Sulfide solid electrolyte powder and electrode binder

Abstract

To provide a sulfide solid electrolyte powder that can maintain good interface contact with an active material even under low confinement pressure when used in a solid-state battery.SOLUTION: The present invention relates to a sulfide solid electrolyte powder that has a crystal phase, where a value expressed by {[(strain value)-0.001] / [specific surface area (m2 / g)]}×100 is 0.010-0.070, and the crystal phase has an argyrodite crystal structure.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to sulfide solid electrolyte powder and an electrode binder containing the same.

Background Art

[0002] Lithium-ion secondary batteries are widely used in portable electronic devices such as mobile phones and notebook computers. Conventionally, liquid electrolytes have been used in lithium-ion secondary batteries. However, due to the expected improvement in safety and high-speed charge and discharge, lithium-ion all-solid-state batteries (hereinafter also referred to as solid batteries) using solid electrolytes as electrolytes for lithium-ion secondary batteries have attracted attention.

[0003] Solid electrolytes are roughly classified into sulfide solid electrolytes and oxide solid electrolytes. Among them, sulfide solid electrolytes contain sulfide ions with a large polarization rate and thus exhibit high ionic conductivity. As sulfide solid electrolytes, LGPS-type crystals such as Li 10 GeP2S 12 etc., argyrodite-type crystals such as Li6PS5Cl, and LPS crystallized glass such as Li7P3S 11 are known.

[0004] When manufacturing all-solid-state batteries such as lithium-ion batteries using the above sulfide solid electrolytes, it is necessary to use a high restraint pressure to maintain the interfacial contact between the positive electrode active material and the negative electrode active material and the solid electrolyte during charge and discharge. This is to prevent the deterioration of the above interfacial contact due to volume changes caused by the expansion and contraction of the positive electrode active material and the negative electrode active material during charge and discharge of the all-solid-state battery.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In order to achieve such a high confinement pressure as described above, it is necessary to use a large confinement jig. Further, even if a all-solid-state battery is obtained with a high confinement pressure, as the charge-discharge cycle is repeated, good interfacial contact cannot be maintained with the volume change, and the battery capacity decreases.

[0007] Therefore, an object of the present invention is to provide a sulfide solid electrolyte powder capable of maintaining good interfacial contact with an active material even at a low confinement pressure when used as an all-solid-state battery, and an electrode binder containing the same.

Means for Solving the Problems

[0008] Patent Document 1 discloses a solid electrolyte containing a crystal phase having an argyrodite-type crystal structure, and it is disclosed that the lattice strain of the compound having the crystal phase is less than 0.10%, and the smaller the lattice strain, the better the lithium ion conductivity. On the other hand, as a result of intensive studies, the present inventors have found that by imparting a certain strain to the crystal phase constituting the sulfide solid electrolyte powder and having a certain relationship with the specific surface area, the above problems can be solved, and the present invention has been completed.

[0009] That is, the present invention relates to the following. [1] A sulfide solid electrolyte powder having a crystal phase, The value represented by [(strain value - 0.001) / specific surface area (m 2 / g)]×100 is 0.010 to 0.070, The crystal phase has an argyrodite-type crystal structure, and the sulfide solid electrolyte powder. [2] Further having an amorphous phase, The content ratio of the amorphous phase is 5% by mass or more, and the sulfide solid electrolyte powder according to [1]. [3] The argyrodite-type crystal structure contains two or more halogen elements as constituent elements, and the sulfide solid electrolyte powder according to [1] or [2]. [4] The halogen element contains Br, The content ratio of Br to the halogen element is 0.1 to 0.9, and the sulfide solid electrolyte powder according to [3] above. [5] The alditol-type crystal structure is Li a MZ b Ha c represented by the composition formula of, In the composition formula, M is at least one element selected from Na, K, and elements existing as cations with a valence of 2 to 5 in the crystal structure, Z is at least one element selected from elements existing as divalent anions in the crystal structure, and Ha is at least one element selected from the group consisting of F, Cl, Br, and I. The composition formula satisfies the relationship of 5 ≦ a ≦ 7, 4 ≦ b ≦ 6, and 1 < c ≦ 2, and the sulfide solid electrolyte powder according to any one of [1] to [4] above. [6] The complex elastic modulus is 5 to 20 GPa, and the sulfide solid electrolyte powder according to any one of [1] to [5] above. [7] An electrode binder containing the sulfide solid electrolyte powder according to any one of [1] to [6] above.

