JP7546111B2 - Sulfide-based inorganic solid electrolyte material, solid electrolyte, solid electrolyte membrane and lithium-ion battery - Google Patents

Description

The present invention relates to a sulfide-based inorganic solid electrolyte material, a solid electrolyte, a solid electrolyte membrane, and a lithium-ion battery.

Lithium-ion batteries are commonly used as power sources for small portable devices such as mobile phones and laptops. Recently, lithium-ion batteries have also begun to be used as power sources for electric vehicles and power storage devices in addition to small portable devices.

Currently commercially available lithium-ion batteries use electrolytes that contain flammable organic solvents. On the other hand, lithium-ion batteries that use a solid electrolyte to create an all-solid-state battery (hereafter referred to as all-solid-state lithium-ion batteries) do not use flammable organic solvents in the battery, which allows for simplified safety devices and is thought to have superior manufacturing costs and productivity.

For example, sulfide-based inorganic solid electrolyte materials are known as solid electrolyte materials used for such solid electrolytes.

Patent Document 1 (JP 2016-27545 A) describes a sulfide-based solid electrolyte material that has a peak at 2θ=29.86°±1.00° in X-ray diffraction measurement using CuKα radiation and has a composition of Li _2y+3 PS ₄ (0.1≦y≦0.175).

JP 2016-27545 A

According to the studies of the present inventors, it has become clear that when a sulfide-based inorganic solid electrolyte material is exposed to the air, the lithium ion conductivity may gradually decrease in some cases.
That is, there is room for improvement in conventional sulfide-based inorganic solid electrolyte materials in terms of suppressing the decrease in lithium ion conductivity when exposed to the air.

The present invention has been made in consideration of the above circumstances, and provides a sulfide-based inorganic solid electrolyte material that can suppress the decrease in lithium ion conductivity when exposed to the air.

In order to provide a sulfide-based inorganic solid electrolyte material capable of suppressing the decrease in lithium ion conductivity when exposed to air, the present inventors have conducted extensive research into the X-ray diffraction profile of a sulfide-based inorganic solid electrolyte material. As a result, they have found that a sulfide-based inorganic solid electrolyte material having diffraction peaks at diffraction angles 2θ = 17.2 ± 0.5° and 2θ = 18.8 ± 0.4° in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source, and these diffraction peaks have a specific relationship, can suppress the decrease in lithium ion conductivity when exposed to air, leading to the present invention.

That is, according to the present invention,
A sulfide-based inorganic solid electrolyte material having lithium ion conductivity,
In a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source, the diffraction peaks are at diffraction angles 2θ=17.2±0.5° and 2θ=18.8±0.4°,
The maximum diffraction intensity of the diffraction peak at the diffraction angle 2θ=17.2±0.5° is defined as _IB .
When the maximum diffraction intensity of the diffraction peak present at a diffraction angle 2θ=18.8±0.4° is defined as I _C , there is provided a sulfide-based inorganic solid electrolyte material having an I _C /I _B value of 0.27 or more.

Further, according to the present invention,
A sulfide-based inorganic solid electrolyte material having lithium ion conductivity,
After heat treatment at 270° C. for 2 hours, the spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source has diffraction peaks at diffraction angles 2θ=17.2±0.5° and 2θ=18.8±0.4°,
The maximum diffraction intensity of the diffraction peak at the diffraction angle 2θ=17.2±0.5° is defined as _IB .
When the maximum diffraction intensity of the diffraction peak present at a diffraction angle 2θ=18.8±0.4° is defined as I _C , there is provided a sulfide-based inorganic solid electrolyte material having an I _C /I _B value of 0.27 or more.

Further, according to the present invention,
A solid electrolyte is provided that includes the sulfide-based inorganic solid electrolyte material.

Further, according to the present invention,
There is provided a solid electrolyte membrane containing the above solid electrolyte as a main component.

Further, according to the present invention,
A lithium ion battery comprising a positive electrode including a positive electrode active material layer, an electrolyte layer, and a negative electrode including a negative electrode active material layer,
There is provided a lithium ion battery in which at least one of the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer contains the sulfide-based inorganic solid electrolyte material.

The present invention provides a sulfide-based inorganic solid electrolyte material that can suppress the decrease in lithium ion conductivity when exposed to the air.

1 is a cross-sectional view showing an example of the structure of a lithium-ion battery according to an embodiment of the present invention. FIG. 2 is a diagram showing an X-ray diffraction spectrum of a sulfide-based inorganic solid electrolyte material obtained in an example. FIG. 2 is a diagram showing an X-ray diffraction spectrum of a sulfide-based inorganic solid electrolyte material obtained in a comparative example.

Below, an embodiment of the present invention will be described with reference to the drawings. In all drawings, similar components are given the same reference numerals and their description will be omitted as appropriate. The drawings are schematic and do not correspond to the actual dimensional ratios. The numerical range "A to B" indicates A or more and B or less unless otherwise specified.

[Sulfide-based inorganic solid electrolyte material]
First, the sulfide-based inorganic solid electrolyte material according to this embodiment will be described.
The sulfide-based inorganic solid electrolyte material according to this embodiment is a sulfide-based inorganic solid electrolyte material having lithium ion conductivity, and has a diffraction angle 2θ The diffraction peaks are at a diffraction angle 2θ=17.2±0.5° and at a diffraction angle 2θ=18.8±0.4°, respectively, and are located at a diffraction angle 2θ=17.2±0.5°. The maximum diffraction intensity of the diffraction peak at the diffraction angle 2θ=18.8±0.4° is defined as I _B , and the maximum diffraction intensity of the diffraction peak at the diffraction angle 2θ=18.8±0.4° is defined as I _{C .} The value of I _C /I _B is It is 0.27 or more, preferably 0.35 or more, more preferably 0.40 or more, even more preferably 0.45 or more, still more preferably 0.50 or more, and particularly preferably 0.60 or more.
The upper limit of the I _C /I _B value is not particularly limited, but is, for example, 2.0 or less, preferably 1.5 or less, more preferably 1.2 or less, and further preferably 1.0 or less.
In addition, the sulfide-based inorganic solid electrolyte material according to this embodiment may have a configuration in which the value of I _C /I _B is equal to or greater than the lower limit after heat treatment at 270° C. for 2 hours. In this case, It is preferable to use the sulfide-based inorganic solid electrolyte material after subjecting it to a heat treatment so that the above-mentioned I _C /I _B value becomes equal to or greater than the above-mentioned lower limit.

The sulfide-based inorganic solid electrolyte material according to this embodiment has diffraction peaks at diffraction angles 2θ=17.2±0.5° and 2θ=18.8±0.4° in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source, and the value of I _C /I _B is equal to or greater than the lower limit, thereby making it possible to suppress a decrease in lithium ion conductivity when exposed to the air.
The reason for this is not entirely clear, but the following reasons are presumed.
First, when the sulfide-based inorganic solid electrolyte material according to this embodiment is exposed to the atmosphere, the diffraction peak at the diffraction angle 2θ=18.8±0.4° gradually disappears. Therefore, it is considered that the sulfide-based inorganic solid electrolyte material according to this embodiment suppresses the decrease in lithium ion conductivity in the atmosphere by reacting the structure due to the diffraction peak at the diffraction angle 2θ=18.8±0.4° with oxygen, moisture, etc. in the atmosphere. Therefore, it is considered that the sulfide-based inorganic solid electrolyte material according to this embodiment can suppress the decrease in lithium ion conductivity when exposed to the atmosphere.
Therefore, the presence of diffraction peaks at diffraction angles 2θ=17.2±0.5° and 2θ=18.8±0.4° in the spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source, and the above _IC / _IB value being equal to or greater than the above lower limit, is considered to indicate the formation of a novel structure different from that of conventional typical sulfide-based inorganic solid electrolyte materials.
In this embodiment, a sulfide-based inorganic solid electrolyte material having diffraction peaks at diffraction angles 2θ=17.2±0.5° and 2θ=18.8±0.4° in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source, and having the above-mentioned _IC / _IB value equal to or greater than the above-mentioned lower limit, can be realized by preventing contact of moisture and oxygen with the inorganic composition to a higher level than conventionally in the composition ratio of the sulfide-based inorganic solid electrolyte material and the process of vitrifying the inorganic composition as a raw material, and by performing a heat treatment at a high temperature of 220° C. or higher.

