Sulfide solid electrolyte powder and electrode mixture

Abstract

The present invention relates to a sulfide solid electrolyte powder having a crystal phase having an argyrodite-type crystal structure, the value represented by ((strain value-0.001) / specific surface area (m2 / g)) * 100 being 0.010-0.070.

Description

TECHNICAL FIELD

[0001] The present application relates to a sulfide solid electrolyte powder and an electrode mixture containing the same. 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 being able to expect improvement in safety, 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 sulfide solid electrolytes, 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] When a lithium ion battery or the like is manufactured using a sulfide solid electrolyte as described above, in order to maintain the interface contact between the positive electrode active material or the negative electrode active material and the solid electrolyte at the time of charge and discharge, a high constraint pressure needs to be applied. This is in order to prevent the volume change caused by the expansion and contraction of the positive electrode active material or the negative electrode active material accompanying the charge and discharge of the all-solid-state battery, and thus to cause the good nature of the above-mentioned interface contact to be impaired.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: International Publication No. 2021 / 085239 SUMMARY

[0010] In order to achieve the above-mentioned high constraint pressure, a large constraint jig needs to be used. In addition, even if the all-solid-state battery is obtained at a high constraint pressure, with repeated charge and discharge cycles, the good interface contact accompanying the volume change cannot be maintained, and the battery capacity decreases.

[0011] Therefore, an object of the present application is to provide a sulfide solid electrolyte powder capable of maintaining a good interface contact with an active material even at a low constraint pressure when an all-solid-state battery is manufactured, and an electrode mixture containing the same.

[0012] A solid electrolyte containing a crystal phase having a crystal structure of argyrodite type is disclosed in Patent Literature 1, and it is disclosed that the crystal lattice strain of the compound having the crystal phase is less than 0.10%, and the smaller the crystal lattice strain, the higher the lithium ion conductivity.

[0013] On the contrary, the present inventors have found as a result of intensive studies that the above problems can be solved by imparting a certain strain to a crystal phase constituting a sulfide solid electrolyte powder, and having a certain relationship with the specific surface area, thereby completing the present application.

[0014] That is, the present application relates to the following constitution.

[0015] [1] A sulfide solid electrolyte powder having a crystal phase,

[0016] a value represented by 〔(strain value - 0.001) / specific surface area (m 2 / g)〕 x 100 is 0.010 to 0.070,

[0017] The above crystal phase has a crystal structure of argyrodite type.

[0018] [2] The sulfide solid electrolyte powder according to the above [1], further having an amorphous phase,

[0019] The above amorphous phase has a content ratio of 5 mass% or more.

[0020] [3] The sulfide solid electrolyte powder according to the above [1] or [2], wherein the crystal structure of argyrodite type contains two or more halogen elements as constituent elements.

[0021] [4] The sulfide solid electrolyte powder according to the above [3], wherein the halogen elements contain Br,

[0022] The content ratio of the above Br with respect to the above halogen elements is 0.1 to 0.9.

[0023] [5] The sulfide solid electrolyte powder according to any one of the above [1] to [4], wherein the crystal structure of argyrodite type is represented by a composition formula of Li a MZ b Ha c ,

[0024] The above M in the above composition formula is at least one element selected from Na, K, and elements that exist in the above crystal structure as 2 to 5 valence cations, the above Z is at least one element selected from elements that exist in the above crystal structure as 2 valence anions, the above Ha is at least one element selected from F, Cl, Br, and I, and the above composition formula satisfies the relationships of 5≤a≤7, 4≤b≤6, and 1

[0025] [6] The sulfide solid electrolyte powder according to any one of the above [1] to [5], wherein a complex elastic modulus is 5 to 20 GPa.

[0026] [7] An electrode mixture comprising the sulfide solid electrolyte powder according to any one of the above [1] to [6].

[0027] According to the present application, a sulfide solid electrolyte powder that can maintain good interface contact with an active material even at a low constraint pressure when a full solid battery is produced can be obtained. Therefore, a full solid battery can be produced without using a large constraint jig, and a full solid battery in which a decrease in battery characteristics when charge and discharge cycles are repeatedly performed is suppressed can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a flowchart showing a method for producing a sulfide solid electrolyte powder according to the present embodiment. DETAILED DESCRIPTION

[0029] The present application is described in detail below, but the present application is not limited to the following embodiments, and can be arbitrarily modified within the scope of the gist of the present application. In addition, "to" indicating a numerical range is used in the meaning that the numerical values recited before and after it are included as lower limit values and upper limit values. In addition, in the present specification, "mass%" and "mass ppm" have the same meaning as "weight%" and "weight ppm", respectively.

[0030] Sulfide Solid Electrolyte Powder

[0031] The sulfide solid electrolyte powder according to the present embodiment has a crystal phase, and the crystal phase has a crystal structure of argyrodite type. In addition, a value represented by 〔(strain value - 0.001) / specific surface area (m 2 / g)〕 x 100 with respect to the above sulfide solid electrolyte powder satisfies 0.010 to 0.070.

[0032] Here, the strain value refers to disorder in the crystal structure.

[0033] Specifically, the average coordinates of each atom in the crystal structure are constant, but the state in which each coordinate has a distribution is referred to as disorder in the crystal structure, and is quantified by a strain value. The present inventors have found that by increasing the above-described disorder in the sulfide solid electrolyte powder, it is possible to suppress a decrease in battery characteristics due to volume change of the active material caused by expansion and contraction accompanying charging and discharging.

[0034] The reason is not certain, but it is believed that, with the disorder in the crystal structure described above, as the volume of the active material changes accompanying charging and discharging, the coordinates of each atom in the crystal structure of the sulfide solid electrolyte powder easily shift. As a result, it is possible to maintain good interface contact of the active material with the sulfide solid electrolyte powder.

[0035] It can be said that, with such disorder in the crystal structure, the coordinates of each atom easily shift, thereby absorbing the volume change of the active material, i.e., the elastic deformation region becomes wider.

[0036] The disorder in the crystal structure in the sulfide solid electrolyte powder can be quantified using a strain value in structure analysis of a powder X-ray diffraction (XRD) pattern, and the higher the strain value, the greater the disorder in the crystal structure.

[0037] Specifically, the above-described strain value is found by analyzing the XRD pattern using the Williamson-Hall method.

[0038] From the viewpoint of maintaining good interface contact, the greater the strain value of the sulfide solid electrolyte powder involved in the present embodiment, the better. In addition, it is known that when the sulfide solid electrolyte is pulverized to make the particle diameter of the sulfide solid electrolyte powder finer and increase the specific surface area, the specific surface area and the strain value are positively correlated. That is, as the specific surface area increases, the strain value becomes larger.

[0039] On the other hand, there is a tendency that the greater the specific surface area of the sulfide solid electrolyte powder, the smaller the ionic conductivity.

[0040] Therefore, in order to obtain good battery characteristics, it is not enough to simply increase the strain value.

[0041] Therefore, the present inventors have conducted further research, and as a result, it was conceived that if the strain value of the sulfide solid electrolyte powder can be made larger than ever with respect to the same specific surface area, it is possible to solve the problem of the present invention while maintaining good ionic conductivity. Furthermore, as a result of further research, it was found that when the strain value and the specific surface area satisfy a certain relationship, it is possible to solve the problem of the present invention, achieve good battery characteristics, and in fact obtain a sulfide solid electrolyte satisfying such characteristics.

