can be provided. Such an all-solid-state battery is not only excellent in safety, but also can improve the output characteristics and capacity characteristics that have been problematic in the conventional all-solid-state battery, so that its industrial significance is extremely large.

In light of the above-described problems, the present inventors have conducted extensive research on a lithium ion conductive solid electrolyte that constitutes an all-solid battery, and as a result, Li ₇ La ₃ Zr ₂ O ₁₂ , which is a garnet-type compound, as a main component. In addition, a predetermined amount of Li ₃ BO ₃ is added, and these mixtures are pressure-molded and heat-treated under predetermined conditions, so that variation in characteristics is small while having relatively high ionic conductivity. The present inventors have obtained knowledge that a lithium ion conductive solid electrolyte can be obtained. The present invention has been completed based on this finding.

1. Lithium ion conductive solid electrolyte The lithium ion conductive solid electrolyte of the present invention (hereinafter referred to as “solid electrolyte”) is Li ₇ La ₃ Zr ₂ O ₁₂ , which is a garnet-type compound having lithium ion conductivity, and Li ₃ BO. ₃ is a solid electrolyte. In particular, the solid electrolyte of the present invention contains 1 to 20 parts by mass of Li ₃ BO ₃ when the content of Li ₇ La ₃ Zr ₂ O ₁₂ is 100 parts by mass, and is a hard Li ₇ La _3. Li ₃ BO ₃ is arranged in the space between the particles made of Zr ₂ O _12, and the particles made of Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₃ BO _{3 are in} surface contact. And That is, in the solid electrolyte of the present invention, Li ₃ BO ₃ is arranged so as to fill the voids in the matrix formed by the particles made of hard Li ₇ La ₃ Zr ₂ O ₁₂ , and Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ are in surface contact with no gap. In such a solid electrolyte, since there are almost no voids in the interior and the composition becomes uniform, not only can the intergranular resistance be suppressed and a relatively high ionic conductivity can be realized, Variations in characteristics including ionic conductivity can be suppressed.

(1) Composition (Li ₇ La ₃ Zr ₂ O ₁₂ )
In the present invention, a garnet-type compound having lithium ion conductivity is used as the main component constituting the solid electrolyte powder. Here, the garnet-type compound is a compound represented by C ₃ A ₂ D ₃ O ₁₂ (C: c-site element, A: a-site element, D: d-site element, O: oxygen atom). In other words, it has a characteristic of exhibiting a relatively high ionic conductivity at room temperature. Examples of the garnet-type compound or the compound having a structure similar to the garnet-type compound include Li ₇ La ₃ Zr ₂ O ₁₂ and Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ described above, and Li ₅ La ₃ M _2. O ₁₂ (M = Nb, Ta) and Li ₇ La ₃ (Zr _X , A _2−X ) O ₁₂ (A = Nb, Ta) are known.

In the present invention, among these garnet type compounds, in particular, Li ₇ La ₃ Zr ₂ O ₁₂ is adopted as a main component. This is because Li ₇ La ₃ Zr ₂ O ₁₂ not only has a high ionic conductivity as a bulk of 10 ⁻⁴ S / cm at room temperature, but is relatively easy to synthesize, and can be easily used in industrial scale production. This is because it can be used. In the present invention, general Li ₇ La ₃ Zr ₂ O ₁₂ can be used as the main component, and the addition of a special element or the like is not required.

The Li ₇ La ₃ Zr ₂ O ₁₂ particles constituting the solid electrolyte preferably have an average particle size of 0.01 μm to 10 μm, more preferably 0.05 μm to 10 μm, and 0.1 μm to 5 μm. More preferably. When the average particle size of the Li ₇ La ₃ Zr ₂ O ₁₂ particles is less than 0.01 μm, the particles are likely to aggregate with each other, and it may be difficult to suppress variation in characteristics of the solid electrolyte. On the other hand, if the average particle size exceeds 10.0 μm, the gap between Li ₇ La ₃ Zr ₂ O ₁₂ particles becomes too large, and this gap cannot be filled by the addition of Li ₃ BO _3. Resistance may increase.