In the sulfide-based inorganic solid electrolyte material according to this embodiment, when the maximum diffraction intensity at a diffraction angle 2θ=35.0±0.1° in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source is defined as background intensity I _A and the maximum diffraction intensity of a diffraction peak present at a diffraction angle 2θ=17.2±0.5° is defined as I _B , the value of I _B /I _A is preferably 2.0 or more, more preferably 3.0 or more, even more preferably 4.0 or more, and particularly preferably 5.0 or more.
By setting the value of I _B /I _A to be equal to or greater than the above lower limit, the lithium ion conductivity can be further improved.
In addition, in the sulfide-based inorganic solid electrolyte material according to this embodiment, the upper limit of the value of I _B /I _A is not particularly limited, but is, for example, 30.0 or less, preferably 20.0 or less, more preferably 15.0 or less, even more preferably 12.0 or less, and particularly preferably 9.0 or less.
Moreover, the sulfide-based inorganic solid electrolyte material according to this embodiment may have a configuration in which the I _B /I _A value falls within the above range after heat treatment at 270° C. for 2 hours.
The above-mentioned I _B /I _A value of the sulfide-based inorganic solid electrolyte material according to this embodiment can be realized by preventing contact of moisture and oxygen with the inorganic composition to a higher level than in the past in the process of vitrifying the inorganic composition as a raw material, and by performing a heat treatment at a high temperature of 220° C. or more.

In the sulfide-based inorganic solid electrolyte material according to this embodiment, when the maximum diffraction intensity at a diffraction angle 2θ=35.0±0.1° in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source is defined as background intensity I _A and the maximum diffraction intensity of a diffraction peak existing at a diffraction angle 2θ=18.8±0.4° is defined as I _C , the value of I _C /I _A is preferably 2.0 or more, more preferably 3.0 or more, and even more preferably 4.0 or more.
By setting the value of I _C /I _A to be equal to or greater than the above lower limit, the decrease in lithium ion conductivity upon exposure to the air can be further suppressed.
In addition, in the sulfide-based inorganic solid electrolyte material according to this embodiment, the upper limit of the I _C /I _A value is not particularly limited, but is, for example, 30.0 or less, preferably 20.0 or less, more preferably 15.0 or less, even more preferably 10.0 or less, and particularly preferably 8.0 or less.
Moreover, the sulfide-based inorganic solid electrolyte material according to this embodiment may have a configuration in which the above-mentioned I _C /I _A value falls within the above-mentioned range after heat treatment at 270° C. for 2 hours.
The above-mentioned I _C /I _A value of the sulfide-based inorganic solid electrolyte material according to this embodiment can be realized by, for example, preventing contact of moisture and oxygen with the inorganic composition to a higher degree than in the past in the process of vitrifying the raw inorganic composition, and by performing heat treatment at a high temperature of 220°C or higher.

In addition, in the sulfide-based inorganic solid electrolyte material according to this embodiment, the spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source may further have diffraction peaks at diffraction angles 2θ=25.6±0.5°, 2θ=26.6±0.4°, and 2θ=29.2±0.8°. By having these diffraction peaks, the lithium ion conductivity can be further improved.
In addition, the sulfide-based inorganic solid electrolyte material according to this embodiment may be configured to further have diffraction peaks at diffraction angles 2θ=25.6±0.5°, 2θ=26.6±0.4°, and 2θ=29.2±0.8° in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source after heat treatment at 270° C. for 2 hours.

The sulfide-based inorganic solid electrolyte material according to this embodiment preferably contains Li, P and S as constituent elements from the viewpoint of further improving electrochemical stability, stability in moisture and air, ease of handling, and the like.
In addition, in the sulfide-based inorganic solid electrolyte material according to this embodiment, from the viewpoint of further improving lithium ion conductivity, electrochemical stability, stability in moisture and air, and ease of handling, the molar ratio Li/P of the Li content to the P content in the sulfide-based inorganic solid electrolyte material is preferably 1.0 or more and 5.0 or less, more preferably 2.0 or more and 4.5 or less, even more preferably 3.0 or more and 4.2 or less, even more preferably 3.3 or more and 4.0 or less, and particularly preferably 3.3 or more and 3.8 or less, and the molar ratio S/P of the S content to the P content is preferably 2.0 or more and 6.0 or less, more preferably 3.0 or more and 5.0 or less, even more preferably 3.5 or more and 4.5 or less, and particularly preferably 3.8 or more and 4.2 or less.
Here, the contents of Li, P, and S in the sulfide-based inorganic solid electrolyte material according to this embodiment can be determined by, for example, ICP emission spectrometry or X-ray analysis.

In the sulfide-based inorganic solid electrolyte material according to this embodiment, the lithium ion conductivity of the sulfide-based inorganic solid electrolyte material measured by an AC impedance method under the measurement conditions of 27.0° C., an applied voltage of 10 mV, and a measurement frequency range of 0.1 Hz to 7 MHz is preferably 0.5×10 ⁻³ S·cm ⁻¹ or more, more preferably 0.6×10 ⁻³ S·cm ⁻¹ or more, even more preferably 0.8×10 ⁻³ S·cm ⁻¹ or more, and particularly preferably 1.0×10 ⁻³ S·cm ⁻¹ or more.
When the lithium ion conductivity of the sulfide-based inorganic solid electrolyte material according to the present embodiment is equal to or higher than the lower limit, a lithium ion battery having better battery characteristics can be obtained. Furthermore, when such a sulfide-based inorganic solid electrolyte material is used, a lithium ion battery having better input/output characteristics can be obtained.

The sulfide-based inorganic solid electrolyte material according to this embodiment may be in the form of particles, for example.
The particulate sulfide-based inorganic solid electrolyte material according to this embodiment is not particularly limited, but the average particle diameter _d50 in the weight-based particle size distribution measured by a laser diffraction scattering particle size distribution measurement method is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 80 μm or less, and even more preferably 5 μm or more and 60 μm or less.
By setting the average particle diameter _d50 of the sulfide-based inorganic solid electrolyte material within the above range, it is possible to maintain good handling properties and further improve the lithium ion conductivity.

The sulfide-based inorganic solid electrolyte material according to this embodiment is preferably excellent in electrochemical stability. Here, electrochemical stability refers to, for example, the property of being difficult to be oxidized and reduced over a wide voltage range. More specifically, in the sulfide-based inorganic solid electrolyte material according to this embodiment, the maximum value of the oxidative decomposition current of the sulfide-based inorganic solid electrolyte material measured under conditions of a temperature of 25° C., a sweep voltage range of 0 to 5 V, and a voltage sweep rate of 5 mV/sec is preferably 0.50 μA or less, more preferably 0.20 μA or less, even more preferably 0.10 μA or less, even more preferably 0.05 μA or less, and particularly preferably 0.03 μA or less.
It is preferable that the maximum value of the oxidative decomposition current of the sulfide-based inorganic solid electrolyte material is equal to or less than the above upper limit value, since the oxidative decomposition of the sulfide-based inorganic solid electrolyte material in the lithium ion battery can be suppressed.
The lower limit of the maximum value of the oxidative decomposition current of the sulfide-based inorganic solid electrolyte material is not particularly limited, but is, for example, 0.0001 μA or more.

The sulfide-based inorganic solid electrolyte material according to this embodiment can be used in any application requiring lithium ion conductivity. In particular, the sulfide-based inorganic solid electrolyte material according to this embodiment is preferably used in a lithium ion battery. More specifically, it is used in a positive electrode active material layer, a negative electrode active material layer, an electrolyte layer, etc. in a lithium ion battery. Furthermore, the sulfide-based inorganic solid electrolyte material according to this embodiment is preferably used in a positive electrode active material layer, a negative electrode active material layer, a solid electrolyte layer, etc. constituting an all-solid-state lithium ion battery, and is particularly preferably used in a solid electrolyte layer constituting an all-solid-state lithium ion battery.
An example of an all-solid-state lithium ion battery using the sulfide-based inorganic solid electrolyte material according to this embodiment is one in which a positive electrode, a solid electrolyte layer, and a negative electrode are laminated in this order.

[Method of producing sulfide-based inorganic solid electrolyte material]
Next, a method for producing the sulfide-based inorganic solid electrolyte material according to this embodiment will be described.
The method for producing a sulfide-based inorganic solid electrolyte material according to this embodiment is different from the conventional method for producing a sulfide-based inorganic solid electrolyte material. That is, the sulfide-based inorganic solid electrolyte material has diffraction peaks at the diffraction angle 2θ=17.2±0.5° and the diffraction angle 2θ=18.8±0.4° in the spectrum obtained by X-ray diffraction using CuKα radiation as the radiation source, and the value of I _C /I _B is equal to or greater than the lower limit, and can be obtained only by adopting the following manufacturing ingenuity: (1) highly controlling the composition ratio of the sulfide-based inorganic solid electrolyte material; (2) preventing the contact of moisture and oxygen with the inorganic composition at a higher level than before in the process of vitrifying the inorganic composition as the raw material; and (3) performing a heat treatment at a high temperature of 220° C. or higher.
Here, since the above-mentioned step (3) may cause a decrease in the film-forming property of the sulfide-based inorganic solid electrolyte material, the above-mentioned step (3) may be performed after the solid electrolyte membrane is formed. That is, the sulfide-based inorganic solid electrolyte material according to this embodiment also includes the sulfide-based inorganic solid electrolyte material in the state before the above-mentioned step (3) is performed.
However, for the sulfide-based inorganic solid electrolyte material according to this embodiment, various specific manufacturing conditions such as mixing conditions of various raw materials can be adopted, on the premise that the above-mentioned three manufacturing method ingenuity is adopted.
Hereinafter, the method for producing the sulfide-based inorganic solid electrolyte material according to this embodiment will be described in more detail.

