JP7002520B2 - Method for manufacturing solid electrolyte, all-solid-state battery, and solid electrolyte - Google Patents

Description

The present invention relates to a solid electrolyte, an all-solid-state battery, and a method for producing a solid electrolyte, which can be suitably used for an all-solid-state battery or the like.

Among the secondary batteries, the all-solid-state battery such as the all-solid-state lithium-ion battery in which the electrolyte is a solid has excellent stability, reliability, and high energy density as compared with the lithium-ion battery using the liquid electrolyte. There is a possibility that high output and a wide operating temperature can be realized. Therefore, all-solid-state batteries are expected to be put into practical use in various applications such as automobiles, electronic devices, and household storage batteries.

The all-solid-state battery is generally classified into a thin film type manufactured by the vapor phase method and a bulk type manufactured by sintering fine particles. Of these, the bulk type all-solid-state battery is formed by laminating and sintering a granular positive electrode active material, a plate-shaped or granular solid electrolyte, and a granular negative electrode active material between collectors. The solid electrolyte of the bulk type all-solid-state battery is generally obtained by sintering the solid electrolyte particles at the time of manufacturing the all-solid-state battery or in advance, and therefore, it may be referred to as a firing type solid electrolyte.

Various materials have been proposed as candidates for materials used for the calcined solid electrolyte of an all-solid-state battery, but the selection of the material is important because it greatly affects the battery performance. Among them, among the oxide-based inorganic solid electrolyte materials, it is represented by A _{2 / 3-x} Li _3x TiO ₃ (0 <x <0.16, A: one or more elements selected from lanthanoids). Complex oxides, particularly composite oxides having a perovskite crystal structure in which A is La (so-called LLTO), are promising because of their high ionic conductivity, stability and durability.

By the way, when an oxide-based inorganic solid electrolyte material comes into contact with graphite or other carbon or lithium metal that can be used as a material for a negative electrode in an all-solid-state battery, it may be reduced by a reaction with the carbon or lithium metal. In this case, the inorganic solid electrolyte material has a problem that electron conductivity is imparted by such a reduction reaction, and as a result, a short circuit is generated between the inorganic solid electrolyte material and the positive electrode.

In relation to this, Patent Document 1 states, "It is an all-solid-state battery configured by laminating at least a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, and the positive electrode layer has a specific crystal plane. It is composed only of a positive electrode active material oriented in the conduction direction of lithium ions, the solid electrolyte layer is composed of an inorganic solid electrolyte, and a polymer solid electrolyte layer is interposed between the positive electrode layer and the solid electrolyte layer. An all-solid-state battery characterized by the above-mentioned characteristics, such as "a polymer solid electrolyte layer is interposed between the negative electrode layer and the solid electrolyte layer" and the like have been proposed. According to this, "improvement of ionic conduction by improving the contact property at the interface between the electrode and the solid electrolyte layer, suppression of resistance layer formation at the interface, improvement of ionic conduction in the electrode, and further improvement of energy density. It can be planned. "

Japanese Unexamined Patent Publication No. 2014-238925

As described in Patent Document 1, when the polymer solid electrolyte material is interposed between the negative electrode and the solid electrolyte, the reduction of the inorganic solid electrolyte material of the solid electrolyte by the material of the negative electrode is the polymer solid electrolyte. It is thought that it can be suppressed to some extent by the material.

However, the polymer solid electrolyte material made of a polymer such as polyethylene oxide or polypropylene oxide has a significantly lower ionic conductivity than the inorganic solid electrolyte material such as LLTO. Therefore, in this case, it is necessary to operate at a relatively high pressure and high temperature in order to improve the ionic conductivity. Therefore, an all-solid-state battery in which a polymer solid electrolyte material is interposed between the negative electrode and the solid electrolyte cannot realize excellent battery performance.
In addition, since polymers such as polyethylene oxide and polypropylene oxide burn at about 300 ° C, there is a problem in terms of safety.

An object of the present invention is to solve such a problem, and an object thereof is to improve ionic conductivity and effectively suppress reduction of an inorganic solid electrolyte material by a negative electrode material. It is an object of the present invention to provide a solid electrolyte, an all-solid-state battery, and a method for producing a solid electrolyte.

The solid electrolyte of the present invention comprises a main body containing an oxide-based inorganic solid electrolyte material having a potential difference of 0.1 V or more from the carbon or lithium metal, and the carbon or lithium metal formed on the main body. It has a reduction prevention layer containing an oxide-based inorganic solid electrolyte material having a potential difference of less than 0.1 V.

In the solid electrolyte of the present invention, it is preferable that the inorganic solid electrolyte material of the main body contains an oxide represented by the following general formula (I).
A _{2 / 3-x} Li _3x TiO ₃ (I)
(In the formula, x satisfies 0.04 <x <0.14, and A is one or more elements selected from lanthanoids.)