[0042] Specifically, it is made up of [(strain value - 0.001) / specific surface area (m²)]. 2 The value expressed by the formula / g)〕×100 is 0.010~0.070.

[0043] Here, the value of 0.001 in the above formula is an approximate value of the strain of the sulfide solid electrolyte before it is crushed into powder, which is a value obtained through the research and conception of the inventors.

[0044] If existing pulverization methods are used to increase the strain value of sulfide solid electrolyte powder, with strict control of pulverization conditions or prolonged pulverization, excessive pulverization will result in an excessively large specific surface area. This leads to a decrease in ionic conductivity, preventing the achievement of good battery characteristics. In this case, [(strain value - 0.001) / specific surface area (m²)]... 2 The value represented by 100 ( / g) is less than 0.010.

[0045] In contrast, this invention conceives of a method for sequentially applying coarse grinding, heat treatment, and wet grinding using a bead mill to the sulfide solid electrolyte, as described later. It was thus discovered that even if the increase in specific surface area resulting from grinding is smaller than before—that is, even if the grinding is not as thorough as before—the strain value of the obtained sulfide solid electrolyte powder can still be increased.

[0046] The sulfide solid electrolyte powder involved in this embodiment has a [(strain value - 0.001) / specific surface area (m²)] ... 2 The value represented by ( / g)×100 is 0.010 to 0.070, preferably 0.015 to 0.060, and more preferably 0.020 to 0.050. From the viewpoint of more effectively obtaining the effects of the present invention, the above value is preferably 0.015 or more, and more preferably 0.020 or more.

[0047] On the other hand, no upper limit is specifically specified for the above value. From the viewpoint of maintaining the crystal structure and ionic conductivity, the upper limit is set to 0.070 or less. From this viewpoint, the above value is preferably 0.060 or less, and more preferably 0.050 or less.

[0048] The strain value of sulfide solid electrolyte powder only needs to be within the range of [(strain value - 0.001) / specific surface area (m²)]. 2The value represented by the equation of (strain value - 0.001) / specific surface area (m2 / g) x 100 within a range of 0.010 to 0.070 is not particularly limited. The specific surface area is, for example, preferably 4 to 35 m2 / g, more preferably 7 to 30 m2 / g, and further preferably 13 to 20 m2 / g.

[0049] The specific surface area of the sulfide solid electrolyte powder is not particularly limited as long as the value represented by the equation of (strain value - 0.001) / specific surface area (m 2 <2 / g) x 100 is within a range of 0.010 to 0.070. The specific surface area is, for example, preferably 4 to 35 m 2 <2 / g, more preferably 7 to 30 m 2 <2 / g, and further preferably 13 to 20 m 2 <2 / g. Here, the specific surface area is preferably 4 m 2 <2 / g or more, more preferably 7 m 2 <2 / g or more, and further preferably 13 m 2 <2 / g or more. In addition, the specific surface area is preferably 35 m 2 <2 / g or less, more preferably 30 m 2 <2 / g or less, further preferably 20 m 2 <2 / g or less.

[0050] Note that the specific surface area in the present specification is referred to as a BET specific surface area, and is a value obtained by a nitrogen adsorption BET multipoint method.

[0051] The sulfide solid electrolyte powder according to the present embodiment has a crystal phase having a crystal structure of argyrodite type. Here, the crystal structure of argyrodite type refers to a crystal structure possessed by a compound group from a mineral represented by a composition formula of Ag8GeS6. In addition, the sulfide solid electrolyte powder according to the present embodiment is not limited to the above-described crystal structure, and a part of the elements can be substituted with other elements.

[0052] The sulfide solid electrolyte powder according to the present embodiment preferably contains a halogen (Ha) element as a constituent element when the sulfide solid electrolyte powder has a crystal structure of argyrodite type, and more preferably contains two or more kinds of Ha elements. As the Ha element, at least one element selected from the group consisting of Cl, Br, and I is more preferable, and two or more kinds of elements are further preferable.

[0053] The crystal structure of argyrodite type in the present embodiment further preferably contains at least one of Cl and Br, and further preferably contains Cl and Br as the Ha element.

[0054] When the crystal structure of argyrodite type contains two or more kinds of halogen elements, one of them is preferably Br, and the content ratio of Br with respect to the halogen elements is more preferably 0.1 to 0.9, further preferably 0.2 to 0.8, and more further preferably 0.3 to 0.7.

[0055] Here, the content ratio of Br is preferably 0.1 or more, more preferably 0.2 or more, and further preferably 0.3 or more from the viewpoint of improving the ion conductivity. In addition, the content ratio of Br is preferably 0.9 or less, more preferably 0.8 or less, and more further preferably 0.7 or less from the viewpoint of suppressing the decrease in ion conductivity.

[0056] The crystal structure of argyrodite type preferably has the above structure, and the composition formula is preferably represented by Li a MZ b Ha c satisfying the relationships of 5≤a≤7, 4≤b≤6, and 1

[0057] In the above composition formula, M represents at least one element selected from the group consisting of Na, K, and elements that exist in the form of a 2- to 5-valent cation in the crystal structure. In addition, Z represents at least one element selected from elements that exist in the form of a 2-valent anion in the crystal structure. In addition, Ha represents a halogen element.

[0058] Here, as the elements that exist in the form of a 2- to 5-valent cation in the above composition formula of M, specific examples include B, Mg, Al, Si, P, Ca, Ti, V, Fe, Zn, Ga, Sr, Y, Zr, Nb, Mo, Sn, Sb, Ba, Ta, W, Bi, and the like.

[0059] From the viewpoint of the redox potential of the elements, it is preferable that the above M mainly contains P. Specifically, the fact that M mainly contains P means that the ratio of the content (at%) of P to the content (atoms%, hereinafter referred to as "at%") of M in the crystal structure of the argyrodite type is 0.6 or greater, and the above ratio is preferably 0.6 to 1. The above ratio is more preferably 0.7 or greater, and further preferably 0.8 or greater. In addition, the upper limit of the above ratio is not particularly limited, and can be 1, can be 0.98 or less, can be 0.97 or less, or can be 0.95 or less.

[0060] In addition to P, the above M can contain at least one element selected from Na, K, Mg, and Ca.

[0061] As a raw material for forming the crystal structure of the argyrodite type, a mixture containing lithium sulfide (Li2S) is sometimes preferably used. Among them, it is known that lithium sulfide is manufactured from lithium hydroxide (LiOH), and the lithium hydroxide can contain at least one element selected from Na, K, Mg, and Ca (hereinafter also referred to as "R") as an impurity. That is, M sometimes contains R, which is an impurity from such a raw material.

[0062] In order to reduce the content of R from the impurity, a high-purity raw material is sometimes required, and there is a concern that the manufacturing cost will increase.

[0063] The ratio of the content (at%) of R to the content (at%) of M is preferably 0.001 to 0.4, and more preferably 0.01 to 0.3. Here, from the viewpoint of suppressing the manufacturing cost, the above ratio is preferably 0.001 or greater, more preferably 0.01 or greater, and further preferably 0.02 or greater. In addition, from the viewpoint of suppressing the decrease in lithium ion conductivity, the above ratio is preferably 0.4 or less, and more preferably 0.3 or less.

[0064] Note that the above range does not at all hinder the intentional inclusion of R in the crystal structure of the argyrodite type, or the case where it is included at a ratio greater than the above.