Advantages of the Invention

[0010] According to the present invention, when a all-solid-state battery is formed, a sulfide solid electrolyte powder capable of maintaining good interfacial contact with the active material even at a low constraint pressure can be obtained. Therefore, a all-solid-state battery can be manufactured without using a large restraint jig, and a all-solid-state battery with suppressed deterioration of battery characteristics when repeating charge and discharge cycles can be obtained.

Brief Description of the Drawings

[0011]

Figure 1

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail. However, the present invention is not limited to the following embodiments and can be arbitrarily modified and implemented without departing from the gist of the present invention. In addition, "~" indicating a numerical range is used to mean that the numerical values described before and after it are included as the lower limit value and the upper limit value.

[0013] 《Sulfide Solid Electrolyte Powder》 The sulfide solid electrolyte powder according to this embodiment has a crystal phase, and the crystal phase has an argyrodite-type crystal structure. Further, the sulfide solid electrolyte powder satisfies 0.010 to 0.070 in terms of the value represented by [(distortion value - 0.001) / specific surface area (m 2 / g)]×100.

[0014] Here, the distortion value means the disorder in the crystal structure. Specifically, although the average coordinates of each atom in the crystal structure are constant, the state in which there is a distribution in each coordinate is referred to as the disorder in the crystal structure and is quantified by the distortion value. The present inventors have found that by increasing the above disorder in the sulfide solid electrolyte powder, it is possible to suppress the deterioration of battery characteristics accompanying the volume change of the active material due to expansion and contraction during charge and discharge.

[0015] Although the reason for this is not clear, due to having the disorder in the crystal structure, it becomes easier for the coordinates of each atom in the crystal structure of the sulfide solid electrolyte powder to shift in accordance with the volume change of the active material accompanying charge and discharge. As a result, it is considered that good interfacial contact between the active material and the sulfide solid electrolyte powder can be maintained. Along with such disorder in the crystal structure, since it becomes easier for the coordinates of each atom to shift, it can be said that the volume change of the active material is absorbed, that is, the elastic deformation region becomes wider.

[0016] The disorder in the crystal structure of the sulfide solid electrolyte powder can be quantified as the distortion value of the structural analysis of the powder X-ray diffraction (XRD; X-ray Diffraction) pattern, and the higher the distortion value, the greater the disorder in the crystal structure.

[0017] Specifically, the above-mentioned strain value is obtained by analysis using the Williamson-Hall method for the XRD pattern.

[0018] From the perspective of maintaining good interfacial contact, it is preferable that the strain value of the sulfide solid electrolyte powder is larger. Also, when the sulfide solid electrolyte is pulverized to reduce the particle size of the sulfide solid electrolyte powder and increase the specific surface area, it was found that the specific surface area and the strain value show a positive correlation. That is, the larger the specific surface area, the larger the strain value. On the other hand, the ionic conductivity tends to decrease as the specific surface area of the sulfide solid electrolyte powder increases. Therefore, simply increasing the strain value alone is not sufficient to obtain good battery characteristics.

[0019] As a result of further studies by the present inventors, it was conceived that if the strain value of the sulfide solid electrolyte powder can be made larger than before for the same specific surface area, the problems of the present invention can be solved while maintaining good ionic conductivity. And as a result of further studies, it was found that when the strain value and the specific surface area satisfy a certain relationship, the problems of the present invention can be solved and good battery characteristics can be realized, and actually, a sulfide solid electrolyte satisfying such characteristics was obtained.

[0020] Specifically, the value represented by the formula [(strain value - 0.001) / specific surface area (m 2 / g)]×100 is set to 0.010 to 0.070. Here, the value of 0.001 in the above formula is approximately the strain value of the sulfide solid electrolyte before pulverization into powder, and is a value conceived by the studies of the present inventors.

[0021] If the conventional pulverization method is adopted and the pulverization conditions are made severe or the pulverization is carried out for a long time in order to increase the strain value of the sulfide solid electrolyte powder, the specific surface area becomes too large due to over-pulverization. As a result, the ionic conductivity decreases and good battery characteristics cannot be realized. In this case, [(strain value - 0.001) / specific surface area (m 2The value represented by [(distortion value - 0.001) / specific surface area (m / g)] × 100 is less than 0.010.

[0022] In contrast, in the present invention, it was conceived to sequentially employ the following coarse pulverization, heat treatment, and wet pulverization method using a bead mill for the sulfide solid electrolyte. As a result, it has been found that even if the increase in specific surface area due to pulverization is less than that of the prior art, that is, even if the pulverization has not progressed as much as the prior art, the distortion value of the obtained sulfide solid electrolyte powder can be increased.

