Sulfide solid electrolyte powder, solid electrolyte layer, and lithium ion secondary battery

Abstract

The present invention relates to a sulfide solid electrolyte powder in which the content of Al is less than 50 ppm, the content of Zr is less than 50 ppm, and the particle diameter D50 is less than 1 [mu] m, on a mass basis.

Description

TECHNICAL FIELD

[0001] The present application relates to a sulfide solid electrolyte powder, a solid electrolyte layer, and a lithium-ion secondary battery. BACKGROUND

[0002] Lithium-ion secondary batteries are widely used for portable electronic devices such as mobile phones, notebook computers, and the like.

[0003] In the past, a liquid electrolyte has been used in lithium-ion secondary batteries, but from the viewpoint of improving safety and desiring high-speed charge and discharge, a lithium-ion all-solid-state battery (hereinafter also referred to as a solid-state battery) using a solid electrolyte as an electrolyte for a lithium-ion secondary battery has attracted attention.

[0004] Solid electrolytes are roughly classified into sulfide solid electrolytes and oxide solid electrolytes. Among them, sulfide solid electrolytes contain sulfide ions having a large polarization rate, and thus exhibit high ionic conductivity.

[0005] As a sulfide solid electrolyte, Li 10 GeP2S 12 crystals, Li6PS5Cl and the like, crystals of a sulfide argyrodite type, Li7P3S 11 crystals, LPS crystalline glass and the like.

[0006] A solid electrolyte has poor permeability into the inside of a positive electrode or a negative electrode compared to a liquid electrolyte. Therefore, in order to improve battery performance, more interfaces with active materials are formed by reducing the particle diameter or by making a solid electrolyte powder not containing coarse particles having a large particle diameter.

[0007] As a technique for reducing the particle diameter of a solid electrolyte powder, for example, there is a method of pulverizing the obtained solid electrolyte or its coarse crushed product using a wet-type bead mill using hard beads having a diameter of about 0.1 to 1 mm.

[0008] As the type of the beads, zirconia beads, alumina beads can be given, but since zirconia beads have a large specific gravity, excessive pulverization easily occurs, and a decrease in lithium ion conductivity is easily caused.

[0009] On the other hand, alumina beads have a smaller specific gravity than zirconia beads, and thus have a feature that the particle size of the pulverized solid electrolyte powder is easily maintained. In fact, a solid electrolyte obtained using a wet-type bead mill using alumina beads is disclosed in Patent Literature 1.

[0010] PRIOR ART DOCUMENTS

[0011] PATENT LITERATURE

[0012] Patent Literature 1: International Publication No. 2020 / 105604 SUMMARY

[0013] On the other hand, there is a demand for further improvement in lithium ion conductivity of sulfide solid electrolyte powder obtained by pulverizing a sulfide solid electrolyte.

[0014] Therefore, an object of the present application is to provide a sulfide solid electrolyte powder which maintains the particle size and exhibits good lithium ion conductivity, and a solid electrolyte layer and a lithium ion secondary battery each containing the sulfide solid electrolyte powder.

[0015] The present inventors have intensively studied, and as a result, have found that if pulverization is performed using a bead mill in order to maintain the particle size of the sulfide solid electrolyte powder, there is contamination of alumina (Al203) and zirconia (Zr02) in the obtained sulfide solid electrolyte powder. Furthermore, as a result of further studies, it has been found that the above-mentioned contamination is one of the causes of the decrease in lithium ion conductivity. That is, the above-mentioned contamination hinders the continuity of the sulfide solid electrolyte powder, interrupts the conduction path of lithium ions, which is considered to be an important factor for the decrease in lithium ion conductivity.

[0016] On the other hand, the present inventors have found that the above-mentioned problem can be solved by making the content of Al (aluminum) and Zr (zirconium) contained in the sulfide solid electrolyte powder be not more than a certain amount, thereby completing the present application.

[0017] That is, the present application relates to the following configurations.

[0018] [1] A sulfide solid electrolyte powder, the content of each of Al and Zr in terms of mass basis satisfies Al: less than 50 ppm and Zr: less than 50 ppm,

[0019] the particle diameter D50 is less than 1 μm.

[0020] [2] The sulfide solid electrolyte powder according to the above-mentioned [1], wherein the BET particle diameter calculated from the BET specific surface area is 0.10 to 0.30 μm.

[0021] [3] The sulfide solid electrolyte powder according to the above-mentioned [1] or [2], wherein the sulfide solid electrolyte constituting the above-mentioned sulfide solid electrolyte powder has a crystal phase,

[0022] the above-mentioned crystal phase has a crystal structure of argyrodite type.

[0023] [4] The sulfide solid electrolyte powder according to the above-mentioned [1] or [2], wherein the sulfide solid electrolyte constituting the above-mentioned sulfide solid electrolyte powder has a composition represented by (5.5 ≤ α ≤ 5.6, 4.3 ≤ β ≤ 4.4). α PS β (5.5 ≤ α ≤ 5.6, 4.3 ≤ β ≤ 4.4).

[0024] [5] A solid electrolyte layer containing the sulfide solid electrolyte powder described in any one of the above [1] to [4].

[0025] [6] A lithium ion secondary battery containing the sulfide solid electrolyte powder described in any one of the above [1] to [4].

[0026] According to the present application, a sulfide solid electrolyte powder that maintains the particle size and has excellent lithium ion conductivity can be obtained. Therefore, a solid electrolyte layer and a lithium ion secondary battery containing the above sulfide solid electrolyte powder can achieve excellent battery characteristics based on the good lithium ion conductivity thereof. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a flowchart showing a method for producing the sulfide solid electrolyte powder to which the present embodiment relates. DETAILED DESCRIPTION

[0028] The present application is described in detail below, but the present application is not limited to the following embodiments, and can be implemented with any modifications within the scope of the gist of the present application. In addition, "to" indicating a numerical range is used in the sense of including the numerical values recited before and after it as lower limit values and upper limit values.

[0029] In the present specification, mass ppm is the same as weight ppm, and mass % is the same as weight %.

[0030] < Sulfide solid electrolyte powder >

[0031] The sulfide solid electrolyte powder to which the present embodiment relates has a content of Al: less than 50 ppm and Zr: less than 50 ppm on a mass basis. In addition, the particle size D50 of the above sulfide solid electrolyte powder is less than 1 μm.