[0065] For example, in the above composition formula representing the crystal structure of the argyrodite type, when O is included as Z, it is preferable to include at least one element selected from Al, Ca, Mg, Na, and K as the above R, and the element is present in the form of M n＋ in the site of Li. Here, M n＋ represents a cation of 1 to 3 valences. In this case, it is more preferable to include Al as the above R. The content (at%) of R with respect to the content (at%) of M in this case can be more than the above range.

[0066] Z in the above composition formula is at least one element selected from elements that exist in the form of a 2-valent anion in the crystal structure, and examples thereof include S, O, Se, Te, and the like.

[0067] In terms of lithium ion conductivity, it is preferable that the above Z mainly contains S. Specifically, the fact that Z mainly contains S means that the ratio of the content (at%) of S in the crystal structure to the content (at%) of Z is 0.6 or greater, and the above ratio is preferably 0.6 to 1. The above ratio is more preferably 0.7 or greater, and further preferably 0.8 or greater. In addition, the upper limit of the above ratio is not particularly limited, and can be 1, can be 0.98 or lower, can be 0.95 or lower, or can be 0.9 or lower.

[0068] In addition, when S is included as the above Z, a part of S can be substituted with Ha, BH4, CN, or the like, in addition to the above O, Se, and Te.

[0069] The halogen element represented by Ha in the above composition formula is preferably at least one element selected from the group consisting of F, Cl, Br, and I. In terms of the ease of acquisition of the crystal structure of argyrodite, the above Ha preferably contains at least one of Cl and Br, more preferably contains Br, and further preferably is Br alone or a mixture of Cl and Br. In addition, in terms of further improving lithium ion conductivity, Ha is preferably a mixture of Cl and Br.

[0070] When Ha contains Cl and Br, the content of Cl in the crystal structure of argyrodite is set to x (at%), and the content of Br is set to y (at%), and the ratio represented by (x / y) is preferably 0.1 to 10, more preferably 0.3 to 3, and further preferably 0.5 to 1.6. Here, the above ratio is preferably 0.1 or greater, more preferably 0.3 or greater, and further preferably 0.5 or greater, and is preferably 10 or lower, more preferably 3 or lower, and further preferably 1.6 or lower.

[0071] By causing the ratio represented by (x / y) to satisfy the above range, the interaction between lithium ions and halide ions becomes weaker, and lithium ion conductivity easily becomes higher. It is considered that this is due to the mixed anion effect of bromide ions, which have a larger ionic radius than chloride ions, weakening the interaction between cations and anions. In addition, the cycle characteristics of lithium ion secondary batteries are also easily improved.

[0072] When Ha contains Cl and Br, the content of Cl in the crystal structure of argyrodite is set to x (at%), and the content of Br is set to y (at%), and the ratio represented by (x / y) is preferably 0.1 to 10, more preferably 0.3 to 3, and further preferably 0.5 to 1.6. Here, the above ratio is preferably 0.1 or greater, more preferably 0.3 or greater, and further preferably 0.5 or greater, and is preferably 10 or lower, more preferably 3 or lower, and further preferably 1.6 or lower. a MZ b Cl c1 Br c2When the ratio representing the content (at%) of the elements constituting the crystal structure of the argyrodite type is c1, c1 is preferably 0.1 to 1.5, more preferably 0.3 to 1.4, and further preferably 0.5 to 1.3. Here, c1 is preferably 0.1 or more, more preferably 0.3 or more, and further preferably 0.5 or more, and is preferably 1.5 or less, more preferably 1.4 or less, and further preferably 1.3 or less.

[0073] Further, c2 described above is preferably 0.1 to 1.9, more preferably 0.3 to 1.6, and further preferably 0.5 to 1.4. Here, c2 is preferably 0.1 or more, more preferably 0.3 or more, and further preferably 0.5 or more, and is preferably 1.9 or less, more preferably 1.6 or less, and further preferably 1.4 or less.

[0074] By causing c1 and c2 to satisfy the above ranges, respectively, the proportion of the halide ions present in the crystal is optimized, the interaction between the anions and the lithium ions in the crystal structure is reduced, and a stable crystal of the argyrodite type is obtained. Thus, the lithium ion conductivity of the sulfide solid electrolyte powder easily becomes higher. Further, by causing c1 and c2 to satisfy the above ranges, the cycle characteristics of the lithium ion secondary battery are easily improved.

[0075] Note that Li a MZ b Cl c1 Br c2 The ratios of the elements in the composition formula represented by a, b, and (c1 + c2) preferably satisfy the same relationships as a, b, and c described below.

[0076] The above Li a MZ b Ha c The ratios of the elements in the composition formula represented by a, b, and (c1 + c2) preferably satisfy the same relationships as a, b, and c described below.

[0077] That is, a is preferably 5 or more, more preferably greater than 5, further preferably greater than 5.1, and further more preferably greater than 5.2, and is preferably 7 or less, more preferably less than 7, further preferably less than 6.3, and further more preferably less than 6.2.

[0078] b is preferably 4 or more, more preferably greater than 4, further preferably greater than 4.1, and is preferably 6 or less, more preferably less than 6, further preferably less than 5.3, and further more preferably less than 5.2.

[0079] For c, it is preferably greater than 1, more preferably 1.3 or greater, further preferably 1.4 or greater, more further preferably 1.5 or greater, and in addition, it is preferably 2 or less, more preferably less than 2, further preferably 1.9 or less, and more further preferably 1.8 or less.

[0080] The crystal structure of the argyrodite type is, for example, cubic crystal (e.g., F-43m), but hexagonal crystal, tetragonal crystal, orthorhombic crystal, monoclinic crystal, and the like having lower symmetry, triclinic crystal having even lower symmetry, and the like can also exist.

[0081] The sulfide solid electrolyte powder according to the present embodiment contains a crystal phase, and the content ratio (crystallinity) of the above crystal phase is preferably 50 to 100% by mass, more preferably 60 to 99% by mass, further preferably 65 to 95% by mass, and more further preferably 70 to 90% by mass.

[0082] Here, the above content ratio is preferably 50% by mass or greater, more preferably 60% by mass or greater, and further preferably 65% by mass or greater, from the viewpoint of ensuring lithium ion conductivity. On the other hand, the above content ratio can be 100% by mass, that is, the crystal phase alone, and from the viewpoint of obtaining the effect of expanding the elastic deformation region due to the presence of the amorphous phase, the above content ratio is preferably 99% by mass or less, more preferably 95% by mass or less, and further preferably 90% by mass or less.

[0083] The crystal phase in the present embodiment can contain a crystal phase having a crystal structure other than the argyrodite type, and the proportion of the crystal phase having the crystal structure of the argyrodite type with respect to the entire crystal phase is preferably 50% by mass or greater, more preferably 80% by mass or greater, and the higher the better.

[0084] As the crystal phase that can have a crystal structure other than the argyrodite type, for example, a crystal phase having a crystal structure of Li7P3S 11 a crystal phase having a crystal structure containing Li, P, and S elements, which is called LPS system, such as Li7P3S 10 a crystal phase having a crystal structure containing Li, P, and S elements, which is called LPS system, such as Li7P3S 12 a crystal phase having a crystal structure containing Li, P, and S elements, which is called LPS system, such as Li7P3S

[0085] The sulfide solid electrolyte powder according to the present embodiment can contain an amorphous phase. It is preferably contained from the viewpoint of expanding the elastic deformation region by the presence of the amorphous phase. The composition of the above amorphous phase is generally the same as that of the above crystal phase. In addition, the details of the above elastic deformation region are described below.

