Sulfide-based inorganic solid electrolyte material and method for producing sulfide-based inorganic solid electrolyte material

Abstract

To provide a sulfide solid electrolyte material, capable of achieving both high lithium ion conductivity and stability against moisture, at a higher level.SOLUTION: A sulfide-based inorganic solid electrolyte material of the present invention contains, as constituent elements, lithium, phosphorus, and sulfur. A molar ratio (S / P) of the content of the sulfur (S) to the content of the phosphorus (S) is equal to or more than 3.7 and less than 4.0, and a molar ratio (Li / P) of the content of the lithium (Li) to the content of the phosphorus (P) is equal to or more than 2.8 and less than 3.0. In a spectrum obtained by X-ray diffraction using CuKα ray as a radiation source, the sulfide-based inorganic solid electrolyte material has diffraction peaks at a position (A) of a diffraction angle 2θ=17.5±0.3°, at a position (B) of a diffraction angle 2θ=18.8±0.3°, at a position (C) of a diffraction angle 2θ=25.8±0.3°, and at a position (D) of a diffraction angle 2θ=29.4±0.3°, respectively.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a sulfide-based inorganic solid electrolyte material and a method for producing the sulfide-based inorganic solid electrolyte material. More specifically, the present invention relates to a sulfide-based inorganic solid electrolyte material, a solid electrolyte membrane and a lithium ion battery using the same, and a method for producing the sulfide-based inorganic solid electrolyte material. [Background technology]

[0002] Conventionally, lithium-ion batteries have used electrolytes containing flammable organic solvents, so to improve safety, development is underway to replace the electrolyte with a solid electrolyte to create all-solid-state lithium-ion batteries. Furthermore, by eliminating the need for flammable organic solvents, safety devices can be simplified, leading to improved manufacturing costs and productivity.

[0003] Known examples of solid electrolyte materials used for such solid electrolytes include sulfide-based inorganic solid electrolyte materials.

[0004] Sulfide solid electrolyte materials are required to have high lithium ion conductivity so that they can handle large current charging and discharging, but at the same time, they are required to suppress the generation of hydrogen sulfide by reaction with moisture in the atmosphere. Therefore, research is being conducted to achieve stability against moisture while maintaining high lithium ion conductivity. For example, Patent Document 1 discloses a sulfide-based solid electrolyte for lithium secondary batteries, in which the surface of a compound containing lithium, phosphorus, sulfur, and a halogen and having a cubic Argyrodite-type crystal structure is coated with a compound containing lithium, phosphorus, and sulfur and having a non-Argyrodite-type crystal structure, and the compound having a non-Argyrodite-type crystal structure has an orthorhombic or triclinic crystal structure. Further, Patent Document 2 discloses a solid electrolyte containing Li7-aPS6-aHa (Ha represents a halogen; A satisfies 0.2 < a ≤ 1.8) and Li3PS4 having an Argyrodite-type crystal structure, and in the XRD pattern, the ratio of the peak intensity appearing at 2θ = 26.0 to 28.8° derived from Li3PS4 to the peak intensity appearing at 2θ = 24.9 to 26.3° derived from the Argyrodite-type crystal structure is 0.04 to 0.3. Further, Patent Document 3 discloses a Li-P-S-based sulfide solid electrolyte material having excellent electrochemical stability and lithium ion conductivity, which contains a composition of Li 3+x+5y P 1-y S4 (0 < x ≤ 0.6, 0 < y < 0.2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the technologies disclosed in Patent Documents 1 to 3 still have room for improvement in achieving both high lithium ion conductivity and stability against moisture, which are in a trade-off relationship.

[0007] The inventor has intensively studied to achieve both high lithium ion conductivity and stability against moisture at a higher level, and found that it is effective to use a sulfide-based material containing Li, P, and S in specific ratios as constituent elements, thereby completing the present invention.

[0008] The present invention has been made in view of the above circumstances, and provides a sulfide solid electrolyte material that can achieve both high lithium ion conductivity and stability against moisture at a higher level. [Means for solving the problem]

[0009] According to the present invention, A sulfide-based inorganic solid electrolyte material containing lithium, phosphorus, and sulfur as constituent elements, The molar ratio (S / P) of the sulfur (S) content to the phosphorus (P) content is 3.7 or more and less than 4.0, a molar ratio (Li / P) of the lithium (Li) content to the phosphorus (P) content is 2.8 or more and less than 3.0; In the spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source, A sulfide-based inorganic solid electrolyte material is provided, which has diffraction peaks at a diffraction angle 2θ=17.5±0.3° (A), a diffraction angle 2θ=18.8±0.3° (B), a diffraction angle 2θ=25.8±0.3° (C), and a diffraction angle 2θ=29.4±0.3° (D).

[0010] Further, according to the present invention, A solid electrolyte containing the sulfide-based inorganic solid electrolyte material is provided.

[0011] Further, according to the present invention, A lithium ion battery including 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 described above.

