WO2023171635A1

WO2023171635A1 - Sulfide-based solid electrolyte powder used in lithium-ion secondary battery, method for producing same, solid electrolyte layer, and lithium-ion secondary battery

Info

Publication number: WO2023171635A1
Application number: PCT/JP2023/008432
Authority: WO
Inventors: 駿一石黒; 公章赤塚; 真弓福峯
Original assignee: Ａｇｃ株式会社
Priority date: 2022-03-10
Filing date: 2023-03-06
Publication date: 2023-09-14

Abstract

The present invention pertains to a sulfide-based solid electrolyte powder which is used in a lithium-ion secondary battery, said sulfide-based solid electrolyte powder containing particles which have an amorphous fluorine-containing layer on the surface thereof.

Description

Sulfide solid electrolyte powder used in lithium ion secondary batteries, manufacturing method thereof, solid electrolyte layer, and lithium ion secondary batteries

The present invention relates to a sulfide-based solid electrolyte powder used in a lithium ion secondary battery, a method for producing the same, a solid electrolyte layer, and a lithium ion secondary battery.

Lithium ion secondary batteries are widely used in portable electronic devices such as mobile phones and notebook computers.
In recent years, there has been a demand for smaller and lighter lithium-ion secondary batteries for portable electronic devices and vehicles, and improvements have been made to the discharge capacity per unit mass, cycle characteristics, rate characteristics, and stability as batteries. Further performance improvements are desired.

Conventionally, liquid electrolytes have been used in lithium-ion secondary batteries, but all-solid-state lithium-ion batteries use solid electrolytes as the electrolyte for lithium-ion secondary batteries because of the potential for improved safety and high-speed charging and discharging. Secondary batteries are attracting attention.

For example, Patent Document 1 discloses a solid electrolyte material containing fluorine for the purpose of suppressing the formation of a high resistance site at the interface with an electrode active material. This solid electrolyte material is obtained by adding fluoride to a raw material composition containing constituent elements and then performing an amorphization treatment.
Patent Document 2 discloses a solid electrolyte containing an alkali metal element, phosphorus, sulfur, and halogen for the purpose of being difficult to hydrolyze and having high ionic conductivity. This solid electrolyte can be obtained by a melt quenching method, a mechanical milling method, a slurry method, a solid phase method, or the like.
Patent Document 3 includes particles having a layer whose surface is fluorinated, the fluorine content on the outermost surface of the fluorinated layer is 95% by mass or more, and the fluorine content in the entire sulfide-based solid electrolyte powder is A sulfide-based solid electrolyte powder having a fluorine content of 10% by mass or less is disclosed. Patent Document 3 aims at suppressing the formation of high resistance sites at the interface between the positive electrode active material and the solid electrolyte and improving hydrolysis resistance by using the above-mentioned sulfide-based solid electrolyte powder.

Japanese Patent Application Publication No. 2010-282948 Japanese Patent Application Publication No. 2013-201110 Japanese Patent Application Publication No. 2021-86796

In

Patent Documents

1 and 2, hydrolysis resistance is improved by including halogens such as fluorine, chlorine, and bromine in the solid electrolyte, and high resistance sites are formed at the interface between the positive electrode active material and the solid electrolyte during charging and discharging. can also be suppressed. On the other hand, halogens such as fluorine, chlorine, and bromine are introduced by mechanical milling. Therefore, halogens such as fluorine, chlorine, and bromine are uniformly dispersed on the surface and inside of the solid electrolyte, and halides are also uniformly present. Adding a small amount of halogen to the entire solid electrolyte improves ionic conductivity, but adding a large amount of halogen to the entire particle, which is sufficient to improve hydrolysis resistance and suppress the formation of high-resistance sites, increases the insulating properties. Lithium halide precipitates, leading to a decrease in the ionic conductivity of the solid electrolyte. That is, there is a trade-off relationship between improving hydrolysis resistance and suppressing the formation of high resistance sites using halogens such as fluorine, chlorine, and bromine, and improving the ionic conductivity of the solid electrolyte, and it has been difficult to achieve both. Furthermore, although introducing fluorine by mechanical milling is simple, there is a limit to the amount of solid electrolyte that can be produced at one time, and productivity is low.

On the other hand, in Patent Document 3, fluorine is introduced into the surface layer of sulfide-based solid electrolyte particles to suppress the formation of high-resistance sites at the interface between the positive electrode active material and the solid electrolyte and to improve hydrolysis resistance. However, in some cases it was insufficient in terms of achieving both of these characteristics. In addition, sulfide-based solid electrolytes have a relatively narrow potential window and tend to react with positive electrode active materials and negative electrode active materials and deteriorate when used as battery materials. Therefore, in addition to improving the above characteristics, sulfide-based solid electrolytes are also required to have improved oxidation-reduction resistance.

Therefore, an object of the present invention is to provide a sulfide-based solid electrolyte powder for lithium ion secondary batteries that improves battery characteristics. Specifically, by specifically containing components different from those inside the particles at the interface of the sulfide-based solid electrolyte particles in a predetermined state, the oxidation resistance and hydrolysis resistance of the sulfide-based solid electrolyte can be improved. The purpose is to maintain the excellent ionic conductivity of the sulfide-based solid electrolyte powder itself. Thereby, performance deterioration due to side reactions during battery operation can be suppressed while maintaining relatively high lithium ion conductivity within the grains.

As a result of extensive studies, the present inventors have discovered that the above problem can be solved by specifically providing an amorphous fluorine-containing layer on the particle surface layer, and have completed the present invention.

That is, the present invention relates to the following [1] to [10].
[1] A sulfide-based solid electrolyte powder used in lithium ion secondary batteries,
The sulfide-based solid electrolyte powder includes particles having an amorphous fluorine-containing layer on the surface.
[2] The sulfide-based solid electrolyte powder according to [1], wherein the particles contain a halogen element inside the fluorine-containing layer.
[3] The sulfide-based solid electrolyte powder according to [1] above, wherein the fluorine content per surface area of the particles is 1×10 ⁻⁷ mol/m ² or more and 1×10 ⁻² mol/m ^{2 or} less.
[4] The sulfide-based solid electrolyte powder according to [1] above, wherein the fluorine content on the outermost surface of the fluorine-containing layer is 0.5% by mass or more and less than 95% by mass.
[5] The sulfide-based solid electrolyte powder according to [1] above, wherein the fluorine content in the entire sulfide-based solid electrolyte powder is 0.01% by mass or more and 50% by mass or less.
[6] The sulfide-based solid electrolyte powder according to [1] above, wherein the particles have an average particle size of 0.1 to 100 μm.
[7] The sulfide-based solid electrolyte powder according to [1] above, wherein the fluorine-containing layer has a thickness of 1 to 100 nm.
[8] A method for producing sulfide-based solid electrolyte powder containing particles having a fluorine-containing layer on the surface by contacting sulfide-based solid electrolyte particles with a gas containing elemental fluorine, the method comprising:
In the gas containing the fluorine element, the volume ratio of the component containing the fluorine element is 80% or less,
The fluorine-containing layer contains amorphous fluorine.
A method for producing sulfide-based solid electrolyte powder.
[9] A solid electrolyte layer comprising the sulfide-based solid electrolyte powder according to any one of [1] to [7] above.
[10] A lithium ion secondary battery comprising the sulfide-based solid electrolyte powder according to any one of [1] to [7] above.