  In the present invention, the average particle size means that when the particle size distribution of the target particles (powder) is accumulated from the smaller particle size, the accumulated volume is 50% of the total volume of all particles. Mean particle size (D50). D50 can be obtained from, for example, a volume integrated value measured with a laser light diffraction / scattering particle size analyzer.

_{Also, Li 7 La 3 Zr 2 O} 12 particles constituting the solid electrolyte is preferably particle size is uniform. The particle size of Li ₇ La ₃ Zr ₂ O ₁₂ particles is non-uniform, that is, the Li ₇ La ₃ Zr ₂ O ₁₂ particles contain many fine particles having a particle size of 0.01 μm or less and coarse particles exceeding 10 μm. If they are present, the characteristics of the solid electrolyte may vary due to their presence.

(Li ₃ BO ₃ )
The solid electrolyte of the present invention contains a predetermined amount of Li ₃ BO ₃ in addition to the above Li ₇ La ₃ Zr ₂ O ₁₂ . Li ₃ BO ₃ has an ionic conductivity of about 10 ⁻⁷ S / cm and is inferior to the above-described Li ₇ La ₃ Zr ₂ O _12, but has a relatively high ionic conductivity. Further, even if the heat treatment step is performed at a relatively low temperature, it can be easily softened or melted and enter the voids between the Li ₇ La ₃ Zr ₂ O ₁₂ particles with high fluidity.

The content of Li ₃ BO ₃ is 1 part by mass to 20 parts by mass, preferably 2 parts by mass to 10 parts by mass when the content of Li ₇ La ₃ Zr ₂ O _{12 in} the solid electrolyte is 100 parts by mass. Is necessary. If the content of Li ₃ BO ₃ is less than 1 part by mass, the effect of reducing intergranular resistance cannot be obtained sufficiently. On the other hand, when the content of Li ₃ BO ₃ exceeds 20 parts by mass, the ionic conductivity is lowered due to a decrease in the content of Li ₇ La ₃ Zr ₂ O _{12 in} the solid electrolyte.

(2) Structure In the solid electrolyte of the present invention, Li ₃ BO ₃ is arranged so as to fill voids in the matrix formed by hard Li ₇ La ₃ Zr ₂ O ₁₂ particles, and Li ₇ La ₃ Zr ₂ It has a structure in which O ₁₂ and Li ₃ BO ₃ are in surface contact. For this reason, the solid electrolyte of the present invention has almost no voids inside and has a uniform composition.

(3) Characteristics The solid electrolyte of the present invention has the above-described composition and structure, so that it is 2.0 × 10 ⁻⁷ S / cm or more, preferably 1.0 × 10 ⁻⁶ S / cm or more, more preferably An ionic conductivity of 5.0 × 10 ⁻⁶ S / cm or more can be realized. The ionic conductivity of the solid electrolyte can be measured by an AC impedance method.

The solid electrolyte of the present invention is composed of a matrix formed of particles made of hard Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₃ BO ₃ disposed so as to fill the voids in the matrix. Yes. Therefore, as in the technique described in JP2013-37992A, the ionic conductivity is higher than that of a solid electrolyte in which a special element is added and a molten flux is solidified to form a base material. Variations in characteristics such as these are small, and excellent quality stability can be realized.

2. Method for Producing Lithium Ion Conductive Solid Electrolyte The method for producing a solid electrolyte of the present invention comprises mixing 1 part by mass to 20 parts by mass of Li ₃ BO ₃ powder with respect to 100 parts by mass of Li ₇ La ₃ Zr ₂ O ₁₂ powder. , a mixing step of obtaining a raw material mixture, the raw material mixture was pressed at ^{1000kg / cm 2 ~2000kg / cm 2} , a forming step to obtain a molded product, the resulting molded body in the air, 600 ° C. to 900 And a heat treatment step of performing heat treatment at a temperature of ° C.

(1) Raw material powder As a raw material powder of the solid electrolyte of the present invention, Li ₇ La ₃ Zr ₂ O ₁₂ powder and Li ₃ BO ₃ powder are used.