[0012] Further, according to the present invention, The method for producing the sulfide-based inorganic solid electrolyte material includes: vitrifying a mixture comprising diphosphorus pentasulfide and lithium sulfide; heating the resulting glassy mixture to crystallize at least a portion of the mixture; Including, The diphosphorus pentasulfide has a molar ratio (S / P) of sulfur (S) content to phosphorus (P) content of 2.4 or more and 2.5 or less, in accordance with a method for producing a sulfide-based inorganic solid electrolyte material. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a sulfide solid electrolyte material that can achieve both high lithium ion conductivity and stability against moisture at a higher level. [Brief explanation of the drawings]

[0014] [Figure 1] 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. DETAILED DESCRIPTION OF THE INVENTION

[0015] In this specification, unless otherwise specified, the expression "a to b" in the description of a numerical range means from a to b. For example, "1 to 5 mass %" means "1 mass % to 5 mass %."

[0016] Hereinafter, embodiments of the present invention will be described. Note that the drawings are for illustrative purposes only. The shapes and dimensional ratios of the components in the drawings do not necessarily correspond to the actual products.

[0017] <Sulfide-based inorganic solid electrolyte materials> The sulfide-based inorganic solid electrolyte material according to this embodiment contains lithium (Li), phosphorus (P), and sulfur (S) as constituent elements from the viewpoint of further improving electrochemical stability, stability in water and air, ease of handling, and the like. Furthermore, the sulfide-based inorganic solid electrolyte material according to this embodiment has a molar ratio (S / P) of sulfur (S) to phosphorus (P) of 3.7 or more and less than 4.0, a molar ratio (Li / P) of lithium (Li) to phosphorus (P) of 2.8 or more and less than 3.0, and in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source, the material has diffraction peaks at a diffraction angle 2θ = 17.5 ± 0.3° (A), a diffraction angle 2θ = 18.8 ± 0.3° (B), a diffraction angle 2θ = 25.8 ± 0.3° (C), and a diffraction angle 2θ = 29.4 ± 0.3° (D). This allows for a high level of both high lithium ion conductivity and stability to moisture.

[0018] The molar ratio of S to P (S / P) is preferably 3.8 or more and 3.9 or less. By setting (S / P) to the lower limit or more, it is possible to obtain high lithium ion conductivity while suppressing the amount of hydrogen sulfide generated. On the other hand, by setting (S / P) to the upper limit or less, it is possible to obtain high lithium ion conductivity while suppressing the amount of hydrogen sulfide generated. The molar ratio of Li to P (Li / P) is preferably 2.9 or more. By setting (S / Li) within the above range, the balance between suppressing the generation of hydrogen sulfide and high lithium ion conductivity can be further improved. The composition of the sulfide-based inorganic solid electrolyte material according to this embodiment and the contents of Li, P, and S can be achieved by appropriately selecting the raw materials.

[0019] 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 spectroscopy or X-ray analysis.

[0020] The sulfide-based inorganic solid electrolyte material according to this embodiment has diffraction peaks at a diffraction angle 2θ=17.5±0.3° (A), a diffraction angle 2θ=18.8±0.3° (B), a diffraction angle 2θ=25.8±0.3° (C), and a diffraction angle 2θ=29.4±0.3° (D) in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source, and the maximum diffraction intensity of the diffraction peak at the diffraction angle 2θ=25.8±0.3° (C) is I C The maximum diffraction intensity of the diffraction peak at the diffraction angle 2θ = 29.4 ± 0.3° (D) is I D When I D / I C The value is preferably 2.1 to 3.2. This makes it possible to stably obtain a sulfide-based inorganic solid electrolyte material having a desired composition, and to simultaneously achieve high lithium ion conductivity and suppression of hydrogen sulfide generation in the sulfide-based inorganic solid electrolyte material.

[0021] Furthermore, the sulfide-based inorganic solid electrolyte material of this embodiment preferably has diffraction peaks at a diffraction angle 2θ=21.4±0.3° (E) and a diffraction angle 2θ=23.6±0.3° (F) in a spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source. This allows the desired sulfide-based inorganic solid electrolyte material to be obtained more stably.

[0022] Here, the diffraction peaks present at positions (A) to (D) are similar to the peaks seen in the crystal structure of Li3PS4, an ortho-composition compound, and are intended to be a crystal structure similar to Li3PS4. Moreover, the diffraction peaks present at positions (E) to (F) indicate improved crystallinity. The sulfide-based inorganic solid electrolyte material of this embodiment has diffraction peaks at the positions (A) to (F) above, which means that the sulfide-based inorganic solid electrolyte material has a crystalline structure and an ordered structure. The solid electrolyte material of this embodiment has such a structure, which can further improve lithium ion conductivity. Furthermore, as a result of manufacturing the solid electrolyte material of this embodiment so as to have such desired diffraction peaks, the generation of hydrogen sulfide can be suppressed, although the details are not clear. A compound obtained by heat-treating a glassy mixture to crystallize it is generally called crystallized glass.