The sulfide-based inorganic solid electrolyte material according to this embodiment can be obtained, for example, by a production method including the following steps (A), (B) and (C). In addition, the production method of the sulfide-based inorganic solid electrolyte material according to this embodiment may further include the following step (D) as necessary.
Step (A): A step of preparing a raw inorganic composition containing two or more kinds of raw inorganic compounds. Step (B): A step of mechanically treating the raw inorganic composition under an atmosphere in which the amount and inflow of moisture and oxygen are suppressed to a higher level than before, thereby vitrifying the raw inorganic compounds while causing a chemical reaction between them, thereby obtaining a sulfide-based inorganic solid electrolyte material in a glassy state. Step (C): A step of heating the obtained sulfide-based inorganic solid electrolyte material in a glassy state to crystallize at least a portion of it. Step (D): A step of pulverizing, classifying, or granulating the obtained sulfide-based inorganic solid electrolyte material.

According to the method for producing a sulfide-based inorganic solid electrolyte material of this embodiment, the amount of moisture and oxygen in the atmosphere and the inflow of moisture and oxygen into the atmosphere during the vitrification process are suppressed to a higher level than in conventional production methods. Therefore, according to the method for producing a sulfide-based inorganic solid electrolyte material of this embodiment, it is possible to highly suppress the oxygen and moisture taken in during the production of a sulfide-based inorganic solid electrolyte material, and as a result, it is believed that a sulfide-based inorganic solid electrolyte material having a novel structure different from conventional structures has been realized.

(Step (A) of Preparing Raw Inorganic Composition)
First, a raw material inorganic composition containing two or more inorganic compounds such as lithium sulfide, phosphorus sulfide, and lithium nitride in a specific ratio is prepared. The mixing ratio of each raw material in the raw material inorganic composition is adjusted so that the sulfide-based inorganic solid electrolyte material to be obtained has a desired composition ratio.
The method for mixing the raw materials is not particularly limited as long as it can uniformly mix the raw materials. For example, the raw materials can be mixed using a ball mill, a bead mill, a vibration mill, an impact grinding device, a mixer (a pug mixer, a ribbon mixer, a tumbler mixer, a drum mixer, a V-type mixer, etc.), a kneader, a two-shaft kneader, an airflow grinder, etc.
The mixing conditions when mixing the raw materials, such as the stirring speed, processing time, temperature, reaction pressure, and gravitational acceleration applied to the mixture, can be appropriately determined depending on the processing amount of the mixture.

The lithium sulfide used as the raw material is not particularly limited, and commercially available lithium sulfide may be used, or lithium sulfide obtained by reacting lithium hydroxide with hydrogen sulfide may be used. From the viewpoint of obtaining a high-purity sulfide-based inorganic solid electrolyte material and suppressing side reactions, it is preferable to use lithium sulfide with few impurities.
In this embodiment, lithium sulfide also includes lithium polysulfide.

_{The phosphorus sulfide used as the raw material is not particularly limited, and commercially available phosphorus sulfides (e.g., P2S5 , P4S3} , _P4S7 , _{P4S5 ,} etc.) can be used. From the viewpoint of obtaining a high-purity _sulfide -based inorganic solid electrolyte material and from the viewpoint of suppressing side reactions, it is preferable to use phosphorus sulfide with few impurities. In addition, instead of phosphorus sulfide, elemental phosphorus (P) and elemental sulfur (S) in the corresponding molar ratio can also be used. Elemental phosphorus (P) and elemental sulfur (S) can be used without any particular limitation as long as they are industrially produced and sold.

Lithium nitride may be used as the raw material. Here, since the nitrogen in lithium nitride is discharged into the system as _N2 , by using lithium nitride as the raw inorganic compound, it becomes possible to increase only the Li composition in a sulfide-based inorganic solid electrolyte material containing Li, P, and S as constituent elements.
The lithium nitride according to the present embodiment is not particularly limited, and may be a commercially available lithium nitride (e.g., Li ₃ N, etc.), or may be obtained by reacting metallic lithium (e.g., Li foil) with nitrogen gas. From the viewpoint of obtaining a high-purity solid electrolyte material and suppressing side reactions, it is preferable to use lithium nitride with a small amount of impurities.

(Step (B) of obtaining a sulfide-based inorganic solid electrolyte material in a glass state)
Next, the raw inorganic composition is mechanically treated in an atmosphere in which the presence and inflow of moisture and oxygen are suppressed to a higher level than in the past, thereby vitrifying the raw inorganic compounds while causing them to chemically react with each other, thereby obtaining a sulfide-based inorganic solid electrolyte material in a glassy state.

Here, the mechanical treatment is a method of mechanically colliding two or more inorganic compounds to cause a chemical reaction and vitrification, such as mechanochemical treatment, etc. Here, the mechanochemical treatment is a method of vitrification by applying mechanical energy such as a shear force or a collision force to a target composition.
In the step (B), the mechanochemical treatment is preferably a dry mechanochemical treatment, from the viewpoint of easily realizing an environment in which moisture and oxygen are removed to a high level.
By using the mechanochemical treatment, the raw materials can be mixed while being pulverized into fine particles, so that the contact area of the raw materials can be increased, thereby accelerating the reaction of the raw materials, and the sulfide-based inorganic solid electrolyte material according to the present embodiment can be obtained more efficiently.

Here, mechanochemical processing is a method of vitrification while applying mechanical energy such as shear force, impact force, or centrifugal force to the mixture. Examples of devices for vitrification by mechanochemical processing (hereinafter referred to as vitrification devices) include crushing and dispersing machines such as ball mills, bead mills, vibration mills, turbo mills, mechanofusion, disk mills, and roll mills; rotary impact crushing devices consisting of a mechanism combining rotation (shear stress) and impact (compressive stress) as represented by rock drills, vibration drills, and impact drivers; high-pressure gliding rolls; and the like. Among these, ball mills and bead mills are preferred from the viewpoint of efficiently generating very high impact energy, and ball mills are particularly preferred. In addition, from the viewpoint of excellent continuous productivity, roll mills; rotary impact crushing devices consisting of a mechanism combining rotation (shear stress) and impact (compressive stress) as represented by rock drills, vibration drills, and impact drivers; high-pressure gliding rolls; and the like are preferred.

In order to obtain the sulfide-based inorganic solid electrolyte material according to this embodiment, it is important that the step (B) is carried out in an atmosphere in which the amount and inflow of moisture and oxygen are suppressed to a higher level than in the past, thereby making it possible to suppress the contact of the raw material inorganic composition with moisture and oxygen to a higher level than in the past.
Here, an atmosphere in which the amounts of moisture and oxygen present and the inflow thereof are suppressed to a higher level than in the past can be created, for example, by the following method.
First, the mixing vessel and the sealed vessel for the vitrification apparatus are placed in the glove box, and then the injection of inert gas such as high-purity dry argon gas or dry nitrogen gas obtained through a gas purification device and vacuum degassing are performed multiple times (preferably three times or more) into the glove box. Here, in the glove box after the above operation, the inert gas such as high-purity dry argon gas or dry nitrogen gas is circulated through the gas purification device to adjust the oxygen concentration and moisture concentration to preferably 1.0 ppm or less, more preferably 0.8 ppm or less, and even more preferably 0.6 ppm or less, respectively.
Next, two or more inorganic compounds are put into a mixing container in the glove box, and then mixed to prepare a raw inorganic composition (meaning step (A)). Here, the two or more inorganic compounds are put into the mixing container in the glove box in the following procedure. First, with the door inside the glove box body closed, two or more inorganic compounds are put into the side box of the glove box. Next, the side box is injected with an inert gas such as high-purity dry argon gas or dry nitrogen gas drawn from inside the glove box and vacuum degassed several times (preferably three or more times), and then the door inside the glove box body is opened, and two or more inorganic compounds are put into the mixing container inside the glove box body, and the mixing container is sealed.
Next, after mixing two or more kinds of inorganic compounds, the obtained raw inorganic composition is taken out from the mixing vessel, transferred to a vessel for a vitrification apparatus, and sealed.
By carrying out such an operation, the amount of moisture and oxygen present in the sealed container containing the raw material inorganic composition can be suppressed to a higher level than in the past, and as a result, in step (B), an atmosphere in which the amount of moisture and oxygen present is suppressed to a higher level than in the past can be created.
Next, the sealed container containing the raw inorganic composition is taken out from the glove box. Then, the sealed container is set in a vitrification apparatus arranged in an atmosphere filled with dry gas such as dry argon gas, dry nitrogen gas, dry air, etc. (for example, in a box filled with dry argon gas, dry nitrogen gas, dry air, etc.), and vitrification is performed. Here, during vitrification, it is preferable to continue to introduce a constant amount of dry gas into the atmosphere filled with dry gas. By taking such measures, in step (B), an atmosphere can be created in which the inflow of moisture and oxygen is suppressed to a higher level than in the past.
In addition, in order to highly suppress the inflow of moisture and oxygen into the sealed container, it is preferable to use a gasket with excellent sealing properties, such as an O-ring or a ferrule gasket, for the lid of the sealed container in order to achieve higher airtightness.