Among these, the Li ₇ La ₃ Zr ₂ O ₁₂ powder has an average particle size of preferably 0.05 μm to 10 μm, more preferably 0.1 μm to 5 μm, and still more preferably 0.5 μm to 1.5 μm. Use things. That is, in the heat treatment step described later, Li ₇ La ₃ Zr ₂ O ₁₂ powder, since hardly softened or melted, as Li ₇ La ₃ Zr ₂ O ₁₂ powder, Li ₇ La ₃ Zr ₂ O solid electrolyte mentioned above It is preferable to use those in the range of the average particle size of ₁₂ particles.

On the other hand, as the Li ₃ BO ₃ powder, one having an average particle diameter of the same level or lower than that of the Li ₇ La ₃ Zr ₂ O ₁₂ powder is used. Specifically, those having an average particle diameter of preferably 0.05 μm to 10 μm, more preferably 0.1 μm to 1.5 μm, and still more preferably 0.5 μm to 1.5 μm are used. By using a Li ₃ BO ₃ powder having an average particle diameter in such a range, the Li ₃ BO ₃ powder is interstitial between Li ₇ La ₃ Zr ₂ O ₁₂ powders at the stage of the mixing step. The solid electrolyte having the structure described above can be easily obtained.

  The method for synthesizing these raw material powders is not particularly limited, and known means can be used.

For example, Li ₇ La ₃ Zr ₂ O ₁₂ powder can be obtained from Ramaswamy Murugan et al., “Fast Lithium Ion Conduction in Garnet-Tyape Li ₇ La ₃ Zr ₂ O ₁₂ ”, Angew. Chem. Int. Ed. 2007, 46, It can be synthesized by the solid phase method described in 7778-7781.

Furthermore, Li ₃ BO ₃ powder, Li ₂ CO _3, LiOH, and the lithium compound powder made of Li (CH _{3 COO),} and a boron compound powder made of _{H 3 BO 3, B 2 O} 3 were mixed, It can synthesize | combine by baking at 600 to 850 degreeC in air | atmosphere, and making the product into a powder form.

  The raw material powder synthesized by these methods may have an average particle size greatly deviating from the above-mentioned range, or may have a wide particle size distribution and may contain fine particles or coarse particles. In this case, it is preferable to adjust the average particle size and particle size distribution by crushing and / or crushing the synthesized raw material powder. As a crushing and pulverizing method, known methods such as a ball mill, a bead mill, and a jet mill can be used.

(2) Mixing step The mixing step is a step of mixing 1 to 20 parts by mass of Li ₃ BO ₃ powder with respect to 100 parts by mass of Li ₇ La ₃ Zr ₂ O ₁₂ powder to obtain a raw material mixture. That is, in the mixing step, the Li ₇ La ₃ Zr ₂ O ₁₂ powder and the Li ₃ BO ₃ powder have the same composition ratio as Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₃ BO _{3 in} the target solid electrolyte. It is necessary to mix with the powder.

As a mixing method, either a wet method or a dry method can be used as long as the Li ₇ La ₃ Zr ₂ O ₁₂ powder and the Li ₃ BO ₃ powder can be uniformly mixed.

In the mixing step, a binder or a solvent may be added to the Li ₇ La ₃ Zr ₂ O ₁₂ powder and Li ₃ BO ₃ powder to make the raw material mixture into a paste. Thereby, the molded object of a desired shape can be obtained easily at a formation process. However, it is necessary to select the binder and the solvent used at this time as those that disappear in the heat treatment step. This is because the ionic conductivity of the obtained solid electrolyte may be hindered if the binder or solvent remains even after the heat treatment. Specifically, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, or the like can be used as the binder, and a nonaqueous solvent such as terpineol can be used as the solvent.

(3) Molding step The molding step is a step of obtaining a molded body having a predetermined shape by pressurizing and press-molding the raw material mixture obtained in the mixing step.

Pressure during pressure molding, it is necessary to adjust appropriately depending on the characteristics of shape and press apparatus of the molded body for the purpose, it is preferable to ^{1000kg / cm 2 ~2000kg / cm 2} . If the pressure at the time of pressure molding is less than 1000 kg / cm ² , the Li ₃ BO ₃ powder is not disposed in the gap between the Li ₇ La ₃ Zr ₂ O ₁₂ powder, and this gap can be filled also by the heat treatment step described later. There are cases where it is not possible. On the other hand, even if the pressure at the time of pressure molding exceeds 2000 kg / cm ² , not only the effect cannot be obtained but also the productivity may be deteriorated.