[0023] For the sulfide solid electrolyte powder according to this embodiment, the value represented by [(distortion value - 0.001) / specific surface area (m 2 / g)] × 100 is 0.010 to 0.070, preferably 0.015 to 0.060, and more preferably 0.020 to 0.050. Here, 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. On the other hand, although the upper limit of the above value is not particularly defined, from the viewpoint of maintaining the crystal structure and retaining the ionic conductivity, the upper limit is set to 0.070 or less. From the above viewpoint, the above value is preferably 0.060 or less, and more preferably 0.050 or less.

[0024] The distortion value of the sulfide solid electrolyte powder is not particularly limited as long as the value represented by [(distortion value - 0.001) / specific surface area (m 2 / g)] × 100 is in the range of 0.010 to 0.070. The above distortion value is preferably, for example, 0.0020 to 0.0080, more preferably 0.0030 to 0.0070, and even more preferably 0.0040 to 0.0060. Here, from the viewpoint of maintaining better interfacial contact with the active material even at a low confinement pressure, the distortion value is preferably 0.0020 or more, more preferably 0.0030 or more, and even more preferably 0.0040 or more. Also, from the viewpoint of maintaining a high ionic conductivity, the distortion value is preferably 0.0080 or less, more preferably 0.0070 or less, and even more preferably 0.0060 or less.

[0025] The specific surface area of the sulfide solid electrolyte powder is [(distortion value - 0.001) / specific surface area (m 2If the value represented by “〔 / g)〕×100” is within the range of 0.010 to 0.070, it is not particularly limited. The specific surface area is, for example, preferably 4 to 35 m 2 / g, more preferably 7 to 30 m 2 / g, and even more preferably 13 to 20 m 2 / g. Here, from the viewpoint of forming more interfaces with the active material and further improving battery characteristics, the specific surface area is preferably 4 m 2 / g or more, more preferably 7 m 2 / g or more, and even more preferably 13 m 2 / g or more. Also, from the viewpoint of suppressing the decrease in ionic conductivity due to refinement, the specific surface area is preferably 35 m 2 / g or less, more preferably 30 m 2 / g or less, and even more preferably 20 m 2 / g or less. In addition, the specific surface area in this specification is a value obtained by the nitrogen adsorption BET multipoint method, which is called the BET specific surface area.

[0026] The sulfide solid electrolyte powder according to this embodiment has a crystal phase having an argyrodite-type crystal structure. Here, the argyrodite-type crystal structure is a crystal structure possessed by a group of compounds derived from a mineral represented by the composition formula Ag8GeS6. Further, the sulfide solid electrolyte powder according to this embodiment is not limited to the above crystal structure, and some elements may be substituted with other elements.

[0027] When the sulfide solid electrolyte powder according to this embodiment has an argyrodite-type crystal structure, it is preferable to contain a halogen (Ha) element as a constituent element, and more preferably to contain two or more Ha elements. More preferably, the Ha element contains at least one element selected from the group consisting of Cl, Br, and I, and even more preferably contains two or more elements.

[0028] In the argyrodite-type crystal structure in this embodiment, it is more preferable to contain at least one of Cl and Br as the Ha element, and it is also more preferable to contain Cl and Br.

[0029] When the above-mentioned alluaudite-type crystal structure contains two or more halogen elements, one of them is preferably Br, and the content ratio of Br to the halogen elements is more preferably 0.1 to 0.9, even more preferably 0.2 to 0.8, and still more preferably 0.3 to 0.7. Here, the content ratio of the above-mentioned Br is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more from the viewpoint of improving the ionic conductivity. Also, from the viewpoint of suppressing the decrease in ionic conductivity, the content ratio of the above-mentioned Br is preferably 0.9 or less, more preferably 0.8 or less, and even more preferably 0.7 or less.

[0030] The alluaudite-type crystal structure preferably has the above structure, but the composition formula is Li a MZ b Ha c and it is preferably represented by and satisfies the relationships of 5 ≦ a ≦ 7, 4 ≦ b ≦ 6 and 1 < c ≦ 2.

[0031] In the above composition formula, M represents at least one element selected from Na, K and elements existing as divalent to pentavalent cations in the crystal structure. Also, Z represents at least one element selected from elements existing as divalent anions in the crystal structure. Also, Ha represents a halogen element.

[0032] Here, among M in the above composition formula, the elements existing as divalent to pentavalent cations specifically include B, Mg, Al, Si, P, Ca, Ti, V, Fe, Zn, Ga, Sr, Y, Zr, Nb, Mo, Sn, Sb, Ba, Ta, W and Bi, etc.