In this case, it is preferable that A in the oxide represented by the general formula (I) is La.

In the solid electrolyte of the present invention, it is preferable that the inorganic solid electrolyte material of the reduction prevention layer contains an oxide containing lithium.

Specifically, the inorganic solid electrolyte material of the reduction prevention layer is Li ₃ BO ₃ , Li ₂ B ₄ O ₇ , Li ₂ CO ₃ -Li ₃ BO ₃ , BLiO ₂ , Li ₂ O, Li ₃ PO ₄ . , Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO), Li ₃ BO ₃ -Li ₂ SO ₄ and Li-Co-PO ₄ preferably comprising at least one selected from the group.

In the solid electrolyte of the present invention, the thickness of the anti-reduction layer is preferably 1 μm to 40 μm.

In the solid electrolyte of the present invention, it is preferable that the main body portion is plate-shaped, and the reduction prevention layer is formed on only one surface of the plate-shaped main body portion so as to cover the entire surface. ..

The all-solid-state battery of the present invention includes a positive electrode, a solid electrolyte, and a negative electrode, and is configured by laminating the positive electrode, the solid electrolyte, and the negative electrode in this order, and the solid electrolyte is any one of the above. The solid electrolyte of the above, wherein the reduction prevention layer is interposed between the main body portion of the solid electrolyte and the negative electrode.

The method for producing a solid electrolyte of the present invention comprises a plate containing an oxide-based inorganic solid electrolyte material having a potential difference of 0.1 V or more from carbon or lithium metal, and a potential difference of less than 0.1 V from carbon or lithium metal. A raw material preparation step for preparing raw material powders constituting a reduction prevention layer containing an oxide-based inorganic solid electrolyte material, a liquid preparation step for preparing a slurry or a solution containing the raw material powder, and a liquid preparation step on the plate material. It includes a coating step of coating the slurry or the solution, and a baking step of heating the plate together with the slurry or the solution coated on the plate to 450 ° C to 650 ° C.

According to the present invention, there is provided a solid electrolyte, an all-solid-state battery, and a method for producing a solid electrolyte, which can improve ionic conductivity and effectively suppress the reduction of an inorganic solid electrolyte material by a negative electrode material. Can be done.

It is sectional drawing which shows the solid electrolyte of one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail.
(Solid electrolyte)
As illustrated in FIG. 1, the solid electrolyte 1 according to the embodiment of the present invention is formed on the main body 2 constituting the main part of the solid electrolyte 1 and the main body 2 to reduce the main body 2. It has a reduction prevention layer 3 that functions to prevent the above. The main body 2 contains an oxide-based inorganic solid electrolyte material, and the inorganic solid electrolyte material of the main body 2 has a potential difference of 0.1 V or more from carbon or lithium metal, and is typically carbon or When in contact with lithium metal, it shall be reduced by reaction with carbon or lithium metal. On the other hand, unlike the above-mentioned inorganic solid electrolyte material of the main body 2, the reduction prevention layer 3 has a lower potential than the inorganic solid electrolyte material of the main body 2 and has a potential difference of less than 0.1 V from carbon or lithium metal. It is assumed to contain a certain oxide-based inorganic solid electrolyte material.

Here, when the potential of the lithium metal is used as a reference (0V), carbon is almost 0V. For example, LLTO, which will be described later, has a potential 1.75 V higher than that of lithium metal or carbon. Therefore, when an inorganic solid electrolyte material such as LLTO that can be used for the main body 2 comes into contact with a negative electrode made of lithium metal or carbon in an all-solid-state battery because the potential difference from carbon or lithium metal is 0.1 V or more. , Lithium metal or carbon is reduced to impart electron conductivity, resulting in a short circuit with the positive electrode.

On the other hand, in this embodiment, a reduction prevention layer 3 containing an oxide-based inorganic solid electrolyte material having a potential difference of less than 0.1V from carbon or lithium metal is formed on the main body portion 2, and the reduction prevention layer 3 is formed. 3 is interposed between the main body 2 and the negative electrode. This makes it possible to effectively suppress the reduction of the inorganic solid electrolyte material of the main body 2 by the carbon or lithium metal of the negative electrode.

As the oxide-based inorganic solid electrolyte material contained in the main body 2, various materials can be used. Specifically, in addition to the oxide represented by the general formula (I) described later, Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ (LATP) or Li _{1 + x} Al _x Ge _2-x Examples thereof include NASICOM type electrolytes such as (PO ₄ ) ₃ (LAGP) and LISION type electrolytes such as Li _{2 + 2x} Zn _1-x GeO ₄ . Such an inorganic solid electrolyte material has high ionic conductivity and can be suitably used for a solid electrolyte of an all-solid-state battery.