[0032] The particle size D50 of the sulfide solid electrolyte powder is less than 1 μm, and is preferably 0.40 μm or more and less than 1 μm.

[0033] Here, by making the above particle size D50 less than 1 μm, more interfaces with active materials can be formed, and the battery characteristics are improved. The particle size D50 is preferably 0.95 μm or less, more preferably 0.90 μm or less, further preferably 0.80 μm or less, and particularly preferably 0.70 μm or less.

[0034] In addition, the lower limit of the above particle size D50 is not particularly limited, and from the viewpoint of operability, the crystallinity is not easily impaired, and from the viewpoint of achieving good lithium ion conductivity, it is preferably 0.40 μm or more, more preferably 0.45 μm or more, and further preferably 0.50 μm or more.

[0035] Note that in the present specification, the particle size D50 refers to a cumulative 50% particle size on a volume basis, which is obtained using a particle size distribution measuring device of the laser diffraction type. That is, the particle size distribution is measured by the laser diffraction / scattering method, the total volume of the sulfide solid electrolyte is assumed to be 100%, and the cumulative curve is obtained, and the particle size at the point where the cumulative volume becomes 50% on the cumulative curve is determined.

[0036] In addition, the particle size D90 and the particle size D10 described later are also the particle sizes at the points where the cumulative volume becomes 90% and 10%, respectively, on the cumulative curve obtained by the same measurement as described above.

[0037] The particle size D50 of the sulfide solid electrolyte powder of less than 1 μm is a particle size that can be mass-produced by pulverization generally performed using a bead mill, and it is not realistic to make the particle size D50 less than 1 μm using mortar pulverization, Atritor (registered trademark), a disc mill, a turbo mill, a vibration mill, or the like as other pulverization means.

[0038] In contrast, for example, by using a bead mill using alumina beads or zirconia beads, the value of the particle size D50 described above can be made less than 1 μm.

[0039] The particle size (particle size D90) at the point where the cumulative volume becomes 90% on the particle size distribution curve on a volume basis of the sulfide solid electrolyte powder according to the present embodiment is preferably 0.80 to 3.0 μm, more preferably 0.90 to 2.5 μm, further preferably 0.90 to 2.0 μm, and particularly preferably 0.90 to 1.8 μm.

[0040] Here, from the viewpoint that a larger interface with an active material can be formed, and the battery characteristics are further improved, the particle size D90 described above is preferably 3.0 μm or less, more preferably 2.5 μm or less, further preferably 2.0 μm or less, and particularly preferably 1.8 μm or less.

[0041] In addition, from the viewpoint that the crystallinity of the sulfide solid electrolyte powder is not easily impaired, and a good lithium ion conductivity is obtained, the particle size D90 described above is preferably 0.80 μm or more, and more preferably 0.90 μm or more.

[0042] The particle size (particle size D10) at the point where the cumulative volume becomes 10% on the particle size distribution curve on a volume basis of the sulfide solid electrolyte powder according to the present embodiment is preferably 0.10 to 0.80 μm, more preferably 0.15 to 0.70 μm, further preferably 0.20 to 0.65 μm, and particularly preferably 0.25 to 0.60 μm.

[0043] From the viewpoint of forming more interfaces with the active material and improving the battery characteristics, the particle size D10 is preferably 0.80 μm or less, more preferably 0.70 μm or less, further preferably 0.65 μm or less, and particularly preferably 0.60 μm or less.

[0044] From the viewpoint of not impairing the crystallinity of the sulfide solid electrolyte powder and obtaining good lithium ion conductivity, the particle size D10 is preferably 0.10 μm or more, more preferably 0.15 μm or more, further preferably 0.20 μm or more, and particularly preferably 0.25 μm or more.

[0045] The BET particle size of the sulfide solid electrolyte powder according to the present embodiment is preferably 0.10 to 0.30 μm, more preferably 0.12 to 0.25 μm, and further preferably 0.13 to 0.23 μm.

[0046] From the viewpoint of not impairing the crystallinity of the sulfide solid electrolyte powder and obtaining good lithium ion conductivity, the BET particle size is preferably 0.10 μm or more, more preferably 0.12 μm or more, and further preferably 0.13 μm or more.

[0047] From the viewpoint of forming more interfaces with the active material and further improving the battery characteristics, the BET particle size is preferably 0.30 μm or less, more preferably 0.25 μm or less, and further preferably 0.23 μm or less.

[0048] Note that in the present specification, the BET particle size refers to a particle size calculated from the specific surface area (BET specific surface area) measured by the BET method using the following equation.

[0049] BET particle size (nm) = 6 / (true density (g / cm 3 ) x BET specific surface area (m 2 / g)) x 1000

[0050] Note that the BET specific surface area refers to a value obtained by the nitrogen adsorption BET multipoint method.

[0051] The BET specific surface area of the sulfide solid electrolyte powder according to the present embodiment is preferably 10 to 28 m 2 / g, more preferably 13 to 26 m 2 / g, and further preferably 13 to 20 m 2 / g.

[0052] From the viewpoint of forming more interfaces with the active material and further improving the battery characteristics, the BET specific surface area is preferably 10 m 2 / g or more, more preferably 13m 2 / g or more.

[0053] Furthermore, from the viewpoint of minimizing damage to the crystallinity of the sulfide solid electrolyte powder and obtaining good lithium-ion conductivity, the preferred BET specific surface area is 28 m². 2 / g or less, more preferably 26m 2 / g or less, more preferably 20m 2 / g or less.

[0054] The particle size D50, BET particle size, and BET specific surface area mentioned above can be adjusted by appropriately changing the conditions during the pulverization of the sulfide solid electrolyte.

[0055] The sulfide solid electrolyte powder involved in this embodiment is an aggregate of sulfide solid electrolyte particles. The sulfide solid electrolyte, before being pulverized, which forms the basis of the sulfide solid electrolyte powder involved in this embodiment, can be a known electrolyte.

