Method for producing sulfide-based solid electrolytes

Abstract

To provide a method for producing sulfide-based solid electrolytes that can improve grinding efficiency during dry grinding and suppress the decrease in lithium ion conductivity after grinding. [Solution] The present invention includes obtaining a sulfide-based solid electrolyte powder by dry grinding a sulfide-based solid electrolyte material in an atmosphere with a dew point of -70°C or higher and -30°C or lower, wherein the specific surface area of ​​the sulfide-based solid electrolyte powder is 3 m². 2 This invention relates to a method for producing a sulfide-based solid electrolyte that is 1 / g or more.

Description

[Technical Field]

[0001] This invention relates to a method for producing sulfide-based solid electrolytes. [Background technology]

[0002] Lithium-ion rechargeable batteries are widely used in portable electronic devices such as mobile phones and laptop computers. Traditionally, lithium-ion rechargeable batteries have used liquid electrolytes. However, in recent years, all-solid-state lithium-ion rechargeable batteries, which use solid electrolytes, have attracted attention due to the potential for improved safety, faster charging and discharging, and smaller case sizes.

[0003] Examples of solid electrolytes used in all-solid-state lithium-ion secondary batteries include sulfide-based solid electrolytes.

[0004] When sulfide-based solid electrolytes are used in all-solid-state lithium-ion secondary batteries, they are sometimes pulverized to a predetermined particle size. One known method for this is wet pulverization, in which the sulfide-based solid electrolyte is pulverized in a solvent. While wet pulverization has the advantage of relatively short processing time to achieve the desired particle size, it has drawbacks such as high production costs due to the cost of the solvent itself and the need for a drying process after pulverization.

[0005] In response to this, the pulverization of sulfide-based solid electrolytes by dry pulverization without the use of solvents is also being considered. For example, Patent Document 1 describes a method for producing sulfide solid electrolyte particles, which involves micronizing the sulfide solid electrolyte and then heat-treating the micronized material, and states that a jet mill, ball mill, or bead mill can be used for such micronization. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2018 / 164224 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, dry grinding sometimes resulted in lower grinding efficiency because the processing time required to achieve the desired particle size was relatively long, reducing the amount that could be processed per unit of time. Furthermore, dry grinding sometimes led to a decrease in the lithium ion conductivity of the sulfide-based solid electrolyte after grinding.

[0008] In view of the above circumstances, the present invention aims to provide a method for producing a sulfide-based solid electrolyte that can improve the grinding efficiency when dry grinding the sulfide-based solid electrolyte and suppress the decrease in lithium ion conductivity after grinding. [Means for solving the problem]

[0009] As a result of diligent research, the inventors of this invention have discovered that by appropriately adjusting the grinding environment during dry grinding, grinding efficiency can be improved and the decrease in lithium ion conductivity after grinding can be suppressed, thus completing the present invention.

[0010] In other words, the present invention relates to the following 1 to 7. 1. A method for producing a sulfide-based solid electrolyte, comprising dry grinding a sulfide-based solid electrolyte material in an atmosphere with a dew point of -70°C or higher and -30°C or lower to obtain a sulfide-based solid electrolyte powder. 2. The method for producing a sulfide-based solid electrolyte according to paragraph 1, wherein the oxygen concentration of the atmosphere is 0.1 ppm or more and less than 5%. 3. A method for producing a sulfide-based solid electrolyte according to claim 1 or 2, wherein the average particle size of the sulfide-based solid electrolyte powder is 0.1 μm or more and 4 μm or less. 4. The specific surface area of ​​the sulfide-based solid electrolyte powder is 3 m². 2 A method for producing a sulfide-based solid electrolyte according to any one of the above 1 to 3, wherein the amount is 1 / g or more. 5. A method for producing a sulfide-based solid electrolyte according to any one of 1 to 4 above, comprising performing the dry grinding using a jet mill. 6. The method for producing a sulfide-based solid electrolyte according to any one of 1 to 5 above, wherein the sulfide-based solid electrolyte powder is a powder of a sulfide-based solid electrolyte containing an argyrodite-type crystal structure. 7. The method for producing a sulfide-based solid electrolyte according to any one of 1 to 6 above, wherein no organic matter adheres to the particle surface of the sulfide-based solid electrolyte powder.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a method for producing a sulfide-based solid electrolyte that can improve the pulverization efficiency and suppress the decrease in lithium ion conductivity after pulverization. According to such a production method, a sulfide-based solid electrolyte that achieves both a desired particle size and quality can be efficiently produced.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a flowchart illustrating one aspect of the present production method.