Among them, the inorganic solid electrolyte material of the main body 2 contains an oxide represented by the general formula (I): A _{2 / 3-x} Li _3x TiO ₃ , which has ionic conductivity or chemical stability. It is preferable from the viewpoint of. Here, in the general formula (I), x satisfies 0.04 <x <0.14, and A is one or more elements selected from lanthanoids. In particular, it is preferable to contain an oxide of La _{2 / 3-x} Li _3x TiO ₃ (0.04 <x <0.14) in which A in the general formula (I) is La. The composite oxide having a perovskite crystal structure in which A in the general formula (I) is La is also referred to as LLTO. For example, the general formula (Ia): La _x Li _2-3x TIM _3-a SrTiO ₃ , the general formula (Ib): La _x Li _2-3x TIM _3-a La _0.5 K _0.5 TiO ₃ , the general formula. (I-c): La _x Li _2-3x Ti _1-a Ma O _{3-a ,} or general formula (Id): Sr _x-1.5a La _a Li _1.5-2x Ti _0.5 Ta _0.5 O ₃ (In the general formulas (Ia) to (Id), x satisfies 0.55 ≦ x ≦ 0.59, a satisfies 0 ≦ a ≦ 0.2, and M is Al. , Fe, Ga is at least one selected from), and examples thereof include those having an Al ₂ O ₃ content of 0.35% by weight or less and a SiO ₂ content of 0.1% by weight or less. Will be.

It is confirmed by performing an X-ray diffraction method on a sample collected from the cross section of the main body 2 that the inorganic solid electrolyte material of the main body 2 contains an oxide represented by the above general formula (I). Can be done. In the X-ray diffraction method, the X-ray diffraction pattern of the inorganic solid electrolyte material obtained by PANalytical X'pert Pro is collated with the ICDD database (PANNalytical Exchange Database and PDF-4 + 2019RDB) and contained in the inorganic solid electrolyte material. The oxide represented by the above general formula (I) is identified.

Here, the X-ray diffraction pattern of the inorganic solid electrolyte material obtained by the X-ray diffraction method and from which noise has been removed is collated with the ICDD database, and the general formula (I) is included in the X-ray diffraction pattern of the inorganic solid electrolyte material. When it is recognized that the X-ray diffraction pattern of the oxide represented by the above is present, it is determined that the inorganic solid electrolyte material contains the oxide represented by the above general formula (I). On the other hand, when it is similarly collated with the ICDD database and it is recognized that the X-ray diffraction pattern of the oxide represented by the general formula (I) does not exist in the X-ray diffraction pattern of the inorganic solid electrolyte material. , It is determined that the inorganic solid electrolyte material does not contain the oxide represented by the above general formula (I). In addition, an oxide-based inorganic solid electrolyte material other than the oxide represented by the general formula (I) can be determined in substantially the same manner.

The oxide represented by the above general formula (I) in the inorganic solid electrolyte material of the main body 2 is a case where a part of oxygen is replaced with another element such as F or Cl, or a part of a transition metal. May be replaced with other metals such as Fe, Cr, Ti, Nb, W, Mo, Na, K, Mg, Ca. In addition, Li and oxygen may be excessive or deficient with respect to the stoichiometric composition of the oxide represented by the general formula (I). Further, the crystal structure of the oxide represented by the above general formula (I) in the inorganic solid electrolyte material may be distorted. The range in which the characteristics as an inorganic solid electrolyte material do not change even when the constituent elements are replaced, deleted or excessive with respect to the chemical quantitative composition of the oxide as described above, or when the crystal structure is distorted. If it is within, it is assumed that it is acceptable as an oxide represented by the above general formula (I).
When each X-ray diffraction pattern of an oxide lacking a constituent element or an oxide having an excess constituent element is collated with the above ICDD database, the X-ray diffraction pattern of the oxide represented by the above general formula (I) is obtained. The peak may shift (peak shift). If the peak shift is within ± 10% of the reference value of the ICDD database, it is determined that the inorganic solid electrolyte material contains the compound represented by the general formula (I). ..

The main body 2 preferably contains an oxide represented by the above general formula (I) as an inorganic solid electrolyte material in an amount of 99.0% by mass or more, and more preferably 99.5% by mass or more. Even more preferable. Since the higher the content of this oxide is, the more desirable it is, there is no particular preferable upper limit value thereof, but it may be, for example, 99.999% by mass or less, typically 99.99% by mass or less. The content of the oxide is measured by ICP (Inductively Coupled Plasma).
In addition to the oxide represented by the general formula (I), the main body 2 may contain at least one selected from the group consisting of Si, Al and Fe as impurities. The content of impurities in the inorganic solid electrolyte material is preferably 1.0% by mass or less, more preferably 0.5% by mass or less.