[0056] Specifically, for the sulfide solid electrolyte in this embodiment, an example is Li7P3S... 11 These are sulfide solid electrolytes, known as LPS-based, which contain Li, P, and S elements in a crystal structure and possess Li... 10 GeP2S 12 This includes sulfide solid electrolytes with crystal structures containing Li, Ge, P, and S elements, referred to as LGPS system; sulfide solid electrolytes with crystal structures of silver-germanium sulfide type containing Li, P, S, and Ha elements; sulfide solid electrolytes composed of Li-PS-Ha system crystalline glass; sulfide solid electrolytes with crystal structures of the thio-LISICON type; and crystalline phases containing oxides. Additionally, sulfide solid electrolytes containing crystalline phases and amorphous phases with the aforementioned crystal structures can also be used. It should be noted that the sulfide solid electrolyte powder constituting this embodiment is not limited to the above-described crystal structures; furthermore, some elements can be replaced by other elements.

[0057] In the above crystal structure, from the viewpoint of lithium-ion conductivity and battery characteristics, it is preferable that the sulfide solid electrolyte constituting the sulfide solid electrolyte powder of this embodiment has a crystalline phase, which has an LPS-based crystal structure or a sulfosilver germanite-type crystal structure.

[0058] When the crystal structure of the sulfide solid electrolyte described above is LPS-based, it is preferable that the sulfide solid electrolyte has a Li... α PS β(5.5 ≤ α ≤ 5.6, 4.3 ≤ β ≤ 4.4) represents. By making the sulfide solid electrolyte powder according to the present embodiment a powder of a sulfide solid electrolyte having a crystal structure of an LPS system of the above composition, high lithium ion conductivity can be ensured.

[0059] In addition, the crystal structure of the LPS system can contain at least one of Cl and Br elements in addition to the Li element, the P element, and the S element.

[0060] When the sulfide solid electrolyte has a crystal structure of a crystal phase of argyrodite type, the crystal structure of the argyrodite type refers to a crystal structure possessed by a compound group from a mineral represented by the composition formula Ag8GeS6.

[0061] When the sulfide solid electrolyte has a crystal structure of the argyrodite type, as the Ha element, it is more preferable to contain at least one element selected from Cl, Br, and I, and it is further preferable to contain two or more elements.

[0062] In the above, as the Ha element, it is further preferable to contain at least one of Cl and Br, and it is also further preferable to contain Cl and Br.

[0063] As the composition formula of the argyrodite type, it is preferable to be represented by Li α’ PS β’ Ha γ’ and satisfies the relationships of 5 ≤ α' ≤ 7, 4 ≤ β' ≤ 6, and 1.3 ≤ γ' ≤ 2. The element ratio is more preferably satisfies the relationships of 5.1 < α' < 6.3, 4 < β' < 5.3, and 1.4 ≤ γ' ≤ 1.9, and further preferably satisfies the relationships of 5.2 < α' < 6.2, 4.1 < β' < 5.2, and 1.5 ≤ γ' ≤ 1.8.

[0064] That is, for α', it is preferable to be 5 or more, more preferably greater than 5.1, and further preferably greater than 5.2, and it is preferable to be 7 or less, more preferably less than 6.3, and further preferably less than 6.2. For β', it is preferable to be 4 or more, more preferably greater than 4, and further preferably greater than 4.1, and it is preferable to be 6 or less, more preferably less than 5.3, and further preferably less than 5.2. For γ', it is preferable to be 1.3 or more, more preferably 1.4 or more, and further preferably 1.5 or more, and it is preferable to be 2 or less, more preferably 1.9 or less, and further preferably 1.8 or less.

[0065] In the crystal structure of the argyrodite type, a part of the S element can be substituted with the Ha element, the O element, and Se, Te, BH4, CN, and the like. In addition, a part of the P element can be substituted with the Si element, the Al element, the Sn element, the In element, the Cu element, the Sb element, the Ge element, and the like.

[0066] Note that in the present specification, the sulfide solid electrolyte having a crystal structure of the LPS system or a crystal structure of the argyrodite-type no crystal structure means that the sulfide solid electrolyte has at least these crystal phases.

[0067] The sulfide solid electrolyte according to the present embodiment can be a sulfide solid electrolyte including a crystal phase and an amorphous phase, and the crystallinity is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and further preferably 90 to 100% by mass.

[0068] Here, the crystallinity is preferably 80% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more from the viewpoint of ensuring lithium ion conductivity.

[0069] In addition, the crystallinity is preferably higher, and can be 100% by mass from the viewpoint of ensuring lithium ion conductivity.

[0070] In the present specification, the crystallinity is the ratio of the crystal phase to the total of the crystal phase and the amorphous phase, and can be measured by X-ray diffraction measurement.

[0071] The sulfide solid electrolyte powder according to the present embodiment contains Al: less than 50 ppm and Zr: less than 50 ppm on a mass basis.

[0072] As described above, in order to make the particle size D50 of the sulfide solid electrolyte powder less than 1 μm, it is necessary to perform micro-pulverization using a bead mill.

[0073] Here, the container of the bead mill is usually made of zirconia-reinforced alumina in view of the thermal conductivity for cooling. There are also cases where it is made of zirconia. In addition, the beads (media) of the bead mill are usually made of alumina (Al2O3) or zirconia (ZrO2).

[0074] On the other hand, if micro-pulverization is performed using a bead mill in order to obtain a sulfide solid electrolyte powder having a particle size D50 of less than 1 μm, as described above, the sulfide solid electrolyte powder is contaminated with Al and Zr from the container and the media. Therefore, at least one of Al and Zr in the existing sulfide solid electrolyte powder is contained in an amount of 50 ppm or more on a mass basis. Furthermore, the present inventors have found that the Al and Zr contained as the above-described contamination are the cause of the decrease in lithium ion conductivity.

[0075] When the sulfide solid electrolyte powder according to the present embodiment contains Al in an amount of 50 ppm or more on a mass basis, the ion conduction path is hindered, and the lithium ion conductivity decreases. On the other hand, the content of Al in the present embodiment is less than 50 ppm on a mass basis, is preferably 49 ppm or less, more preferably 20 ppm or less, further preferably 10 ppm or less, particularly preferably 5 ppm or less, and most preferably 1 ppm or less.

[0076] The lower limit of the Al content is not particularly limited, and is, for example, 0.01 ppm.