According to the sulfide-based solid electrolyte powder according to the present invention, the surface of the particles contained in the powder is selectively fluorinated and contains an amorphous fluorine-containing layer on the surface, so that the sulfide-based solid electrolyte can be hydrolyzed. The resistance and oxidation resistance can be improved, and the excellent lithium ion conductivity of the sulfide-based solid electrolyte powder itself can be maintained. Thereby, the battery characteristics of the lithium ion secondary battery can be improved.

FIG. 1 is a diagram showing the results of transmission electron energy loss spectroscopy, in which (a) is a diagram showing the Li-K edge, and (b) is a diagram showing the FK edge. FIG. 2 is an enlarged view of the results near the particle surface in FIG. 1(a). FIG. 3 is a cross-sectional image (bright field image) of particles observed using a transmission electron microscope (TEM). FIG. 4 is a diagram showing the results of electron beam diffraction measurement, in which (a) is a diagram showing the measurement results for region 1, and (b) is a diagram showing the measurement results for region 2. FIG. 5 is a flowchart illustrating an example of the method for manufacturing the sulfide-based solid electrolyte powder according to the present embodiment.

The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and can be implemented with arbitrary modifications within the scope of the gist of the present invention. In addition, "~" indicating a numerical range is used to include the numerical values written before and after it as a lower limit value and an upper limit value.

<Sulfide-based solid electrolyte powder>
The sulfide-based solid electrolyte powder according to this embodiment is used in a lithium ion secondary battery. The sulfide-based solid electrolyte powder includes particles having an amorphous fluorine-containing layer on the surface. Hereinafter, the amorphous fluorine-containing layer may be simply referred to as the fluorine-containing layer.
In this specification, "the fluorine content at the outermost surface of the fluorine-containing layer" refers to the proportion of fluorine atoms contained in the elements constituting the layer at a depth of less than 10 nm from the surface of the fluorine-containing layer. That's a thing.

In this embodiment, the oxidation resistance and hydrolysis resistance of the sulfide solid electrolyte are improved by specifically containing a component different from that inside the grain in a predetermined state at the interface of the sulfide solid electrolyte particle. At the same time, the excellent ionic conductivity of the sulfide-based solid electrolyte powder itself can be maintained.

Although the reason for this is not clear, it is assumed as follows.
First, regarding the improvement of hydrolysis resistance, the surface of the particles contained in the sulfide-based solid electrolyte powder is highly fluorinated, resulting in an amorphous fluorine-containing layer. It is thought that the particle surface is stabilized by partially existing in the state of crystalline lithium fluoride. As a result, it is presumed that hydrolysis resistance is improved.

In addition, regarding the improvement of oxidation resistance, the surface of the particles contained in the sulfide-based solid electrolyte powder has an amorphous fluorine-containing layer by selectively introducing fluorine. It is thought that due to the formation of lithium chloride, the upper end of the valence band of the corresponding portion shifts to the lower energy side, thereby increasing the oxidative decomposition potential. It is presumed that this suppresses side reactions due to oxidative decomposition of the solid electrolyte at the interface with the positive electrode active material exposed to high potential.

In addition, by selectively introducing fluorine to the surface of the particles to form an amorphous fluorine-containing layer, for example, the fluorine forms amorphous lithium fluoride, and the sulfide system inside the particles It is thought that the lithium ion conductivity of the solid electrolyte is not easily impaired and can be maintained in an excellent state.

The sulfide-based solid electrolyte powder according to the present embodiment has excellent hydrolysis resistance, which improves handling properties and can suppress its deterioration. Furthermore, by having excellent oxidation resistance, deterioration when used in lithium ion batteries can be suppressed. That is, the sulfide-based solid electrolyte powder according to the present embodiment has excellent hydrolysis resistance and oxidation resistance, and can maintain excellent lithium ion conductivity inside the particles, so it can be used in lithium ion secondary batteries. It is expected that the battery characteristics will improve when the battery is used.

The sulfide-based solid electrolyte powder according to the present embodiment includes sulfide-based solid electrolyte particles having an amorphous fluorine-containing layer on the surface. The components constituting the particles, that is, the components other than those introduced by the fluorination treatment described below, are not particularly limited as long as they are sulfide-based solid electrolytes, contain sulfur (S), and have lithium ion conductivity. Those having the following can be suitably used. Specific examples of the sulfide-based solid electrolyte constituting such particles include, for example, a sulfide-based solid electrolyte containing Li, P, and S, a sulfide-based solid electrolyte containing Li, P, S, and Ha, and the like. Here, Ha represents at least one element selected from halogen elements. Specifically, Ha is, for example, at least one element selected from the group consisting of F, Cl, Br, and I. The sulfide-based solid electrolyte constituting the particles preferably contains Ha from the viewpoint of improving lithium ion conductivity. In this case, the sulfide-based solid electrolyte particles having a fluorine-containing layer on the surface contain Ha inside the fluorine-containing layer.

Among sulfide-based solid electrolytes containing Ha, sulfide-based solid electrolytes containing argyrodite-type crystals, which will be described later, are more preferred. In order to obtain an argyrodite crystal structure, Ha preferably contains at least one of Cl and Br, even more preferably contains Cl, and even more preferably Cl alone or a mixture of Cl and Br.

The sulfide-based solid electrolyte may be an amorphous sulfide-based solid electrolyte or a sulfide-based solid electrolyte with a specific crystal structure, depending on its purpose, and may have a crystalline phase and an amorphous solid electrolyte. A sulfide-based solid electrolyte containing a solid phase may also be used.

The sulfide-based solid electrolyte preferably includes a crystal structure from the viewpoint of improving lithium ion conductivity. When the sulfide-based solid electrolyte includes a crystal structure, the crystals contained in the sulfide-based solid electrolyte are preferably ion-conductive crystals. Specifically, the ion conductive crystal is a crystal whose lithium ion conductivity is preferably greater than 10 ⁻⁴ S/cm, more preferably greater than 10 ⁻³ S/cm.