The mixing conditions, such as the rotation speed, processing time, temperature, reaction pressure, and gravitational acceleration applied to the raw inorganic composition when mechanically processing the raw inorganic composition, can be appropriately determined depending on the type and processing amount of the raw inorganic composition. In general, the faster the rotation speed, the faster the glass production rate, and the longer the processing time, the higher the conversion rate to glass.
Typically, when X-ray diffraction analysis is performed using CuKα radiation as a radiation source, if the diffraction peak derived from the raw material disappears or decreases, it can be determined that the raw material inorganic composition has been vitrified and the desired sulfide-based inorganic solid electrolyte material has been obtained.

Here, in step (B), the vitrification treatment is preferably performed until the lithium ion conductivity of the sulfide-based inorganic solid electrolyte material measured by an AC impedance method under the measurement conditions of 27.0° C., an applied voltage of 10 mV, and a measurement frequency range of 0.1 Hz to 7 MHz is preferably 1.0×10 ⁻⁴ S·cm ⁻¹ or more, more preferably 2.0×10 ⁻⁴ S·cm ⁻¹ or more, even more preferably 3.0×10 ⁻⁴ S·cm ⁻¹ or more, and particularly preferably 4.0×10 ⁻⁴ S·cm ⁻¹ or more. This makes it possible to obtain a sulfide-based inorganic solid electrolyte material with even better lithium ion conductivity.

(Step (C) of crystallizing at least a part of the sulfide-based inorganic solid electrolyte material)
Next, the obtained sulfide-based inorganic solid electrolyte material in a glass state is heated to crystallize at least a portion of the sulfide-based inorganic solid electrolyte material, thereby producing a sulfide-based inorganic solid electrolyte material in a glass ceramic state (also called crystallized glass). In this way, a sulfide-based inorganic solid electrolyte material having even better lithium ion conductivity can be obtained.
That is, the sulfide-based inorganic solid electrolyte material according to this embodiment is preferably in a glass ceramic state (crystallized glass state) because it has excellent lithium ion conductivity.

The temperature at which the sulfide-based inorganic solid electrolyte material in a glassy state is heated is preferably within the range of 220°C or more and 500°C or less, and more preferably within the range of 250°C or more and 350°C or less.
The time for heating the sulfide-based inorganic solid electrolyte material in a glass state is not particularly limited as long as it is a time that can obtain a sulfide-based inorganic solid electrolyte material in a desired glass ceramic state, but is, for example, in the range of 0.5 hours to 24 hours, preferably 1 hour to 3 hours. The heating method is not particularly limited, but for example, a method using a firing furnace can be mentioned. The conditions such as temperature and time during such heating can be appropriately adjusted to optimize the properties of the sulfide-based inorganic solid electrolyte material according to this embodiment.

In addition, the sulfide-based inorganic solid electrolyte material in a glassy state is preferably heated, for example, in an inert gas atmosphere, which can prevent deterioration (for example, oxidation) of the sulfide-based inorganic solid electrolyte material.
Examples of inert gases used when heating the sulfide-based inorganic solid electrolyte material in a glassy state include argon gas, helium gas, and nitrogen gas. These inert gases are preferably as pure as possible in order to prevent impurities from being mixed into the product, and preferably have a dew point of −70° C. or less, particularly preferably −80° C. or less, in order to avoid contact with moisture. The method of introducing the inert gas into the mixed system is not particularly limited as long as the mixed system is filled with an inert gas atmosphere, and examples of the method include a method of purging the inert gas and a method of continuously introducing a constant amount of the inert gas.

(Pulverizing, classifying, or granulating step (D))
In the method for producing a sulfide-based inorganic solid electrolyte material according to this embodiment, a step of pulverizing, classifying, or granulating the obtained sulfide-based inorganic solid electrolyte material may be further performed as necessary. For example, a sulfide-based inorganic solid electrolyte material having a desired particle size can be obtained by pulverizing to obtain fine particles, and then adjusting the particle size by a classification operation or a granulation operation. The above-mentioned pulverizing method is not particularly limited, and known pulverizing methods such as a mixer, airflow pulverization, a mortar, a rotary mill, and a coffee mill can be used. The above-mentioned classification method is also not particularly limited, and known methods such as a sieve can be used.
The pulverization or classification is preferably carried out in an inert gas atmosphere or a vacuum atmosphere, since this can prevent contact with moisture in the air.

In order to obtain the sulfide-based inorganic solid electrolyte material according to this embodiment, it is important to appropriately adjust each of the above steps. However, the method for producing the sulfide-based inorganic solid electrolyte material according to this embodiment is not limited to the above method, and the sulfide-based inorganic solid electrolyte material according to this embodiment can be obtained by appropriately adjusting various conditions.

[Solid electrolyte]
Next, the solid electrolyte according to the present embodiment will be described. The solid electrolyte according to the present embodiment includes the sulfide-based inorganic solid electrolyte material according to the present embodiment.
The solid electrolyte according to the present embodiment is not particularly limited, but may contain, as a component other than the sulfide-based inorganic solid electrolyte material according to the present embodiment, for example, a solid electrolyte material of a type different from the sulfide-based inorganic solid electrolyte material according to the present embodiment described above, within a range that does not impair the object of the present invention.

The solid electrolyte according to this embodiment may contain a solid electrolyte material of a different type from the sulfide-based inorganic solid electrolyte material according to this embodiment described above. The solid electrolyte material of a different type from the sulfide-based inorganic solid electrolyte material according to this embodiment is not particularly limited as long as it has ion conductivity and insulating properties, but materials generally used in lithium ion batteries can be used. For example, inorganic solid electrolyte materials such as sulfide-based inorganic solid electrolyte materials, oxide-based inorganic solid electrolyte materials, and other lithium-based inorganic solid electrolyte materials different from the sulfide-based inorganic solid electrolyte material according to this embodiment; organic solid electrolyte materials such as polymer electrolytes can be mentioned.

Examples of sulfide-based inorganic solid electrolyte materials different from the sulfide-based inorganic solid electrolyte material according to the present embodiment described above include Li ₂ S-P ₂ S ₅ material, Li ₂ S-SiS ₂ material, Li ₂ S-GeS ₂ material, Li ₂ S-Al ₂ S ₃ material, Li ₂ S-SiS ₂ -Li ₃ PO ₄ material, Li ₂ S-P ₂ S ₅ -GeS ₂ material, Li ₂ S-Li ₂ O-P ₂ S ₅ -SiS ₂ material, Li ₂ S-GeS ₂ -P ₂ S ₅ -SiS ₂ material, Li ₂ S-SnS ₂ -P ₂ S ₅ -SiS ₂ material, Li ₂ S-P ₂ S ₅ -Li ₃ N material, Li ₂ S _2+X −P ₄ S ₃ material, Li ₂ S—P ₂ S ₅ −P ₄ S ₃ material, etc. These may be used alone or in combination of two or more.
Among these, the Li ₂ S-P ₂ S ₅ material is preferred because it has excellent lithium ion conductivity and is stable over a wide voltage range without decomposition, etc. Here, for example, the Li ₂ S-P ₂ S ₅ material refers to an inorganic material obtained by chemically reacting an inorganic composition containing at least Li ₂ S (lithium sulfide) and P ₂ S ₅ with each other through a mechanical treatment.
In this embodiment, lithium sulfide also includes lithium polysulfide.

Examples of the oxide-based inorganic solid electrolyte material include NASICON-type materials such as LiTi ₂ (PO ₄ ) ₃ , LiZr ₂ (PO ₄ ) ₃ , and LiGe ₂ (PO ₄ ) ₃ , perovskite-type materials such as (La _0.5+x Li _0.5-3x )TiO ₃ , Li ₂ O-P ₂ O ₅ materials, and Li ₂ O-P ₂ O ₅ -Li ₃ N materials.
Other examples of lithium-based inorganic solid electrolyte materials include LiPON, LiNbO ₃ , LiTaO ₃ , Li ₃ PO ₄ , LiPO _4-x N _x (x is 0<x≦1), LiN, LiI, and LISICON.
Furthermore, glass ceramics obtained by precipitating crystals of these inorganic solid electrolytes can also be used as inorganic solid electrolyte materials.