Embodiments for Carrying Out the Invention

[0013] [[ID=​​​​​​​​A method for producing a sulfide-based solid electrolyte according to an embodiment of the present invention (hereinafter also referred to as "this production method") includes a dry grinding step of obtaining sulfide-based solid electrolyte powder by dry grinding a sulfide-based solid electrolyte material in an atmosphere with a dew point of -70°C or higher and -30°C or lower. Figure 1 is a flowchart illustrating one aspect of this production method. This production method includes step S11 of obtaining sulfide-based solid electrolyte powder by dry grinding a sulfide-based solid electrolyte material. In this production method, the dry grinding of the sulfide-based solid electrolyte material is performed in an atmosphere with a dew point of -70°C or higher and -30°C or lower.

[0016] (Sulfide solid electrolyte material) In the method for producing a sulfide-based solid electrolyte according to an embodiment of the present invention, various sulfide-based solid electrolytes can be used as the sulfide-based solid electrolyte material, and the sulfide-based solid electrolyte powder obtained by pulverizing it may also be various sulfide-based solid electrolytes. Examples of sulfide-based solid electrolytes include sulfide-based solid electrolytes containing Li, P, and S, and sulfide-based solid electrolytes containing Li, P, S, and Ha. Here, Ha represents at least one element selected from the group consisting of F, Cl, Br, and I.

[0017] Depending on the purpose, the sulfide-based solid electrolyte may be an amorphous sulfide-based solid electrolyte, a sulfide-based solid electrolyte having a specific crystal structure, or a sulfide-based solid electrolyte containing both a crystalline phase and an amorphous phase.

[0018] When a sulfide-based solid electrolyte contains a crystalline phase, the crystals contained in the sulfide-based solid electrolyte are preferably ion-conducting crystals. Specifically, ion-conducting crystals have a lithium ion conductivity of preferably 10 -4 Greater than S / cm, more preferably 10 -3 The crystal has a value greater than S / cm. From the standpoint of excellent lithium ion conductivity, the argyrodite crystal phase is more preferable.

[0019] More specifically, as a sulfide-based solid electrolyte, Li 10 GeP2S 12Sulfide solid electrolytes containing an LGPS-type crystal structure such as, Li6PS5Cl, Li 5.4 PS 4.4 Cl 1.6 and Li 5.4 PS 4.4 Cl 0.8 Br 0.8 Sulfide solid electrolytes containing an argyrodite-type crystal structure such as, Li-P-S-Ha-based crystallized glass, and LPS crystallized glass such as Li7P3S 11 etc. are exemplified. From the viewpoint of excellent lithium ion conductivity, as the sulfide solid electrolyte, a sulfide solid electrolyte containing an argyrodite-type crystal structure is preferable.

[0020] In order to adopt an argyrodite-type crystal structure, the crystal phase contains Ha in addition to Li, P, and S. Ha more preferably contains at least one of Cl and Br, still more preferably contains Cl, and even more preferably contains Cl alone or a mixture of Cl and Br.

[0021] An argyrodite-type crystal contains Li, P, S, and Ha, and can be defined as having peaks at positions of 2θ = 15.7 ± 0.5° and 30.2 ± 0.5° in an X-ray powder diffraction (XRD) pattern. In addition to the above, the XRD pattern preferably further has a peak at a position of 2θ = 18.0 ± 0.5°, and more preferably further has a peak at a position of 2θ = 25.7 ± 0.5°.

[0022] An argyrodite-type crystal is Li a PS b Ha c When represented by, it is preferable that the relationship of 5 < a < 7, 4 < b < 6 and 0 < c < 2 is satisfied because the crystal is likely to be of the argyrodite type. Such an elemental ratio more preferably satisfies the relationship of 5.1 < a < 6.3, 4 < b < 5.3 and 0.7 < c < 1.9, and still more preferably satisfies the relationship of 5.2 < a < 6.2, 4.1 < b < 5.2 and 0.8 < c < 1.8.

[0023] That is, for a, 5 < a < 7 is preferred, 5.1 < a < 6.3 is more preferred, and 5.2 < a < 6.2 is even more preferred. For b, 4 < b < 6 is preferred, 4 < b < 5.3 is more preferred, and 4.1 < b < 5.2 is even more preferred. For c, 0 < c < 2 is preferred, 0.7 < c < 1.9 is more preferred, and 0.8 < c < 1.8 is even more preferred. In this specification, "element ratio" means the ratio of the contents (at%) of elements.

[0024] In the case of an aldirodite-type crystal, a preferred crystal structure is a cubic crystal such as F-43m, etc., but there may also be hexagonal, tetragonal, orthorhombic, monoclinic, etc. with reduced symmetry, and even triclinic, etc. with further reduced symmetry.

[0025] When Ha constituting the aldirodite-type crystal contains Cl and Br, when the content of Cl in the aldirodite-type crystal is x (at%) and the content of Br is y (at%), the ratio represented by (x / y) is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more. Also, the ratio represented by (x / y) is preferably 10 or less, more preferably 3 or less, and even more preferably 1.6 or less.