More specifically, sulfide-based solid electrolytes include sulfide-based solid electrolytes containing LGPS-type crystals such as Li ₁₀ GeP ₂ S ₁₂ , and sulfide-based solids containing argyrodite-type crystals such as Li ₆ PS ₅ Cl ₁ . Examples include electrolyte, Li-P-S-Ha type crystallized glass, and LPS crystallized glass such as Li ₇ P ₃ S ₁₁ . The sulfide-based solid electrolyte may be a combination of these or may contain multiple types of crystals with different compositions and crystal structures. As the sulfide-based solid electrolyte, a sulfide-based solid electrolyte containing argyrodite-type crystals is preferable because of its excellent lithium ion conductivity.

When the sulfide-based solid electrolyte includes crystals, it is preferable that the crystal structure includes an argyrodite type from the viewpoint of symmetry of the crystal structure. Crystals with high symmetry tend to spread the lithium ion conduction path three-dimensionally, which is preferable when molding powder.

In order to have an argyrodite-type crystal structure, the crystal phase contains Ha in addition to Li, P, and S. Ha more preferably contains at least one of Cl and Br, still more preferably contains Cl, and even more preferably Cl alone or a mixture of Cl and Br.

Argyrodite-type crystals contain Li, P, S, and Ha, and have peaks at 2θ = 15.7 ± 0.5° and 30.2 ± 0.5° in the X-ray powder diffraction (XRD) pattern. It can be defined as something that has. In addition to the above, the XRD pattern preferably has a peak at 2θ = 18.0 ± 0.5°, and more preferably also at 2θ = 25.7 ± 0.5°. preferable.

The composition of the sulfide-based solid electrolyte is determined by composition analysis using, for example, ICP emission spectrometry, atomic absorption spectrometry, ion chromatography, or the like. Further, the type of crystal contained in the sulfide-based solid electrolyte can be analyzed from an X-ray powder diffraction (XRD) pattern.

The shape of the particles contained in the sulfide-based solid electrolyte powder according to the present embodiment may be primary particles, secondary particles formed by agglomeration of primary particles, or primary particles and secondary particles. It may be a combination of secondary particles. When the particle shape is a primary particle, the surface of the primary particle may be fluorinated, and when the particle shape is a secondary particle, the surface of the secondary particle formed by agglomeration of the primary particles may be fluorinated. may be In the sulfide-based solid electrolyte powder according to the present embodiment, it is preferable that the surfaces of the primary particles are fluorinated from the viewpoint of suitably obtaining the effects of the present invention.

In the sulfide-based solid electrolyte powder according to the present embodiment, the fluorine-containing layer preferably has a fluorine content of 0.5% by mass or more and less than 95% by mass, and 3% by mass or more and less than 80% by mass. % or less, more preferably 10% by mass or more and 80% by mass or less. When the content of fluorine on the outermost surface is 0.5% by mass or more, the particle surface is covered with fluoride, and stability to the positive electrode active material and atmospheric components is further improved. The content of fluorine on the outermost surface is preferably 0.5% by mass or more, more preferably 3% by mass or more, and even more preferably 10% by mass or more. In addition, the content of fluorine on the outermost surface is preferably less than 95% by mass, and is preferably 80% by mass or less, from the viewpoint of easily maintaining the excellent ion conductivity of the sulfide-based solid electrolyte powder itself by not inhibiting Li ion conduction. is more preferable.

The fluorine-containing layer contains amorphous fluorine. In other words, the amorphous fluorine-containing layer refers to a layer containing amorphous fluorine. Amorphous fluorine refers to a fluorine compound in an amorphous state, and includes, for example, amorphous lithium fluoride. When the fluorine-containing layer contains amorphous fluorine such as amorphous lithium fluoride, the relevant part becomes poorly soluble in water and chemically stable, resulting in excellent hydrolysis resistance and oxidation resistance as described above. It is presumed that sex can be obtained. Whether the fluorine-containing layer is amorphous or contains lithium fluoride can be determined, for example, by a method using electron beam diffraction measurement and transmission electron energy loss spectroscopy, which will be described later in Examples.

For example, when the fluorine-containing layer contains amorphous lithium fluoride, all of the F elements contained in the fluorine-containing layer may form amorphous lithium fluoride. may be contained in. Specifically, the F element may be incorporated into the crystal lattice or amorphous of the sulfide-based solid electrolyte by element substitution, or may react with elements other than Li to form fluoride etc. on the surface. It's okay.

The fluorine content on the outermost surface of the fluorine-containing layer is measured by the following method. That is, 10 nm from the surface of the fluorine-containing layer is determined by elemental mapping using a transmission electron microscope (TEM) or electron energy loss spectroscopy, or by depth elemental profile analysis from the particle surface to the grain interior using ESCA (X-ray photoelectron spectroscopy). Evaluate the content ratio of fluorine element and the chemical bonding state of fluorine at a depth below .

In this embodiment, the fluorine content per surface area of the particles is preferably 1×10 ⁻⁷ mol/m ² or more and 1×10 ⁻² mol/m ² or less, and 1×10 ⁻⁶ mol/m ² or more and 8×10 ^-3 mol/m ² or less is more preferable, and 1×10 ⁻⁵ mol/m ² or more and 5×10 ⁻³ mol/m ² or less is even more preferable. In this embodiment, the particle has an amorphous fluorine-containing layer on its surface. That is, when the content (content ratio) of fluorine in the entire sulfide-based solid electrolyte powder is approximately the same, the concentration of fluorine on the surface of the particles contained in the powder can also vary depending on the surface area of the particles in the powder. Therefore, the fluorine concentration on the particle surface can be evaluated based on the fluorine content per particle surface area. From the viewpoint of improving hydrolysis resistance and oxidation resistance, the fluorine content per particle surface area is preferably 1×10 ⁻⁷ mol/m ² or more, more preferably 1×10 ⁻⁶ mol/m ² or more, and 1× More preferably, it is 10 ⁻⁵ mol/m ² or more. The fluorine content per particle surface area is preferably 1×10 ⁻² mol/m ² or less, more preferably 8×10 ⁻³ mol/m ² or less from the viewpoint of maintaining the excellent Li ion conductivity inherent in the sulfide solid electrolyte. It is preferably 5×10 ⁻³ mol/m ² or less, and more preferably 5×10 −3 mol/m 2 or less. The fluorine content per surface area of particles is determined by measuring the fluorine content (mol/g) of the powder using a fluoride ion composite electrode, and converting this to the specific surface area (m ² /g) of the powder obtained by BET measurement. ) is calculated by dividing by

The fluorine content in the entire sulfide-based solid electrolyte powder according to this embodiment is preferably 50% by mass or less. In a powder containing particles having a fluorine-containing layer on the surface, the smaller the fluorine content in the entire powder, the relatively smaller the amount of fluorine present inside the particles tends to be. This can reduce the decrease in lithium ion conductivity caused by deterioration of crystallinity or excessive presence of low ion conductivity components. The fluorine content in the entire sulfide-based solid electrolyte powder is more preferably 40% by mass or less, and more preferably 30% by mass or less. Further, the fluorine content in the entire powder is preferably 0.01% by mass or more in order to form a fluorine-containing layer on the surface of the particles, more preferably 0.1% by mass or more, and 0.5% by mass or more. is even more preferable. That is, the fluorine content in the entire sulfide-based solid electrolyte powder is preferably 0.01% by mass to 50% by mass, more preferably 0.1% to 40% by mass, and even more preferably 0.5% to 30% by mass. preferable.
Note that the fluorine content in the entire sulfide-based solid electrolyte powder is determined from the results of analysis using a fluoride ion composite electrode as described in Examples below.