[0033] From the perspective of the redox potential of the elements, M preferably mainly contains P. That M mainly contains P specifically means that the ratio of the content of P (atoms%, hereinafter referred to as "at%") to the content of M (at%) in the argyrodite-type crystal structure is 0.6 or more, and the above ratio is preferably 0.6 to 1. The above ratio is more preferably 0.7 or more, and even more preferably 0.8 or more. Also, the upper limit of the above ratio is not particularly limited and may be 1, may be 0.98 or less, may be 0.97 or less, or may be 0.95 or less.

[0034] In addition to P, M may contain at least one element selected from Na, K, Mg, and Ca. As a raw material for forming an argyrodite-type crystal structure, a mixture containing lithium sulfide (Li2S) may be preferably used. Here, although it is widely known that lithium sulfide is produced from lithium hydroxide (LiOH), lithium hydroxide may contain at least one element (hereinafter also referred to as "R") selected from the group consisting of Na, K, Mg, and Ca as an impurity. That is, M may contain R derived from such impurities in the raw material.

[0035] In order to reduce the content of R derived from impurities, high-purity raw materials may be required, and there is a concern about an increase in manufacturing cost. The ratio of the content of R (at%) to the content of M (at%) is preferably 0.001 to 0.4, and more preferably 0.01 to 0.3. Here, from the perspective of suppressing manufacturing cost, the above ratio is preferably 0.001 or more, more preferably 0.01 or more, and even more preferably 0.02 or more. Also, from the perspective of suppressing a decrease in lithium ion conductivity, the above ratio is preferably 0.4 or less, and more preferably 0.3 or less.

[0036] Note that the above range does not prevent intentionally containing R in the argyrodite-type crystal structure or containing more than the above-mentioned ratio at that time. For example, in the above composition formula showing an argyrodite-type crystal structure, when O is included as Z, at least one element selected from Al, Ca, Mg, Na, and K is contained as the above R, and this element is M n+ It is preferably present at the site of Li as. Here, M n+ represents a cation with a valence of 1 to 3. 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 may be more than the above-mentioned range.

[0037] Z in the above composition formula is at least one element selected from elements that exist as divalent anions in the crystal structure, and examples include S, O, Se, Te, etc. Among them, from the perspective of lithium ion conductivity, it is preferable that the above Z mainly contains S. That the Z mainly contains S specifically means that the ratio of the content (at%) of S to the content (at%) of Z in the crystal structure is 0.6 or more, and the above ratio is preferably 0.6 to 1. The above ratio is more preferably 0.7 or more, and even more preferably 0.8 or more. Also, the upper limit of the above ratio is not particularly limited and may be 1, may be 0.98 or less, may be 0.95 or less, or may be 0.9 or less.

[0038] Also, when S is included as the above Z, a part of S may be substituted with the above O, Se, Te, as well as Ha, BH4, CN, etc.

[0039] 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. From the perspective of the ease of taking on an argyrodite-type crystal structure, it is preferable that the above Ha includes at least one of Cl and Br, more preferably includes Br, and even more preferably is Br alone or a mixture of Cl and Br. Also, from the perspective of further improving the lithium ion conductivity, Ha is preferably a mixture of Cl and Br.

[0040] When Ha contains Cl and Br, when the content of Cl in the argyrodite-type crystal structure is x (at%) and the content of Br is y (at%), the ratio represented by (x / y) is preferably from 0.1 to 10, more preferably from 0.3 to 3, and even more preferably from 0.5 to 1.6. Here, the above ratio is preferably 0.1 or more, more preferably 0.3 or more, even more preferably 0.5 or more, and preferably 10 or less, more preferably 3 or less, and even more preferably 1.6 or less. When the ratio represented by (x / y) satisfies the above range, the interaction between lithium ions and halide ions is weakened, and the lithium ion conductivity tends to be good. This is considered to be due to the influence of the mixed anion effect, which weakens the interaction between cations and anions by mixing bromide ions with a larger ionic radius than chloride ions. Also, the cycle characteristics of the lithium ion secondary battery tend to be improved.

[0041] When Ha contains Cl and Br, the ratio of the content (at%) of the elements constituting the argyrodite-type crystal structure is Li a MZ b Cl c1 Br c2 When expressed as, c1 is preferably from 0.1 to 1.5, more preferably from 0.3 to 1.4, and even more preferably from 0.5 to 1.3. Here, c1 is preferably 0.1 or more, more preferably 0.3 or more, even more preferably 0.5 or more, and preferably 1.5 or less, more preferably 1.4 or less, and even more preferably 1.3 or less. Also, the above c2 is preferably from 0.1 to 1.9, more preferably from 0.3 to 1.6, and even more preferably from 0.5 to 1.4. Here, c2 is preferably 0.1 or more, more preferably 0.3 or more, even more preferably 0.5 or more, and preferably 1.9 or less, more preferably 1.6 or less, and even more preferably 1.4 or less. By satisfying the above ranges for c1 and c2 respectively, the proportion of halide ions in the crystal is optimized, and a stable argyrodite-type crystal can be obtained while reducing the interaction between anions and lithium ions in the crystal structure. As a result, the lithium ion conductivity of the sulfide solid electrolyte powder is likely to be good. Also, by satisfying the above ranges for c1 and c2, the cycle characteristics of the lithium ion secondary battery are likely to be improved. In addition, Li a MZ b Cl c1 Br c2 In the compositional formula represented by a, b, and (c1 + c2), it is preferable to satisfy the same relationships as a, b, and c described below.