[0077] In addition, when the sulfide solid electrolyte powder according to the present embodiment contains 50 ppm or more of Zr on a mass basis, Zr, like Al, can hinder the ion conduction path, and the lithium ion conductivity can decrease. In contrast, the content of Zr in the present embodiment is less than 50 ppm on a mass basis, preferably 49 ppm or less, more preferably 20 ppm or less, further preferably 10 ppm or less, particularly preferably 5 ppm or less, and most preferably 1 ppm or less.

[0078] The lower limit of the content of Zr is not particularly limited, and is, for example, 0.01 ppm.

[0079] The content of Al and Zr contained in the sulfide solid electrolyte powder can be measured by ICP (inductively coupled plasma) emission spectroscopy, and specifically, can be measured by the method described in the Examples below.

[0080] The content of Al and Zr described above can be achieved, for example, by further performing micro-pulverization using high-purity alumina beads on the coarsely pulverized product obtained by coarsely pulverizing the obtained sulfide solid electrolyte. The high purity is, for example, 99.9% or more.

[0081] The lithium ion conductivity of the sulfide solid electrolyte powder according to the present embodiment is preferably 2 mS / cm or more, more preferably 3 mS / cm or more, further preferably 3.5 mS / cm or more, particularly preferably 4 mS / cm or more, and is higher, the better, from the viewpoint of obtaining good battery characteristics when used in a lithium ion secondary battery.

[0082] The upper limit of the lithium ion conductivity is not particularly limited, and is, for example, 15 mS / cm.

[0083] Note that the lithium ion conductivity in the present specification is a value obtained by using an alternating current impedance measuring device for a measurement sample, which is a pressed powder obtained by applying a pressure of 380 MPa to the sulfide solid electrolyte powder. Here, the measurement conditions for the alternating current impedance measurement are a measurement frequency: 100 Hz to 1 MHz, a measurement voltage: 100 mV, and a measurement temperature: 25°C.

[0084] The sulfide solid electrolyte powder according to the present embodiment is processed as needed by a method known per se, and is used to produce a positive electrode layer or a negative electrode layer as an electrode mixture by applying a pressure to the positive electrode active material or the negative electrode active material as needed, or to produce a solid electrolyte layer by applying a pressure to an additive such as a binder as needed, and is suitable for use in a lithium ion secondary battery of a full solid type.

[0085] <Method for manufacturing sulfide solid electrolyte powder>

[0086] As Figure 1 illustrated, the method for manufacturing sulfide solid electrolyte powder according to the present embodiment sequentially includes the following processes.

[0087] Process 1: Process of preparing sulfide solid electrolyte

[0088] Process 2: Process of obtaining a coarsely pulverized product of sulfide solid electrolyte by coarsely pulverizing the above-described sulfide solid electrolyte as Step S1

[0089] Process 3: Process of obtaining sulfide solid electrolyte powder by finely pulverizing the coarsely pulverized product of sulfide solid electrolyte as Step S2

[0090] Hereinafter, each process will be described sequentially.

[0091] • Process 1

[0092] Process 1 is a process of preparing sulfide solid electrolyte. The sulfide solid electrolyte can be synthesized or a commercially available product can be used. When the sulfide solid electrolyte is synthesized, a method known heretofore can be adopted, but from the viewpoint of homogeneity of the electrolyte, a melting method is preferred.

[0093] When the sulfide solid electrolyte is synthesized, for example, a process of obtaining a raw material mixture, a process of reacting the raw material mixture, and a process of crystallizing or amorphizing are preferably included.

[0094] The reaction in the process of reacting the raw material mixture can be a thermal reaction or a mechanochemical reaction. In addition, the raw material mixture can be heated to crystallize or amorphize to obtain the sulfide solid electrolyte, in which case, the process of crystallizing or amorphizing can not be separately included. In addition, a process of improving the crystallinity, a process of rearranging the crystal can be included in addition to the process of obtaining a crystalline phase or an amorphous phase.

[0095] In the case of the melting method, each raw material can be heated and melted after being made into a mixture as needed, and cooled and solidified to obtain the sulfide solid electrolyte.

[0096] The raw materials differ depending on the composition of the desired crystalline phase or amorphous phase, and for example, raw materials containing Li, P, and S can be used. When a crystalline glass containing a Ha-containing argyrodite-type crystalline phase or a Ha-containing LPSHa-type is desired, a raw material containing Ha in addition to Li, P, and S can be further used.

[0097] Specifically, for example, to obtain a crystal of argyrodite type or a crystallized glass of Li-P-S-Ha system, raw materials containing Li, P, S, and Ha are used. To obtain a crystal of LPS system such as Li7P3S 11 To obtain a crystal of LPS system such as Li7P3S 10 To obtain a crystal of LGPS system such as GeP2S 12 To obtain a crystal of LGPS system such as GeP2S

[0098] The above raw materials can each employ a substance known heretofore.

[0099] The conditions in the process of mixing the raw materials and the reaction can employ conditions known heretofore. For example, in the case of a melting method, the heating temperature at the time of heating and melting, the time at the time of heating and melting or cooling and solidification, the atmosphere, the pressure, the dew point, and the like can employ conditions known heretofore. In addition, an intermediate obtained by causing the raw materials to react before melting can be used, and the melting synthesis can be performed starting from the intermediate.

[0100] • Process 2

[0101] Process 2 is a process (step S1) of coarsely pulverizing the sulfide solid electrolyte obtained in process 1 to obtain a coarsely pulverized product of the sulfide solid electrolyte.

[0102] In order to obtain a sulfide solid electrolyte powder having a particle diameter D50 of less than 1 μm by the fine pulverization of process 3 described later, the coarsely pulverization by process 2 is performed to a degree of about one-tenth of the diameter of the medium, i.e., beads, used in the bead mill of process 3.

[0103] As the method of coarsely pulverizing, a non-wet type pulverization method is preferred, and for example, a cutting mill is preferred.

[0104] The cutting mill refers to a method of pulverizing the raw material by high-speed rotation of a rotor provided with a blade or the like, using shearing force or cutting force.

[0105] In the cutting mill, by using, for example, a pulverizing blade made of stainless steel coated with a low-wear coating material, contamination of the stainless steel component can be suppressed. Furthermore, the coarsely pulverization in the cutting mill is different from the coarsely pulverization using a planetary ball mill, and does not require the use of alumina or zirconia balls, and the content of Al and Zr in the sulfide solid electrolyte powder finally obtained can be appropriately reduced.