The reduction prevention layer 3 formed on the main body 2 of the solid electrolyte 1 is assumed to contain an oxide-based inorganic solid electrolyte material having a lower potential than the inorganic solid electrolyte material of the main body 2. By interposing such a reduction prevention layer 3 between the main body 2 and the negative electrode, it is possible to effectively prevent the inorganic solid electrolyte material of the main body 2 from being reduced by the carbon or lithium metal of the negative electrode. .. The potentials of various inorganic solid electrolyte materials have been elucidated, and as a document describing such potentials, for example, Yizhou Zhu et al., "Origin of Outstanding Stability in the Lithium Solid Electrolyte Materials: Insights from" Thermodynamic Analyses Based on First-Principles Calculations ”, ACS, Applied Materials & Interfaces, October 6, 2015, p. 23685-23693, etc.
It is assumed that the potential difference between the potential and the potential of the lithium metal of the inorganic solid electrolyte material of the main body 2 in which the reaction reduced by carbon or lithium metal occurs is 0.1 V or more.

It is assumed that the reduction prevention layer 3 has a potential difference of less than 0.1 V from carbon or lithium metal.
Specifically, as the inorganic solid electrolyte material of the reduction prevention layer 3, Li ₃ BO ₃ , Li ₂ B ₄ O ₇ , Li ₂ CO ₃ -Li ₃ BO ₃ , BLiO ₂ , Li ₂ O, Li ₃ PO ₄ , Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO), Li ₃ BO ₃ -Li ₂ SO _4, Li-Co-PO ₄ , and the like, but are not limited thereto.

The inorganic solid electrolyte material of the reduction prevention layer 3 preferably contains an oxide containing lithium. Specifically, the inorganic solid electrolyte material of the reduction prevention layer 3 has high conductivity or is easily available, so Li ₃ BO ₃ , Li ₂ B ₄ O ₇ , and Li ₂ CO. Group consisting of ₃ -Li ₃ BO ₃ , BLiO ₂ , Li ₂ O, Li ₃ PO ₄ , Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO), Li ₃ BO ₃ -Li ₂ SO ₄ and Li-Co-PO ₄ . It is preferable to include at least one selected from.
Li ₃ BO ₃ , Li ₂ B ₄ O ₇ , Li ₂ CO ₃ -Li ₃ BO ₃ , BLiO ₂ , Li ₂ O, Li ₃ PO ₄ , Li ₇ La ₃ Zr as the inorganic solid electrolyte material of the reduction prevention layer 3. Whether or not ₂ O ₁₂ (LLZO), Li ₃ BO ₃ -Li ₂ SO ₄ , Li-Co-PO ₄ , etc. are contained is checked for confirmation of the oxide represented by the above general formula (I). As a matter of fact, it can be confirmed by the same method and procedure as the above-mentioned X-ray diffractometry.

The reduction prevention layer 3 is an inorganic solid electrolyte material such as Li ₃ BO ₃ , Li ₂ B ₄ O ₇ , Li ₂ CO ₃ -Li ₃ BO ₃ , BLiO ₂ , Li ₂ O, Li ₃ PO ₄ , Li ₇ La ₃ Zr. If at least one selected from the group consisting of ₂ O ₁₂ (LLZO), Li ₃ BO ₃ -Li ₂ SO ₄ and Li-Co-PO ₄ is contained, the total of them is preferably 99.90 mass. It is preferably contained in%, and more preferably 99.5% by mass or more.

By the way, the thickness Tp of the reduction prevention layer 3 in the solid electrolyte 1 is preferably 1 μm to 40 μm, preferably 2 μm to 30 μm. By setting the thickness Tp of the reduction prevention layer 3 within the above range, it is possible to effectively suppress the reduction of the inorganic solid electrolyte material of the main body 2 by the material of the negative electrode. If the thickness Tp of the reduction prevention layer 3 is less than 1 μm, it may not be possible to suppress the reduction of the inorganic solid electrolyte material of the main body 2 by the material of the negative electrode. If the thickness Tp of the reduction prevention layer 3 is more than 40 μm, the amount of reagents may increase or the labor of work may increase. The thickness Tp of the reduction prevention layer 3 is measured by a reflected electron image or an image analysis of EDS mapping.

The thickness Tb of the main body 2 is, for example, 0.8 mm to 2.0 mm, typically 1.0 mm to 1.5 mm. The thickness Tb of the main body 2 is measured with a caliper.

If the main body 2 is in the shape of a plate such as a flat plate as shown in FIG. 1, a negative electrode is provided in an all-solid-state battery among the two surfaces S1 and S2 of the plate-shaped main body 2 facing opposite sides. It is preferable that the reduction prevention layer 3 is formed only on one surface S1 on the side. Since the inorganic solid electrolyte material of the main body 2 is not reduced depending on the material of the positive electrode, it is not necessary to form a reduction prevention layer on the other surface S2 of the main body 2 on the side where the positive electrode is provided. In this case, on the other surface S2 side, high ionic conductivity due to the desirable inorganic solid electrolyte material of the main body 2 can be realized.