[0023] 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 3 MHz is preferably 1.3 × 10 -3 S cm -1 More preferably, it is 1.4×10 -3 S cm -1 More preferably, it is 1.5×10 -3 S cm -1 More preferably, 1.6 × 10 -3 S cm -1 That's all. When the lithium ion conductivity of the sulfide-based inorganic solid electrolyte material according to the present embodiment is equal to or greater than the above lower limit, a lithium ion battery with even better battery characteristics can be obtained. Furthermore, by using such a sulfide-based inorganic solid electrolyte material, a lithium ion battery with even better input / output characteristics can be obtained.

[0024] 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 has an average particle diameter d 50However, it is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 80 μm or less, and further preferably 5 μm or more and 60 μm or less. Average particle diameter d of sulfide-based inorganic solid electrolyte material 50 By setting the value of the total mass of the polymer in the above range, it is possible to maintain good handling properties and further improve the lithium ion conductivity.

[0025] 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 lithium ion batteries. More specifically, it is used in the positive electrode active material layer, negative electrode active material layer, electrolyte layer, etc. of lithium ion batteries. Furthermore, the sulfide-based inorganic solid electrolyte material according to this embodiment is preferably used in the positive electrode active material layer, negative electrode active material layer, solid electrolyte layer, etc. that constitute all-solid-state lithium ion batteries, and is particularly preferably used in the solid electrolyte layer that constitutes all-solid-state lithium ion batteries. 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 stacked in this order.

[0026] <Method for 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 the sulfide-based inorganic solid electrolyte material according to this embodiment includes the steps of: (Step 1) vitrifying a raw material composition containing diphosphorus pentasulfide and lithium sulfide; (Step 2) heating the resulting glassy mixture to crystallize at least a portion of the mixture; and (Step 3) A step of pulverizing, classifying, or granulating the obtained sulfide-based inorganic solid electrolyte material may be included. Each step will be described in detail below.

[0027] (Process 1) First, a raw material composition containing phosphorus pentasulfide and lithium sulfide as raw materials is prepared. Here, as the raw material composition, phosphorus compounds other than phosphorus pentasulfide and lithium compounds other than lithium sulfide may be used as appropriate depending on the case, but the mixing ratio of each raw material in the raw material composition is adjusted so that the sulfide-based inorganic solid electrolyte material finally obtained has the desired composition ratio. For example, an example of a phosphorus compound other than phosphorus pentasulfide is red phosphorus, and an example of a lithium compound other than lithium sulfide is lithium nitride, which will be described later. The method for mixing the raw materials is not particularly limited as long as it can mix the raw materials uniformly. For example, mixing can be performed using a ball mill, bead mill, vibration mill, impact crusher, mixer (pug mixer, ribbon mixer, tumbler mixer, drum mixer, V-type mixer, etc.), kneader, twin-shaft kneader, air flow crusher, crusher, rotary blade crusher, etc. The mixing conditions when mixing the raw materials, such as the stirring speed, treatment time, temperature, reaction pressure, and gravitational acceleration applied to the mixture, can be appropriately determined depending on the amount of the mixture to be treated.

[0028] (diphosphorus pentasulfide) The diphosphorus pentasulfide used as the raw material may have a molar ratio (S / P) of sulfur (S) content to phosphorus (P) content of 2.4 or more and 2.5 or less. From the viewpoint of further improving the stability over time of the obtained sulfide-based inorganic solid electrolyte material, the lower limit of S / P is preferably 2.41 or more, more preferably 2.42 or more, and even more preferably 2.43 or more, while it is preferably 2.48 or less, more preferably 2.47 or more. When the diphosphorus pentasulfide according to this embodiment has an S / P ratio within the above range, the lithium ion conductivity of the resulting sulfide-based inorganic solid electrolyte material can be improved. In this embodiment, diphosphorus pentasulfide having an S / P ratio within the above range can be obtained, for example, by subjecting a raw material of diphosphorus pentasulfide to vacuum heating to reduce the amount of sulfur components in diphosphorus pentasulfide. The conditions such as pressure, heating temperature, and treatment time when the diphosphorus pentasulfide raw material composition is vacuum heated can be appropriately determined depending on the amount of diphosphorus pentasulfide raw material composition to be treated. The pressure inside the vacuum heating device when the diphosphorus pentasulfide raw material composition is vacuum heated is, for example, −0.01 MPa or less, and preferably −0.07 MPa or less. The heating temperature when the diphosphorus pentasulfide raw material composition is vacuum heated is, for example, 220°C or higher and 500°C or lower, and preferably 250°C or higher and 350°C or lower. The time for vacuum heating the diphosphorus pentasulfide raw material composition is, for example, 0.5 hours or more and 24 hours or less, and preferably 1 hour or more and 5 hours or less.

[0029] The diphosphorus pentasulfide of this embodiment is not particularly limited, and commercially available P2S5 can be used. From the viewpoint of obtaining a high-purity solid electrolyte material and suppressing side reactions, it is preferable to use P2S5 with few impurities. Furthermore, instead of P2S5, elemental phosphorus (P) and elemental sulfur (S) can be used in the corresponding molar ratio. The elemental phosphorus (P) and elemental sulfur (S) can be used without particular limitation as long as they are industrially produced and commercially available.