[0042] The above Li a MZ b Ha c Regarding the ratios of the respective elements in the compositional formula represented by, it is preferable to satisfy the relationships of 5 ≤ a ≤ 7, 4 ≤ b ≤ 6, and 1 < c ≤ 2. More preferably, it satisfies the relationships of 5 < a < 7, 4 < b < 6, and 1 < c < 2. Even more preferably, it satisfies the relationships of 5.1 < a < 6.3, 4 < b < 5.3, and 1.4 ≤ c ≤ 1.9. Even more preferably, it satisfies the relationships of 5.2 < a < 6.2, 4.1 < b < 5.2, and 1.5 ≤ c ≤ 1.8.

[0043] That is, for a, 5 or more is preferable, more than 5 is more preferable, more than 5.1 is even more preferable, more than 5.2 is even more preferably. Also, 7 or less is preferable, less than 7 is more preferable, less than 6.3 is even more preferable, less than 6.2 is even more preferably. For b, 4 or more is preferable, more than 4 is more preferable, more than 4.1 is even more preferable. Also, 6 or less is preferable, less than 6 is more preferable, less than 5.3 is even more preferable, less than 5.2 is even more preferably. For c, more than 1 is preferable, 1.3 or more is more preferable, 1.4 or more is even more preferable, 1.5 or more is even more preferably. Also, 2 or less is preferable, less than 2 is more preferable, less than 1.9 is even more preferable, less than 1.8 is even more preferably.

[0044] The argyrodite-type crystal structure is, for example, cubic (e.g., F-43m), but there may also be hexagonal, tetragonal, orthorhombic, monoclinic, etc. with reduced symmetry, and even triclinic with further reduced symmetry, etc.

[0045] The sulfide solid electrolyte powder according to this embodiment contains a crystal phase, and the content ratio (crystallinity) of the crystal phase is preferably 50 to 100% by mass, more preferably 60 to 99% by mass, still more preferably 65 to 95% by mass, and even more preferably 70 to 90% by mass. Here, from the viewpoint of ensuring lithium ion conductivity, the above content ratio is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 65% by mass or more. On the other hand, the above content ratio may be 100% by mass, that is, it may consist only of the crystal phase, but 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 still more preferably 90% by mass or less.

[0046] The crystal phase in this embodiment may have a crystal phase having a crystal structure other than the argyrodite type, but the ratio of the crystal phase having the argyrodite-type crystal structure to the whole crystal phase is preferably 50% by mass or more, more preferably 80% by mass or more, and the higher the better. The crystal phase that may be present in addition to the argyrodite-type crystal structure includes, for example, a crystal phase having a crystal structure containing Li element, P element, and S element called the LPS system such as Li7P3S 11 etc., a crystal phase having a crystal structure containing Li element, Ge element, P element, and S element called the LGPS system such as Li 10 GeP2S 12 etc., a crystal phase having a thio-LISICON type crystal structure, a crystal phase containing an oxide, and the like.

[0047] The sulfide solid electrolyte powder according to this embodiment may contain an amorphous phase. The presence of the amorphous phase is preferable because the elastic deformation region is expanded. Generally, the composition of the amorphous phase is the same as that of the crystal phase. The details of the elastic deformation region will be described below.

[0048] 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, still more preferably 10 to 40% by mass, and even more preferably 15 to 30% by mass. Here, from the viewpoint of further exerting the effect due to the presence of the amorphous phase, the above content ratio is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 15% by mass or more. Further, from the viewpoint of maintaining the ionic conductivity, it is preferably 50% by mass or less, more preferably 40% by mass or less, and still more preferably 30% by mass or less. In addition, the crystal structure and the content ratio of the crystal phase in the sulfide solid electrolyte powder are determined by analyzing the XRD pattern. Further, the content ratio of the amorphous phase is determined from the remaining amount obtained by analyzing the above XRD pattern and subtracting the ratio of all crystal phases.