[0026] When the ratio represented by (x / y) satisfies the above range, the interaction between lithium ions and halide ions is weakened, and the lithium ion conductivity of the sulfide-based solid electrolyte tends to be good. This is considered to be due to the influence of the mixed anion effect of weakening the interaction between cations and anions by mixing bromide ions with a larger ionic radius than chloride ions. Also, when the ratio represented by (x / y) satisfies the above range, the cycle characteristics of the lithium ion secondary battery tend to be improved.

[0027] Also, when Ha contains Cl and Br, the ratio of the contents (at%) of the elements constituting the aldirodite-type crystal is Li a -P-S b -Cl c1 -Br c2When expressed as follows, c1 is preferably 0.1 or higher, more preferably 0.3 or higher, and even more preferably 0.5 or higher. c1 is preferably 1.5 or lower, more preferably 1.4 or lower, and even more preferably 1.3 or lower. c2 is preferably 0.1 or higher, more preferably 0.3 or higher, and even more preferably 0.5 or higher. c2 is preferably 1.9 or lower, more preferably 1.6 or lower, and even more preferably 1.4 or lower.

[0028] By satisfying the above ranges for c1 and c2, the proportion of halide ions in the crystal is optimized, and a stable argyrodite-type crystal is obtained while reducing the interaction between anions and lithium ions in the crystal. This tends to result in good lithium ion conductivity of the solid electrolyte. In addition, the above ranges for c1 and c2 tend to improve the cycle characteristics of lithium-ion secondary batteries. Here, it is preferable that a, b, and (c1+c2) satisfy the same relationship as a, b, and c described above.

[0029] From the viewpoint of obtaining good lithium-ion conductivity when the crystal phase is formed into a battery, a smaller crystallite size is preferable. Specifically, a crystallite size of 1000 nm or less is preferable, 500 nm or less is more preferable, and 250 nm or less is even preferable. There is no particular lower limit to the crystallite size, but it is usually 5 nm or more. Crystallite size can be calculated using the full width at half maximum (FMAX) of the peaks in the XRD pattern and Scherrer's formula.

[0030] The composition of sulfide-based solid electrolytes can be determined by compositional analysis using methods such as ICP emission spectrometry, atomic absorption spectrometry, and ion chromatography. Furthermore, the structure of crystals contained in sulfide-based solid electrolytes can be analyzed from X-ray powder diffraction (XRD) patterns.

[0031] As the sulfide-based solid electrolyte material, commercially available sulfide-based solid electrolytes may be used, or sulfide-based solid electrolytes may be manufactured from raw materials and used. Furthermore, these sulfide-based solid electrolyte materials may be subjected to known pretreatments. In other words, this manufacturing method may appropriately include steps for manufacturing sulfide-based solid electrolyte materials and steps for pretreatment of sulfide-based solid electrolyte materials.

[0032] When producing a sulfide-based solid electrolyte material from raw materials, the raw materials and manufacturing methods can be appropriately selected from known raw materials and manufacturing methods according to the desired composition, etc.

[0033] As a pretreatment for sulfide-based solid electrolyte materials, there are no particular limitations, but examples include a process in which the sulfide-based solid electrolyte material is pulverized to a predetermined size or average particle diameter (coarse pulverization). Coarse pulverization can adjust the sulfide-based solid electrolyte material to a size or average particle diameter suitable for use in the dry pulverization process. The average particle diameter of the sulfide-based solid electrolyte material can be appropriately adjusted depending on the type of pulverizer used in the dry pulverization process, but for example, about 5 μm to 200 μm is preferred. In this specification, the average particle diameter refers to the median diameter (D50) obtained from the volume-based particle size distribution chart obtained by measuring the particle size distribution using a Microtrac MT3300EXII laser diffraction particle size distribution analyzer.

[0034] (Dry grinding process) This manufacturing method involves dry grinding a sulfide-based solid electrolyte material in an atmosphere with a dew point of -70°C or higher and -30°C or lower to obtain a sulfide-based solid electrolyte powder.

[0035] As a result of diligent research, the inventors have found that by adjusting the dew point within an appropriate range in the atmosphere during dry grinding (hereinafter also referred to as the grinding atmosphere), the efficiency of grinding can be improved and the decrease in lithium ion conductivity after grinding can be suppressed.

[0036] Specifically, it was found that by having a dew point of the grinding atmosphere above a predetermined value, sulfide-based solid electrolyte materials can be ground to the desired particle size in a shorter time, thereby improving grinding efficiency. In other words, it was found that by having a dew point of the grinding atmosphere above a predetermined value, the amount of material ground per unit of time can be increased.

[0037] The reason for this is thought to be as follows: A relatively high dew point means that a certain amount of moisture is present in the grinding atmosphere. Under such conditions, the grinding energy can cause sulfur (S) near the particle surface of the sulfide-based solid electrolyte material being ground to react with water molecules. Here, grinding energy refers to the energy released when particles of the sulfide-based solid electrolyte material collide with other particles, the grinder, and the media (grinding medium). When S near the particle surface reacts with water molecules, it is thought that S escapes from the vicinity of the particle surface, and oxygen (O) enters the vicinity of the particle surface in its place. This is thought to cause the crystal structure of the sulfide-based solid electrolyte material particles to collapse or localized strain to occur within the structure, making the particles softer, easier to grind, and thus shortening the time required for grinding.