Further, here, it is preferable that the reduction prevention layer 3 is formed so as to cover the entire surface S1 of the main body portion 2. By doing so, it is possible to more effectively suppress the reduction of the entire surface S1 of the main body 2 by the material of the negative electrode by the reduction prevention layer 3 over the entire surface S1 of the main body 2. ..

When the solid electrolyte 1 as described above is applied to a power generation material of a secondary battery, for example, the lithium ion conductivity when measured at 27 ° C. is, for example, 2.5 × 10 ^-4 Scm ^-1 or more, and further 2. It is preferably 7 × 10 ^-4 Scm ^-1 or more. An impedance method is used to measure the lithium ion conductivity of the solid electrolyte 1.
An example of measuring the lithium ion conductivity of the solid electrolyte 1 by the impedance method is as shown below. A 1 M aqueous solution of LiCl is impregnated into two 10 mm square filter papers and attached to both sides of a plate of a solid electrolyte 1 having a thickness of 2 mm. The solid electrolyte 1 is prepared in a 14 mm square and the filter paper is prepared in a 10 mm square. This is sandwiched between electrodes made of stainless steel. Here, the LiCl aqueous solution soaked in the filter paper is used as the electrolyte. In order to clarify the influence of the grain boundary of the solid electrolyte 1, the lithium ion conductivity is measured by the AC impedance method using an LCR meter (HP4192A, manufactured by Hured Packard) in a frequency range of 5 Hz up to 13 MHz.

In the solid electrolyte 1 of this embodiment, since each of the main body 2 and the reduction prevention layer 3 is made of an inorganic solid electrolyte material, a solid containing a polymer solid electrolyte material as described in Patent Document 1. Compared to the electrolyte, high ionic conductivity as described above can be realized. As a result, the all-solid-state battery manufactured by using the solid electrolyte 1 can exhibit the required performance even at normal pressure and normal temperature.

It should be noted that a solid electrolyte is generally recognized as a solid capable of moving ions (charged substances) by an electric field applied from the outside. In addition, electric power can be extracted from the solid electrolyte by utilizing the movement of ions. The solid electrolyte 1 of the embodiment of the present invention can be used as a power generation material for a secondary battery or an electrode conductor of an electrolytic capacitor, and may also be applied to various solid electrolyte devices such as gas sensors and gas separation / manufacturing. ..

(All solid state battery)
In order to manufacture an all-solid battery using the above-mentioned solid electrolyte 1, the negative electrode active material particles are arranged on the reduction prevention layer 3 on the surface S1 side of the solid electrolyte 1, and the negative electrode active material particles are arranged on the surface S2 of the solid electrolyte 1. Place positive electrode active material particles. Then, the positive electrode active material particles and the negative electrode active material particles are heated to a predetermined temperature together with the solid electrolyte 1 between them and sintered. As a result, an all-solid state including a layered positive electrode formed by sintering positive electrode active material particles, a layered negative electrode formed by sintering negative electrode active material particles, and a solid electrolyte 1 located between the positive electrode and the negative electrode. Batteries are obtained. In this all-solid-state battery, since the reduction prevention layer 3 is interposed between the main body 2 of the solid electrolyte 1 and the negative electrode, the inorganic solid electrolyte material of the main body 2 made of carbon or lithium metal, which is the material of the negative electrode, is used. The reduction of the above can be effectively suppressed.

Some oxide-based inorganic solid electrolyte materials may be present in the positive electrode and the negative electrode. In this case, the ionic conduction path at the positive electrode and the negative electrode is secured, and the conductor has high conductivity.
The all-solid-state battery is generally further provided with a current collector provided on the outside of each of the positive electrode and the negative electrode so as to sandwich the positive electrode, the solid electrolyte, and the negative electrode from both sides.
Such an all-solid-state battery may be referred to as a bulk-type all-solid-state battery in distinction from a thin-film type all-solid-state battery formed by laminating thin films by a vapor phase method such as a vacuum vapor deposition method.

(Production method)
An example of the method for producing the solid electrolyte 1 described above is a plate material containing an oxide-based inorganic solid electrolyte material having a potential difference of 0.1 V or more from carbon or lithium metal, and a potential difference from carbon or lithium metal. A raw material preparation step for preparing raw material powders constituting a reduction prevention layer containing an oxide-based inorganic solid electrolyte material having a value of less than 0.1 V, and a liquid preparation step for preparing a slurry or a solution containing the raw material powder. The plate includes a coating step of coating the plate material with the slurry or the solution, and a baking step of heating the plate together with the slurry or the solution coated on the plate to 450 ° C. to 650 ° C.