The thickness of the fluorine-containing layer is preferably 1 nm or more, more preferably 1.25 nm or more, even more preferably 1.5 nm or more, and even more preferably 2 nm or more, from the viewpoint of making the effects of the present invention more sufficient. Further, the thickness of the fluorine-containing layer is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less, from the viewpoint of suppressing a decrease in lithium ion conductivity. That is, the thickness of the fluorine-containing layer is preferably 1 nm to 100 nm, more preferably 1.25 nm to 50 nm, even more preferably 1.5 nm to 30 nm, even more preferably 2 nm to 30 nm.
Note that the thickness of the fluorine-containing layer is determined by analysis such as X-ray photoelectron spectroscopy, elemental mapping from a particle cross section, and electron energy loss spectroscopy.
Further, evaluation of the crystallinity of the entire particle is obtained by analysis such as X-ray diffraction and TEM electron beam diffraction.

The average particle diameter of the particles having a fluorine-containing layer is preferably 0.1 μm or more, more preferably 0.5 μm or more from the viewpoint of improving handleability. Further, from the viewpoint of ease of movement of lithium ions, the average particle diameter is preferably 100 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. That is, the average particle size of particles having a fluorine-containing layer is preferably 0.1 μm to 100 μm, more preferably 0.5 μm to 20 μm, and even more preferably 0.5 μm to 10 μm. The average particle size of particles with a fluorine-containing layer can be reduced, for example, by grinding the particles before fluorination. Alternatively, particles within a specific particle size range may be selected by classification. Classification may be performed before or after fluorinating the particles.
Note that the average particle size of particles having a fluorine-containing layer on the surface includes the thickness of the fluorine-containing layer, and is determined by a particle size distribution measuring device. As the average particle diameter, a D50 average particle diameter (median diameter: particle diameter at which the cumulative frequency is 50%) can be adopted.
Specifically, sulfide-based solid electrolyte powder is placed in a non-aqueous solvent, sufficiently dispersed by ultrasonication, and the particles are measured using a laser diffraction/scattering particle size distribution measuring device. A volume-based particle size distribution is obtained by obtaining a frequency distribution and a cumulative volume distribution curve, and the particle size at a point of 50% on the cumulative volume distribution curve is defined as the D50 average particle size.

The oxidation potential of the sulfide-based solid electrolyte powder is evaluated, for example, by cyclic voltammetry (CV) measurement using a potentiogalvanostat. As the electrochemical cell used for the measurement, for example, an all-solid-state cell using stainless steel foil as the working electrode, the sulfide-based solid electrolyte to be evaluated as the solid electrolyte layer, and Li metal foil as the counter electrode and reference electrode is used. Can be mentioned. It is preferable to insert a mixture of electron conductor powder such as carbon powder and solid electrolyte powder between the working electrode and the solid electrolyte layer. This is to make it easier to measure minute oxidation currents in CV measurements by increasing the effective electrode area, and this is because the interface between the electron conductor powder and the solid electrolyte powder becomes a substantial working electrode surface. Moreover, carbon powder with a large specific surface area, such as acetylene black, is particularly preferable as the electron conductor powder because of the effect of increasing the effective working electrode area. Although this section specifically described an example of the oxidation potential evaluation method, the evaluation method is not limited to the above.

The hydrolysis resistance (water resistance) of the above sulfide-based solid electrolyte powder can be evaluated, for example, by exposing the sulfide-based solid electrolyte powder to a gas atmosphere with controlled humidity for a certain period of time and measuring the amount of hydrogen sulfide gas generated. Implemented. Examples of the gas species used include air, nitrogen, argon, etc., and from the viewpoint of evaluating only the reactivity with water, inert gases such as nitrogen and argon are preferred. In addition, the humidity of the gas may be adjusted by using a cylinder gas whose humidity has been adjusted in advance, or by mixing dry gas and gas moistened by bubbling in water in any ratio. , a desired moisture concentration gas may be obtained. In addition, the method of exposing sulfide-based solid electrolyte powder to gas may be to seal it in a container with a certain volume and measure the hydrogen sulfide concentration inside the container after a certain period of time has passed, or to expose the powder to gas at a constant flow rate. You can apply the gas with a flow and monitor the hydrogen sulfide concentration in the gas that comes out at any time. A gas flow method is preferable from the viewpoints of checking changes in the amount of hydrogen sulfide generated with respect to exposure time and of not changing the humidity of the exposure atmosphere even if it reacts with moisture. By these methods, it is possible to measure the amount and rate of generation of hydrogen sulfide in a constant humidity atmosphere, and it is possible to evaluate the resistance to decomposition of a sulfide-based solid electrolyte due to contact with water, that is, its water resistance. Although this section specifically described an example of a water resistance evaluation method, the evaluation method is not limited to the above.

The lithium ion conductivity of the sulfide-based solid electrolyte powder is not particularly limited as it varies depending on its composition, etc., but from the viewpoint of improving battery characteristics when used in a lithium ion secondary battery, it is 0.5 at 25°C. It is preferably at least ×10 ⁻³ S/cm, more preferably at least 1.0×10 ⁻³ S/cm, and even more preferably at least 2.0×10 ⁻³ S/cm. Lithium ion conductivity can be measured by the AC impedance method described later in Examples.

<Method for manufacturing sulfide solid electrolyte powder>
The method for producing the sulfide-based solid electrolyte powder according to the present embodiment is not particularly limited, but for example, as shown in FIG. ) is a method for producing a sulfide-based solid electrolyte powder containing particles having a fluorine-containing layer on the surface according to the above embodiment. In this method, the fluorine-containing layer according to the above embodiment is formed by appropriately adjusting the volume ratio of the component containing the fluorine element in the gas containing the fluorine element, the partial pressure of the gas containing the fluorine element, the temperature, and the contact time. Sulfide-based solid electrolyte powder can be produced. The fluorine-containing layer contains amorphous fluorine.