[0086] The content ratio of the amorphous phase in the sulfide solid electrolyte powder is preferably 5% by mass or more, more preferably 5 to 50% by mass, further preferably 10 to 40% by mass, and more further preferably 15 to 30% by mass. Here, the content ratio is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass or more from the viewpoint of further exerting the effects brought about by the presence of the amorphous phase. In addition, the content ratio is preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass or less from the viewpoint of maintaining the ion conductivity.

[0087] Note that the crystal structure of the crystalline phase in the sulfide solid electrolyte powder and the content ratio thereof are determined by analyzing the XRD pattern. In addition, the content ratio of the amorphous phase is determined by subtracting the proportion of the entire crystalline phase from the remaining amount obtained by analyzing the XRD pattern.

[0088] The sulfide solid electrolyte powder according to the present embodiment has a large elastic modulus as compared with a sulfide solid electrolyte powder having a small strain value. Specifically, the composite elastic modulus determined by the nanoindentation test using a spherical indenter having a tip radius of 100 μm is, for example, 5 GPa or more when a pellet having a relative density of 90% is produced using the sulfide solid electrolyte powder.

[0089] Generally, a crystalline solid electrolyte has a small elastic deformation region and cannot absorb the volume change of the active material accompanying charge and discharge. Therefore, a full solid battery needs to be produced under a high constraint pressure to maintain the contact interface between the solid electrolyte and the active material. However, even when a high constraint pressure is used, the solid electrolyte material slowly undergoes plastic deformation with repeated charge and discharge, and the cycle characteristics deteriorate.

[0090] On the other hand, it is considered that the sulfide solid electrolyte powder according to the present embodiment has a large elastic deformation region due to the disorder of the crystal structure, that is, the strain. In addition, it is considered that the elastic deformation region is further enlarged by the presence of the amorphous phase. As a result, even when a full solid battery is produced under a low constraint pressure, the contact interface between the solid electrolyte and the active material can be maintained, and good battery characteristics can be obtained, and furthermore, the deterioration of the cycle characteristics can be suppressed.

[0091] The composite elastic modulus according to the present embodiment is preferably 5 GPa or more, more preferably 5 to 20 GPa, further preferably 7 to 18 GPa, and more further preferably 10 to 15 GPa. Here, the composite elastic modulus is preferably 20 GPa or less, more preferably 18 GPa or less, and further preferably 15 GPa or less from the viewpoint of obtaining more excellent battery characteristics. On the other hand, in practice, the composite elastic modulus can be 5 GPa or more, can be 7 GPa or more, and can be 10 GPa or more.

[0092] The particle diameter D50 of the sulfide solid electrolyte powder according to the present embodiment is related to the above-mentioned BET specific surface area, and therefore the particle diameter D50 is adjusted so as to become an appropriate BET specific surface area. For example, when the BET specific surface area is 10 to 30 m 2 / g, the particle diameter D50 is 0.4 μm or more and less than 1.0 μm.

[0093] Note that, in the present specification, the particle diameter D50 means the volume-based cumulative 50% particle diameter obtained by a particle size distribution measuring device of the laser diffraction type. That is, it means that the particle size distribution is measured by the laser diffraction / scattering method, the total volume of the sulfide solid electrolyte is set to 100%, and the particle diameter at the point where the cumulative volume becomes 50% on the cumulative curve is obtained.

[0094] The BET specific surface area and the particle diameter D50 of the sulfide solid electrolyte powder can be adjusted by the pulverization method and the pulverization conditions when the sulfide solid electrolyte is pulverized to produce the sulfide solid electrolyte powder.

[0095] As the pulverization method of the sulfide solid electrolyte, there can be mentioned pulverization using a bead mill. It was found that even if the particle diameter D50 is not excessively reduced, the strain value can be increased to a desired degree.

[0096] The grain size in the crystal structure of the argyrodite type in the sulfide solid electrolyte powder according to the present embodiment is preferably 100 to 3000 A, more preferably 200 to 2500 A, and further preferably 300 to 2000 A. Here, from the viewpoint of the ion conductivity, the above-mentioned grain size is preferably 100 A or more, more preferably 200 A or more, and further preferably 300 A or more. In addition, considering that if the particle diameter is made fine, the grain size is necessarily made small, from the viewpoint of achieving the particle diameter D50 and the BET specific surface area which are desired as the sulfide solid electrolyte powder, the above-mentioned grain size is preferably 3000 A or less, more preferably 2500 A or less, and further preferably 2000 A or less.

[0097] Note that, in the present specification, the grain size means a value obtained together with the strain value when the XRD pattern of the sulfide solid electrolyte powder is analyzed by the Williamson-Hall method.

[0098] From the viewpoint of obtaining good battery characteristics when used for a lithium ion secondary battery, the lithium ion conductivity of the sulfide solid electrolyte powder according to the present embodiment is preferably 0.1 mS / cm or more, more preferably 0.5 mS / cm or more, further preferably 1.0 mS / cm or more, particularly preferably 1.5 mS / cm or more, and the higher the better.

[0099] The upper limit of the lithium ion conductivity is not particularly limited, and is, for example, 15 mS / cm.

[0100] 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 body obtained by applying a pressure of 380 MPa to a sulfide solid electrolyte powder. Here, the measurement conditions of 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.

[0101] The sulfide solid electrolyte powder according to the present embodiment is, as needed, processed by a method known per se, and, together with a positive electrode active material or a negative electrode active material, is subjected to a pressure to form a positive electrode layer or a negative electrode layer as an electrode mixture, or, as needed, together with an additive such as a binder, is subjected to a pressure to form a solid electrolyte layer, and is appropriately used for a lithium ion secondary battery of a full solid type.

[0102] <Method for manufacturing sulfide solid electrolyte powder>

[0103] As shown in Figure 1 , the method for manufacturing a sulfide solid electrolyte powder according to the present embodiment sequentially includes the following steps.

[0104] Step 1: a step of preparing a sulfide solid electrolyte

[0105] Step 2: a step of obtaining a coarsely pulverized product of a sulfide solid electrolyte by coarsely pulverizing the above-described sulfide solid electrolyte as Step S1

[0106] Step 3: a step of obtaining a powder by performing a heat treatment while suppressing agglomeration of the above-described coarsely pulverized product as Step S2

[0107] Step 4: a step of obtaining a sulfide solid electrolyte powder by finely pulverizing the powder after the heat treatment as Step S3

[0108] The following describes each step in order.

[0109] • Step 1

[0110] Step 1 is a step of preparing a 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 per se can be used, but from the viewpoint of obtaining a sulfide solid electrolyte having a high strain value, a melting method is preferable.

[0111] When the sulfide solid electrolyte is synthesized, for example, the following steps are preferably included: a step of obtaining a raw material mixture, a step of reacting the raw material mixture, and a step of performing crystallization or amorphization.

[0112] The reaction in the process of mixing the raw material mixture can be a heating reaction or a mechanochemical reaction. In addition, when the sulfide solid electrolyte is obtained by the heating reaction described above, a process of performing crystallization or amorphization can not be included.

[0113] In the case of the melting method, the raw materials are mixed as needed and then heated and melted, and the sulfide solid electrolyte is obtained by cooling and solidification.

[0114] The raw materials differ depending on the desired crystalline phase or amorphous phase composition, and for example, raw materials containing Li, P, S, and Ha can be used.

[0115] The raw materials described above can be materials known heretofore.