[0038] Furthermore, the sulfur near the particle surface of sulfide-based solid electrolyte materials includes sulfur that forms PS4 structures and is bonded to cations, and S 2- This suggests that sulfur exists in this state. Furthermore, although the bond strength of PO bonds is generally greater than that of PS bonds, even if PO bonds are formed near the particle surface, the effects of disruption of the particle's crystal structure or local strain occurring within the structure are greater, and as a result, the particles are thought to become softer.

[0039] Conversely, it was found that if there is an excess of moisture in the grinding atmosphere, the crystal structure of the particles may collapse too much, or too much sulfur may be removed, which can easily lead to a decrease in lithium ion conductivity after dry grinding. Therefore, it was found that by keeping the dew point of the grinding atmosphere below a predetermined value and suppressing the excess of moisture in the grinding atmosphere, the decrease in lithium ion conductivity after dry grinding can be suppressed.

[0040] Based on the above, the inventors have found that by adjusting the dew point of the grinding atmosphere to an appropriate range, it is possible to achieve both improved grinding efficiency and suppression of the decrease in lithium ion conductivity, thus completing the present invention.

[0041] In other words, from the viewpoint of improving grinding efficiency, the dew point of the grinding atmosphere should be -70°C or higher, preferably -65°C or higher, and more preferably -60°C or higher.

[0042] On the other hand, from the viewpoint of suppressing a decrease in lithium ion conductivity, the dew point of the grinding atmosphere is -30°C or lower, preferably -35°C or lower, and more preferably -40°C or lower. The dew point of the grinding atmosphere is -70°C or higher and -30°C or lower, preferably -65°C or higher and -35°C or lower, and more preferably -60°C or higher and -40°C or lower. In this specification, the dew point refers to the dew point at atmospheric pressure, and is a value measured using a capacitive moisture meter or a mirror-cooled dew point meter for the atmosphere inside the grinding chamber.

[0043] In this manufacturing method, it is preferable to adjust the oxygen concentration of the grinding atmosphere. The reaction between sulfur (S) and oxygen (O) due to grinding energy can also occur between sulfur near the particle surface of the sulfide-based solid electrolyte material and oxygen (O) from oxygen molecules (O2) in the grinding atmosphere. Therefore, by adjusting the oxygen concentration in addition to the dew point, it becomes easier to obtain effects such as improved grinding efficiency and suppression of the decrease in lithium ion conductivity after grinding.

[0044] From the viewpoint of further improving grinding efficiency, the oxygen concentration of the grinding atmosphere is preferably 0.1 ppm or higher, more preferably 0.25 ppm or higher, and even more preferably 0.5 ppm or higher. The oxygen concentration of the grinding atmosphere may also be 1 ppm or higher, 3 ppm or higher, or 5 ppm or higher.

[0045] From the viewpoint of further suppressing the decrease in lithium ion conductivity, the oxygen concentration of the grinding atmosphere is preferably less than 5%, more preferably 1% or less, even more preferably 5000 ppm or less, and particularly preferably 1000 ppm or less. The oxygen concentration of the grinding atmosphere is preferably 0.1 ppm or more and less than 5%, more preferably 0.25 ppm or more and 1% or less, even more preferably 0.5 ppm or more and 5000 ppm or less, and particularly preferably 0.25 ppm or more and 1000 ppm or less. The oxygen concentration can be measured using a zirconia oxygen concentration meter, a galvanic cell oxygen concentration meter, etc. Note that ppm refers to the volume-based ratio (volume ppm) of the oxygen concentration.

[0046] The gas that mainly constitutes the grinding atmosphere is not particularly limited as long as the effects of the present invention can be obtained, but gases selected from the group consisting of inert gases such as N2, He and Ar, dry air, and mixtures thereof are preferred, and a mixture of N2 and dry air is more preferred because it is easier to suppress the supply gas cost.

[0047] With these gases, the dew point can be adjusted, for example, by selecting and using a gas of appropriate purity or by mixing them in an appropriate ratio. Also, since dry air contains oxygen (O2), the oxygen concentration can be adjusted by mixing it with an inert gas and dry air, for example, and adjusting the mixing ratio. More specifically, one example of a preferred method for adjusting the dew point and oxygen concentration is to prepare an inert gas and dry air, each having the same dew point, and mix them to achieve the desired oxygen concentration. With this method, the oxygen concentration can be adjusted while fixing the dew point when mixing the inert gas and dry air, so both the dew point and oxygen concentration can be adjusted relatively easily.