The fluorinable gas is a gas containing elemental fluorine, and more specifically, a gas containing a component containing elemental fluorine. Examples of the component containing elemental fluorine include fluorine gas (F ₂ gas), hydrogen fluoride gas (HF gas), BF ₃ gas, NF ₃ gas, PF ₅ gas, SiF ₄ gas, SF ₆ gas, and the like. In a gas containing elemental fluorine, in order to keep the volume ratio of the component containing elemental fluorine to 80% or less, it is possible to use a mixed gas of an inert gas such as nitrogen gas or argon gas and the above-mentioned component containing elemental fluorine. preferable. The fluorine-containing layer in this embodiment may contain these gas constituents as impurities as long as the effects of the present invention are not impaired.

Among the components containing the fluorine element, fluorine gas (F ₂ gas) or hydrogen fluoride gas (HF gas) is preferable because it does not contain other elements in the sense that only fluorine is reacted. When a fluorine-containing layer is formed by contacting the particles with _F2 gas or HF gas, the surface of the sulfide-based solid electrolyte particles contains only fluorine atoms or hydrogen atoms. By confirming the elements, it can be determined that a fluorine-containing layer was formed due to contact with such gas. Further, the fact that the fluorine-containing layer is amorphous and the chemical bonding state of fluorine can be confirmed by the method described above. In particular, from the viewpoint of easily forming the fluorine-containing layer efficiently, fluorine gas is preferable as the component containing elemental fluorine.

In the gas containing elemental fluorine, the volume percentage of the component containing elemental fluorine is 80% or less. This is preferable because it makes it easier to control the reaction with the sulfide-based solid electrolyte. The volume ratio of the component containing elemental fluorine is preferably 50% or less, more preferably 20% or less. On the other hand, the volume percentage of the component containing elemental fluorine is more than 0%, and from the viewpoint of promoting reaction and economics, it is preferably 0.01% or more, and more preferably 0.1% or more. That is, the volume percentage of the component containing elemental fluorine is more than 0% to 80%, preferably 0.01% to 50%, and more preferably 0.1% to 20%.

The time for contacting the particles of the sulfide-based solid electrolyte with the gas containing elemental fluorine is preferably 10 seconds or more, more preferably 1 minute or more, and preferably 240 minutes or less, and more preferably 150 minutes or less. By setting it within this range, a fluorine-containing layer with a controlled concentration can be formed on the surface of the particles with high precision. That is, the time for contacting the particles of the sulfide-based solid electrolyte with the gas containing elemental fluorine is preferably 10 seconds to 240 minutes, more preferably 1 minute to 150 minutes.

It is preferable to control the temperature when bringing the particles of the sulfide-based solid electrolyte into contact with the gas containing elemental fluorine, and the temperature range is preferably in the range of -50 to 600°C. When it is desired to increase the fluorine concentration on the particle surface, it is also preferable to increase the reactivity between the particle surface and fluorine by increasing the temperature. Thereby, the fluorine-containing layer can be formed reliably and efficiently.

When bringing particles into contact with a gas containing elemental fluorine, it is preferable to control the fluorine partial pressure from the viewpoint of controlling the reaction, and it is preferable to carry out the process while controlling the pressure inside the reactor. When controlling by pressure, specifically, the pressure is preferably 1.0 MPa (gauge pressure) or less, and more preferably 0.5 MPa (gauge pressure) or less. On the other hand, from the viewpoint of promoting the reaction, the pressure is preferably -0.1 MPa (gauge pressure) or higher, more preferably -0.098 MPa (gauge pressure) or higher. That is, the pressure is preferably -0.1 to 1.0 MPa, more preferably -0.098 to 0.5 MPa.

In this embodiment, when the particles are brought into contact with the gas containing elemental fluorine, it is preferable that the gas containing elemental fluorine is brought into contact with the particles in an atmosphere in which the partial pressure of the component containing elemental fluorine is 0.1 MPa or less. . The present inventors have successfully controlled the amount and state of fluorine introduced at the outermost surface of the resulting particles by appropriately controlling the partial pressure of the component containing the fluorine element when it comes into contact with the gas containing the fluorine element. I found out what I can do. The partial pressure of the component containing elemental fluorine is preferably 0.1 MPa or less, more preferably 0.05 MPa or less, and even more preferably 0.02 MPa or less, from the viewpoint of suppressing excessive reaction. On the other hand, such partial pressure is preferably 0.01 kPa or more, more preferably 0.1 kPa or more, and even more preferably 0.5 kPa or more from the viewpoint of promoting the reaction. That is, the partial pressure is preferably 0.01 kPa to 0.1 MPa, more preferably 0.1 kPa to 0.05 MPa, and even more preferably 0.5 kPa to 0.02 MPa. Note that the fluorine partial pressure refers to a value determined by (volume ratio of a fluorine-containing component in a fluorine-containing gas) x (pressure at the time of contact between particles and a fluorine-containing gas). Furthermore, in the case of a batch reaction, it refers to the value at the time of charging, and in the case where the gas containing the fluorine element is continuously supplied, it refers to the value at the time of supply.

The contact between the particles and the gas containing elemental fluorine is preferably carried out by a flow method or a batch method.
In the case of the flow type, the particles are placed in a stationary state in a reaction vessel, and a gas containing fluorine at a predetermined concentration is continuously supplied into the open type reaction vessel to mix the particles and the gas containing fluorine. A method of contact is preferred.
In the case of a batch method, it is preferable to house the particles in a sealed reaction vessel with a gas atmosphere containing elemental fluorine at a predetermined concentration, and to bring the particles into contact with the gas containing elemental fluorine.

In the case of a flow-through method, from the viewpoint of uniformly contacting the particles with a gas containing the fluorine element, a reactor equipped with a fluidized bed in which the particles are placed and fluidized, or a kiln such as a tube furnace can also be used. It is particularly preferable to use a fluidized bed because it can shorten the fluorination treatment time, suppress excessive fluorination, and achieve more uniform fluorination.
When carried out in a batch manner, it can also be carried out while stirring and mixing the particles in order to uniformly contact the gas containing the fluorine element to the particles.

<Solid electrolyte layer>
The solid electrolyte layer according to this embodiment includes the sulfide-based solid electrolyte powder and is used in a lithium ion secondary battery. Further, the solid electrolyte layer may further contain additives such as a binder, if necessary.
The content of the sulfide-based solid electrolyte powder in the solid electrolyte layer is not particularly limited, and may be appropriately determined depending on the intended performance of the battery. For example, the content of the sulfide-based solid electrolyte powder is preferably 80% by mass or more, more preferably 90% by mass or more with respect to the entire sulfide-based solid electrolyte layer.