As the organic solid electrolyte material, for example, a polymer electrolyte such as a dry polymer electrolyte or a gel electrolyte can be used.
As the polymer electrolyte, any of those generally used in lithium ion batteries can be used.

[Solid electrolyte membrane]
Next, the solid electrolyte membrane according to this embodiment will be described.
The solid electrolyte membrane according to this embodiment contains, as a main component, a solid electrolyte containing the sulfide-based inorganic solid electrolyte material according to this embodiment described above.

The solid electrolyte membrane according to this embodiment is used, for example, as a solid electrolyte layer constituting an all-solid-state lithium ion battery.
An example of an all-solid-state lithium ion battery using the solid electrolyte membrane according to this embodiment is one in which a positive electrode, a solid electrolyte layer, and a negative electrode are laminated in this order, where the solid electrolyte layer is made of the solid electrolyte membrane.

The average thickness of the solid electrolyte membrane according to this embodiment is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 200 μm or less, and even more preferably 20 μm or more and 100 μm or less. When the average thickness of the solid electrolyte membrane is equal to or more than the lower limit, the loss of the solid electrolyte and the occurrence of cracks on the surface of the solid electrolyte membrane can be further suppressed. Furthermore, when the average thickness of the solid electrolyte membrane is equal to or less than the upper limit, the impedance of the solid electrolyte membrane can be further reduced. As a result, the battery characteristics of the obtained all-solid-state lithium ion battery can be further improved.

The solid electrolyte membrane according to the present embodiment is preferably a pressure-molded body of a particulate solid electrolyte containing the sulfide-based inorganic solid electrolyte material according to the present embodiment described above. That is, it is preferable to pressurize the particulate solid electrolyte to form a solid electrolyte membrane having a certain strength by the anchor effect between the solid electrolyte materials.
By forming the solid electrolyte into a pressure-molded body, the solid electrolyte particles bond together, and the strength of the resulting solid electrolyte membrane is further increased, which further suppresses chipping of the solid electrolyte and the occurrence of cracks on the surface of the solid electrolyte membrane.

The content of the sulfide-based inorganic solid electrolyte material according to the present embodiment in the solid electrolyte membrane according to the present embodiment is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, when the entire solid electrolyte membrane is taken as 100% by mass. This improves the contact between the solid electrolytes, and reduces the interface contact resistance of the solid electrolyte membrane. As a result, the lithium ion conductivity of the solid electrolyte membrane can be further improved. And, by using such a solid electrolyte membrane having excellent lithium ion conductivity, the battery characteristics of the obtained all-solid-state lithium ion battery can be further improved.
The upper limit of the content of the sulfide-based inorganic solid electrolyte material according to the present embodiment in the solid electrolyte membrane according to the present embodiment is not particularly limited, but is, for example, 100 mass % or less.

The planar shape of the solid electrolyte membrane is not particularly limited and can be selected appropriately to match the shapes of the electrodes and current collectors, but can be rectangular, for example.

The solid electrolyte membrane according to the present embodiment may contain a binder resin, but the content of the binder resin is preferably less than 0.5 mass%, more preferably 0.1 mass% or less, even more preferably 0.05 mass% or less, and even more preferably 0.01 mass% or less, when the entire solid electrolyte membrane is taken as 100 mass%. It is even more preferable that the solid electrolyte membrane according to the present embodiment does not substantially contain a binder resin, and it is most preferable that it does not contain a binder resin.
This improves the contact between the solid electrolytes, and reduces the interface contact resistance of the solid electrolyte film. As a result, the lithium ion conductivity of the solid electrolyte film can be further improved. By using such a solid electrolyte film with excellent lithium ion conductivity, the battery characteristics of the obtained all-solid-state lithium ion battery can be improved.
In addition, "substantially free of binder resin" means that the binder resin may be contained to the extent that the effect of the present embodiment is not impaired. In addition, when an adhesive resin layer is provided between the solid electrolyte layer and the positive electrode or the negative electrode, the adhesive resin originating from the adhesive resin layer present in the vicinity of the interface between the solid electrolyte layer and the adhesive resin layer is excluded from the "binder resin in the solid electrolyte membrane."

The binder resin is a binder that is generally used in lithium ion batteries to bond inorganic solid electrolyte materials together, and examples of such binders include polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, and polyimide.

The solid electrolyte membrane according to this embodiment can be obtained, for example, by depositing particulate solid electrolyte into a film on a cavity surface of a mold or on a substrate surface, and then pressurizing the solid electrolyte deposited in the film form.
The method for pressurizing the solid electrolyte is not particularly limited. For example, when a particulate solid electrolyte is deposited on the cavity surface of a mold, pressing with a mold and a stamping die can be used. When a particulate solid electrolyte is deposited on the surface of a substrate, pressing with a mold and a stamping die, roll pressing, flat plate pressing, or the like can be used.
The pressure applied to the solid electrolyte is, for example, 10 MPa or more and 500 MPa or less.

If necessary, the inorganic solid electrolyte deposited in the form of a film may be heated while being pressurized. By applying heat and pressure, the solid electrolytes are fused and bonded to each other, and the strength of the resulting solid electrolyte film is further increased. As a result, chipping of the solid electrolyte and the occurrence of cracks on the surface of the solid electrolyte film can be further suppressed.
The temperature to which the solid electrolyte is heated is, for example, 40° C. or higher and 500° C. or lower.

[Lithium-ion battery]
FIG. 1 is a cross-sectional view showing an example of the structure of a lithium-ion battery 100 according to an embodiment of the present invention.
The lithium ion battery 100 according to this embodiment includes, for example, a positive electrode 110 including a positive electrode active material layer 101, an electrolyte layer 120, and a negative electrode 130 including a negative electrode active material layer 103. At least one of the positive electrode active material layer 101, the negative electrode active material layer 103, and the electrolyte layer 120 contains the sulfide-based inorganic solid electrolyte material according to this embodiment. It is preferable that all of the positive electrode active material layer 101, the negative electrode active material layer 103, and the electrolyte layer 120 contain the sulfide-based inorganic solid electrolyte material according to this embodiment. In this embodiment, unless otherwise specified, the layer including the positive electrode active material is called the positive electrode active material layer 101. The positive electrode 110 may further include a current collector 105 in addition to the positive electrode active material layer 101 as necessary, or may not include the current collector 105. In this embodiment, unless otherwise specified, the layer including the negative electrode active material is called the negative electrode active material layer 103. The negative electrode 130 may further include a current collector 105 in addition to the negative electrode active material layer 103 as necessary, or may not include the current collector 105 .
The shape of the lithium ion battery 100 according to this embodiment is not particularly limited, and examples thereof include a cylindrical shape, a coin shape, a square shape, a film shape, and any other shape.

The lithium ion battery 100 according to this embodiment is manufactured according to a generally known method. For example, the positive electrode 110, the electrolyte layer 120, and the negative electrode 130 are stacked together to form a cylindrical, coin-shaped, rectangular, film-shaped, or other shape, and a nonaqueous electrolyte is sealed in as necessary.

(Positive electrode)
The positive electrode 110 is not particularly limited, and any electrode generally used in lithium ion batteries can be used. The positive electrode 110 is not particularly limited, and can be manufactured according to a generally known method. For example, the positive electrode 110 can be obtained by forming a positive electrode active material layer 101 containing a positive electrode active material on the surface of a current collector 105 such as aluminum foil.
The thickness and density of the positive electrode active material layer 101 are appropriately determined depending on the intended use of the battery, and are not particularly limited, and can be set in accordance with generally known information.

The positive electrode active material layer 101 contains a positive electrode active material.
The positive electrode active material is not particularly limited, and generally known materials can be used. For example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), solid solution oxide (Li ₂ MnO ₃ -LiMO ₂ (M=Co, Ni, etc.)), lithium-manganese-nickel oxide (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), olivine-type lithium phosphate oxide (LiFePO ₄ ), and other composite oxides; conductive polymers such as polyaniline and polypyrrole; Li ₂ S, CuS, Li-Cu-S compounds, TiS ₂ , FeS, and MoS ₂ , sulfide-based positive electrode active materials such as Li-Mo-S compounds, Li-Ti-S compounds, Li-V-S compounds, and Li-Fe-S compounds; materials using sulfur as an active material such as sulfur-impregnated acetylene black, sulfur-impregnated porous carbon, and mixed powder of sulfur and carbon; etc. These positive electrode active materials may be used alone or in combination of two or more.
Among these, from the viewpoint of having a higher discharge capacity density and being superior in cycle characteristics, a sulfide-based positive electrode active material is preferred, and one or more selected from Li-Mo-S compounds, Li-Ti-S compounds, and Li-V-S compounds are more preferred.