[0106] In addition, in addition to the coarsely pulverization using the cutting mill, a substance equivalent to the coarsely pulverized product can be obtained, for example, by a method of directly obtaining a coarse powder from a molten liquid.

[0107] Note that the rough pulverization by the bead mill using the easily-worn alumina beads (e.g., alumina beads having a purity of 99.5% or less and a Vickers hardness HV10 of 1300 or less) or zirconia beads makes the Al and Zr contents in the rough pulverized product of the sulfide solid electrolyte high. As a result, it is difficult to make the Al content and the Zr content of the obtained sulfide solid electrolyte powder both less than 50 mass ppm.

[0108] The rough pulverization is preferably performed in such a manner that the particle size D95 of the rough pulverized product of the sulfide solid electrolyte is less than 100 μm. This is to suit the case of the bead mill pulverization in Step 3.

[0109] Specifically, depending on the model, a filter called a screen is installed at the outlet of the pulverization chamber of the bead mill, and the filter is used to pass only the slurry while separating from the beads. The gap of the filter is preferably about 100 μm or less.

[0110] The gap size of the filter can be selected, but when a particularly fine powder is desired as in the present embodiment, the bead size is preferably small beads having a diameter of 0.3 mm rather than beads having a diameter of 0.5 mm. In this case, the gap size of the filter needs to be 100 μm rather than 200 μm, taking into account the size error of the beads and the like.

[0111] Therefore, to prevent clogging of the filter, the particle size D95 of the rough pulverized product obtained in Step 2 is preferably at least less than 100 μm.

[0112] The rough pulverization is preferably performed in such a manner that the particle size D95 of the rough pulverized product becomes 10 to 99 μm, and the particle size D95 is more preferably 10 to 70 μm, and further preferably 10 to 50 μm. Here, from the viewpoint of preventing clogging of the filter (screen) at the outlet of the pulverization chamber, the particle size D95 of the rough pulverized product is preferably less than 100 μm, more preferably 99 μm or less, and further preferably 70 μm or less, and still further preferably 50 μm or less. In addition, from the viewpoint of suppressing an increase in the viscosity of the slurry containing the rough pulverized product and the solvent to be supplied to Step 3 or agglomeration of the rough pulverized product, the particle size D95 is preferably 10 μm or more.

[0113] In addition, from the viewpoint of preventing clogging of the filter, the particle size D50 of the rough pulverized product obtained in Step 2 is preferably 5 to 30 μm, and further preferably 8 to 20 μm. Here, the particle size D50 is preferably 30 μm or less, more preferably 20 μm or less, and in addition, preferably 5 μm or more, and more preferably 8 μm or more.

[0114] In addition, the sulfide solid electrolyte can be classified (sifted, etc.) as needed after the coarse pulverization, to obtain the coarse pulverization product of the sulfide solid electrolyte.

[0115] • Step 3

[0116] Step 3 is a step of performing micro-pulverization on the coarse pulverization product of the sulfide solid electrolyte obtained in Step 2, to obtain a sulfide solid electrolyte powder (Step S2).

[0117] The micro-pulverization is preferably performed using a bead mill. The bead mill differs depending on the model, and one of them is a method of making a fine powder by so-called impact pulverization, in which hard beads are rotated in a cylindrical container to pulverize the material by colliding it with the beads. By appropriately selecting the bead size and performing the micro-pulverization using such a method, a fine sulfide solid electrolyte powder having a particle size D50 of less than 1 μm can be obtained.

[0118] From the viewpoint of having good lithium ion conductivity and being able to obtain a fine sulfide solid electrolyte powder, and the viewpoint of improving the lithium ion conductivity by suppressing contamination of aluminum and zirconium, the type of beads for micro-pulverization is preferably high-purity alumina beads.

[0119] In addition, from the viewpoint of not easily causing abrasion of the aluminum beads and suppressing contamination of aluminum, the high-purity alumina beads preferably satisfy at least one of a purity of 99.9% or more and a Vickers hardness of 1800 HV10 or more, and more preferably satisfy both. By using high-purity alumina beads as described above, abrasion of the beads to the container can be further suppressed, and thus contamination of the sulfide solid electrolyte powder with zirconium contained in the container can also be suppressed.

[0120] The purity of the alumina beads is preferably 99.9% or more, more preferably 99.93% or more, further preferably 99.95% or more, particularly preferably 99.99% or more, and the higher the better.

[0121] The Vickers hardness of the alumina beads is preferably 1800 HV10 to 2300 HV10. Here, from the viewpoint of abrasion resistance, the Vickers hardness is preferably 1800 HV10 or more, more preferably 1900 HV10 or more, further preferably 2000 HV10 or more, and particularly preferably 2100 HV10 or more. In addition, from the viewpoint of suppressing abrasion of the pulverization chamber (container) and the rotor, the Vickers hardness is preferably 2300 HV10 or less.

[0122] The purity of the alumina beads can be determined by ICP emission spectroscopy analysis to determine the amount of impurities, and the total of the amounts of impurities is subtracted from 100%. In addition, the Vickers hardness can be determined by pressing a pyramid-shaped indenter made of diamond against a test piece, observing the indentation formed with a microscope, and measuring the length of the diagonal.

[0123] In addition, the fine pulverization can be dry pulverization or wet pulverization using a dispersion medium, but from the viewpoint of obtaining a finer sulfide solid electrolyte powder having a particle size D50 of less than 1 μm, wet pulverization is preferable. Dry pulverization is suitable for obtaining a powder having a particle size D50 = 1 to 3 μm, and wet pulverization is suitable for obtaining a fine powder having a particle size D50 of less than 1 μm.

[0124] In the wet pulverization method, the coarsely pulverized product of the sulfide solid electrolyte can be dispersed or dissolved in a dispersion medium to prepare a slurry, and pulverization can be performed. In addition, in the slurry, an additive such as a dispersant can be further added in addition to a solvent for the sulfide solid electrolyte.

[0125] The dispersion medium is not particularly limited, and from the viewpoint that the sulfide solid electrolyte has a property of easily reacting with moisture to deteriorate, a non-aqueous solvent is preferable.