[0116] The conditions in the process of mixing or reacting the raw materials can be conditions known heretofore. For example, in the case of the melting method, the heating temperature at the time of heating and melting, the time, atmosphere, pressure, dew point, and the like at the time of heating and melting or cooling and solidification can be conditions known heretofore. In addition, an intermediate obtained by reacting the raw materials before melting can be used, and the melting synthesis can be performed from the intermediate.

[0117] • Process 2

[0118] Process 2 is a process (step S1) of performing coarse pulverization on the sulfide solid electrolyte obtained in process 1 to obtain a coarse pulverized product of the sulfide solid electrolyte.

[0119] By performing coarse pulverization before the heat treatment of process 3 described later, the particle size is made to be somewhat finer. Then, by performing the process of heat treatment while suppressing aggregation in the following process 3, a sulfide solid electrolyte powder having high ion conductivity is obtained. As a result, the load of the further pulverization process thereafter is reduced, and the ion conductivity can be suppressed from decreasing, and the process load can also be reduced.

[0120] The method of coarse pulverization is not particularly limited as long as the value represented by 〔(strain value - 0.001) / specific surface area (m 2 / g)〕 x 100 of the sulfide solid electrolyte powder finally obtained becomes a desired value, and a non-wet pulverization method is preferred. For example, coarse pulverization using a cutting mill can be mentioned. In addition, the coarse powder can be obtained by a method such as directly obtaining a coarse powder from a melt of the sulfide solid electrolyte.

[0121] 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 shear force or cutting force.

[0122] By performing the rough pulverization using the cutting mill, it is possible to increase the value represented by [(strain value - 0.001) / specific surface area (m 2 / g)] x 100 of the sulfide solid electrolyte powder after the heat treatment performed while suppressing aggregation in the following process 3 and the micropulverization of process 4, and obtain a sulfide solid electrolyte powder capable of maintaining good interface contact with an active material even under a low constraint pressure.

[0123] In addition, as a rough pulverization method other than the cutting mill, for example, a planetary ball mill, a jet mill, or the like can be used, in which case, dry pulverization without using a dispersion medium is preferred.

[0124] The rough pulverization is preferably performed in such a manner that the particle diameter D50 of the rough pulverization product of the sulfide solid electrolyte becomes 5 to 300 μm, and the particle diameter D50 is more preferably 10 to 200 μm, and further preferably 10 to 150 μm. Here, from the viewpoint of reducing the load of the micropulverization process in process 4, the particle diameter D50 of the rough pulverization product is preferably 300 μm or less, more preferably 200 μm or less, and further preferably 150 μm or less. In addition, from the viewpoint of powder handling, the particle diameter D50 is preferably 5 μm or more, and more preferably 10 μm or more.

[0125] In addition, after the rough pulverization of the sulfide solid electrolyte, classification (sieving or the like) can be performed as needed to obtain a rough pulverization product of the sulfide solid electrolyte.

[0126] • Process 3

[0127] Process 3 is a process (step S2) of performing heat treatment on the rough pulverization product of the sulfide solid electrolyte obtained in process 2 while suppressing aggregation to obtain a powder.

[0128] By performing the heat treatment, the homogeneity is improved, and the quality as a solid electrolyte is stabilized, and as a result, even if micropulverization is performed in the following process 4, a high ion conductivity can be maintained.

[0129] The heating temperature in the heat treatment is preferably, for example, 200 to 600°C, more preferably 350 to 500°C, further preferably 380 to 460°C, and particularly preferably 400 to 450°C. Here, from the viewpoint of homogenization of the particles and stabilization of the quality, the heating temperature is preferably 200°C or more, more preferably 350°C or more, further preferably 380°C or more, and particularly preferably 400°C or more. In addition, from the viewpoint of preventing sintering of the particles to each other, it is preferably 600°C or less, more preferably 500°C or less, further preferably 460°C or less, and particularly preferably 450°C or less.

[0130] The heating time in the heat treatment is, for example, preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, further preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. Here, the heating time in the heat treatment is preferably longer than or equal to 10 minutes, more preferably longer than or equal to 30 minutes, and further preferably longer than or equal to 45 minutes, particularly preferably longer than or equal to 1 hour, from the viewpoint of homogenization of the particles and stabilization of the quality. Further, the heating time in the heat treatment is preferably shorter than or equal to 10 hours, more preferably shorter than or equal to 9.5 hours, and further preferably shorter than or equal to 9 hours, from the viewpoint of manufacturing cost.

[0131] The atmosphere in the heat treatment is preferably an inactive atmosphere. As the inactive atmosphere, for example, a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, or the like can be given.

[0132] Here, in order to perform the heat treatment while suppressing agglomeration of the coarse pulverized matter, the heat treatment is preferably performed in the presence of the above-described inactive gas. The flow rate of the inactive gas is, for example, preferably 1 to 1000 L / min, more preferably 5 to 500 L / min, and further preferably 10 to 100 L / min. Here, the flow rate is preferably higher than or equal to 1 L / min, more preferably higher than or equal to 5 L / min, and further preferably higher than or equal to 10 L / min, from the viewpoint of appropriately suppressing agglomeration of the coarse pulverized matter. Further, the flow rate is preferably lower than or equal to 1000 L / min, more preferably lower than or equal to 500 L / min, and further preferably lower than or equal to 100 L / min, from the viewpoint of suppressing scattering of the coarse pulverized matter.

[0133] Further, agglomeration can be suppressed by performing the heat treatment in an atmosphere in which the SO2 concentration is, for example, 1 to 1000 ppm by volume, in addition to the above-described inactive gas.

[0134] Further, agglomeration can be suppressed by making the container in the heat treatment have a shape in which the height is low and the bottom is wide.

[0135] The dew point in the heat treatment is preferably lower than or equal to -20 °C, and there is no particular limitation on the lower limit, and it is typically around -80 °C. The oxygen concentration is preferably lower than or equal to 1000 ppm by volume.

[0136] Further, agglomeration of the coarse pulverized matter can be suppressed by flowing the inactive gas when cooling is performed after the heat treatment is completed. The flow rate of the inactive gas at this time is, for example, preferably 1 to 1000 L / min, more preferably 5 to 500 L / min, and further preferably 10 to 100 L / min. Here, the flow rate is preferably higher than or equal to 1 L / min, more preferably higher than or equal to 5 L / min, and further preferably higher than or equal to 10 L / min, from the viewpoint of appropriately suppressing agglomeration of the coarse pulverized matter. Further, the flow rate is preferably lower than or equal to 1000 L / min, more preferably lower than or equal to 500 L / min, and further preferably lower than or equal to 100 L / min, from the viewpoint of suppressing scattering of the coarse pulverized matter.

[0137] • Step 4

[0138] Step 4 is a step of performing fine pulverization on the heat-treated powder obtained in Step 3 to obtain a sulfide solid electrolyte powder (Step S3).

[0139] The fine pulverization is preferably performed using a bead mill. The bead mill refers to a method of making a fine powder by grinding and pulverizing a material by rotating hard beads in a cylindrical container. By performing the fine pulverization by such a method, it is possible to increase the strain value without excessively pulverizing, and it is possible to increase the value represented by ((strain value - 0.001) / specific surface area (m 2 / g)) x 100.