[0049] The sulfide solid electrolyte powder according to the present embodiment has a higher elastic modulus than those with a small strain value. Specifically, a pellet with a relative density of 90% is produced using the sulfide solid electrolyte powder, and the composite elastic modulus measured by a nanoindentation test using a spherical indenter with a tip radius of 100 μm can be, for example, 5 GPa or more.

[0050] 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, it is necessary to fabricate an all-solid-state battery with 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, if charge and discharge are repeated, the solid electrolyte material also gradually undergoes plastic deformation, resulting in a deterioration of the cycle characteristics. On the other hand, it is considered that the sulfide solid electrolyte powder according to the present embodiment has an expanded elastic deformation region due to the disorder of the crystal structure, that is, strain. Further, it is considered that the above elastic deformation region is further expanded by including an amorphous phase. As a result, even when an all-solid-state battery is fabricated with a low constraint pressure, the contact interface between the solid electrolyte and the active material can be maintained, good battery characteristics can be obtained, and furthermore, the deterioration of the cycle characteristics can be suppressed.

[0051] The above-mentioned composite elastic modulus in this embodiment is preferably 5 GPa or more, more preferably 5 to 20 GPa, still more preferably 7 to 18 GPa, and even more preferably 10 to 15 GPa. Here, from the viewpoint of obtaining better battery characteristics, the above-mentioned composite elastic modulus is preferably 20 GPa or less, more preferably 18 GPa or less, still more preferably 15 GPa or less, and the lower the better. On the other hand, in reality, the above-mentioned composite elastic modulus may be 5 GPa or more, 7 GPa or more, or 10 GPa or more.

[0052] Since the particle size D50 of the sulfide solid electrolyte powder according to this embodiment correlates with the above BET specific surface area, the particle size D50 is adjusted so as to obtain a suitable BET specific surface area. For example, when the BET specific surface area is 10 to 30 m 2 / g, the particle size D50 is about 0.4 μm or more and less than 1.0 μm. In this specification, the particle size D50 refers to the volume-based cumulative 50% diameter obtained by a laser diffraction type particle size distribution measuring device. That is, the particle size distribution is measured by the laser diffraction / scattering method, the cumulative curve is obtained with the total volume of the sulfide solid electrolyte as 100%, and it is the particle size at the point where the cumulative volume becomes 50% on the cumulative curve.

[0053] The BET specific surface area and the particle size D50 of the sulfide solid electrolyte powder can be adjusted by the pulverization method and pulverization conditions when the sulfide solid electrolyte is pulverized into the sulfide solid electrolyte powder. Examples of the pulverization method of the sulfide solid electrolyte include pulverization using a bead mill. As a result, it has been found that the strain value can be increased to a desired level without making the particle size D50 too small.

[0054] In the sulfide solid electrolyte powder according to this embodiment, the crystallite size in the argyrodite-type crystal structure is preferably 100 to 3000 Å, more preferably 200 to 2500 Å, and even more preferably 300 to 2000 Å. Here, from the viewpoint of ionic conductivity, the crystallite size is preferably 100 Å or more, more preferably 200 Å or more, and even more preferably 300 Å or more. Further, considering that the crystallite size inevitably becomes smaller as the particle size is made finer, from the viewpoint of realizing the desired particle size D50 and BET specific surface area as the sulfide solid electrolyte powder, the crystallite size is preferably 3000 Å or less, more preferably 2500 Å or less, and even more preferably 2000 Å or less. Note that the crystallite size in this specification is a value obtained together with the strain value when analyzing the XRD pattern of the sulfide solid electrolyte powder using the Williamson-Hall method.

[0055] The lithium ion conductivity of the sulfide solid electrolyte powder according to this embodiment is preferably 0.1 mS / cm or more, more preferably 0.5 mS / cm or more, even more preferably 1.0 mS / cm or more, and particularly preferably 1.5 mS / cm or more, and the higher the better, from the viewpoint of obtaining good battery characteristics when used in a lithium ion secondary battery. The upper limit of the lithium ion conductivity is not particularly limited, but is, for example, 15 mS / cm.

[0056] Note that the lithium ion conductivity in this specification uses the value obtained using an alternating current impedance measuring device for a measurement sample that is a compacted 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: measurement frequency: 100 Hz to 1 MHz, measurement voltage: 100 mV, and measurement temperature: 25°C.

[0057] The sulfide solid electrolyte powder according to the present embodiment can be processed by a conventionally known method if desired, and then pressure is applied together with a positive electrode active material or a negative electrode active material to form a positive electrode layer or a negative electrode layer as an electrode binder, or pressure is applied together with an additive such as a binder as necessary to form a solid electrolyte layer, and it is suitably used for an all-solid-state lithium-ion secondary battery.