Here, the Li-Mo-S compound contains Li, Mo, and S as constituent elements, and can usually be obtained by chemically reacting an inorganic composition containing molybdenum sulfide and lithium sulfide, which are raw materials, with each other through a mechanical treatment.
In addition, the Li-Ti-S compound contains Li, Ti, and S as constituent elements, and can usually be obtained by chemically reacting inorganic compositions containing titanium sulfide and lithium sulfide, which are raw materials, with each other through a mechanical treatment.
The Li-V-S compound contains Li, V, and S as constituent elements, and can usually be obtained by chemically reacting an inorganic composition containing vanadium sulfide and lithium sulfide, which are raw materials, with each other through a mechanical treatment.

The positive electrode active material layer 101 is not particularly limited, but may contain, as a component other than the positive electrode active material, one or more materials selected from, for example, a binder resin, a thickener, a conductive assistant, a solid electrolyte material, etc. Each material will be described below.

The positive electrode active material layer 101 may contain a binder resin that serves to bind the positive electrode active materials together and between the positive electrode active material and the current collector 105 .
The binder resin according to the present embodiment is not particularly limited as long as it is a typical binder resin that can be used in lithium ion batteries, and examples thereof include polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polyimide, etc. These binders may be used alone or in combination of two or more.

The positive electrode active material layer 101 may contain a thickener to ensure the fluidity of the slurry suitable for application. The thickener is not particularly limited as long as it is a normal thickener that can be used in lithium ion batteries, but examples include cellulose-based polymers such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose, and ammonium salts and alkali metal salts thereof, water-soluble polymers such as polycarboxylic acids, polyethylene oxide, polyvinylpyrrolidone, polyacrylates, and polyvinyl alcohol. These thickeners may be used alone or in combination of two or more.

The positive electrode active material layer 101 may contain a conductive assistant from the viewpoint of improving the conductivity of the positive electrode 110. The conductive assistant is not particularly limited as long as it is a normal conductive assistant that can be used in lithium ion batteries, but examples of the conductive assistant include carbon black such as acetylene black and ketjen black, and carbon materials such as vapor-grown carbon fiber.

The positive electrode according to this embodiment may contain a solid electrolyte containing the sulfide-based inorganic solid electrolyte material according to the embodiment described above, or may contain a solid electrolyte containing a solid electrolyte material of a type different from the sulfide-based inorganic solid electrolyte material according to this embodiment. The solid electrolyte material of a type different from the sulfide-based inorganic solid electrolyte material according to this embodiment is not particularly limited as long as it has ion conductivity and insulating properties, but those generally used in lithium ion batteries can be used. For example, inorganic solid electrolyte materials such as sulfide-based inorganic solid electrolyte materials, oxide-based inorganic solid electrolyte materials, and other lithium-based inorganic solid electrolyte materials; organic solid electrolyte materials such as polymer electrolytes can be mentioned. More specifically, the inorganic solid electrolyte materials mentioned in the description of the solid electrolyte according to this embodiment can be used.

The mixing ratio of the various materials in the positive electrode active material layer 101 is not particularly limited and can be set according to generally known information, as it is determined appropriately depending on the intended use of the battery, etc.

(Negative electrode)
The negative electrode 130 is not particularly limited, and any electrode generally used in lithium ion batteries can be used. The negative electrode 130 is not particularly limited, and can be manufactured according to a generally known method. For example, the negative electrode 130 can be obtained by forming a negative electrode active material layer 103 containing a negative electrode active material on the surface of a current collector 105 made of copper or the like.
The thickness and density of the negative electrode active material layer 103 are not particularly limited since they are appropriately determined depending on the intended use of the battery, and can be set in accordance with generally known information.

The negative electrode active material layer 103 contains a negative electrode active material.
The negative electrode active material is not particularly limited as long as it is a normal negative electrode active material that can be used for the negative electrode of a lithium ion battery, and examples thereof include carbonaceous materials such as natural graphite, artificial graphite, resin carbon, carbon fiber, activated carbon, hard carbon, and soft carbon; metal-based materials mainly composed of lithium, lithium alloys, tin, tin alloys, silicon, silicon alloys, gallium, gallium alloys, indium, indium alloys, aluminum, and aluminum alloys; conductive polymers such as polyacene, polyacetylene, and polypyrrole; and lithium titanium composite oxides (e.g., Li ₄ Ti ₅ O ₁₂ ). These negative electrode active materials may be used alone or in combination of two or more.

The negative electrode active material layer 103 is not particularly limited, and may contain, as a component other than the negative electrode active material, one or more materials selected from, for example, a binder resin, a thickener, a conductive assistant, a solid electrolyte material, etc. These materials are not particularly limited, and may include, for example, the same materials as those used for the positive electrode 110 described above.
The blending ratio of the various materials in the negative electrode active material layer 103 is appropriately determined depending on the intended use of the battery, and is not particularly limited, and can be set in accordance with generally known information.

(Electrolyte layer)
Next, a description will be given of the electrolyte layer 120. The electrolyte layer 120 is a layer formed between the positive electrode active material layer 101 and the negative electrode active material layer 103.
The electrolyte layer 120 may be a separator impregnated with a non-aqueous electrolyte solution or a solid electrolyte layer containing a solid electrolyte.

The separator in this embodiment is not particularly limited as long as it electrically insulates the positive electrode 110 and the negative electrode 130 and allows lithium ions to pass through, but for example, a porous membrane can be used.

As the porous membrane, a microporous polymer film is preferably used, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, polyester, etc. In particular, a porous polyolefin film is preferable, and specific examples include a porous polyethylene film, a porous polypropylene film, etc.

The non-aqueous electrolyte is a solution in which an electrolyte is dissolved in a solvent.
Any known lithium salt can be used as the electrolyte, and it may be selected according to the type of active material. For example, _LiClO4 , _LiBF6 , _LiPF6 , _LiCF3SO3 , LiCF3CO2 _{, LiAsF6} , _{LiSbF6 ,} LiB10Cl10 _, LiAlCl4 _, LiCl _{, LiBr} , LiB( _C2H5 ) ₄ , _CF3SO3Li , _{CH3SO3Li , LiCF3SO3} , _LiC4F9SO3 , Li( _{CF3SO2 ) 2N , lithium lower} fatty _acid carboxylate _, etc. can be mentioned.

The solvent for dissolving the electrolyte is not particularly limited as long as it is a solvent that is commonly used as a liquid for dissolving electrolytes, and examples of such solvents include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), vinylene carbonate (VC), etc.; lactones such as γ-butyrolactone and γ-valerolactone; ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; Examples of such compounds include sulfoxides such as dimethyl sulfoxide; oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; nitrogen-containing compounds such as acetonitrile, nitromethane, formamide, and dimethylformamide; organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and ethyl propionate; phosphate triesters and diglymes; triglymes; sulfolanes such as sulfolane and methyl sulfolane; oxazolidinones such as 3-methyl-2-oxazolidinone; sultones such as 1,3-propane sultone, 1,4-butane sultone, and naphtha sultone; and the like. These compounds may be used alone or in combination of two or more.

The solid electrolyte layer according to this embodiment is a layer formed between the positive electrode active material layer 101 and the negative electrode active material layer 103, and is a layer formed of a solid electrolyte containing a solid electrolyte material. The solid electrolyte contained in the solid electrolyte layer is not particularly limited as long as it has lithium ion conductivity, but in this embodiment, it is preferable that the solid electrolyte is a solid electrolyte containing the sulfide-based inorganic solid electrolyte material according to this embodiment.
The content of the solid electrolyte in the solid electrolyte layer according to the present embodiment is not particularly limited as long as the desired insulating properties can be obtained, but is preferably, for example, in the range of 10 volume % or more and 100 volume % or less, and more preferably, in the range of 50 volume % or more and 100 volume % or less. In particular, in the present embodiment, it is preferable that the solid electrolyte layer is composed only of a solid electrolyte containing the sulfide-based inorganic solid electrolyte material according to the present embodiment.

The solid electrolyte layer according to this embodiment may also contain a binder resin. By containing a binder resin, a flexible solid electrolyte layer can be obtained. Examples of the binder resin include fluorine-containing binders such as polytetrafluoroethylene and polyvinylidene fluoride. The thickness of the solid electrolyte layer is preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 0.1 μm to 300 μm.

Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can also be adopted.
The present invention is not limited to the above-described embodiment, and modifications and improvements within the scope of the present invention that can achieve the object of the present invention are included in the present invention.

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[1] Measurement Method First, the measurement methods in the following examples and comparative examples will be described.