[0140] That is, if it is intended to pulverize an existing sulfide solid electrolyte powder, for example, to have a specific surface area of 15 m 2 / g, the strain value is 0.0010 or more and less than 0.0020, but the sulfide solid electrolyte powder according to the present embodiment can have a strain value of 0.0020 or more. In addition, for example, if it is intended to pulverize to obtain a sulfide solid electrolyte powder having a strain value of about 0.0025, it is necessary to have a specific surface area of 30 m 2 / g or more, but the sulfide solid electrolyte powder according to the present embodiment can have a specific surface area of about 10 to 15 m 2 / g.

[0141] The container of the bead mill used in the fine pulverization can use a container known from the past, and for example, alumina (AI2O3), zirconia (ZrO2), zirconia-reinforced alumina, and the like can be mentioned.

[0142] As the kind of the beads for the fine pulverization, for example, alumina beads, zirconia beads, glass beads, and the like can be mentioned, and from the viewpoint of wear resistance, zirconia beads, alumina beads, and the like are preferred.

[0143] When zirconia beads are used, from the viewpoint of enhancing the fracture toughness, yttria-stabilized zirconia is preferred.

[0144] When alumina beads are used, from the viewpoint of enhancing the fracture toughness, high-purity alumina beads are preferred.

[0145] 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 the high-purity alumina beads as described above, it is possible to improve the wear resistance of the beads and suppress contamination from the beads, and thus is preferred.

[0146] The purity of the alumina beads is preferably 99.9% or more, more preferably 99.93% or more, further preferably 99.95% or more, and particularly preferably 99.99% or more, and the higher the better.

[0147] The Vickers hardness of the alumina beads is preferably 1800 HV10 to 2300 HV10. Here, from the viewpoint of wear 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 wear of the pulverization chamber (vessel) or the rotor, the Vickers hardness is preferably 2300 HV10 or less.

[0148] 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 amount of impurities is subtracted from 100%.

[0149] The Vickers hardness of the alumina beads 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.

[0150] In addition, even if a dry pulverization method or a pulverization method other than a bead mill is used, a fine powder having a small particle size D50 can be obtained, but from the viewpoint of easily achieving a value represented by [(strain value - 0.001) / specific surface area (m 2 / g] x 100 in a range of 0.010 to 0.070 without making the BET specific surface area too large with respect to the strain value, wet pulverization using a bead mill is preferably used.

[0151] In the wet pulverization method, the coarsely pulverized product of the sulfide solid electrolyte can be dispersed or dissolved in a dispersion medium to produce a slurry, and pulverization can be performed. In addition, in addition to the solvent of the sulfide solid electrolyte, an additive such as a dispersant can be further added to the slurry.

[0152] The dispersion medium is not particularly limited, and from the viewpoint that the sulfide solid electrolyte has a property of easily reacting with moisture and deteriorating, a non-aqueous solvent is preferable.

[0153] 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.

[0154] 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, 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.

[0155] In the fine pulverization of the coarsely pulverized product of the sulfide solid electrolyte, from the viewpoint of preventing the decrease in lithium ion conductivity caused by the reaction of the sulfide solid electrolyte with water, the moisture concentration in the above dispersion medium is preferably lower. The moisture concentration in the above 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.

[0156] When a dispersant is used as an additive, for example, ether compounds, ester compounds, nitrile compounds, or the like can be given.

[0157] In addition, the content of the coarsely pulverized product of the sulfide solid electrolyte in the slurry is preferably 5 to 35 mass%, more preferably 10 to 33 mass%, and further preferably 20 to 30 mass%. Here, from the viewpoint of the pulverization efficiency and the ease of operation of the slurry, the above content is preferably 5 mass% or more, more preferably 10 mass% or more, and further preferably 20 mass% or more, and is preferably 35 mass% or less, more preferably 33 mass% or less, and further preferably 30 mass% or less.

[0158] The solid content concentration in the slurry is preferably 5 to 35 mass%, more preferably 10 to 33 mass%, and further preferably 20 to 30 mass%. Here, from the viewpoint of the pulverization efficiency and the ease of operation of the slurry, the above solid content concentration is preferably 5 mass% or more, more preferably 10 mass% or more, and further preferably 20 mass% or more, and is preferably 35 mass% or less, more preferably 33 mass% or less, and further preferably 30 mass% or less.

[0159] When the fine pulverization is performed using a bead mill, the diameter of the beads for fine 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, from the viewpoint of obtaining a sulfide solid electrolyte powder having good lithium ion conductivity, the above diameter is preferably 0.1 mm or more, more preferably 0.2 mm or more, and further preferably 0.3 mm or more. In addition, from the viewpoint of obtaining a fine pulverized product having a desired small particle diameter, the above diameter is preferably 1 mm or less, more preferably 0.8 mm or less, and further preferably 0.5 mm or less.

[0160] The sulfide solid electrolyte powder obtained in Step 4 can be further subjected to a drying step. Even in the case where a dispersing medium or an additive remains in the sulfide solid electrolyte powder, they can be removed by drying.

[0161] 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.

[0162] The temperature in the drying step is not particularly limited, and for example, 50 to 300°C can be mentioned. In addition, when the dispersing medium is used for the pulverization, heating and drying can be performed at a temperature above the boiling point of the dispersing medium.

[0163] The time in the drying step is also not particularly limited, and for example, 10 minutes to 24 hours can be mentioned.

[0164] In addition, the drying step can be performed under reduced pressure, and for example, the absolute pressure can be 50 kPa or less.

[0165] <Electrode Mixture>

[0166] The sulfide solid electrolyte powder according to the present embodiment can be used for an electrode mixture. That is, the electrode mixture according to the present embodiment contains the sulfide solid electrolyte powder described in the above-mentioned <Sulfide Solid Electrolyte Powder>, and the preferable modes of the sulfide solid electrolyte powder are also the same as those described in the above-mentioned <Sulfide Solid Electrolyte Powder>.

[0167] The electrode mixture according to the present embodiment is preferably used for a lithium ion secondary battery, and is formed by applying pressure to the sulfide solid electrolyte powder together with an active material. That is, when the electrode mixture according to the present embodiment is a negative electrode mixture, it contains at least a negative electrode active material and the sulfide solid electrolyte powder, and when it is a positive electrode mixture, it contains at least a positive electrode active material and the sulfide solid electrolyte powder.

[0168] The active material contained in the electrode mixture can use a material known per se.

[0169] For example, as the positive electrode active material, there is no particular limitation as long as it can reversibly occlude and release lithium ions, deintercalate and intercalate lithium ions (intercalation), or dope and undope counter anions of the lithium ions. Specifically, lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel-manganese oxide, a composite metal oxide, a polyanion olivine-type positive electrode, or the like can be mentioned.

[0170] For the negative active material, there is no particular limitation as long as it can reversibly occlude and release lithium ions, deintercalate and intercalate lithium ions (intercalation), or dope and undope counter anions of the lithium ions. Specifically, carbon-based materials such as lithium metal, 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 can be given.

[0171] <solid electrolyte layer>

[0172] 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 modes of the sulfide solid electrolyte powder are also the same as those described in the above-mentioned <sulfide solid electrolyte powder>.

[0173] The solid electrolyte layer according to the present embodiment is preferably used for a lithium-ion secondary battery.

[0174] In addition, the solid electrolyte layer according to the present embodiment can contain a binder as needed.

[0175] 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 determined depending on 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, relative to the entire solid electrolyte layer.

[0176] As the binder that 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 given. The content of the binder in the solid electrolyte layer can be the same as in the past.