[0048] In this specification, dry grinding refers to a method of grinding a material under a gaseous atmosphere without using a solvent, as opposed to wet grinding, which grinds the material in a solvent. The pulverizer used for dry grinding is not particularly limited; it may be a pulverizer that uses media (grinding medium) or a pulverizer that does not use media. Furthermore, dry grinding may be performed continuously or in batches. Examples of grinders that use media include bead mills, planetary ball mills and other ball mills, and Atrita®. Examples of grinders that do not use media include air-jet grinders, blade mills, hammer mills, pin mills, and disc mills. Specifically, an example of an air-jet grinder is a jet mill.

[0049] In dry grinding, a grinding aid may be added to suppress the aggregation of sulfide-based solid electrolyte powder (sulfide-based solid electrolyte material). Organic solvents, inorganic materials, etc., can be used as grinding aids as appropriate, and the type is not particularly limited as long as it does not hinder the effects of the present invention. For example, organic solvents used as grinding aids include water, ethanol, acetone, hydrocarbon solvents, and ether-based solvents. The grinding aid may be in solid, liquid, or gaseous form. The amount of grinding aid added is preferably 1% by weight or less relative to the total weight of the sulfide-based solid electrolyte powder (sulfide-based solid electrolyte material).

[0050] As for the grinder, bead mills, planetary ball mills (planetary ball mills), and jet mills are preferred from the viewpoint of reducing production costs and grinding more efficiently, and jet mills are more preferred from the viewpoint of reducing the load of internal cleaning and media cleaning.

[0051] In dry grinding using various types of grinders, the atmosphere in the space where the material to be ground is substantially pulverized can be considered the grinding atmosphere. That is, typically, if the dew point in the grinding chamber of various grinders is between -70°C and -30°C, then the dew point of the grinding atmosphere can be said to be similar. Similarly, the oxygen concentration in the grinding chamber and the oxygen concentration in the grinding atmosphere can be said to be similar.

[0052] Furthermore, the atmosphere to which the sulfide-based solid electrolyte material and sulfide-based solid electrolyte powder are exposed, other than the grinding atmosphere, i.e., before and after dry grinding, may be the same as or different from the grinding atmosphere. When the sulfide-based solid electrolyte material or sulfide-based solid electrolyte powder is exposed to an atmosphere different from the grinding atmosphere, from the viewpoint of suppressing deterioration due to reaction with moisture, oxygen, etc., such an atmosphere is preferably selected from the group consisting of an inert gas atmosphere, a dry air atmosphere, and a mixed atmosphere thereof, and an inert gas atmosphere is more preferred.

[0053] In the dry grinding process, the grinding time can be appropriately adjusted according to the type of grinder and the desired particle size. For example, if the grinder is a jet mill, the grinding time is preferably 1 minute or more, and more preferably 5 minutes or more. If the grinder is a jet mill, the grinding time may be 30 minutes or more, or even 50 minutes or more. By making the grinding time sufficiently long, the amount of residual raw material can be reduced.

[0054] On the other hand, when the pulverizer is a jet mill and pulverization is performed in a batch manner, the pulverization time is preferably 2 hours or less, and more preferably 1 hour or less, from the viewpoint of efficient pulverization. The pulverization time is preferably 1 minute or more and 2 hours or less, and more preferably 5 minutes or more and 1 hour or less. In addition, when dry pulverization is performed continuously, the continuous operating time of the pulverizer may be longer than the above. According to this manufacturing method, sulfide-based solid electrolyte materials can be pulverized to the desired particle size in a shorter time. Furthermore, according to this manufacturing method, the pulverization time required to obtain sulfide-based solid electrolyte powder with an appropriate particle size distribution can also be made relatively short.

[0055] In addition, if the grinder is a jet mill, the grinding gas pressure is preferably 0.2 MPa or higher, and more preferably 0.3 MPa or higher. By sufficiently increasing the grinding gas pressure, collisions between particles are accelerated, not only allowing for the acquisition of a desired average particle size, but also reducing the variation in particle size distribution. By reducing the particle size, the contact area between the sulfide-based solid electrolyte powder particles and the electrolytes themselves, or with the active material and conductive additives, can be increased, making it easier to reduce the contact interface resistance, which can contribute to improving the battery performance when used in all-solid-state lithium-ion secondary batteries.

[0056] Furthermore, if the pulverizer is a jet mill, from the viewpoint of efficient pulverization, the pulverization gas pressure is preferably 0.95 MPa or less, and more preferably 0.85 MPa or less. The pulverization gas pressure is preferably 0.2 MPa or more and 0.95 MPa or less, and more preferably 0.3 MPa or more and 0.85 MPa or less.

[0057] In the dry grinding process, various conditions such as temperature, pressure, and volume of the grinding chamber are not particularly limited as long as they do not hinder the effects of the present invention, and can be appropriately set according to the type of grinder, the type and average particle size of the sulfide-based solid electrolyte material, and the desired average particle size and properties of the sulfide-based solid electrolyte powder.

[0058] (Sulfide solid electrolyte powder) Dry grinding pulverizes the sulfide-based solid electrolyte material, yielding a sulfide-based solid electrolyte powder.