[0058] <Manufacturing method of sulfide solid electrolyte powder> As shown in FIG. 1, the manufacturing method of the sulfide solid electrolyte powder according to the present embodiment sequentially includes the following steps. Step 1: Step of preparing a sulfide solid electrolyte Step 2: As step S1, step of coarsely pulverizing the sulfide solid electrolyte to obtain a coarsely pulverized product of the sulfide solid electrolyte Step 3: As step S2, step of obtaining a powder obtained by heat-treating the coarsely pulverized product while suppressing aggregation Step 4: As step S3, step of finely pulverizing the powder after the heat treatment to obtain a sulfide solid electrolyte powder

[0059] Hereinafter, each step will be described in order.

[0060] · Step 1 Step 1 is a step of preparing a sulfide solid electrolyte. The sulfide solid electrolyte may be synthesized or a commercially available product may be used. When synthesizing the sulfide solid electrolyte, a conventionally known method can be adopted, but the melting method is preferable from the viewpoint of obtaining a sulfide solid electrolyte with a high strain value.

[0061] When synthesizing the sulfide solid electrolyte, for example, it preferably includes a step of obtaining a raw material mixture, a step of reacting the raw material mixture, and a step of crystallization or amorphization.

[0062] The reaction in the step of reacting the raw material mixture may be a heating reaction or a mechanochemical reaction. Further, when the sulfide solid electrolyte is obtained by the heating reaction, a separate step of crystallization or amorphization may not be included. In the case of the melting method, each raw material is made into a mixture as necessary, then heated and melted, and cooled and solidified to obtain a sulfide solid electrolyte.

[0063] The raw materials vary depending on the composition of the desired crystal phase or amorphous phase. For example, raw materials containing Li, P, S, and Hal can be used. As each of the above raw materials, those conventionally known can be adopted. For each condition in the steps of mixing and reacting the raw materials, those conventionally known can be adopted. For example, in the case of the melting method, for the heating temperature during heating and melting, the time, atmosphere, pressure, dew point, etc. during heating and melting or cooling and solidification, those conventionally known can be adopted. Also, an intermediate obtained by reacting the raw materials before melting may be used, and melt synthesis may be performed therefrom.

[0064] · Step 2 Step 2 is a step of roughly pulverizing the sulfide solid electrolyte obtained in Step 1 to obtain a roughly pulverized product of the sulfide solid electrolyte (Step S1). By performing rough pulverization before performing the heat treatment in Step 3 described later, the particle size is made finer to some extent. Then, by passing through a step of performing heat treatment while suppressing aggregation in the next Step 3, a sulfide solid electrolyte powder with high ionic conductivity can be obtained. As a result, the load of the further pulverization step therefrom is reduced, a decrease in ionic conductivity can be suppressed, and the process load can also be reduced.

[0065] The method of rough pulverization is not particularly limited as long as the value represented by [(distortion value - 0.001) / specific surface area (m 2 / g)]×100 of the finally obtained sulfide solid electrolyte powder becomes the desired value, but a method other than wet pulverization is preferred. For example, rough pulverization by a cutter mill can be mentioned. Also, coarse powder may be obtained by a method of directly obtaining coarse powder from the melt of the sulfide solid electrolyte.

[0066] A cutter mill is a method of rotating a rotor equipped with a cutter or the like at high speed and pulverizing the raw material by a shearing force or a cutting force. By performing coarse pulverization with a cutter mill, the value represented by [(strain value - 0.001) / specific surface area (m 2 / g)]×100 of the sulfide solid electrolyte powder after heat treatment while suppressing aggregation in the subsequent step 3 and fine pulverization in step 4 can be increased, and a sulfide solid electrolyte powder that maintains good interfacial contact with the active material even at a low confinement pressure can be obtained.

[0067] Also, as a method of coarse pulverization other than a cutter mill, for example, a planetary ball mill, a jet mill, etc. may be adopted. In this case, dry pulverization without using a dispersion medium is preferable.

[0068] Coarse pulverization is preferably performed so that the particle size D50 of the coarsely pulverized product of the sulfide solid electrolyte is 5 to 300 μm. The above particle size D50 is more preferably 10 to 200 μm, and even more preferably 10 to 150 μm. Here, from the viewpoint of reducing the load of the fine pulverization step in step 4, the particle size D50 of the coarsely pulverized product is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. Also, from the viewpoint of powder handling, the above particle size D50 is preferably 5 μm or more, and more preferably 10 μm or more.

[0069] Also, after coarse pulverization of the sulfide solid electrolyte, classification (such as sieving) may be performed as necessary to obtain a coarsely pulverized product of the sulfide solid electrolyte.