(1) Particle size distribution The particle size distribution of the sulfide-based inorganic solid electrolyte material obtained in the examples and comparative examples was measured by a laser diffraction method using a laser diffraction scattering type particle size distribution measurement device (Malvern Instruments, Mastersizer 3000). From the measurement results, the particle size ( _D50 , average particle size) at 50% accumulation in the cumulative distribution based on weight for the sulfide-based inorganic solid electrolyte material was obtained.

(2) Measurement of Composition Ratio Using an ICP optical emission spectrometer (Seiko Instruments Inc., SPS3000), measurements were performed by ICP optical emission spectroscopic analysis to determine the mass percentages of Li, P, and S in the sulfide-based inorganic solid electrolyte materials obtained in the examples and comparative examples, and the molar ratios of each element were calculated based on the results.

(3) X-ray diffraction analysis Using an X-ray diffractometer (Rigaku Corporation, RINT2000), the diffraction spectrum of the sulfide-based inorganic solid electrolyte material obtained in the examples and comparative examples was obtained by X-ray diffraction analysis. Note that CuKα radiation was used as the radiation source. Here, the maximum diffraction intensity at the position of diffraction angle 2θ = 35.0 ± 0.1 ° was defined as background intensity I _A , the maximum diffraction intensity of the diffraction peak at the position of diffraction angle 2θ = 17.2 ± 0.5 ° was defined as I _B , the maximum diffraction intensity of the diffraction peak at the position of diffraction angle 2θ = 18.8 ± 0.4 ° was defined as I _C , the maximum diffraction intensity of the diffraction peak at the position of diffraction angle 2θ = 25.6 ± 0.5 ° was defined as I _D , the maximum diffraction intensity of the diffraction peak at the position of diffraction angle 2θ = 26.6 ± 0.4 ° was defined as I _E , and the maximum diffraction intensity of the diffraction peak at the position of diffraction angle 2θ = 29.2 ± 0.8 ° was defined as I _F. In addition, I _B /I _A and I _C /I _A were determined.

(4) Measurement of lithium ion conductivity The lithium ion conductivity of the sulfide-based inorganic solid electrolyte materials obtained in the examples and comparative examples was measured by an AC impedance method. In addition, after exposing 1.0 g of the sulfide-based inorganic solid electrolyte materials obtained in the examples and comparative examples to the air at 25° C. for 10 minutes, the lithium ion conductivity of the sulfide-based inorganic solid electrolyte materials was also measured.
The lithium ion conductivity was measured using a potentiostat/galvanostat SP-300 manufactured by Biologic Corp. The sample size was 9.5 mm in diameter and 1.2 to 2.0 mm in thickness, and the measurement conditions were an applied voltage of 10 mV, a measurement temperature of 27.0° C., a measurement frequency range of 0.1 Hz to 7 MHz, and a Li foil electrode.
Here, as the sample for measuring lithium ion conductivity, a plate-shaped sulfide-based inorganic solid electrolyte material having a diameter of 9.5 mm and a thickness of 1.2 to 2.0 mm was used, which was obtained by pressing 150 mg of the powdered sulfide-based inorganic solid electrolyte material obtained in the examples and comparative examples at 270 MPa for 10 minutes using a pressing device.

(5) Measurement of maximum value of oxidative decomposition current Using a press device, 120 to 150 mg of the powdered sulfide-based inorganic solid electrolyte material obtained in the examples and comparative examples was pressed at 270 MPa for 10 minutes to obtain a plate-shaped sulfide-based inorganic solid electrolyte material (pellet) having a diameter of 9.5 mm and a thickness of 1.3 mm. Next, Li foil was pressed and compressed as a reference electrode and counter electrode on one side of the obtained pellet under conditions of 18 MPa and 10 minutes, and SUS314 foil was adhered to the other side as a working electrode.
Next, using a potentiostat/galvanostat SP-300 manufactured by Biologic, Inc., the maximum value of the oxidative decomposition current of the sulfide-based inorganic solid electrolyte material was determined under conditions of a temperature of 25° C., a sweep voltage range of 0 to 5 V, and a voltage sweep rate of 5 mV/sec, and was evaluated according to the following criteria.
◎: 0.03 μA or less ○: Exceeding 0.03 μA 0.50 μA or less ×: Exceeding 0.50 μA

[2] Production of solid electrolyte material <Example 1>
A sulfide-based inorganic solid electrolyte material was prepared by the following procedure.
The raw materials used were Li ₂ S (manufactured by Furukawa Co., Ltd., purity 99.9%), P ₂ S ₅ (manufactured by Kanto Chemical Co., Ltd.) and Li ₃ N (manufactured by Furukawa Co., Ltd.).
First, a rotary blade grinder and an alumina pot (internal volume 400 mL) were placed in a glove box, and then high-purity dry argon gas (H ₂ O < 1 ppm, O ₂ < 1 ppm) obtained through a gas purification device was injected into the glove box and vacuum degassed three times.
Next, in a glove box, a rotary blade grinder (rotation speed 18,000 rpm) was used to mix a total of ₅ g of _Li2S powder, _P2S5 powder, and _Li3N powder ( _Li2S : _P2S5 : _Li3N = 71.1: _23.7 :5.3 (mol%)) (10 times of mixing for 10 seconds and leaving for 10 seconds (cumulative mixing time: 100 seconds)), to prepare a raw inorganic composition.
Here, the Li ₂ S powder, P ₂ S ₅ powder, and Li ₃ N powder were put into the rotary blade type pulverizer in the glove box in the following procedure. First, the Li ₂ S powder, P ₂ S ₅ powder, and Li ₃ N powder were put into the side box of the glove box with the door inside the glove box closed. Next, high-purity dry argon gas was introduced from the glove box into the side box and vacuum degassing was performed three times. Next, the door inside the glove box was opened, and the Li ₂ S powder, P ₂ S ₅ powder, and Li ₃ N powder were put into the rotary blade type pulverizer inside the glove box, and the pulverizer was sealed.

Next, the raw inorganic composition and 500 g of _ZrO2 balls with a diameter of 10 mm were placed in an alumina pot (capacity 400 mL) in the glove box, and the pot was sealed. An O-ring (standard P-75) was used as a packing for the lid of the alumina pot. Dry argon gas was circulated in the glove box to adjust the moisture concentration to 0.5 ppm and the oxygen concentration to 0.6 ppm.
Next, the alumina pot was taken out of the glove box, and the alumina pot was attached to a ball mill machine installed under an atmosphere of dry air introduced through a membrane air dryer, and the raw material inorganic composition was vitrified by mixing at 120 rpm for 500 hours. At this time, the moisture concentration of the dry air obtained through the membrane air dryer was 600 ppm. After every 48 hours of mixing, the powder on the inner wall of the pot was scraped off in the glove box, and after sealing, milling was continued under a dry air atmosphere.
Next, an alumina pot was placed in the glove box, and the obtained powder was transferred from the alumina pot to a carbon crucible and subjected to a heat treatment at 270° C. for 2 hours in a heating furnace installed in the glove box.
The sulfide-based inorganic solid electrolyte material thus obtained was evaluated. The results are shown in Table 1.

Example 2
A sulfide-based inorganic solid electrolyte material was prepared in the _same manner as in Example 1, except that the mixing ratio of the _Li2S powder, _{the P2S5} powder, and the _Li3N powder was changed to _Li2S : _P2S5 :Li3N=67.5:22.5:10.0 (mol%), and each evaluation was performed. The obtained results are shown in Table ₁ .

Example 3
A sulfide-based inorganic solid electrolyte material was prepared in the _same manner as in Example 1, except that the mixing ratio of the _Li2S powder, _{the P2S5} powder, and the _Li3N powder was changed to _Li2S : _P2S5 : _Li3N =65.9:22.0:12.2 (mol%), and each evaluation was performed. The obtained results are shown in Table 1.

Example 4
The raw materials used were Li ₂ S (manufactured by Furukawa Co., Ltd., purity 99.9%) and P ₂ S ₅ (a reagent manufactured by Kanto Chemical Co., Ltd.) P ₄ S ₃ was prepared by the following procedure.
First, in an argon glove box, stoichiometric amounts of sulfur (Kanto Chemical Co., Ltd., 99.5% reagent) and red phosphorus (Wako Pure Chemical Industries, Ltd., 98% reagent) were placed in a quartz distillation apparatus, slowly heated to 180°C, and then reacted while thoroughly stirring. After being held at ₃₂₀ °C for 1 hour, the temperature was raised to 420°C to recover _P4S3 as a distillate. _The extracted _P4S3 was crushed in an agate mortar and sieved with a stainless steel sieve, and powders of 75 μm or less were recovered and used as the raw material for the solid electrolyte material.
Next, _a sulfide solid electrolyte material _{was prepared} in the same manner as in Example 1, except that the mixing ratio of the _Li2S powder, _{the P2S5} powder, and _{the P4S3 powder} was changed to _Li2S :P2S5: _P4S3 = 77.8:21.1:1.1 (mol%), and each evaluation was performed. The obtained results are shown in Table 1.