Examples of the binder that can be contained in the solid electrolyte layer include butadiene rubber (BR), acrylate butadiene rubber (ABR), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and the like. It will be done. The content of the binder in the solid electrolyte layer may be the same as the conventional one.

The thickness of the solid electrolyte layer is not particularly limited, and may be appropriately determined depending on the intended performance of the battery. For example, the thickness is preferably 10 μm or more, more preferably 15 μm or more. By setting the thickness of the solid electrolyte layer to 10 μm or more, it is possible to obtain a solid electrolyte layer that has increased mechanical strength, is resistant to stress such as vibration and bending, and has high reliability.
Moreover, the thickness of the solid electrolyte layer is preferably 1000 μm or less, more preferably 200 μm or less. By setting the thickness of the solid electrolyte layer to 1000 μm or less, the ionic conductivity between the positive and negative electrodes can be increased, and the energy density of the battery can also be increased.
That is, the thickness of the solid electrolyte layer is preferably 10 to 1000 μm, more preferably 15 to 200 μm.

The method of forming the solid electrolyte layer is not particularly limited. For example, the solid electrolyte layer can be formed by dispersing or dissolving the components constituting the solid electrolyte layer described above in a solvent to form a slurry, coating it in a layered form (sheet form), drying it, and optionally pressing it. If necessary, heat may be applied to remove the binder. By adjusting the coating amount of the slurry, etc., the thickness of the solid electrolyte layer can be easily adjusted.
In addition, instead of the wet molding as described above, the solid electrolyte layer may be formed by dry press molding a solid electrolyte powder or the like on the surface of the object (positive electrode, negative electrode, etc.) on which the solid electrolyte layer is to be formed. Alternatively, the solid electrolyte layer may be formed on another base material and transferred onto the surface of the object on which the solid electrolyte layer is to be formed. From the viewpoint of industrially and stably forming a strong solid electrolyte layer on the surface of the object on which the solid electrolyte layer is to be formed, it is preferable to form the solid electrolyte layer on the surface of the object by wet molding using a solvent. .

<Lithium ion secondary battery>
The lithium ion secondary battery according to this embodiment includes the sulfide-based solid electrolyte powder according to this embodiment. Such a lithium ion secondary battery includes, for example, the solid electrolyte layer, a positive electrode, and a negative electrode, but is not limited to the exemplified form. Conventionally known positive electrodes and negative electrodes are used. Specific examples are shown below, but the invention is not limited to these.

(positive electrode)
The positive electrode contains at least a positive electrode current collector and a positive electrode active material.

The positive electrode current collector may be any conductive plate material, and for example, a thin metal plate (metal foil) such as aluminum or an alloy thereof, or stainless steel can be used. These are preferable because they have excellent electrolyte resistance and oxidation resistance.

The positive electrode active material can reversibly absorb and release lithium ions, desorb and insert (intercalate) lithium ions, or dope and dedope counter anions (for example, PF ₆ ^- ) of lithium ions. There is no particular limitation as long as it is allowed to proceed, and any known positive electrode active material can be used. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), lithium nickel manganate, and Li( _Nix Co _y Mn _z M _a )O. ₂ (x+y+z+a=1, 0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦a≦1, M is selected from Al, Mg, Nb, Ti, Cu, Zn and Cr Li _a M _b (PO ₄ ) c (1≦a≦4, 1≦b≦2, 1≦c≦3, where M is Fe, V, Co , Mn, Ni, and VO), and the like.

The positive electrode may include a binder that binds the positive electrode active materials together and also binds the positive electrode active material and the positive electrode current collector. As the binder, conventionally known binders can be used.
Further, the positive electrode may include a known conductive additive for positive electrodes, such as carbon-based materials such as graphite and carbon black, metals such as copper, nickel, stainless steel, and iron, indium tin oxide (ITO), etc. conductive oxides.
In addition to the above, from the viewpoint of lithium ion conductivity, the positive electrode may contain the above-mentioned sulfide-based solid electrolyte powder in addition to the above-mentioned positive electrode active material.

(Negative electrode)
The negative electrode contains at least a negative electrode current collector and a negative electrode active material.

The negative electrode current collector may be any conductive plate material, for example, a thin metal plate (metal foil) made of copper, aluminum, or the like. These are preferable because they have excellent electrolyte resistance and oxidation resistance.

The negative electrode active material is not particularly limited, and any material capable of intercalating and deintercalating lithium ions may be used. For example, lithium metal, carbon-based materials, silicon, silicon alloys, tin, etc. can be used.
The negative electrode active material can reversibly absorb and release lithium ions, desorb and insert (intercalate) lithium ions, or dope and dedope counter anions (for example, PF ₆ ^- ) of the lithium ions. There are no particular limitations as long as the process can proceed, and any known negative electrode active material can be used. Examples of the negative electrode active material include carbon-based materials such as graphite, hard carbon, and soft carbon, metals that can form alloys with lithium such as aluminum, silicon, and tin, and amorphous materials such as silicon oxide and tin oxide. , lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and the like.

In addition, the negative electrode may include a binder that binds the negative electrode active materials together and also binds the negative electrode active material and the negative electrode current collector. As the binder, conventionally known binders can be used.
Further, the negative electrode may include a known conductive additive for negative electrodes, and the same conductive additive as the above-mentioned conductive additive for positive electrodes can be used.
In addition to the above, from the viewpoint of lithium ion conductivity, the negative electrode may contain the above-mentioned sulfide-based solid electrolyte powder in addition to the above-mentioned negative electrode active material.

The components of the lithium ion secondary battery, such as the solid electrolyte layer, positive electrode, and negative electrode, are stored in the battery exterior. Conventionally known materials can be used for the battery exterior, and specific examples include nickel-plated iron, stainless steel, aluminum or alloys thereof, nickel, titanium, resin materials, film materials, and the like.

The shape of the lithium ion secondary battery includes a coin shape, a sheet shape (film shape), a folded shape, a wound type bottomed cylindrical shape, a button shape, etc., and can be appropriately selected depending on the purpose.

According to the lithium ion secondary battery according to the present embodiment, the contained sulfide-based solid electrolyte powder has excellent hydrolysis resistance and oxidation resistance, and maintains excellent ionic conductivity, resulting in good battery characteristics. can be realized.

The present invention will be specifically described below with reference to Examples, but the present invention is not limited thereto. Examples 1 to 5 are examples, and example 6 is a comparative example.