[0126] The type of the non-aqueous organic solvent is not particularly limited, and for example, a hydrocarbon-based solvent, an organic solvent containing a hydroxyl group, an organic solvent containing an ether group, an organic solvent containing a carbonyl group, an organic solvent containing an ester group, an organic solvent containing an amino group, an organic solvent containing a formyl group, an organic solvent containing a carboxyl group, an organic solvent containing an amide group, an organic solvent containing a benzene ring, an organic solvent containing a mercapto group, an organic solvent containing a sulfide group, an organic solvent containing a thioester group, an organic solvent containing a disulfide group, a halogenated alkane, or the like can be given.

[0127] As the hydrocarbon-based solvent, for example, cyclohexane, heptane, octane, toluene can be given, and from the viewpoint of low saturated moisture concentration, cyclohexane, heptane, and octane are preferable. In addition, from the viewpoint of adjusting the moisture concentration, a mixed solvent in which these hydrocarbon-based solvents are mixed with toluene or dibutyl ether or the like is also preferable.

[0128] In the fine pulverization of the coarsely pulverized product of the sulfide solid electrolyte, from the viewpoint of preventing a decrease in lithium ion conductivity caused by a reaction of the sulfide solid electrolyte with water, the moisture concentration in the above-described dispersion medium is preferably as low as possible. The moisture concentration in the above-described dispersion medium can be, for example, 170 mass ppm or less, 150 mass ppm or less, 120 mass ppm or less, 100 mass ppm or less, or the like.

[0129] When a dispersant is used as the additive, for example, an ether compound, an ester compound, a nitrile compound, or the like can be given.

[0130] In addition, the content of the coarsely pulverized sulfide solid electrolyte in the slurry is preferably 5 to 35% by mass, more preferably 10 to 33% by mass, and further preferably 20 to 30% by mass. Here, the content is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more, and is preferably 35% by mass or less, more preferably 33% by mass or less, and further preferably 30% by mass or less, from the viewpoint of the pulverization efficiency and the ease of operation of the slurry.

[0131] The solid content concentration in the slurry is preferably 5 to 35% by mass, more preferably 10 to 33% by mass, and further preferably 20 to 30% by mass. Here, the solid content concentration is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more, and is preferably 35% by mass or less, more preferably 33% by mass or less, and further preferably 30% by mass or less, from the viewpoint of the pulverization efficiency and the ease of operation of the slurry.

[0132] When the micro-pulverization is performed using a wet-type bead mill, the diameter of the bead for micro-pulverization is preferably 0.1 to 1 mm, more preferably 0.2 to 0.8 mm, and further preferably 0.3 to 0.5 mm. Here, the diameter is preferably 0.1 mm or more, more preferably 0.2 mm or more, and further preferably 0.3 mm or more, from the viewpoint of obtaining a sulfide solid electrolyte powder having good lithium ion conductivity. In addition, the diameter is preferably 1 mm or less, more preferably 0.8 mm or less, and further preferably 0.5 mm or less, from the viewpoint of obtaining a micro-pulverized product having a desired small particle diameter.

[0133] When the micro-pulverization is performed using a wet-type bead mill, the peripheral speed of the mill is preferably 6 to 12 m / sec, and more preferably 8 to 10 m / sec. By setting the peripheral speed of the mill within the above range, excessive pulverization of the sulfide solid electrolyte can be prevented, and the aggregation of particles in the sulfide solid electrolyte powder can be suppressed.

[0134] In addition, the pulverization time using a wet-type bead mill varies depending on the amount of the coarsely pulverized product to be pulverized, and is, for example, preferably 30 to 480 minutes, and more preferably 60 to 240 minutes, when the coarsely pulverized product is about 150 to 165 g. Here, the pulverization time is preferably 30 minutes or more, and more preferably 60 minutes or more, from the viewpoint of reducing the particle diameter of the sulfide solid electrolyte powder. In addition, the pulverization time is preferably 480 minutes or less, and more preferably 240 minutes or less, from the viewpoint of suppressing excessive pulverization and ensuring good lithium ion conductivity.

[0135] The sulfide solid electrolyte powder obtained in Step 3 can be further subjected to a drying step. Even in the case where a dispersing medium, an additive, or the like remains in the sulfide solid electrolyte powder, they can be removed by drying.

[0136] The drying method can employ a method known per se, and for example, a hot plate, a drying furnace, an electric furnace, or the like can be used.

[0137] The temperature in the drying step is not particularly limited, and for example, 50 to 300°C can be mentioned. In addition, in the case where the dispersing medium is used for the pulverization, heating and drying can be performed at a temperature equal to or higher than the boiling point of the dispersing medium.

[0138] The time in the drying step is also not particularly limited, and for example, 10 minutes to 24 hours can be mentioned.

[0139] In addition, the drying step can be performed under reduced pressure, and for example, the absolute pressure can be 50 kPa or less.

[0140] In addition, the sulfide solid electrolyte powder obtained in Step 3 can be subjected to a heat treatment (annealing treatment). By performing the annealing treatment, the lithium ion conductivity can be improved.

[0141] The temperature and the time of the annealing treatment can be appropriately adjusted, and for example, 200 to 600°C can be performed for 10 to 600 minutes. In addition, the above-mentioned heat treatment can be performed between Step 2 and Step 3.

[0142] < Solid electrolyte layer >

[0143] The sulfide solid electrolyte powder according to the present embodiment can be used for a solid electrolyte layer. That is, the solid electrolyte layer according to the present embodiment contains the sulfide solid electrolyte powder described in the above-mentioned <Sulfide solid electrolyte powder>, and the preferable aspects are also the same.

[0144] The solid electrolyte layer according to the present embodiment is preferably used for a lithium ion secondary battery.

[0145] In addition, the solid electrolyte layer according to the present embodiment can contain a binder as needed.

[0146] The content of the above-mentioned sulfide solid electrolyte powder in the solid electrolyte layer according to the present embodiment is not particularly limited, and can be appropriately decided in accordance with the performance of the target battery. For example, the content of the sulfide solid electrolyte powder is preferably 80% by mass or more, and more preferably 90% by mass or more, with respect to the entire solid electrolyte layer.

[0147] As the binder which can be contained in the solid electrolyte layer, for example, butadiene rubber (BR), acrylate butadiene rubber (ABR), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and the like can be mentioned. The content of the binder in the solid electrolyte layer can be the same as in the past.