[0177] 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-mentioned thickness is preferably 10 to 50 μm, and more preferably 15 to 20 μm. Here, from the viewpoint of obtaining a solid electrolyte layer that is improved in mechanical strength, is strong against stress such as vibration or bending, and has high reliability, the above-mentioned 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 and negative electrodes and improving the energy density of the battery, the above-mentioned thickness is preferably 50 μm or less, and more preferably 20 μm or less.

[0178] The method of forming the solid electrolyte layer is not particularly limited. For example, the components constituting the solid electrolyte layer described above 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. If necessary, heat can be applied to perform debinding treatment. By adjusting the coating amount of the slurry and the like, the thickness of the solid electrolyte layer can be easily adjusted.

[0179] Note that, instead of the wet molding described above, the solid electrolyte layer can be formed by dry-pressing 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.

[0180] < Lithium-ion secondary battery >

[0181] 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-mentioned < sulfide solid electrolyte powder >, and the preferable modes are also the same.

[0182] 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-mentioned sulfide solid electrolyte powder can be contained in one or more of the above-mentioned 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.

[0183] The components of the solid electrolyte layer, positive electrode layer, and negative electrode layer other than the above-mentioned sulfide solid electrolyte powder can employ substances known heretofore.

[0184] Example

[0185] The present application will be specifically described below by way of examples, but the present application is not limited thereto. In addition, Examples 1 to 8 are examples, and Example 9 is a comparative example.

[0186] < Test example >

[0187] (Example 1)

[0188] In a dry nitrogen atmosphere, 0.5 g of Li2S, 0.5 g of P2S5, and 0.5 g of SiS2were mixed and heated at 650°C for 5 hours to obtain a sulfide solid electrolyte powder. 5.4 PS 4.4 Cl 0.8 Br 0.8The lithium sulfide powder (manufactured by Sigma, purity 99.98%), the phosphorus pentasulfide powder (manufactured by Sigma, purity 99%), the lithium chloride powder (manufactured by Sigma, purity 99.99%), and the lithium bromide powder (manufactured by Sigma, purity 99.995%) were weighed in a heat-resistant container, dissolved at 750°C for 1 hour in an atmosphere of a gas containing sulfur, and then cooled to room temperature at 5°C / second to obtain a sulfide solid electrolyte. The gas containing sulfur was a mixed gas of sulfur gas (Sx (x = 2 to 8)) and nitrogen gas (N2 gas) as a carrier gas, and the content of the sulfur gas in the mixed gas was 10% by volume.

[0189] The obtained sulfide solid electrolyte was coarsely pulverized using a cutting mill, and after adjusting the average particle diameter (D50) to 10 to 20 μm, the coarsely pulverized sulfide solid electrolyte was obtained by passing through a 100-μm sieve.

[0190] Next, 200 g of the obtained coarsely pulverized material was put into a carbon container with a capacity of 1.0 L, and put into an electric furnace divided into a heating zone and a cooling zone. In the heating zone, the coarsely pulverized material was heated at 430°C for 15 minutes while circulating N2 gas at 10 L / minute. Then, it was moved to the cooling zone at room temperature, and cooled while circulating N2 gas at 20 L / minute to obtain a powder without agglomeration.

[0191] The obtained powder was added to dehydrated dibutyl ether 385 g to obtain a slurry (slurry solid content concentration: 30% by mass). The slurry 550 g and zirconia beads (manufactured by NIKKATO Corporation, YTZ-0.3) 468 g with a diameter of 0.3 mm were put into a zirconia sample container (container), and wet pulverization was performed using a bead mill installed in a Labostar Mini LMZ015 manufactured by Ashizawa Finetech Corporation.

[0192] Subsequently, the sulfide solid electrolyte powder was obtained by heating and drying at a temperature above the boiling point of the solvent under a nitrogen atmosphere.

[0193] (Examples 2 to 5)

[0194] The peripheral speed and the pulverization time in the wet pulverization conditions using the bead mill were appropriately changed so that the specific surface area of the obtained sulfide solid electrolyte powder was the value described in Table 1, and otherwise, the sulfide solid electrolyte powder was obtained by the same method as in Example 1.

[0195] (Examples 6 and 7)

[0196] When wet grinding using a bead mill, high-purity Al2O3 beads (0.3 mm in diameter, Daming Chemical, TB-03, purity ≥ 99.99%) were used instead of zirconium oxide beads, and the circumferential speed and grinding time in the wet grinding conditions of the bead mill were appropriately changed so that the specific surface area of ​​the obtained sulfide solid electrolyte powder was the value recorded in Table 1. Otherwise, the sulfide solid electrolyte powder was obtained by the same method as in Example 1.

[0197] (Example 8)

[0198] Under a dry nitrogen atmosphere, replacing Li 5.4 PS 4.4 Cl 0.8 Br 0.8 The composition, according to Li 5.4 PS 4.4 Cl 1.6 The raw materials were mixed according to the composition, and the circumferential speed and grinding time in the wet grinding conditions of the bead mill were appropriately changed so that the specific surface area of ​​the obtained sulfide solid electrolyte powder was the value recorded in Table 1. Otherwise, the sulfide solid electrolyte powder was obtained by the same method as in Example 1.

[0199] (Example 9)

[0200] Under a dry nitrogen atmosphere, lithium sulfide powder (Sigma-Aldrich, 99.98% purity), phosphorus pentasulfide powder (Sigma-Aldrich, 99% purity), lithium chloride powder (Sigma-Aldrich, 99.99% purity), and lithium bromide powder (Sigma-Aldrich, 99.995% purity) were weighed and mixed in a mortar to form Li... 5.4 PS 4.4 Cl 0.8 Br 0.8 The components were then further mixed using a planetary ball mill (Ito Seisakusho Co., Ltd., LP-M2) to obtain the sulfide precursor.

[0201] Next, the sulfide precursor powder was calcined by heating at 400°C for 5 hours under a dry nitrogen atmosphere, and then cooled to room temperature at 1°C / second to obtain a coarsely pulverized sulfide solid electrolyte.

[0202] The next step is to appropriately change the circumferential speed and grinding time in the wet grinding conditions of the bead mill so that the specific surface area of ​​the obtained sulfide solid electrolyte powder is the value recorded in Table 1. Otherwise, the same method as in Example 1 is used to obtain the sulfide solid electrolyte powder.

[0203] <Evaluation>

[0204] [Lithium-ion conductivity]

[0205] The sulfide solid electrolyte powder was made into a press powder at a pressure of 380 MPa, and used for measurement of the sample.

[0206] Measurement was performed using an alternating current impedance measurement device (POTENTIOSTAT / GALVANOSTAT VSP, manufactured by Bio-Logic Sciences Instruments) under the following conditions.

[0207] Measurement frequency: 100 Hz to 1 MHz

[0208] Measurement voltage: 100 mV

[0209] Measurement temperature: 25°C

[0210] The lithium ion conductivity at 25°C was calculated from the obtained Nyquist plot. The results are shown in Table 1.

[0211] [Crystal structure, crystallinity, strain value, grain size]

[0212] The sulfide solid electrolyte powders were measured by X-ray diffraction (XRD), and it was confirmed that the obtained sulfide solid electrolyte powders each contained a crystal phase having a crystal structure of argyrodite type.