[0030] The average particle diameter d50 of the diphosphorus pentasulfide of this embodiment in the weight-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is preferably 30 μm or less, more preferably 20 μm or less, and particularly preferably 10 μm or less. By setting the average particle diameter d50 to the above upper limit or less, the contact area between Li2S, P2S5, and Li3N can be increased. This promotes the reaction between Li2S, P2S5, and Li3N, allowing the solid electrolyte material of this embodiment to be obtained more efficiently. The lower limit of the average particle diameter d50 of diphosphorus pentasulfide is not particularly limited, but from the viewpoint of ease of handling, it is, for example, 1 μm or more.

[0031] The phosphorus (P) and sulfur (S) contents of diphosphorus pentasulfide can be determined by semi-quantitative analysis using, for example, energy dispersive X-ray analysis (EDX).

[0032] The diphosphorus pentasulfide according to this embodiment may be in the form of, for example, a powder. Since the production of a sulfide-based inorganic solid electrolyte material, which will be described later, is generally carried out by a dry method, if the diphosphorus pentasulfide according to this embodiment is in the form of a powder, the production of the sulfide-based inorganic solid electrolyte material becomes easier.

[0033] (lithium sulfide) The lithium sulfide used as a raw material is not particularly limited, and commercially available lithium sulfide may be used, or lithium sulfide obtained by, for example, reacting lithium hydroxide with hydrogen sulfide may 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 lithium sulfide with few impurities. In this embodiment, lithium sulfide also includes lithium polysulfide.

[0034] In this embodiment, the blending ratio of diphosphorus pentasulfide and lithium sulfide in the raw material composition is adjusted as appropriate depending on the purpose. When the total of diphosphorus pentasulfide and lithium sulfide in the raw material composition is taken as 100 mol %, it is preferable that the lithium sulfide content be 35 mol % or more and 75 mol % or less, and the diphosphorus pentasulfide content be 25 mol % or more and 65 mol % or less. The sulfide-based inorganic solid electrolyte material of this embodiment can effectively improve lithium ion conductivity by using diphosphorus pentasulfide and lithium sulfide as raw materials.

[0035] The sulfide-based inorganic solid electrolyte material of this embodiment may use lithium nitride as a raw material. Lithium nitride, which is used as a raw material, releases nitrogen into the system as N2. Therefore, by using lithium nitride as the raw inorganic compound, it is possible to increase only the Li composition in sulfide-based inorganic solid electrolyte materials, which contain Li, P, and S as constituent elements. The lithium nitride according to the present embodiment is not particularly limited, and may be commercially available lithium nitride (e.g., LiN, etc.), or may be lithium nitride 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 few impurities.

[0036] In this embodiment, when lithium nitride is used as a raw material, the respective blending ratios of diphosphorus pentasulfide, lithium sulfide, and lithium nitride in the raw material composition are adjusted as appropriate depending on the purpose. When the total of diphosphorus pentasulfide, lithium sulfide, and lithium nitride in the raw material composition is taken as 100 mol%, it is preferable that the lithium sulfide content be 35 mol% or more and 75 mol% or less, the diphosphorus pentasulfide content be 15 mol% or more and 55 mol% or less, and the lithium nitride content be 0.1 mol% or more and 10 mol% or less.

[0037] Subsequently, the raw material composition is vitrified. As a vitrification method, for example, the raw material composition is mechanically treated to vitrify the raw materials, i.e., diphosphorus pentasulfide, lithium sulfide, and lithium nitride, while causing a chemical reaction therebetween, thereby obtaining a sulfide-based inorganic solid electrolyte material in a glassy state.

[0038] Here, the mechanical treatment may be any treatment that can mechanically collide two or more inorganic compounds to cause a chemical reaction and vitrification. Examples of mechanical treatment include mechanochemical treatment. Mechanochemical treatment is a method of vitrifying a target composition by applying mechanical energy such as shear force or collision force to the composition. Furthermore, in step 2, 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 degree. By using the mechanochemical treatment, the raw materials can be mixed while being pulverized into fine particles, thereby increasing the contact area between the raw materials, thereby accelerating the reaction between the raw materials, and thereby enabling the sulfide-based inorganic solid electrolyte material according to this embodiment to be obtained more efficiently.

[0039] Mechanochemical processing is a method of vitrifying a mixture by applying mechanical energy such as shear, impact, or centrifugal force. Examples of equipment for vitrification by mechanochemical processing (hereinafter referred to as vitrification equipment) include grinding and dispersing machines such as ball mills, bead mills, vibration mills, turbo mills, mechanofusion machines, disk mills, and roll mills; rotary and impact crushing machines that combine rotation (shear stress) and impact (compression stress), such as jackhammers, vibration drills, and impact drivers; high-pressure gliding rolls; and vertical mills such as roller-type vertical mills and ball-type vertical mills. Among these, ball mills and bead mills are preferred, with ball mills being particularly preferred, due to their ability to efficiently generate extremely high impact energy. Furthermore, from the viewpoint of excellent continuous productivity, preferred are roll mills; rotary / impact crushing devices consisting of a mechanism combining rotation (shear stress) and impact (compression stress), such as those typified by rock drills, vibration drills, and impact drivers; high-pressure gliding rolls; and vertical mills such as roller-type vertical mills and ball-type vertical mills.