<Comparative Example 1>
A sulfide-based inorganic solid electrolyte material was prepared in the _same manner as in Example 1, except that the mixing ratio of the _Li2S powder, _{the P2S5} powder, and the _Li3N powder was changed to _Li2S : _P2S5 : _Li3N =72.6:24.2:3.2 (mol%), and each evaluation was performed. The obtained results are shown in Table 1.

<Comparative Example 2>
A sulfide-based inorganic solid electrolyte material was prepared in the _same manner as in Example 1, except that the mixing ratio of the _Li2S powder, _{the P2S5} powder, and the _Li3N powder was changed to _Li2S : _P2S5 : _Li3N =73.8:24.6:1.6 (mol%), and each evaluation was performed. The obtained results are shown in Table 1.

<Comparative Example 3>
Except for adjusting the water concentration in the glove box to 4000 ppm, sulfide-based inorganic solid electrolyte materials were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Comparative Example 4>
Except for adjusting the water concentration in the glove box to 4000 ppm, sulfide-based inorganic solid electrolyte materials were prepared and evaluated in the same manner as in Example 2. The results are shown in Table 1.

<Comparative Example 5>
Except for adjusting the water concentration in the glove box to 4000 ppm, sulfide-based inorganic solid electrolyte materials were prepared and evaluated in the same manner as in Example 3. The results are shown in Table 1.

<Comparative Example 6>
Except for adjusting the water concentration in the glove box to 4000 ppm, sulfide-based inorganic solid electrolyte materials were prepared and evaluated in the same manner as in Example 4. The results are shown in Table 1.

The sulfide-based inorganic solid electrolyte material of the Example exhibited less decrease in lithium ion conductivity even when exposed to the air than the sulfide-based inorganic solid electrolyte material of the Comparative Example. That is, it can be understood that the sulfide-based inorganic solid electrolyte material of the Example can suppress the decrease in lithium ion conductivity when exposed to the air.
Here, the X-ray diffraction spectra of the sulfide-based inorganic solid electrolyte materials obtained in the examples and comparative examples are shown in FIG. 2 and FIG. 3, respectively.

100 Lithium ion battery 101 Positive electrode active material layer 103 Negative electrode active material layer 105 Current collector 110 Positive electrode 120 Electrolyte layer 130 Negative electrode

Claims (18)

A sulfide-based inorganic solid electrolyte material having lithium ion conductivity,
In a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source, the diffraction peaks are at diffraction angles 2θ=17.2±0.5° and 2θ=18.8±0.4°,
The maximum diffraction intensity of the diffraction peak at the diffraction angle 2θ=17.2±0.5° is defined as _IB .
When the maximum diffraction intensity of the diffraction peak present at the position of the diffraction angle 2θ=18.8±0.4° is defined as I _C , the value of I _C /I _B is 0.35 or more and 1.0 or less,
A sulfide-based inorganic solid electrolyte material further having diffraction peaks at a diffraction angle 2θ=25.6±0.5° and a diffraction peak at a diffraction angle 2θ=26.6±0.4° in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source. The sulfide-based inorganic solid electrolyte material according to claim 1,
A sulfide-based inorganic solid electrolyte material in which, when the maximum diffraction intensity at a diffraction angle 2θ=35.0±0.1° in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source is defined as intensity _IA , and the maximum diffraction intensity of a diffraction peak existing at a diffraction angle 2θ=17.2±0.5° is defined as intensity _IB , the value of _IB / _IA is 2.0 or more. The sulfide-based inorganic solid electrolyte material according to claim 1 or 2,
A sulfide-based inorganic solid electrolyte material in which, when the maximum diffraction intensity at a diffraction angle 2θ=35.0±0.1° in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source is defined as intensity _IA , and the maximum diffraction intensity of a diffraction peak existing at a diffraction angle 2θ=18.8±0.4° is defined as intensity _IC , the value of _IC / _IA is 2.0 or more. The sulfide-based inorganic solid electrolyte material according to any one of claims 1 to 3,
The sulfide-based inorganic solid electrolyte material further has a diffraction peak at a diffraction angle 2θ=29.2±0.8° in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source. A sulfide-based inorganic solid electrolyte material having lithium ion conductivity,
When the sulfide-based inorganic solid electrolyte material is heat-treated at 270° C. for 2 hours and then subjected to X-ray diffraction measurement using CuKα radiation as a radiation source, the spectrum obtained by the X-ray diffraction measurement has diffraction peaks at diffraction angles 2θ=17.2±0.5° and 2θ=18.8±0.4°,
The maximum diffraction intensity of the diffraction peak at the diffraction angle 2θ=17.2±0.5° is defined as _IB .
A sulfide-based inorganic solid electrolyte material having an _IC / _IB value of 0.35 or more and 1.0 or less, where _IC is the maximum diffraction intensity of a diffraction peak present at a diffraction angle 2θ=18.8±0.4°. The sulfide-based inorganic solid electrolyte material according to claim 5,
When the sulfide-based inorganic solid electrolyte material is heat-treated at 270°C for 2 hours and then subjected to X-ray diffraction measurement using CuKα radiation as a radiation source, in the spectrum obtained by the X-ray diffraction measurement, the maximum diffraction intensity at a diffraction angle 2θ = 35.0 ± 0.1° is defined as intensity I _A and the maximum diffraction intensity of the diffraction peak present at a diffraction angle 2θ = 17.2 ± 0.5° is defined as intensity I _B , and the sulfide-based inorganic solid electrolyte material has an I _B /I _A value of 2.0 or more. The sulfide-based inorganic solid electrolyte material according to claim 5 or 6,
When the sulfide-based inorganic solid electrolyte material is heat-treated at 270°C for 2 hours and then subjected to X-ray diffraction measurement using CuKα radiation as a radiation source, in the spectrum obtained by the X-ray diffraction measurement, the maximum diffraction intensity at a diffraction angle 2θ = 35.0 ± 0.1° is defined as intensity _IA , and the maximum diffraction intensity of the diffraction peak present at a diffraction angle 2θ = 18.8 ± 0.4° is defined as intensity _IC , and the value of _IC / _IA is 2.0 or more. The sulfide-based inorganic solid electrolyte material according to any one of claims 5 to 7,
When the sulfide-based inorganic solid electrolyte material is heat-treated at 270° C. for 2 hours and then subjected to X-ray diffraction measurement using CuKα radiation as a radiation source, the spectrum obtained by the X-ray diffraction measurement further has diffraction peaks at diffraction angles 2θ=25.6±0.5°, 2θ=26.6±0.4°, and 2θ=29.2±0.8°. The sulfide-based inorganic solid electrolyte material according to any one of claims 1 to 8,
A sulfide-based inorganic solid electrolyte material containing Li, P and S as constituent elements. The sulfide-based inorganic solid electrolyte material according to claim 9,
A sulfide-based inorganic solid electrolyte material, in which a molar ratio Li/P of the Li content to the P content in the sulfide-based inorganic solid electrolyte material is 1.0 or more and 5.0 or less, and a molar ratio S/P of the S content to the P content in the sulfide-based inorganic solid electrolyte material is 2.0 or more and 6.0 or less. The sulfide-based inorganic solid electrolyte material according to any one of claims 1 to 10,
The sulfide-based inorganic solid electrolyte material has a particulate shape,
The particulate sulfide-based inorganic solid electrolyte material has an average particle diameter _d50 of 1 μm or more and 100 μm or less in a weight-based particle size distribution measured by a laser diffraction scattering particle size distribution measurement method. The sulfide-based inorganic solid electrolyte material according to any one of claims 1 to 11,
A sulfide-based inorganic solid electrolyte material used in lithium-ion batteries. A solid electrolyte comprising the sulfide-based inorganic solid electrolyte material according to any one of claims 1 to 12. A solid electrolyte membrane containing the solid electrolyte according to claim 13 as a main component. The solid electrolyte membrane according to claim 14,
A solid electrolyte membrane which is a pressure-molded body of the particulate solid electrolyte. The solid electrolyte membrane according to claim 14 or 15,
A solid electrolyte membrane, wherein the content of the binder resin in the solid electrolyte membrane is less than 0.5% by mass, where the entire solid electrolyte membrane is taken as 100% by mass. The solid electrolyte membrane according to any one of claims 14 to 16,
A solid electrolyte membrane, wherein the content of the sulfide-based inorganic solid electrolyte material in the solid electrolyte membrane is 50 mass % or more when the entire solid electrolyte membrane is taken as 100 mass %. A lithium ion battery comprising a positive electrode including a positive electrode active material layer, an electrolyte layer, and a negative electrode including a negative electrode active material layer,
A lithium ion battery, wherein at least one of the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer contains the sulfide-based inorganic solid electrolyte material according to claim 1 .

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