In the raw material preparation step, a plate material containing an oxide-based inorganic solid electrolyte material having a potential difference of 0.1 V or more from carbon or lithium metal and an oxide-based material having a potential difference of less than 0.1 V from carbon or lithium metal. Prepare raw material powders constituting the reduction prevention layer containing the inorganic solid electrolyte material.

Here, as the above-mentioned plate material, those already produced can be used, but they can be produced as described below. However, the method is not limited to this manufacturing method.
First, lithium compounds such as lithium hydroxide and lithium carbonate are used as lithium raw materials, and titanium compounds such as titanium oxide, metatitanic acid and orthotitanic acid are used as titanium raw materials (for example, average particle size D50: 0.1 μm to 1.0 μm, BET ratio). Surface area: 5.0 m ² / g to 100.0 m ² / g) and lanthanum oxide as a lantern raw material are both prepared in the form of powder. If necessary, at least one hydroxide, chloride and / or carbonate selected from the group consisting of Sr, K, Fe, Ga and Ta is also prepared.

Next, as the first wet pulverization, the above-mentioned raw materials such as lithium raw material, titanium raw material and lantern raw material are mixed with a mixed solvent such as pure water and ethanol at a predetermined molar ratio by a ball mill or the like and pulverized. After pulverization, it is dried using a spray dryer dryer, a fluidized bed dryer, a rolling granulation dryer, a freeze dryer, a hot air dryer, or the like to obtain a first pulverized powder. Then, as calcination, the first pulverized powder is heated at 1000 ° C. to 1200 ° C. for 1 to 12 hours under an oxygen or atmospheric atmosphere or an atmosphere of an inert gas such as nitrogen, whereby the calcination powder is obtained. Be done.

After that, as the second wet pulverization, the calcined powder is pulverized by adding a solvent with a ball mill or the like and then dried to obtain a second pulverized powder. Then, as dry pulverization, the second pulverized powder is pulverized by a dry method using a ball mill or the like, and further atomized by a dry or wet jet mill or the like as necessary, and then solid electrolyte particles are obtained.
The solid electrolyte particles are subjected to, for example, uniaxial compression of 80 MPa to 120 MPa, preferably 100 MPa to 120 MPa, and heat sintering of 1300 ° C to 1450 ° C, preferably 1350 ° C to 1450 ° C. , Solid electrolyte particles are formed on the plate material of the sintered body. The plate material is made of the manufactured solid electrolyte 1 to form the main body 2.

Further, here, the above-mentioned raw material powder is prepared according to the inorganic solid electrolyte material of the reduction prevention layer 3 of the solid electrolyte 1 to be produced. For example, when the reduction prevention layer 3 contains Li ₃ BO ₃ , lithium hydroxide powder and boric acid powder are prepared as raw material powders. When the reduction prevention layer 3 contains Li ₂ B ₄ O ₇ , (lithium hydroxide) powder and (boric acid) powder are prepared as raw material powders. When the reduction prevention layer 3 contains Li ₂ CO ₃ -Li ₃ BO ₃ , (lithium carbonate) powder and (boric acid) powder are prepared as raw material powders. When the reduction prevention layer 3 contains BLiO ₂ , (lithium hydroxide) powder and (boric acid) powder are prepared as raw material powders. When the reduction prevention layer 3 contains Li ₂ O, Li ₂ O powder is prepared as a raw material powder. When the reduction prevention layer 3 contains Li ₃ PO ₄ , (lithium hydroxide) powder and (phosphoric acid) powder are prepared as raw material powders.

In the liquid preparation step for producing a slurry or a solution, the above-mentioned raw material powder is added to a liquid such as pure water to prepare a slurry or a dissolved solution in which the raw material powder is suspended in the liquid. Some of the raw material powder may dissolve in the liquid.
Here, when preparing a slurry, the raw material powder is added to the liquid at room temperature. When preparing a solution, the raw material powder is added to the liquid at room temperature to 90 ° C.

In the coating step, the slurry or solution is coated on the plate material. As illustrated in FIG. 1, when the solid electrolyte 1 in which the reduction prevention layer 3 is formed only on one surface S1 of the main body portion 2, the slurry or the solution is coated on only one surface of a plate material such as a flat plate. do.

In the coating step, it is preferable to use a spin coater from the viewpoint of uniformly coating the slurry or the solution on the plate material. A spin coater is a device that rotates a base material at a high speed to form a thin film on the base material based on the action of centrifugal force, and may also be referred to as spin coating.
When a spin coater is used, it is particularly preferable that the plate material set in the spin coater is rotated at a speed of 1000 rpm to 2000 rpm.