[0040] 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 material composition of a sulfide-based inorganic solid electrolyte material, can be appropriately determined depending on the type and processing amount of the raw inorganic composition. Generally, the faster the rotation speed, the faster the glass production rate, and the longer the processing time, the higher the conversion rate to glass. For example, the processing time may be 5 to 100 hours, or 20 to 50 hours. Generally, when X-ray diffraction analysis is performed using CuKα radiation as a radiation source, if the diffraction peaks derived from the raw materials disappear or decrease, it can be determined that the raw material composition of the sulfide-based inorganic solid electrolyte material has been vitrified and the desired sulfide-based inorganic solid electrolyte material has been obtained.

[0041] (Process 2) Next, the resulting glassy mixture is heated to crystallize at least a portion of the mixture, i.e., 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). This allows the sulfide-based inorganic solid electrolyte material according to this embodiment to be in a glass ceramic state (crystallized glass state), and as a result, the lithium ion conductivity can be further improved.

[0042] The heating temperature of the glassy mixture is preferably in the range of 180°C or higher and 350°C or lower, more preferably 230°C or higher and 320°C or lower, and even more preferably 270°C or higher and 300°C or lower. The heating time is not particularly limited as long as it is a time that allows a sulfide-based inorganic solid electrolyte material in a desired glass ceramic state to be obtained, but is, for example, in the range of 0.5 hours to 24 hours, and 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.

[0043] Furthermore, the glassy mixture 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 during heating include argon gas, helium gas, and nitrogen gas. These inert gases are preferably as pure as possible to prevent impurities from being mixed into the product, and to avoid contact with moisture, the dew point is preferably −30° C. or lower, more preferably −70° C. or lower, and particularly preferably −80° C. or lower. The method for 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 include a method of purging the inert gas and a method of continuously introducing a constant amount of inert gas.

[0044] The conditions such as the temperature and time during heating can be adjusted as appropriate to optimize the properties of the sulfide-based inorganic solid electrolyte material according to this embodiment.

[0045] (Step 3) In the method for producing a sulfide-based inorganic solid electrolyte material according to this embodiment, the obtained sulfide-based inorganic solid electrolyte material may further be subjected to a step of pulverizing, classifying, or granulating, if necessary. For example, a sulfide-based inorganic solid electrolyte material having a desired particle size can be obtained by pulverizing the material to obtain fine particles, and then adjusting the particle size by a classification or granulation operation. The pulverizing method is not particularly limited, and known pulverizing methods such as a mixer, airflow pulverizer, mortar, rotary mill, and coffee mill can be used. The 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.

[0046] 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.

[0047] <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. The solid electrolyte membrane according to this embodiment is used, for example, in a solid electrolyte layer constituting an all-solid-state lithium ion battery. An example of an all-solid-state lithium ion battery to which the solid electrolyte membrane according to this embodiment is applied is one in which a positive electrode, a solid electrolyte layer, and a negative electrode are stacked in this order. In this case, the solid electrolyte layer is composed of the solid electrolyte membrane. Details will be described later.

[0048] 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 greater than the lower limit, chipping of the solid electrolyte and cracking of 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.

[0049] The solid electrolyte membrane according to this embodiment is preferably a pressure-molded body of particulate solid electrolyte containing the sulfide-based inorganic solid electrolyte material according to this embodiment described above. That is, it is preferable to pressurize the particulate solid electrolyte to form a solid electrolyte membrane having a certain strength due to the anchor effect between the solid electrolyte materials. By forming the solid electrolyte into a pressure-molded body, the solid electrolyte molecules bond together, further increasing the strength of the resulting solid electrolyte membrane, thereby further suppressing chipping of the solid electrolyte and cracks on the surface of the solid electrolyte membrane.

[0050] 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 contact between solid electrolytes and reduces the interfacial contact resistance of the solid electrolyte membrane. As a result, the lithium ion conductivity of the solid electrolyte membrane can be further improved. Furthermore, by using such a solid electrolyte membrane with excellent lithium ion conductivity, the battery characteristics of the resulting 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 this embodiment in the solid electrolyte membrane according to this embodiment is not particularly limited, but is, for example, 100 mass % or less.

[0051] The planar shape of the solid electrolyte membrane is not particularly limited and can be appropriately selected in accordance with the shapes of the electrodes and current collectors, but can be, for example, rectangular.

[0052] The solid electrolyte membrane according to this 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 this embodiment does not substantially contain a binder resin, and most preferably does not contain a binder resin. This improves contact between solid electrolytes and reduces the interfacial contact resistance of the solid electrolyte membrane. As a result, the lithium ion conductivity of the solid electrolyte membrane can be further improved. Furthermore, by using such a solid electrolyte membrane with excellent lithium ion conductivity, the battery characteristics of the resulting all-solid-state lithium ion battery can be improved.

[0053] The phrase "substantially free of binder resin" means that the binder resin may be contained to an extent that does not impair the effects of the present embodiment. 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."