[0059] The average particle size of the sulfide-based solid electrolyte powder can be adjusted as appropriate depending on the application and desired battery characteristics. For example, from the viewpoint of improving battery characteristics, an average particle size of 4 μm or less is preferred, 3 μm or less is more preferred, 2 μm or less is even more preferred, and 1 μm or less is particularly preferred. On the other hand, considering the particle size that can be achieved in a realistic time by dry grinding, an average particle size of 0.1 μm or more is preferred, 0.3 μm or more is more preferred, and 0.5 μm or more is even more preferred. An average particle size of 0.1 to 4 μm is preferred, 0.3 to 3 μm is more preferred, 0.5 to 2 μm is even more preferred, and 0.5 to 1 μm is particularly preferred.

[0060] The specific surface area of ​​sulfide-based solid electrolyte powder can be adjusted as appropriate, similar to the average particle size, depending on the application and desired battery characteristics. For example, from the viewpoint of improving battery characteristics, the specific surface area can be set to 3 m². 2 Preferably 5m / g or more, 2 More preferably 10m / g or more, 2 A value of 100 m² or more is even more preferable. On the other hand, from the viewpoint of long-term storage, the specific surface area should be 100 m². 2 Preferably less than / g, 50m 2 Less than / g is more preferable, 30m 2 A value of less than / g is even more preferable. The specific surface area should be 3 to 100 m². 2 / g is preferred, 5-50m 2 / g is more preferable, 10-30m 2 / g is even more preferable. The specific surface area can be measured by BET specific surface area measurement, for example using the ASAP-2020 high-performance specific surface area and pore distribution analyzer manufactured by Micromeritics.

[0061] Generally, the smaller the average particle size of the powder, the larger the specific surface area. However, the larger the specific surface area, the greater the influence of the surrounding atmosphere. Therefore, in so-called fine grinding, where the average particle size after grinding falls within the preferred range described above, the effects of the present invention are more easily and thus preferable.

[0062] The lithium ion conductivity of sulfide-based solid electrolyte powder varies depending on the type of sulfide-based solid electrolyte and the average particle size, and is not particularly limited. For example, when sulfide-based solid electrolyte powder is compacted at a pressure of 380 MPa and used as a measurement sample, the lithium ion conductivity at 25°C is preferably 2 mS / cm or higher, and more preferably 3 mS / cm or higher. A higher lithium ion conductivity is preferable, but an upper limit of about 10 mS / cm is practical. The lithium ion conductivity may be between 2 and 10 mS / cm, or between 3 and 10 mS / cm. The lithium ion conductivity of sulfide-based solid electrolyte powder can be measured, for example, by an AC impedance meter. According to this manufacturing method, the decrease in lithium ion conductivity in sulfide-based solid electrolyte powder after dry grinding is suppressed, making it easier to obtain sulfide-based solid electrolyte powder with relatively excellent lithium ion conductivity.

[0063] The sulfide-based solid electrolyte powder obtained by this manufacturing method does not have organic matter adhering to the surface of the powder particles. Sulfide-based solid electrolyte powder pulverized by wet milling retains solvent-derived organic matter on the surface of the powder particles even after the solvent used for pulverization has dried. Such organic matter contributes to a decrease in battery performance when sulfide-based solid electrolyte powder is used in all-solid-state lithium-ion secondary batteries. Specifically, it is thought that the organic matter reacts at the interface between the sulfide-based solid electrolyte powder particles and the active material particles, hindering the battery reaction at this interface. In contrast, since the sulfide-based solid electrolyte powder obtained by this manufacturing method does not have organic matter adhering to the surface of the powder particles, the decrease in battery characteristics caused by organic matter adhesion can be suppressed. The absence of organic matter adhering to the surface of the sulfide-based solid electrolyte powder can be confirmed by the change in the color of the powder when it is heated at 350°C or higher for 30 minutes or more. Specifically, if no organic matter is attached to the particle surface, the powder's color does not change before and after heating. However, if organic matter is attached to the particle surface, the color changes to brown or gray after heating. The color of sulfide-based solid electrolyte powders before heating varies depending on the composition, but is generally white or light yellow. The change in color after heating when organic matter is attached to the particle surface can be visually confirmed.

[0064] This manufacturing method may include a step of heat-treating the sulfide-based solid electrolyte powder as needed. The heat treatment is performed as appropriate for purposes such as stabilizing the composition of the sulfide-based solid electrolyte powder or stabilizing the crystalline structure contained in the powder. The heat treatment temperature is preferably such that the sulfide-based solid electrolyte powder does not aggregate, for example, heat treatment at 200°C to 500°C for 1 to 120 minutes is preferred.

[0065] This manufacturing method may further include known post-processing steps, such as a step of classifying or a step of crushing the sulfide-based solid electrolyte powder.