[0148] The thickness of the solid electrolyte layer is not particularly limited and can be appropriately determined depending on the performance of the target battery. For example, the above thickness is preferably 10 to 50 μm, and more preferably 15 to 20 μm. Here, from the viewpoint of obtaining a solid electrolyte layer which is improved in mechanical strength, is strong against stress such as vibration or bending, and has high reliability, the above thickness is preferably 10 μm or more, and more preferably 15 μm or more. In addition, from the viewpoint of improving the ion conductivity between the positive electrode and the negative electrode, and improving the energy density of the battery, the above thickness is preferably 50 μm or less, and more preferably 20 μm or less.

[0149] The method of forming the solid electrolyte layer is not particularly limited. For example, the components constituting the above solid electrolyte layer can be dispersed or dissolved in a liquid medium to prepare a slurry, which is coated in a layered (sheet-like) shape, dried, and optionally pressed to form the solid electrolyte layer. As needed, heat can be applied to perform a binder removal treatment. By adjusting the coating amount of the slurry and the like, the thickness of the solid electrolyte layer can be easily adjusted.

[0150] Note that, instead of the wet molding as described above, the solid electrolyte layer can be formed by dry molding of a solid electrolyte powder or the like on the surface of the object (positive electrode, negative electrode, or the like) on which the solid electrolyte layer is to be formed. Alternatively, the solid electrolyte layer can be formed on another substrate and transferred to the surface of the object on which the solid electrolyte layer is to be formed. From the viewpoint of being able to stably form a firm solid electrolyte layer on the surface of the object on which the solid electrolyte layer is to be formed in industry, it is preferable to form the solid electrolyte layer on the surface of the object by wet molding using a liquid medium.

[0151] < Lithium-ion secondary battery >

[0152] The sulfide solid electrolyte powder according to the present embodiment can be used in a lithium-ion secondary battery. That is, the lithium-ion secondary battery according to the present embodiment contains the sulfide solid electrolyte described in the above <Sulfide solid electrolyte powder>, and the preferable modes are the same.

[0153] The lithium-ion secondary battery according to the present embodiment contains a solid electrolyte layer, a positive electrode layer, and a negative electrode layer. The above sulfide solid electrolyte powder can be contained in one or more of the above solid electrolyte layer, positive electrode layer, and negative electrode layer, can be contained in two or more of them, and can be contained in all of them.

[0154] The constitution of the solid electrolyte layer, the positive electrode layer, and the negative electrode layer other than the above-mentioned sulfide solid electrolyte powder can employ substances known heretofore.

[0155] The following shows specific examples, but is not limited to these.

[0156] (The positive electrode layer)

[0157] The positive electrode layer contains at least a positive electrode current collector and a positive electrode active material. The positive electrode layer can further contain the sulfide solid electrolyte powder related to the present embodiment.

[0158] The positive electrode current collector can be a conductive sheet material, and for example, an aluminum or its alloy, a metal thin plate (metal foil) such as stainless steel can be used. These substances are excellent in electrolyte resistance and oxidation resistance, and are thus preferred.

[0159] As the positive electrode active material, there is no particular limitation as long as it can reversibly perform occlusion and release of lithium ions, deintercalation and intercalation (interlayer insertion) of lithium ions, or doping and dedoping of counter anions (for example, PF6 - ) of the lithium ions, and known positive electrode active materials can be used. As the above-mentioned positive electrode active material, for example, lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganate (LiMnO2), lithium nickel-manganate, a composite metal oxide represented by Li x Co y Mn z M a )O2 (x + y + z + a = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ a ≤ 1, M is at least one selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), a polyanion olivine-type positive electrode represented by Li a M b (PO4) c (1 ≤ a ≤ 4, 1 ≤ b ≤ 2, 1 ≤ c ≤ 3, M is at least one selected from Fe, V, Co, Mn, Ni, VO), and the like can be cited.

[0160] The positive electrode layer can have a binder that binds the positive electrode active materials to each other and binds the positive electrode active material to the positive electrode current collector. The binder can use a binder known heretofore.

[0161] In addition, the positive electrode layer can have a known positive electrode conductive aid, and for example, carbon-based materials such as graphite, carbon black, metals such as copper, nickel, stainless steel, iron, and conductive oxides such as indium tin oxide (ITO) can be cited.

[0162] (The negative electrode layer)

[0163] The negative electrode layer contains at least a negative electrode current collector and a negative electrode active material. The negative electrode layer can further contain the sulfide solid electrolyte powder according to the present embodiment.

[0164] The negative electrode current collector can be a conductive sheet such as a metal thin plate (metal foil) made of copper, aluminum, or the like. These materials are excellent in electrolyte resistance and oxidation resistance, and are thus preferred.

[0165] The negative electrode active material is not particularly limited, and can be any material capable of intercalating and deintercalating lithium ions. For example, lithium metal, carbon-based materials, silicon, silicon alloys, tin, or the like can be used.

[0166] The negative electrode active material is not particularly limited, and can be any material capable of reversibly intercalating and deintercalating lithium ions, deintercalating and intercalating lithium ions (intercalation), or doping and dedoping counter anions (e.g., PF6 - ) of the lithium ions. Any known negative electrode active material can be used. As the negative electrode active material, for example, carbon-based materials such as graphite, hard carbon, and soft carbon, metals such as aluminum, silicon, and tin that can form alloys with lithium, amorphous oxides such as silicon oxide and tin oxide, and lithium titanate (Li4Ti5O 12 ) or the like can be used.

[0167] In addition, the negative electrode layer can have a binder that binds the negative electrode active materials to each other and binds the negative electrode active material to the negative electrode current collector. Any known binder can be used.

[0168] In addition, the negative electrode layer can have a known negative electrode conductive aid, and the same materials as the positive electrode conductive aid described above can be used.

[0169] The components such as the solid electrolyte layer, the positive electrode layer, and the negative electrode layer that constitute the lithium ion secondary battery are stored in a battery exterior body. The material of the battery exterior body can be any known material, and specifically, for example, nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, a resin material, a film material, or the like can be used.

[0170] As the shape of the lithium ion all-solid-state battery, for example, a coin type, a sheet type (film type), a folded type, a wound type, a bottomed cylindrical type, a button type, or the like can be used, and the shape can be appropriately selected according to the use.