In the molding step, it is preferable to perform pressure molding after heating the raw material mixture. As a result, the Li ₃ BO ₃ powder softens and can easily enter the gaps between the Li ₇ La ₃ Zr ₂ O ₁₂ powders. The heating temperature at this time needs to be appropriately adjusted depending on the mixing ratio of the Li ₇ La ₃ Zr ₂ O ₁₂ powder and the Li ₃ BO ₃ powder. However, when adding a binder to a raw material mixture, it is necessary to make heating temperature into the range of the decomposition temperature from the softening point of a binder, and about 100 to 300 degreeC.

(4) Heat treatment step The heat treatment step is a step of heat-treating the molded body obtained in the molding step at 600 ° C to 900 ° C in the atmosphere. By such heat treatment, the Li ₃ BO ₃ powder disposed in the gaps between the Li ₇ La ₃ Zr ₂ O ₁₂ powders is softened or melted, and has a high fluidity, and the gaps between the Li ₇ La ₃ Zr ₂ O ₁₂ powders. It is possible to enter and fill this gap.

The heat treatment temperature is a temperature at which the Li ₃ BO ₃ powder softens or melts, specifically 600 ° C. to 900 ° C., preferably 600 ° C. to 800 ° C., more preferably 650 ° C. to 750 ° C. When the heat treatment temperature is less than 600 ° C., Li ₃ BO ₃ does not soften and the voids in the matrix cannot be filled. On the other hand, if the heat treatment temperature exceeds 900 ° C., the ionic conductivity may decrease due to the volatilization of Li or the generation of a different phase.

  The atmosphere during the heat treatment needs to be an oxidizing atmosphere, and the oxygen concentration is preferably 20% or more, that is, in an air atmosphere. Thereby, the production | generation of an oxygen defect can be suppressed.

  Moreover, although it is necessary to adjust heat processing time suitably according to heat processing conditions, the apparatus to be used, etc., it is preferable to set it as 5 minutes-5 hours, and it is more preferable to set it as 10 minutes-1 hour. If the heat treatment time is less than 5 minutes, the voids in the matrix may not be sufficiently filled. On the other hand, even if the heat treatment time exceeds 5 hours, not only a further effect cannot be obtained, but there is a possibility that a problem of volatilization of Li or generation of a different phase may occur.

  The equipment used for such heat treatment is not particularly limited as long as it can heat the molded body in an oxidizing atmosphere, and an electric furnace that does not generate gas can be suitably used.

3. All-solid-state battery The all-solid-state battery of the present invention includes a positive electrode, a negative electrode, and a solid electrolyte, as in the conventional all-solid-state battery, and uses the solid electrolyte of the present invention as a solid electrolyte. It is characterized by.

  Such an all-solid battery of the present invention has not only high safety but also excellent output characteristics because the solid electrolyte has relatively high ionic conductivity.

  Further, as described above, the solid electrolyte of the present invention can exhibit its function even when heat-treated at a relatively low temperature. For this reason, the all solid state battery of the present invention can stack a positive electrode material, a solid electrolyte, and a negative electrode material, lower the temperature during heat treatment, and is called decomposition of an electrode active material that occurs when heat treatment is performed at a high temperature. It is possible to avoid problems.

  Hereinafter, the lithium ion conductive solid electrolyte of the present invention will be specifically described with reference to Examples and Comparative Examples.

(Example 1)
[Li ₇ La ₃ Zr ₂ O ₁₂ powder]
According to the solid phase method described in Ramaswamy Murugan et al., “Fast Lithium Ion Conduction in Garnet-Tyape Li ₇ La ₃ Zr ₂ O ₁₂ ”, Angew. Chem. Int. Ed. 2007, 46, 7778-7781 ₇ La ₃ Zr ₂ O ₁₂ was synthesized. Next, the obtained Li ₇ La ₃ Zr ₂ O ₁₂ was pulverized and pulverized using a ball mill, processed into a powder form, and its average particle size was adjusted to 1 μm.

When the ionic conductivity of the Li ₇ La ₃ Zr ₂ O ₁₂ powder thus obtained was measured by an alternating current impedance method, it was confirmed to be 1.2 × 10 ⁻⁸ S / cm.