In the firing step, the above plate material is heated together with the slurry or solution coated on the plate material to sinter the raw material powder in the slurry or solution.
At this time, it is important to set the heating temperature to 450 ° C to 650 ° C. When the heating temperature exceeds 650 ° C, the reaction between the inorganic solid electrolyte of the plate material and the raw material powder such as Li ₃ BO ₃ in the slurry or the solution is likely to occur, and the ionic conductivity decreases at the interface between them. .. If the heating temperature is less than 450 ° C., sintering may not proceed sufficiently. From such a viewpoint, the heating temperature is preferably 450 ° C. to 650 ° C., and more preferably 470 ° C. to 600 ° C.

The time for maintaining the above temperature in the firing step is preferably 2 hours to 6 hours, more preferably 3 hours to 5 hours. If the holding time is more than 6 hours, Li in the raw material powder constituting the reduction prevention layer is splashed, so that the ionic conductivity may decrease. If the holding time is too short, the inorganic solid material of the main body and the raw material powder constituting the reduction prevention layer may not react with each other to form the reduction prevention layer.

Through the firing step, the raw material powder in the slurry is sintered on the plate material to form a layered sintered body, and the reduction prevention layer 3 of the sintered body is formed on the main body portion 2 corresponding to the plate material. Solid electrolyte 1 can be produced.

Next, since the solid electrolyte of the present invention was prototyped, it will be described below. However, the description here is for the purpose of mere illustration, and is not intended to be limited thereto.

(Example 1)
Reduction containing Li ₃ BO ₃ having a potential difference of 0 V from carbon or lithium metal on a 1 mm flat plate made of LLTO (manufactured by Toho Titanium) having a potential difference of 1.75 V mainly from carbon or lithium metal. To form the protective layer, 2 g of Li ₃ BO ₃ was crushed in a mortar and the resulting pulverized material was dispersed in 20 g of water to prepare a Li ₃ BO ₃ slurry.
Next, a plate material was set on the spin coater ACT-300A II (manufactured by Active Co., Ltd.), and the plate material was prepared with Li ₃ BO ₃ slurry in an air atmosphere (temperature 20 ° C., humidity 30%) at 0. At the same time as dropping 5 drops with a 5 g dropper, spin coating was performed under the conditions of 1000 rpm for 30 seconds, and further, spin coating was performed under the conditions of 2000 rpm for 10 seconds.
Then, it was dried in a dryer at 90 ° C. for 10 minutes.
Then, after repeating the above spin coating and drying 5 times, heat treatment was performed at 500 ° C. (heating rate: 10 ° C./min) for 4 hours.
As a result, the raw material powder in the slurry is sintered on the plate material, and a solid electrolyte (solid electrolyte of Example 1) in which Li ₃ BO ₃ which is a reduction prevention layer is formed on one surface of the main body is obtained. Was done.

<Film thickness measurement>
The thickness of the reduction prevention layer formed on the main body was 10 μm as a result of measuring the film thickness under the following measurement conditions using a Schottky field emission scanning electron microscope JSM-7900F (manufactured by JEOL Ltd.). The results are shown in Table 1.
Acceleration voltage: 10kV
Measurement distance: 10 mm
Detector: RBSD
Measurement mode: Reflected electron image Sample platinum vapor deposition: 40 seconds

<Measurement of ionic conductivity>
When the ionic conductivity of the solid electrolyte of Example 1 was measured by the method described above, the ionic conductivity was 2.7 × 10 ^-4 S / cm. The results are shown in Table 1.

<Visual evaluation of reduction resistance>
A Li foil is bonded onto the reduction prevention layer formed on the main body of the solid electrolyte of Example 1 and press-processed, and then left to stand in an air atmosphere (20 ° C., humidity 30%) for 72 hours, as described below. The reduction resistance was evaluated by visual evaluation using the evaluation criteria. The results are shown in Table 1.
<Evaluation criteria>
-No change + Slight gray coloring was observed ++ Gray coloring was observed

(Example 2)
A solution was prepared by dissolving 11.6 g of LiOH and 10 g of H ₃ BO ₃ in 125 mL of water at room temperature (20 ° C.).
A solid electrolyte in which the anti-reduction layer Li ₃ BO ₃ is formed on one surface of the main body by the same method as in Example 1 except for spin coating with the prepared solution (solid of Example 2). Electrolyte) was obtained.
Further, the film thickness measurement, the ionic conductivity measurement, and the reduction resistance were visually evaluated by the same method of Example 1.
The above results are shown in Table 1.

(Example 3)
A solution was prepared by dissolving 11.6 g of LiOH and 10 g of H ₃ BO ₃ in 125 mL of water at 90 ° C.
A solid electrolyte in which the anti-reduction layer Li ₃ BO ₃ is formed on one surface of the main body by the same method as in Example 1 except for spin coating with the prepared solution (solid of Example 3). Electrolyte) was obtained.
Further, the film thickness measurement, the ionic conductivity measurement, and the reduction resistance were visually evaluated by the same method of Example 1.
The above results are shown in Table 1.