[Example 1 Fluorinated sulfide solid electrolyte powder]
0.500 g of sulfide-based solid electrolyte powder (Li ₆ PS ₅ Cl, manufactured by Ampcera) containing argyrodite-type crystals was placed in a Hastelloy reactor having an internal volume of 0.3 L. Note that the average particle diameter (D50) of the sulfide-based solid electrolyte powder used was 2.9 μm. Although this average particle diameter is the value before the fluorination treatment, it has been confirmed through scanning electron microscopy and the like that the average particle diameter hardly changes before and after the fluorination treatment of this example. Using a mixed gas of N ₂ gas and F ₂ gas containing 20% by volume of F 2 gas, _the pressure inside the container was -0.095 MPa (gauge pressure) and the partial pressure of the component containing the fluorine element (F ₂ gas) was reduced to 0. Fluorination treatment was performed by contacting the particles with a mixed gas at .001 MPa and room temperature for 30 minutes to obtain a sulfide-based solid electrolyte powder containing argyrodite-type crystals and having an amorphous fluorine-containing layer on the particle surface. .

[Example 2 Fluorinated sulfide solid electrolyte powder]
The process was carried out in the same manner as in Example 1, except that the pressure in the reactor was -0.098 MPa (gauge pressure) and the partial pressure of the component containing elemental fluorine was 0.0004 MPa, and an amorphous fluorine-containing layer was formed on the particle surface. A sulfide-based solid electrolyte powder containing argyrodite-type crystals was obtained.

[Example 3 Fluorinated sulfide solid electrolyte powder]
The process was carried out in the same manner as in Example 1, except that the pressure in the reactor was -0.099 MPa (gauge pressure) and the partial pressure of the component containing elemental fluorine was 0.0002 MPa, and an amorphous fluorine-containing layer was formed on the particle surface. A sulfide-based solid electrolyte powder containing argyrodite-type crystals was obtained.

[Example 4 Fluorinated sulfide solid electrolyte powder]
The process was carried out in the same manner as in Example 1, except that the pressure in the reactor was -0.085 MPa (gauge pressure) and the partial pressure of the component containing elemental fluorine was 0.003 MPa, and an amorphous fluorine-containing layer was formed on the particle surface. A sulfide-based solid electrolyte powder containing argyrodite-type crystals was obtained.

[Example 5 Fluorinated sulfide solid electrolyte powder]
The process was carried out in the same manner as in Example 1, except that the pressure in the reactor was -0.055 MPa (gauge pressure) and the partial pressure of the component containing elemental fluorine was 0.009 MPa, and an amorphous fluorine-containing layer was formed on the particle surface. A sulfide-based solid electrolyte powder containing argyrodite-type crystals was obtained.

[Example 6 Fluorinated untreated sulfide solid electrolyte powder]
A sulfide-based solid electrolyte powder containing argyrodite-type crystals similar to that in Example 1 was used as it was without fluorination treatment.

[evaluation]
The sulfide-based solid electrolyte powder obtained above was evaluated as follows.
(Fluorine content on the outermost surface)
As X-ray photoelectron spectroscopy, the abundance ratio of each element on the outermost surface of the particle (depth less than 10 nm from the surface) was quantitatively analyzed using PHI VersaProbe III (trade name) manufactured by ULVAC-PHI. The results are shown in Table 1.

(Depth profile and electron diffraction measurement of fluorine content)
After cutting the particles using a cryoplasma focused ion beam processing device (Helios G4 PFIB CXe, manufactured by Thermo Scientific) to expose the cross section, using a transmission electron microscope (JEM-F200, manufactured by JEOL Ltd.), Cross-sectional observations, electron beam diffraction measurements, and transmission electron energy loss spectroscopy measurements were performed.

1 to 4 are diagrams showing the results of the above measurements on the sulfide-based solid electrolyte powder obtained in Example 1, respectively. FIG. 1 is a diagram showing the results of transmission electron energy loss spectrometry, in which (a) is a diagram showing the Li-K edge, and (b) is a diagram showing the FK edge. FIG. 2 is an enlarged view of the results near the particle surface in FIG. 1(a).

In FIGS. 1 and 2, graphs with the horizontal axis representing loss energy (eV) and the vertical axis representing intensity are shown for each distance (depth) from the particle surface. From the results shown in Figures 1 and 2, Li exists regardless of the distance from the particle surface, but the chemical bond state changes specifically near the surface, and F exists only near the particle surface. I can see that there is. That is, it was confirmed that in the sulfide-based solid electrolyte powder obtained in Example 1, F was introduced to a depth of 10 nm from the surface, causing Li-F bonds (ACS Nano, 5 (2), 2011 , 1190).

FIG. 3 is a cross-sectional observation image (bright field image) using a transmission electron microscope (TEM). In FIG. 3, region 1 corresponds to the center of the particle, and region 2 corresponds to the vicinity of the particle surface. FIG. 4 is a diagram showing the results of electron diffraction measurement, in which (a) is a diagram showing the measurement results for region 1, and (b) is a diagram showing the measurement results for region 2. In FIG. 4, the diffraction patterns whose indices are indicated only by numbers are derived from the argyrodite-type crystals constituting the particles. Moreover, the diffraction patterns shown next to the numbers as Li ₂ O or LiOH are derived from Li ₂ O or LiOH, respectively. That is, from the electron diffraction results shown in FIG. 4, it can be seen that no crystalline LiF was observed near the center or near the surface of the particle. From these results, it can be inferred that amorphous LiF is contained in the fluorine-containing layer on the particle surface. That is, from these results, it was confirmed that the sulfide-based solid electrolyte obtained in Example 1 contained particles having an amorphous fluorine-containing layer on the surface. In addition, in Examples 2 to 5, the fluorination treatment was performed under the same conditions as in Example 1, except that the partial pressure of the component containing the fluorine element was different by adjusting the pressure inside the reactor. Therefore, in these examples, although the fluorine content per surface area of the particles is different from each other as shown later, it is considered that they are the same as Example 1 in that an amorphous fluorine-containing layer is formed on the particle surface. .

(Fluorine content in the entire sulfide solid electrolyte powder)
After performing alkali extraction treatment on the sulfide-based solid electrolyte powder of each example, a fluoride ion composite electrode (manufactured by DKK Toa Corporation, F-2021) was used to detect the fluorine content in the sulfide-based solid electrolyte powder. The amount was quantitatively analyzed. The results are shown in Table 2.

(Fluorine content per particle surface area)
The specific surface area (m ² /g) of the sulfide-based solid electrolyte powder of each example was measured by the krypton adsorption BET multipoint method (device: Micromeritics, pore distribution measuring device ASAP-2020). The fluorine content per particle surface area ( ^mol /m ² ) was calculated. The results are shown in Tables 2 and 3.