[0054] The binder resin is a binder generally used in lithium-ion batteries to bind 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.

[0055] The solid electrolyte membrane according to this embodiment can be obtained, for example, by depositing particulate solid electrolyte in the form of a film on the cavity surface of a mold or on the surface of a substrate, and then pressurizing the solid electrolyte deposited in the form of a film. 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 using a mold and a stamping die can be used. When a particulate solid electrolyte is deposited on the surface of a substrate, pressing using 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.

[0056] If necessary, the inorganic solid electrolyte deposited in the form of a film may be heated while being pressurized. Heating and pressurizing causes fusion and bonding of the solid electrolytes, further increasing the strength of the resulting solid electrolyte film. 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.

[0057] <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. The shape of the lithium ion battery 100 according to this embodiment is not particularly limited, and may be a cylindrical shape, a coin shape, a square shape, a film shape, or any other shape. The lithium-ion battery 100 according to this embodiment is manufactured according to a generally known method, for example, by forming a stack of the positive electrode 110, the electrolyte layer 120, and the negative electrode 130 into a cylindrical, coin-shaped, rectangular, film-shaped, or other arbitrary shape, and then sealing in a nonaqueous electrolyte solution as necessary.

[0058] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations can also be adopted. The present invention is not limited to the above-described embodiment, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. [Example]

[0059] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0060] <Measurement method> The measurement methods used in the following Examples and Comparative Examples will be explained.

[0061] (1) X-ray diffraction analysis The diffraction spectra of the sulfide-based inorganic solid electrolyte materials obtained in the examples and comparative examples were determined by X-ray diffraction analysis using an X-ray diffractometer (Rigaku Corporation, RINT2000). CuKα radiation was used as the radiation source. The maximum diffraction intensity of the diffraction peak at the diffraction angle 2θ = 25.8 ± 0.3° (C) is I CThe maximum diffraction intensity of the diffraction peak at the diffraction angle 2θ = 29.4 ± 0.3° (D) is I D It was decided.

[0062] (2) Measurement of lithium ion conductivity The sulfide-based inorganic solid electrolyte materials obtained in the examples and comparative examples were subjected to measurement of lithium ion conductivity by an AC impedance method. The lithium ion conductivity was measured using a potentiostat / galvanostat SP-300 manufactured by Hokuto Denko Co., Ltd. The sample size was φ9.5 mm, thickness 1.3 mm, 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 3 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 thickness of 1.3 mm was used, which was obtained by pressing the powdered sulfide-based inorganic solid electrolyte material obtained in the examples and comparative examples using a press machine at 270 MPa for 10 minutes.

[0063] (3) Determination of phosphorus (P) and sulfur (S) in diphosphorus pentasulfide The phosphorus pentasulfide compositions used in the examples and comparative examples were subjected to semi-quantitative analysis of phosphorus and sulfur by energy dispersive X-ray analysis (EDX). First, particles of 0.5 mm or larger were selected from diphosphorus pentasulfide in an argon atmosphere and crushed by gently pressing with a pestle. Next, the crushed diphosphorus pentasulfide composition was fixed to the sample pedestal of a scanning electron microscope (Hitachi S-4700) using carbon conductive tape, with the flat surface facing up. Gold was then deposited by sputtering to ensure electrical continuity with the pedestal. This procedure stabilized the image by suppressing charge buildup and promoted the detection of characteristic X-rays. After confirming the smoothness of the flat surface, the crushed diphosphorus pentasulfide composition was observed at an electron beam acceleration voltage of 15 kV, an emission current of 10 ± 1 μA, a working distance of 12 mm, and a magnification of 500x. Then, semi-quantitative analysis of phosphorus (P) and sulfur (S) was performed using an energy dispersive analyzer (Horiba EMAX-7000). Semi-quantitative analysis was performed using an electron beam accelerating voltage of 15 kV, an electron beam incidence angle of 90°, an X-ray takeoff angle of 35°, a pulse processing time of P3, and a dead time of 10-30% for 300 seconds. The background points were set to 0.67, 1.14, 1.70, 2.86, and 4.04 keV. The quantitative correction method was standardless φ(ρz), the peak separation method was overlap factor, and no mass concentration normalization, no atom number normalization, or low-energy GB correction was used. Phosphorus (P) and sulfur (S) concentrations were measured at five random locations on the flat surface of the crushed diphosphorus pentasulfide composition within a 0.25 mm × 0.17 mm observation field, and the average values ​​were used.

[0064] (4) Measurement of the amount of hydrogen sulfide gas generated Each sulfide-based inorganic solid electrolyte material (10 mg) obtained in the Examples and Comparative Examples was placed in a glass container (1.9 L) filled with air and controlled to have a dew point of −10td° C., and the container was sealed. 60 minutes after sealing, the hydrogen sulfide gas concentration in the glass container was measured using a gas detector (pocketable multi-gas monitor GX-2009 (TYPE E), manufactured by Riken Keiki Co., Ltd.). A gas detector was installed inside the glass container, allowing the hydrogen sulfide gas concentration inside the container to be measured without opening the glass container.