(Comparative Example 1)
A reduction prevention layer was not formed on the flat plate mainly made of LLTO used in Example 1, and only the plate was used as a solid electrolyte (solid electrolyte of Comparative Example 1).
Further, the film thickness measurement, the ionic conductivity measurement, and the reduction resistance were visually evaluated by the same method of Example 1.
The above results are shown in Table 1.

(Comparative Example 2)
A film-shaped all-solid polymer electrolyte, which is a composite material of a polymer made of polyethylene oxide and lithium bis (trifluoromethylsulfonyl) imide, is attached onto a flat plate mainly made of LLTO used in Example 1, and the main body is attached. A solid electrolyte (solid electrolyte of Comparative Example 2) having a polymer solid electrolyte layer formed on one surface of the portion was obtained.
Further, the film thickness measurement, the ionic conductivity measurement, and the reduction resistance were visually evaluated by the same method of Example 1.
The above results are shown in Table 1.

From the results in Table 1, the solid electrolytes of Examples 1 to 3 have an ionic conductivity [S / cm] higher than 2.5 × 10 ^-4 , have very excellent battery performance, and have resistance. It was found to be excellent in reducing property. Among them, the solid electrolyte of Example 1 was found to have the best reduction resistance.
On the other hand, the solid electrolyte of Comparative Example 1 has an ionic conductivity [S / cm] lower than 2.5 × 10 ^-4 , but has a very low reduction resistance, although it does not affect the battery performance. It was bad.
Further, although the solid electrolyte of Comparative Example 2 was excellent in reduction resistance, the ionic conductivity [S / cm] was as low as 1.7 × 10 ^-4 .

1 Solid electrolyte 2 Main body 3 Reduction prevention layer Tp Reduction prevention layer thickness Tb Main body thickness S1, S2 Main body surface

Claims (6)

When the potential difference between the main body containing the oxide-based inorganic solid electrolyte material having a potential difference of 0.1 V or more from the carbon or lithium metal and the main body formed on the main body and the potential difference between the carbon or the lithium metal is less than 0.1 V. It has an anti-reduction layer containing a certain oxide-based inorganic solid electrolyte material, and has.
The inorganic solid electrolyte material of the main body contains an oxide represented by the following general formula (I).
The inorganic solid electrolyte material of the anti-reduction layer consists of a group consisting of Li ₃ BO ₃ , Li ₂ B ₄ O ₇ , Li ₂ CO ₃ − Li ₃ BO ₃ , B Li O ₂ and Li ₃ BO ₃ − Li ₂ SO ₄ . A solid electrolyte containing at least one selected .
La _{2 / 3-x} Li _3x TiO ₃ (I)
(In the formula, x satisfies 0.04 <x <0.14.) The solid electrolyte according to claim 1 , wherein the reduction prevention layer has a thickness of 1 μm to 40 μm. The solid electrolyte according to claim 1 or 2 , wherein the main body portion is plate-shaped, and the reduction prevention layer is formed on only one surface of the plate-shaped main body portion so as to cover the entire surface. An all-solid-state battery including a positive electrode, a solid electrolyte, and a negative electrode, wherein the positive electrode, the solid electrolyte, and the negative electrode are laminated in this order.
The solid electrolyte is the solid electrolyte according to any one of claims 1 to 3 , and is an all-solid-state battery in which the reduction prevention layer is interposed between the main body portion of the solid electrolyte and the negative electrode. .. A plate containing an oxide-based inorganic solid electrolyte material having a potential difference of 0.1 V or more from carbon or lithium metal, and an oxide-based inorganic solid electrolyte material having a potential difference of less than 0.1 V from carbon or lithium metal. A raw material preparation process for preparing each of the raw material powders constituting the reduction prevention layer including
A liquid preparation step for preparing a slurry or a solution containing the raw material powder,
A coating step of coating the slurry or the solution on the plate material,
A baking step of heating the plate material together with the slurry or the solution coated on the plate material at 450 ° C. to 650 ° C. for 2 hours to 6 hours is included .
The inorganic solid electrolyte material of the plate material contains an oxide represented by the following general formula (I).
The inorganic solid electrolyte material of the anti-reduction layer consists of a group consisting of Li ₃ BO ₃ , Li ₂ B ₄ O ₇ , Li ₂ CO ₃ − Li ₃ BO ₃ , B Li O ₂ and Li ₃ BO ₃ − Li ₂ SO ₄ . A method for producing a solid electrolyte, including at least one selected .
La _{2 / 3-x} Li _3x TiO ₃ (I)
(In the formula, x satisfies 0.04 <x <0.14.) The method for producing a solid electrolyte according to claim 5, wherein in the liquid preparation step, the raw material powder is added to water to prepare the slurry or the solution.

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