[0171] The lithium ion secondary battery according to the present embodiment can achieve good lithium ion conductivity.

[0172] Example

[0173] The present application will be specifically described below using examples, but the present application is not limited thereto. In addition, Example 1 is an example, and Example 2 is a comparative example.

[0174] < Test Example >

[0175] Example 1

[0176] Under a dry nitrogen atmosphere, lithium sulfide powder (manufactured by Sigma, purity 99.98%), phosphorus pentasulfide powder (manufactured by Sigma, purity 99%), lithium chloride powder (manufactured by Sigma, purity 99.99%), and lithium bromide powder (manufactured by Sigma, purity 99.995%) were weighed in such a manner as to become Li 5.4 PS 4.4 Cl 0.8 Br 0.8 Under a dry nitrogen atmosphere, lithium sulfide powder (manufactured by Sigma, purity 99.98%), phosphorus pentasulfide powder (manufactured by Sigma, purity 99%), lithium chloride powder (manufactured by Sigma, purity 99.99%), and lithium bromide powder (manufactured by Sigma, purity 99.995%) were weighed in such a manner as to become Li

[0177] The sulfide solid electrolyte obtained was coarsely pulverized using a cutting mill, and a coarsely pulverized product of the sulfide solid electrolyte was obtained.

[0178] Next, 165 g of the coarsely pulverized product of the sulfide solid electrolyte obtained above was added to 385 g of dehydrated dibutyl ether, and a slurry (slurry solid content concentration: 30 mass%) was obtained. In a zirconia-reinforced alumina sample container (container), 550 g of the slurry and 288 g of high-purity alumina beads (Daming Chemical, TB-03, purity 99.99 mass% or more) having a diameter of 0.3 mm were put in, and wet pulverization was performed in a Labostar Mini LMZ015 manufactured by Ashizawa Finetech Co., Ltd. under the following conditions.

[0179] (Conditions)

[0180] • Bead filling rate with respect to the sample container: 70.2 vol%

[0181] • Circumferential speed: 8 m / sec

[0182] • Pulverization time: 240 minutes

[0183] • Slurry flow rate: about 1 l / min

[0184] Thereafter, heating and drying were performed under a nitrogen atmosphere above the boiling point of the solvent, and a sulfide solid electrolyte powder was obtained.

[0185] Example 2

[0186] Instead of the high-purity alumina beads having a diameter of 0.3 mm, alumina beads (Biyarado Ceramics Co., Ltd.: AL9-0.3) having a purity of 99.5 mass% and a diameter of 0.3 mm were used, and other than that, the same method as in Example 1 was performed, and a sulfide solid electrolyte powder of Example 2 was obtained.

[0187] <Evaluation>

[0188] [Particle size distribution: particle size D50, particle size D90]

[0189] The particle size D10, the particle size D50, and the particle size D90 in the volume-based cumulative particle size distribution were measured using a Microtrac MT3300EX II manufactured by MicrotracBEL Co., Ltd. and a Microtrac USVR as a laser diffraction type particle size distribution measuring device.

[0190] [BET particle size]

[0191] The BET specific surface area obtained by the nitrogen adsorption BET multipoint method was measured, and the value calculated by the following equation was used as the BET particle size.

[0192] BET particle size (nm) = 6 / 〔true density (g / cm 3 ) x BET specific surface area (m 2 / g) 〕 x 1000

[0193] [Lithium ion conductivity]

[0194] The sulfide solid electrolyte powder was made into a press powder at a pressure of 380 MPa, and used for measurement of the sample.

[0195] Measurement was performed using an alternating current impedance measuring device (POTENTIOSTAT / GALVANOSTAT VSP manufactured by Bio-Logic Sciences Instruments Co., Ltd.) under the following conditions.

[0196] Measurement frequency: 100 Hz to 1 MHz

[0197] Measurement voltage: 100 mV

[0198] Measurement temperature: 25°C

[0199] The lithium ion conductivity at 25°C was obtained from the Nyquist diagram obtained.

[0200] [Al content and Zr content]

[0201] The sulfide solid electrolyte powder was subjected to alkali dissolution treatment to form a solution. At this time, the residue generated at the time of the dissolution treatment was recovered, and acid dissolution was performed to form a solution. The Al and Zr in each solution were quantified by ICP (high-frequency inductively coupled plasma) emission spectroscopy analysis, and used as the Al content and the Zr content in the powder.

[0202] [Crystallinity]

[0203] The crystallinity was determined by X-ray diffraction (XRD) measurement of the sulfide solid electrolyte powder, with the ratio of the crystalline phase relative to the total of the amorphous phase and the crystalline phase set as the crystallinity.

[0204]

[0205] As shown in Table 1, in the case of the pulverization, the sulfide solid electrolyte powder of Example 1 using an alumina bead of high purity had a significantly reduced Al content and Zr content compared to the sulfide solid electrolyte of Comparative Example 2, and in addition, a high lithium ion conductivity could also be achieved.

[0206] The present application has been described in detail with reference to specific embodiments, but it will be apparent to those skilled in the art that various changes, modifications and corrections can be made without departing from the spirit and scope of the present application. This application is based on Japanese Patent Application (Tokugan 2023-110731) filed on July 5, 2023, the contents of which are incorporated herein by reference.

Claims

1. A sulfide solid electrolyte powder, wherein the content, based on mass, satisfies the following conditions: Al: less than 50 ppm and Zr: less than 50 ppm. The particle size D50 is less than 1 μm.

2. The sulfide solid electrolyte powder according to claim 1, wherein, The particle size of BET, calculated from its specific surface area, is 0.10–0.30 μm.

3. The sulfide solid electrolyte powder according to claim 1, wherein, The sulfide solid electrolyte constituting the sulfide solid electrolyte powder has a crystalline phase. The crystal phase has a sulfogermanium ore-type crystal structure.

4. The sulfide solid electrolyte powder according to claim 1, wherein, The sulfide solid electrolyte constituting the sulfide solid electrolyte powder has Li α PS β The composition is represented by , where 5.5≤α≤5.6 and 4.3≤β≤4.

4.

5. A solid electrolyte layer comprising the sulfide solid electrolyte powder according to any one of claims 1 to 4.

6. A lithium-ion secondary battery comprising the sulfide solid electrolyte powder according to any one of claims 1 to 4.

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