[Li ₃ BO ₃ powder]
Li ₂ CO ₃ powder (manufactured by Nacalai Tesque, special grade reagent) and H ₃ BO ₃ powder (manufactured by Kanto Chemical Co., Ltd., special grade reagent) are weighed so that the molar ratio of Li and B is 3: 1. At the same time, these powders were uniformly mixed using a mortar. The mixture thus obtained was calcined in the atmosphere at 650 ° C. for 24 hours using an electric furnace, and then pulverized in a mortar to obtain Li ₃ BO ₃ powder. Finally, this Li ₃ BO ₃ powder was pulverized and pulverized in the same manner as Li ₇ La ₃ Zr ₂ O ₁₂ powder, and the average particle size was adjusted to 1 μm.

Incidentally, an endothermic peak of Li ₃ BO ₃ powder obtained, measured using a differential thermal analyzer (DTA), was determined the melting point of Li ₃ BO ₃ powder, was confirmed to be 699 ° C.. Further, the ionic conductivity of the Li ₃ BO ₃ powder was measured by the AC impedance method, it was confirmed that 3.5 × 10 ^-7 S / cm.

[Production of solid electrolyte]
The Li ₃ BO ₃ powder was weighed to 1 part by mass with respect to 100 parts by mass of the Li ₇ La ₃ Zr ₂ O ₁₂ powder, and these powders were mixed using a mortar. The thus obtained raw material mixture, a hot press (AS ONE Corporation, AH-2003C) using a pressurized at ^{1000kg / cm 2 ~2000kg / cm 2} , diameter 10 mm, a thickness of 1.1mm After forming into a cylindrical pellet, the solid electrolyte pellet was produced by baking at 700 ° C. for 1 hour in the air.

[Evaluation of solid electrolyte]
The solid electrolyte was evaluated by measuring the ionic conductivity of the solid electrolyte pellet. Specifically, an Au thin film layer having a thickness of 800 mm is formed on both surfaces of the solid electrolyte pellet obtained by the above-described method using a sputtering apparatus, and this Au thin film layer is used as an electrode by an AC impedance method. The ionic conductivity of each solid electrolyte pellet was measured and evaluated by determining the average value.

  For measurement of lithium ion conductivity, a modular potentiostat / galvanostat (manufactured by Biologic, VSP-300) was used. At this time, the voltage amplitude was set to ± 10 mV, the measurement frequency was set to 7 MHz to 1 Hz, and the measurement temperature was set to 25 ° C. The results are shown in Table 1.

(Examples 2 to 8)
Other than controlling the conditions such as the addition amount of Li ₃ BO ₃ powder, the heat treatment temperature, the average particle size (D50) of Li ₃ BO ₃ powder and Li ₇ La ₃ Zr ₂ O ₁₂ powder as described in Table 1 Produced a solid electrolyte pellet in the same manner as in Example 1, and measured lithium ion conductivity. The results are shown in Table 1.

(Comparative Example 1)
A solid electrolyte pellet was prepared and lithium ion conductivity was measured in the same manner as in Example 1 except that no Li ₃ BO ₃ powder was added. The results are shown in Table 1.

(Comparative Examples 2 to 5)
A solid electrolyte pellet was prepared and its lithium ion conductivity was measured in the same manner as in Example 1 except that the addition amount of Li ₃ BO ₃ powder and the heat treatment temperature were controlled as described in Table 1. The results are shown in Table 1.

(Comparative Example 6)
Instead of Li ₃ BO ₃ powder, Li ₃ PO ₄ powder having an average particle diameter of 1 μm was added, and the amount of Li ₃ BO ₃ powder added was 3.4 parts by mass, that is, Li ₇ La ₃ Zr. the volume ratio of Li ₃ PO ₄ powder to ₂ O ₁₂ powder, except that the same as Li ₃ BO ₃ powder volume ratio of for Li ₇ La ₃ Zr ₂ O ₁₂ powder in example 2 same as example 1 Then, a solid electrolyte pellet was prepared, and lithium ion conductivity was measured. The results are shown in Table 1.