[0066] According to this manufacturing method, when dry grinding sulfide-based solid electrolytes, the sulfide-based solid electrolyte can be ground to the desired particle size in a shorter time, thereby improving grinding efficiency and suppressing the decrease in lithium ion conductivity after grinding. With this manufacturing method, sulfide-based solid electrolytes that achieve both the desired particle size and quality can be efficiently produced. The sulfide-based solid electrolyte produced by this manufacturing method is suitable as a solid electrolyte material used in, for example, all-solid-state lithium-ion secondary batteries. The sulfide-based solid electrolyte produced by this manufacturing method is also expected to improve the battery characteristics of all-solid-state lithium-ion secondary batteries. [Examples]

[0067] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Examples 1 to 6 are examples of the present manufacturing method, and Examples 7 to 9 are comparative examples.

[0068] (Manufacturing Example 1) Li2S:P2S5:LiCl:LiBr = 1.9:0.5:0.8:0.8. Lithium sulfide powder (Sigma, 99.98% purity), phosphorus pentasulfide powder (Sigma, 99% purity), lithium chloride powder (Sigma, 99.99% purity), and lithium bromide powder (Sigma, 99.995% purity) were weighed and mixed in a mortar to achieve a molar ratio of Li2S:P2S5:LiCl:LiBr = 1.9:0.5:0.8. This mixture was then vacuum-sealed in a quartz tube and heated at 750°C for 1 hour to obtain the composition Li 5.4 PS 4.4 Cl 0.8 Br 0.8 A sulfide-based solid electrolyte was obtained. The obtained sulfide-based solid electrolyte was pulverized in a mortar and passed through a mesh with a mesh size of 100 μm to obtain a sulfide-based solid electrolyte material with an average particle size of 10 μm.

[0069] (Example 1) 25 g of the sulfide-based solid electrolyte material obtained in Production Example 1 was prepared. The prepared sulfide-based solid electrolyte material was dry-milled for 30 minutes using a jet mill (Pocket Jet Jr., manufactured by Kurimoto Iron Works Co., Ltd.) to obtain sulfide-based solid electrolyte powder. During dry milling, a mixture of N2 and dry air was used as the grinding gas and purge gas, and the dew point and oxygen concentration of this mixture were adjusted to the values ​​listed in Table 1, thereby adjusting the dew point and oxygen concentration of the grinding atmosphere to the values ​​listed in Table 1. The grinding conditions using the jet mill are as follows. Purge gas pressure: 0.2 MPa Grinding gas pressure: 0.6 MPa

[0070] (Examples 2, 3, 6-8) A sulfide-based solid electrolyte powder was obtained in the same manner as in Example 1, except that the dew point and oxygen concentration of the grinding gas and purging gas were changed to the values ​​shown in Table 1, respectively.

[0071] (Examples 4, 5, 9) 25 g of the sulfide-based solid electrolyte material obtained in Production Example 1 was prepared. A planetary ball mill (Ito Seisakusho Co., Ltd., LP-M2) was used as the grinding machine, and the gas in the grinding chamber was a mixture of N2 and dry air. The dew point and oxygen concentration of the mixture were adjusted to the values ​​shown in Table 1. Super-dehydrated toluene (Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the sulfide-based solid electrolyte material as a grinding aid at a concentration of 0.1% by mass. Dry grinding was performed at 200 rpm for 30 minutes using balls with a particle size of 2 mm to obtain sulfide-based solid electrolyte powder.

[0072] Each sulfide-based solid electrolyte powder obtained using the methods described in Examples 1-9 was evaluated as follows. The results of each evaluation are shown in Table 1.

[0073] (Average particle size evaluation) The average particle size of sulfide-based solid electrolyte powders was measured and evaluated according to the following criteria. The average particle size was determined by measuring the particle size distribution using a Microtrac MT3300EXII laser diffraction particle size distribution analyzer, and the median diameter (D50) was calculated from the volume-based particle size distribution chart obtained. (Evaluation Criteria) A: The average particle size was 3 μm or less. B: The average particle size was greater than 3 μm and less than or equal to 4 μm. C: The average particle size was larger than 4 μm.

[0074] (Lithium-ion conductivity evaluation) A sulfide-based solid electrolyte powder was compacted into a powder at a pressure of 380 MPa and used as a measurement sample. The lithium-ion conductivity was measured using an AC impedance measuring device (Bio-Logic Sciences Instruments, potentiostat / galvanostat VSP) and evaluated according to the following criteria. The measurement conditions were: measurement frequency: 100Hz to 1MHz, measurement voltage: 100mV, and measurement temperature: 25℃. (Evaluation Criteria) A: The lithium-ion conductivity was 4 mS / cm or higher. B: The lithium-ion conductivity was between 3 mS / cm and less than 4 mS / cm. C: The lithium-ion conductivity was between 2 mS / cm and less than 3 mS / cm. D: The lithium-ion conductivity was less than 2 mS / cm.