[0065] Example 1 A sulfide-based inorganic solid electrolyte material was prepared by the following procedure. The raw materials used were diphosphorus pentasulfide (Perimeter Solutions, Normal / S, S / P ratio 2.47), Li2S (Furukawa Co., Ltd., purity 99.9%), and red phosphorus (Kojundo Chemical Laboratory, purity 99%). All operations were carried out under an Ar atmosphere. A total of 2.1 g of Li2S powder, P2S5 powder, and red phosphorus powder (Li2S:P2S5:P=38.0:61.3:0.62 (wt %)) was mixed in a mortar to prepare a raw inorganic composition. Next, 2.1 g of the raw inorganic composition was subjected to mechanochemical treatment for 30 hours in a planetary ball mill (45 mL zirconia pot, 18 10 mm diameter zirconia balls used) (120 cycles of 10 minutes of mechanical milling at 400 rpm followed by 5 minutes of static standing, with the powder adhering to the pot wall and balls being scraped off after 15 hours). The resulting mixture was then placed in a carbon crucible and heated in a heating furnace at 290 °C for 2 hours to obtain a sulfide-based inorganic solid electrolyte material. The sulfide inorganic solid electrolyte material thus obtained was subjected to the above measurements (1) and (2). Furthermore, the sulfide inorganic solid electrolyte material thus obtained was sieved using a sieve with a mesh size of 20 μm, and then the above measurement (3) was performed. The results are shown in Tables 1 and 2.

[0066] <Example 2> A sulfide-based inorganic solid electrolyte material was prepared by the following procedure. The raw materials used were diphosphorus pentasulfide A (Furukawa Co., Ltd., S / P ratio 2.42) and Li2S (Furukawa Co., Ltd., purity 99.9%), which were prepared by the following procedure. All operations were carried out in an Ar atmosphere. A total of 2.1 g of Li2S powder and P2S5 powder (Li2S:P2S5=38.3:61.7 (wt %)) was mixed in a mortar to prepare a raw material inorganic composition. Next, 2.1 g of the raw inorganic composition was subjected to mechanochemical treatment for 30 hours in a planetary ball mill (45 mL zirconia pot, 18 10 mm diameter zirconia balls used) (120 cycles of 10 minutes of mechanical milling at 400 rpm followed by 5 minutes of static standing, with the powder adhering to the pot wall and balls being scraped off after 15 hours). The resulting mixture was then placed in a carbon crucible and heated in a heating furnace at 290 °C for 2 hours to obtain a sulfide-based inorganic solid electrolyte material. The sulfide inorganic solid electrolyte material thus obtained was subjected to the above measurements (1) to (3). Furthermore, the sulfide inorganic solid electrolyte material thus obtained was sieved using a sieve with a mesh size of 20 μm, and then the above measurement (4) was performed. The results are shown in Tables 1 and 2.

[0067] [Preparation of diphosphorus pentasulfide A] As a raw material for diphosphorus pentasulfide A, diphosphorus pentasulfide manufactured by LIAONING RUIXING CHEMICAL GROUP (product name: SUPERIOR GRADE Powder) was used. Next, the above raw materials were placed in a quartz container and set in a vacuum heating device (manufactured by Furukawa Co., Ltd.). The lower half of the quartz container was covered with a mantle heater, and the upper half was exposed and air-cooled, and vaporized diphosphorus pentasulfide gradually precipitated on this upper half. Next, the container was vacuum heated at 300°C for 2 hours under a reduced pressure of -0.094 MPa. During this 2-hour heating period, the temperature of the upper half of the quartz container was controlled at 140°C. The precipitate in the upper half of the quartz container was collected to obtain diphosphorus pentasulfide A. The resulting phosphorus pentasulfide A was analyzed for composition by ICP, and the S / P ratio was found to be 2.42.

[0068] <Comparative Example 1> A sulfide-based inorganic solid electrolyte material was prepared by the following procedure. The raw materials used were diphosphorus pentasulfide (Kanto Chemical, S / P ratio 2.50) and Li2S (Furukawa Co., Ltd., purity 99.9%). All operations were carried out under an Ar atmosphere. A total of 2.1 g of Li2S powder and diphosphorus pentasulfide powder (Li2S:P2S5=38.3:61.7 (wt %)) was mixed in a mortar to prepare a raw material inorganic composition. Next, 2.1 g of the raw inorganic composition was subjected to mechanochemical treatment for 30 hours in a planetary ball mill (45 mL zirconia pot, 18 10 mm diameter zirconia balls used) (120 cycles of 10 minutes of mechanical milling at 400 rpm followed by 5 minutes of static standing, with the powder adhering to the pot wall and balls being scraped off after 15 hours). The resulting mixture was then placed in a carbon crucible and heated in a heating furnace at 290 °C for 2 hours to obtain a sulfide-based inorganic solid electrolyte material. The sulfide inorganic solid electrolyte material thus obtained was subjected to the above measurements (1) to (3). Furthermore, the sulfide inorganic solid electrolyte material thus obtained was sieved using a sieve with a mesh size of 20 μm, and then the above measurement (4) was performed. The results are shown in Tables 1 and 2.