The endothermic peak of the Li ₃ PO ₄ powder used in this comparative example was measured using a differential thermal analyzer, and its melting point was determined. As a result, it was confirmed to be 837 ° C. Moreover, when the ionic conductivity of the Li ₃ PO ₄ powder was measured by the alternating current impedance method, it was 1.0 × 10 ⁻⁷ S / cm, and it was confirmed that the ionic conductivity was the same as that of Li ₃ BO _3. It was done.

(Evaluation)
From Table 1, it is confirmed that in Examples 1 to 5 belonging to the technical scope of the present invention, the ion conductivity is 2.0 × 10 ⁻⁷ S / cm or more and the variation is small.

In contrast, Comparative Examples 1 to 3 are examples in which the content of Li ₃ BO ₃ deviates from the range defined in the present invention. In Comparative Example 1 containing no Li ₃ BO _3, it shows a low ionic conductivity values. This is considered to be caused by voids between the Li ₇ La ₃ Zr ₂ O ₁₂ particles. On the other hand, in Comparative Examples 2 and 3 in which the content of Li ₃ BO ₃ exceeds 20 parts by mass, the ionic conductivity cannot be improved because the ratio of Li ₇ La ₃ Zr ₂ O ₁₂ in the solid electrolyte is low. It was.

Comparative Examples 4 and 5 are examples in which the heat treatment temperature deviates from the range defined in the present invention. In Comparative Example 4 where the heat treatment temperature was less than 600 ° C., Li ₃ BO ₃ could not be sufficiently softened or melted during the heat treatment, so the porosity was high and the ionic conductivity could not be improved. On the other hand, in Comparative Example 5 in which the heat treatment temperature exceeds 900 ° C., the ionic conductivity could not be improved due to the volatilization of Li or the generation of a different phase.

Further, Comparative Example 6 is an example in which Li ₃ PO ₄ is used in place of Li ₃ BO ₃ . In this comparative example, due to the high melting point of Li ₃ PO ₄ , the heat treatment at about 700 ° C. could not be sufficiently softened or melted. Therefore, it is impossible to fill the voids between Li ₇ La ₃ Zr ₂ O ₁₂ particles sufficiently, it was not possible to improve the ionic conductivity.

Claims (7)

A lithium ion conductive electrolyte comprising Li ₇ La ₃ Zr ₂ O ₁₂ , which is a garnet-type compound having lithium ion conductivity, and Li ₃ BO ₃ ,
When the content of the Li ₇ La ₃ Zr ₂ O ₁₂ is 100 parts by mass, the Li ₃ BO ₃ is contained in an amount of 1 to 20 parts by mass,
The Li ₃ BO ₃ is disposed in the gap between the particles made of Li ₇ La ₃ Zr ₂ O _12, and the particles made of Li ₇ La ₃ Zr ₂ O ₁₂ and the Li ₃ BO ₃ are Lithium ion conductive solid electrolyte in surface contact. _2. The lithium ion conductive solid electrolyte according to claim 1, wherein an average particle diameter of the particles made of Li ₇ La ₃ Zr ₂ O ₁₂ is 0.05 μm to 10 μm. 3. The lithium ion conductive solid electrolyte according to claim 1, wherein the ion conductivity is 2.0 × 10 ⁻⁷ S / cm or more as measured by an impedance method. A mixing step of mixing 1 to 20 parts by mass of Li ₃ BO ₃ powder with respect to 100 parts by mass of Li ₇ La ₃ Zr ₂ O ₁₂ powder to obtain a raw material mixture;
A molding step of pressure-molding the raw material mixture to obtain a molded body; and
The manufacturing method of the lithium ion conductive solid electrolyte in any one of Claims 1-5 provided with the heat processing process which heat-processes the said molded object at the temperature of 600 to 900 degreeC in air | atmosphere. The Li ₇ La mean grain size of ₃ Zr ₂ O ₁₂ powder is 0.05 m to 10 m, the manufacturing method of the lithium ion conductive solid electrolyte according to claim 4. The method for producing a lithium ion conductive solid electrolyte according to claim 4 or 5, wherein the Li ₃ BO ₃ powder has an average particle size of 0.05 µm to 10 µm. An all-solid battery comprising a positive electrode, a negative electrode, and a solid electrolyte, wherein the lithium ion conductive solid electrolyte according to claim 1 is used as the solid electrolyte.