(Hydrolysis resistance)
The sulfide-based solid electrolyte powder was exposed to a humidified N ₂ atmosphere with a dew point of -30°C, and hydrolysis resistance was evaluated by detecting changes over time in the amount of hydrogen sulfide generated and the total amount generated. 10 mg of each sample was weighed out, placed in a sample tube, and humidified N ₂ gas was passed through it. The total amount of hydrogen sulfide generated was calculated by monitoring the hydrogen sulfide concentration in the flowing gas until hydrogen sulfide generation stopped. As the detection tube, a hydrogen sulfide concentration meter (Model 3000RS, manufactured by Techne Keizoku Co., Ltd.) was used. Table 2 shows the results of the hydrolysis resistance test for each example. However, an example where the column "Hydrogen sulfide generation amount" is blank means that it has not been evaluated. Note that it can be said that the smaller the amount of H ₂ S generated, the better the hydrolysis resistance.

From the above results, it was confirmed that the fluorinated sulfide-based solid electrolyte powders of Examples 1 and 5 had improved hydrolysis resistance compared to the sulfide-based solid electrolyte powder of Example 6. This result is presumed to be because the particle surface was fluorinated and the fluorine-containing layer contained amorphous lithium fluoride, which improved the surface stability of the sulfide-based solid electrolyte powder.

(Measurement of lithium ion conductivity)
Lithium ion conductivity was measured using the AC impedance method.
The lithium ion conductivity was measured using a potentiogalvanostat VSP manufactured by Bio-Logic. For the measurement, 100 mg of powder was placed in a compact powder conductivity measurement jig consisting of an insulating die and a pair of electrode plates, and a pressure of 30 kN was applied to compact the powder into a pellet, and the applied voltage was 100 mV. The measurement was conducted at a temperature of 25° C. and a measurement frequency range of 1 MHz to 1 mHz. By analyzing the Nyquist plot obtained by AC impedance measurement, the movement resistance of Li ions was determined, and the Li ion conductivity was calculated from the area and thickness of the pellet sample used for measurement. Note that the measured value was the average value of a total of three measurements.

(oxidation resistance evaluation)
Oxidation resistance was evaluated by potential window measurement using cyclic voltammetry (CV).
225 mg of sulfide-based solid electrolyte powder was used as the solid electrolyte layer, a composite material consisting of sulfide-based solid electrolyte powder and carbon black mixed at a weight ratio of 3:1 was used as the working electrode, and Li metal was used as the counter electrode, for potential window measurement. An electrochemical cell was created (Chem. Mater. 2019, 31, 707-713). For CV measurement, a potentiogalvanostat VSP manufactured by Bio-Logic was used, and the measurement was performed five times in the range of 2.5-5V at a potential sweep rate of 0.1 mV/s. Multiple peaks are confirmed in the first sweep, and a single peak is confirmed in the high potential region from the second sweep onward. Regarding the peak that appeared after the second round, the oxidation start potential was calculated by differentiating the current value with respect to the potential. The results are shown in Table 3.

From the results in Table 3, in Examples 1 to 5, the oxidation start potential was 0.2 V or more higher than in Example 6, which was a significant improvement, and a large improvement in oxidation resistance was confirmed.

As explained above, the following matters are disclosed in this specification.
[1] A sulfide-based solid electrolyte powder used in lithium ion secondary batteries,
The sulfide-based solid electrolyte powder includes particles having an amorphous fluorine-containing layer on the surface.
[2] The sulfide-based solid electrolyte powder according to [1], wherein the particles contain a halogen element inside the fluorine-containing layer.
[3] The sulfide system according to [1] or [2] above, wherein the fluorine content per surface area of the particles is 1 x 10 ^-7 mol/m ² or more and 1 x 10 ^-2 mol/m ² or less. Solid electrolyte powder.
[4] The sulfide-based solid electrolyte powder according to any one of [1] to [3] above, wherein the fluorine content on the outermost surface of the fluorine-containing layer is 0.5% by mass or more and less than 95% by mass. .
[5] The sulfide-based solid electrolyte according to any one of [1] to [4] above, wherein the fluorine content in the entire sulfide-based solid electrolyte powder is 0.01% by mass or more and 50% by mass or less. powder.
[6] The sulfide-based solid electrolyte powder according to any one of [1] to [5] above, wherein the particles have an average particle size of 0.1 to 100 μm.
[7] The sulfide-based solid electrolyte powder according to any one of [1] to [6] above, wherein the fluorine-containing layer has a thickness of 1 to 100 nm.
[8] A method for producing sulfide-based solid electrolyte powder containing particles having a fluorine-containing layer on the surface by contacting sulfide-based solid electrolyte particles with a gas containing elemental fluorine, the method comprising:
In the gas containing the fluorine element, the volume ratio of the component containing the fluorine element is 80% or less,
The fluorine-containing layer contains amorphous fluorine.
A method for producing sulfide-based solid electrolyte powder.
[9] A solid electrolyte layer comprising the sulfide-based solid electrolyte powder according to any one of [1] to [7] above.
[10] A lithium ion secondary battery comprising the sulfide-based solid electrolyte powder according to any one of [1] to [7] above.

Although the invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application (Japanese Patent Application No. 2022-037222) filed on March 10, 2022, the contents of which are incorporated herein by reference.

Claims

A sulfide-based solid electrolyte powder used in lithium ion secondary batteries,
The sulfide-based solid electrolyte powder includes particles having an amorphous fluorine-containing layer on the surface.
The sulfide-based solid electrolyte powder according to claim 1, wherein the particles contain a halogen element inside the fluorine-containing layer.
The sulfide-based solid electrolyte powder according to claim 1, wherein the fluorine content per surface area of the particles is 1×10 −7 mol/m 2 or more and 1×10 −2 mol/m 2 or less.
The sulfide-based solid electrolyte powder according to claim 1, wherein the fluorine content on the outermost surface of the fluorine-containing layer is 0.5% by mass or more and less than 95% by mass.
The sulfide-based solid electrolyte powder according to claim 1, wherein the fluorine content in the entire sulfide-based solid electrolyte powder is 0.01% by mass or more and 50% by mass or less.
The sulfide-based solid electrolyte powder according to claim 1, wherein the particles have an average particle size of 0.1 to 100 μm.
The sulfide-based solid electrolyte powder according to claim 1, wherein the fluorine-containing layer has a thickness of 1 to 100 nm.
A method for producing sulfide-based solid electrolyte powder containing particles having a fluorine-containing layer on the surface by contacting sulfide-based solid electrolyte particles with a gas containing elemental fluorine, the method comprising:
In the gas containing the fluorine element, the volume ratio of the component containing the fluorine element is 80% or less,
The fluorine-containing layer contains amorphous fluorine.
A method for producing sulfide-based solid electrolyte powder.
A solid electrolyte layer comprising the sulfide-based solid electrolyte powder according to any one of claims 1 to 7.
A lithium ion secondary battery comprising the sulfide solid electrolyte powder according to any one of claims 1 to 7.