[0069] <Comparative Example 2> A sulfide-based inorganic solid electrolyte material was prepared by the following procedure. The raw materials used were diphosphorus pentasulfide (manufactured by Perimeter Solutions, normal / s, S / P ratio 2.47) and Li2S (manufactured by Furukawa Co., Ltd., purity 99.9%). All operations were carried out in an Ar atmosphere. A total of 2.1 g of Li2S powder and diphosphorus pentasulfide powder (Li2S:P2S5=38.3:61.7 (wt %)) was mixed in a mortar to prepare a raw material inorganic composition. Next, 2.1 g of the raw inorganic composition was subjected to mechanochemical treatment for 30 hours in a planetary ball mill (45 mL zirconia pot, 18 10 mm diameter zirconia balls used) (120 cycles of 10 minutes of mechanical milling at 400 rpm followed by 5 minutes of static standing, with the powder adhering to the pot wall and balls being scraped off after 15 hours). The resulting mixture was then placed in a carbon crucible and heated in a heating furnace at 290 °C for 2 hours to obtain a sulfide-based inorganic solid electrolyte material. The sulfide inorganic solid electrolyte material thus obtained was subjected to the above measurements (1) to (3). Furthermore, the sulfide inorganic solid electrolyte material thus obtained was sieved using a sieve with a mesh size of 20 μm, and then the above measurement (4) was performed. The results are shown in Tables 1 and 2.

[0070] [Table 1]

[0071] [Table 2] [Explanation of symbols]

[0072] 100 Lithium-ion batteries 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

1. A sulfide-based inorganic solid electrolyte material containing lithium, phosphorus, and sulfur as constituent elements, a molar ratio (S / P) of the sulfur (S) content to the phosphorus (P) content is 3.7 or more and less than 4.0; a molar ratio (Li / P) of the lithium (Li) content to the phosphorus (P) content is 2.8 or more and less than 3.0; In the spectrum obtained by X-ray diffraction using CuKα radiation as a radiation source, A sulfide-based inorganic solid electrolyte material having diffraction peaks at a diffraction angle 2θ=17.5±0.3° (A), a diffraction angle 2θ=18.8±0.3° (B), a diffraction angle 2θ=25.8±0.3° (C), and a diffraction angle 2θ=29.4±0.3° (D).

2. The sulfide-based inorganic solid electrolyte material according to claim 1, The maximum diffraction intensity of the diffraction peak present at the position (C) of the diffraction angle 2θ = 25.8 ± 0.3° is I Ｃ The maximum diffraction intensity of the diffraction peak at the position (D) of the diffraction angle 2θ = 29.4 ± 0.3° is defined as I Ｄ When I Ｄ / I Ｃ The sulfide-based inorganic solid electrolyte material has a value of 2.1 to 3.

2.

3. The sulfide-based inorganic solid electrolyte material according to claim 1 or 2, In the above spectrum, A sulfide-based inorganic solid electrolyte material having diffraction peaks at a diffraction angle 2θ=21.4±0.3° (E) and a diffraction peak at a diffraction angle 2θ=23.6±0.3° (F).

4. The sulfide-based inorganic solid electrolyte material according to any one of claims 1 to 3, A sulfide-based inorganic solid electrolyte material used in lithium-ion batteries.

5. A solid electrolyte comprising the sulfide-based inorganic solid electrolyte material according to claim 1 .

6. A solid electrolyte membrane comprising the solid electrolyte according to claim 5 .

7. The solid electrolyte membrane according to claim 6, A solid electrolyte membrane is a pressure-molded body of the particulate solid electrolyte.

8. The solid electrolyte membrane according to claim 6 or 7, A solid electrolyte membrane, wherein the content of the binder resin in the solid electrolyte membrane is less than 0.5% by mass when the entire solid electrolyte membrane is taken as 100% by mass.

9. The solid electrolyte membrane according to any one of claims 6 to 8, 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 %.

10. A lithium ion battery including 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 .

11. A method for producing the sulfide-based inorganic solid electrolyte material according to any one of claims 1 to 4, vitrifying a mixture comprising diphosphorus pentasulfide and lithium sulfide; heating the resulting glassy mixture to crystallize at least a portion of the mixture; Including, a molar ratio (S / P) of the sulfur (S) content to the phosphorus (P) content of the diphosphorus pentasulfide of 2.4 or more and 2.5 or less;

12. A method for producing the sulfide-based inorganic solid electrolyte material according to claim 11, In the step of vitrifying the mixture, The method for producing a sulfide-based inorganic solid electrolyte material comprises vitrifying the mixture by mechanical milling.

13. A method for producing a sulfide-based inorganic solid electrolyte material according to claim 11 or 12, The step of crystallizing at least a portion of the mixture in a glassy state comprises: The method for producing a sulfide-based inorganic solid electrolyte material comprises heating the mixture at 180°C or higher and 350°C or lower for 0.5 hours or higher and 24 hours or lower under an inert gas atmosphere.

Images