[0075] (Battery performance evaluation) The battery performance of using sulfide-based solid electrolyte powder in all-solid-state lithium-ion secondary batteries was evaluated. First, cathode composite materials and all-solid-state lithium-ion secondary batteries were prepared using the following method, and charge-discharge tests were conducted. The results of the charge-discharge tests were evaluated according to the following evaluation criteria. (Preparation of positive electrode composite material) As the positive electrode active material, layered rock salt type LiCoO2 powder (volume-average particle size: 10 μm) coated with LiNbO3 was used. A positive electrode composite material was prepared by mixing 35 parts of sulfide-based solid electrolyte powder obtained by the method in each example, 60 parts of the positive electrode active material, and 5 parts of a conductive additive (acetylene black, manufactured by Denka Co., Ltd., HS100). The thickness of the LiNbO3 coating was 7 nm, as observed by TEM. (Fabrication of all-solid-state lithium-ion secondary batteries) 80 mg of sulfide-based solid electrolyte powder obtained by the method described in each example was placed in a 10 mm diameter plastic cylinder and molded under pressure to form a solid electrolyte layer. Next, 10 mg of the positive electrode composite material prepared above was placed in the same cylinder and molded under pressure again to form a positive electrode layer. Furthermore, indium foil and lithium foil were placed on the opposite side from the positive electrode composite material to form a negative electrode layer. In this way, an all-solid-state lithium-ion secondary battery was fabricated, and a battery performance evaluation test was conducted at a confinement pressure of 10 kN.

[0076] (Battery performance evaluation test) Using the fabricated all-solid-state lithium-ion secondary batteries, a constant current charge-discharge test was performed for one cycle at 25°C, with a charge / discharge current density of 0.05C and a charge / discharge potential range of 1.9-3.7V. The discharge capacity in the first cycle of each battery performance evaluation test was evaluated relative to the discharge capacity in the first cycle of Example 5, i.e., (discharge capacity in the first cycle of each example) / (discharge capacity in the first cycle of Example 5).

[0077] (Evaluation Criteria) A: The relative value was greater than 1.1. B: The relative value was greater than 1.0 and less than or equal to 1.1. C: The relative value was greater than 0.9 and less than or equal to 1.0. D: The relative value was 0.9 or less.

[0078] [Table 1]

[0079] Examples 1 to 6, which are examples, all showed superior lithium ion conductivity evaluation compared to comparative examples 7 to 9. In other words, even though the sulfide-based solid electrolyte powder was obtained by dry grinding the same sulfide-based solid electrolyte material, the powders obtained in Examples 1 to 6, which are examples, showed suppressed decrease in lithium ion conductivity during grinding, and it is considered that the lithium ion conductivity of the sulfide-based solid electrolyte powder was higher. Furthermore, the methods in Examples 1-3 and 6, which used a jet mill, were able to reduce the average particle size of the sulfide-based solid electrolyte powder more effectively than the method in Example 8, within the same grinding time. Similarly, the methods in Examples 4 and 5, which used a planetary ball mill, were able to reduce the average particle size of the sulfide-based solid electrolyte powder more effectively than the method in Example 9, within the same grinding time. These results confirm that the methods in Examples 1-6 are superior in terms of grinding efficiency and can grind sulfide-based solid electrolytes to the desired particle size in a shorter time. In Example 7, however, the dew point was too high, and the oxygen concentration was also excessive. Therefore, although the average particle size after grinding was comparable to that of Examples 1-3 and 6, the decrease in lithium-ion conductivity could not be suppressed, and both conditions could not be met. Based on the above results, it was confirmed that in Examples 1 to 6, the dew point of the grinding atmosphere was appropriately adjusted, which enabled both grinding efficiency and suppression of the decrease in lithium ion conductivity after grinding. Furthermore, all of Examples 1 to 6 showed superior battery performance compared to Comparative Examples 7 to 9.

[0080] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2021-161739 filed on 30 September 2021, the contents of which are incorporated herein by reference.

Claims

1. The method involves dry grinding a sulfide-based solid electrolyte material in an atmosphere with a dew point of -70°C or higher and -30°C or lower to obtain a sulfide-based solid electrolyte powder, wherein the specific surface area of ​​the sulfide-based solid electrolyte powder is 3 m². ２ A method for producing a sulfide-based solid electrolyte that is 1 / g or more.

2. The method for producing a sulfide-based solid electrolyte according to claim 1, wherein the average particle size of the sulfide-based solid electrolyte powder is 0.1 μm or more and 4 μm or less.

3. A method for producing a sulfide-based solid electrolyte according to claim 1 or 2, comprising performing the dry grinding using a jet mill.

4. The method for producing a sulfide-based solid electrolyte according to claim 1 or 2, wherein the sulfide-based solid electrolyte powder is a powder of a sulfide-based solid electrolyte containing an argyrodite-type crystal structure.

5. A method for producing a sulfide-based solid electrolyte according to claim 1 or 2, wherein no organic matter is attached to the particle surface of the sulfide-based solid electrolyte powder.

Images