[0213] The XRD measurement was performed on each of the sulfide solid electrolyte powders mixed with Si powder as an internal standard, using a holder not exposed to the atmosphere (SmartLab, manufactured by Rigaku). The crystal structure refinement based on the Rietveld method was performed on the obtained XRD pattern using the RIETAN-FP software. The structure having the lowest Rwp value was determined as the crystal structure of each example in the analysis. The Rwp value refers to the reliability factor Rwp (R-weighted pattern) as a general standard with respect to the entire analysis range in the fitting of the structure refinement by the Rietveld analysis. The lower the Rwp value, the better, and in the present analysis, the lowest Rwp value was less than 10%. Thus, the crystallinity (mass %) of the argyrodite-type crystal in the sulfide solid electrolyte powder, i.e., the ratio of the crystal phase to the total of the amorphous phase and the crystal phase, was calculated.

[0214] The results are shown in Table 1.

[0215] In addition, the Williamson-Hall method was used to analyze the results obtained in the above analysis, and the strain value and the grain size were calculated.

[0216] The calculation method was as follows: the peak value (2θ) and the half-value width (β) were selected and converted into 2sinθ / λ1 and βcosθ / λ1, respectively. Here, λ1 was 1.5405 of the wavelength of CuKα1 ray in Å.

[0217] The obtained 2sinθ / λl and βcosθ / λl are plotted as X axis and Y axis, respectively, and only peaks from the argyrodite crystal structure are plotted. The slope of the line approximating the obtained graph to a straight line is taken as the strain value, and the reciprocal of the intercept value with the Y axis is taken as the grain size, to obtain each value.

[0218] The results are shown in Table 1.

[0219] The XRD measurement conditions are as described below.

[0220] The ray source: CuKα ray (λ = 1.5418 A (CuKαl ray wavelength 1.5405 A, CuKα2 ray wavelength 1.5443 A, each intensity ratio Kα2 / Kαl = 0.497)), tube voltage: 45 kV, tube current: 200 mA, scanning angle: 10 to 120°, scanning speed: 5° / minute, step number: 0.01° / step.

[0221] [BET specific surface area]

[0222] The BET specific surface area (specific surface area, m 2 / g) was measured by nitrogen adsorption BET multipoint method. The results are shown in Table 1.

[0223] [Strain value parameter]

[0224] From the above obtained strain value and BET specific surface area, a value represented by 〔(strain value - 0.001) / specific surface area (m 2 / g)〕 x 100 was calculated. The results are shown in Table 1.

[0225] [Battery evaluation]

[0226] The obtained sulfide solid electrolyte powder: LiNi 1／3 Co 1／ 3Mn 1／3 O2 particles (positive electrode active material): conductive aid: binder = 1.1 g: 5.0 g: 0.1 g: 0.6 g were mixed, and a slurry was obtained by stirring in a butyl butyrate solution. The above slurry was coated on an Al foil as a current collector by a doctor blade method using an applicator, vacuum dried at 80°C for 4 hours, to obtain a positive electrode sheet. The obtained sheet was punched out with a die of 10 mm in diameter, to obtain a positive electrode mixture.

[0227] On the other hand, a green body (diameter 10 mm, thickness 1 mm) of the sulfide solid electrolyte powder thus obtained was prepared, and the positive electrode mixture was placed on the green body, which was then pressed at 500 MPa, and then the Li-In alloy was attached to the electrode. Then, a lithium-ion secondary battery (half cell) was produced by restraining at a restraint pressure of 10 MPa or 100 MPa. Note that the half cell was of a structure in which the internal substance was not exposed to the atmosphere.

[0228] The obtained half cell was repeatedly subjected to charge and discharge at 25°C in the range of 4.3 to 2.5 V vs. Li ＋ / Li at a rate of 0.1 C for 5 cycles. The rate of charge and discharge was 0.1 C.

[0229] At the 6th cycle, the half cell was charged to 4.3 V vs. Li ＋ / Li at a rate of 0.1 C, and then discharged to 1.9 V vs. Li ＋ / Li at a rate of 1 C, and the discharge capacity at this time was determined.

[0230] The ratio of the discharge capacity of the half cell restrained at a pressure of 10 MPa to the discharge capacity of the half cell restrained at a pressure of 100 MPa was determined. The results are shown in Table 1, in which the ratio of the discharge capacity is shown after being normalized. Specifically, the ratio of the discharge capacity of Example 9 was normalized so as to become 1.00. Furthermore, the larger the ratio of the discharge capacity after the normalization is compared to Example 9, the more it indicates that good interface contact with the active material can be maintained even at a low restraint pressure.

[0231] [Complex Elastic Modulus]

[0232] The complex elastic modulus of the sulfide solid electrolyte powder obtained in Example 1 was determined.

[0233] Specifically, 0.1 g of the sulfide solid electrolyte powder was molded into a green body (pellet) having a diameter of 10 mm. The green body was produced by applying pressure so that the relative density became 90%, and the sample of Example 1 was molded by applying pressure of 570 MPa.

[0234] Nanoindentation test was performed on the pellet using a spherical indenter having a tip radius of 100 μm.

[0235] As a result, the complex elastic modulus of Example 1 was confirmed to be 11 GPa. Note that the sample was handled and measured in an environment not exposed to the atmosphere.

[0236]

[0237] As shown in Table 1, by obtaining the sulfide solid electrolyte by the melting method, and sequentially performing coarse pulverization using a cutting mill, heat treatment for suppressing agglomeration, and fine pulverization using a bead mill, even if the particle diameter of the obtained sulfide solid electrolyte powder is not excessively reduced, the strain value can be increased, and the value represented by ((strain value - 0.001) / specific surface area (m 2 / g)) x 100 can be increased. As a result, in the case where a lithium ion battery is assembled at a low constraint pressure such as 10 MPa without reducing the lithium ion conductivity of the sulfide solid electrolyte powder, good interface contact is also accompanied, and good battery characteristics can be achieved even if repeated charge and discharge cycles are performed.

[0238] The present application has been described in detail with reference to specific embodiments, but it is clear to those skilled in the art that various changes, modifications can be made without departing from the spirit and scope of the present application. This application is based on Japanese Patent Application (Tokugan 2023-110732) filed on July 5, 2023, the contents of which are incorporated herein by reference.

Claims

1. A sulfide solid electrolyte powder having a crystalline phase, From [(strain value - 0.001) / specific surface area (m²)] 2 The value represented by ( / g)×100 is 0.010 to 0.

070. The crystal phase has a sulfogermanium ore-type crystal structure.

2. The sulfide solid electrolyte powder according to claim 1 further comprises an amorphous phase. The amorphous phase is present in a proportion of 5% by mass or more.

3. The sulfide solid electrolyte powder according to claim 1, wherein, The crystal structure of the sulfosilver germanite type contains two or more halogen elements as constituent elements.

4. The sulfide solid electrolyte powder according to claim 3, wherein, The halogen element includes Br. The content of Br relative to the halogen element is 0.1 to 0.

9.

5. The sulfide solid electrolyte powder according to claim 1, wherein, The crystal structure of the silver-germanium sulfide type is composed of Li a MZ b Ha c The compositional expression is represented as follows: In the compositional formula, M is selected from Na, K, and at least one element present in the crystal structure as a 2- to 5-valent cation; Z is selected from at least one element present in the crystal structure as a divalent anion; and Ha is selected from at least one element selected from F, Cl, Br, and I. The compositional formula satisfies the relationships 5≤a≤7, 4≤b≤6, and 1<c≤2.

6. The sulfide solid electrolyte powder according to claim 1 has a composite elastic modulus of 5 to 20 GPa.

7. An electrode mixture comprising the sulfide solid electrolyte powder according to any one of claims 1 to 6.

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