[0070] · Step 3 Step 3 is a step of heat-treating the coarsely pulverized product of the sulfide solid electrolyte obtained in step 2 while suppressing aggregation to obtain a powder (step S2).

[0071] By performing heat treatment, the homogeneity is enhanced and the quality as a solid electrolyte is stabilized. As a result, even when fine pulverization is performed in the subsequent step 4, a high ionic conductivity can be maintained.

[0072] The heating temperature in the heat treatment is preferably, for example, 200 to 600 °C, more preferably 350 to 500 °C, still more preferably 380 to 460 °C, and particularly preferably 400 to 450 °C. Here, from the viewpoints of homogenization of the particles and stabilization of the quality, the heating temperature is preferably 200 °C or higher, more preferably 350 °C or higher, still more preferably 380 °C or higher, and particularly preferably 400 °C or higher. Further, from the viewpoint of preventing sintering of the particles, it is preferably 600 °C or lower, more preferably 500 °C or lower, still more preferably 460 °C or lower, and particularly preferably 450 °C or lower.

[0073] The heating time in the heat treatment is preferably, for example, 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, still more preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. Here, from the viewpoints of homogenization of the particles and stabilization of the quality, the heating time is preferably 10 minutes or longer, more preferably 30 minutes or longer, still more preferably 45 minutes or longer, and particularly preferably 1 hour or longer. Further, from the viewpoint of manufacturing cost, the heating time is preferably 10 hours or shorter, more preferably 9.5 hours or shorter, and still more preferably 9 hours or shorter.

[0074] The atmosphere in the heat treatment is preferably an inert atmosphere. Examples of the inert atmosphere include a nitrogen gas atmosphere, an argon gas atmosphere, a helium gas atmosphere, and the like.

[0075] Here, in order to perform the heat treatment while suppressing aggregation of the coarsely pulverized material, it is preferable to perform the heat treatment while flowing the inert gas. The flow rate of the inert gas is preferably, for example, 1 to 1000 L / min, more preferably 5 to 500 L / min, and still more preferably 10 to 100 L / min. Here, from the viewpoint of suitably suppressing aggregation of the coarsely pulverized material, the flow rate is preferably 1 L / min or higher, more preferably 5 L / min or higher, and still more preferably 10 L / min or higher. Further, from the viewpoint of suppressing scattering of the coarsely pulverized material, the flow rate is preferably 1000 L / min or lower, more preferably 500 L / min or lower, and still more preferably 100 L / min or lower.

[0076] In addition to the above inert gas, aggregation can also be suppressed by performing heat treatment in an atmosphere with an SO2 concentration of, for example, 1 to 1000 volume ppm. Furthermore, aggregation can also be suppressed by making the container during heat treatment have a low height and a wide-bottomed shape.

[0077] The dew point during heat treatment is preferably -20°C or lower, and the lower limit is not particularly limited but is usually about -80°C. The oxygen concentration is preferably 1000 volume ppm or lower.

[0078] Also, when cooling after the heat treatment, the aggregation of the coarsely pulverized material can be suppressed by flowing an inert gas. The flow rate of the inert gas at this time is preferably, for example, 1 to 1000 L / min, more preferably 5 to 500 L / min, and even more preferably 10 to 100 L / min. Here, from the viewpoint of suitably suppressing the aggregation of the coarsely pulverized material, the above flow rate is preferably 1 L / min or more, more preferably 5 L / min or more, and even more preferably 10 L / min or more. Also, from the viewpoint of suppressing the scattering of the coarsely pulverized material, the above flow rate is preferably 1000 L / min or less, more preferably 500 L / min or less, and even more preferably 100 L / min or less.

[0079] · Step 4 Step 4 is a step of finely pulverizing the heat-treated powder obtained in Step 3 to obtain a sulfide solid electrolyte powder (Step S3).

[0080] Fine pulverization is preferably performed using a bead mill. A bead mill is a method of making fine powder by grinding materials by rotating hard beads in a cylindrical container. By performing fine pulverization in such a method, the strain value can be increased without excessive pulverization, and the value represented by [(strain value - 0.001) / specific surface area (m 2 / g)]×100 can be increased.

[0081] That is, conventional sulfide solid electrolyte powders, for example, are pulverized to have a specific surface area of 15 m 2If we try to set it to / g, the strain value will be 0.0010 or more and less than 0.0020. However, the sulfide solid electrolyte powder according to this embodiment can have a strain value of 0.0020 or more. Also, for example, if we try to obtain a sulfide solid electrolyte powder with a strain value of about 0.0025 by pulverization, it was necessary to set its specific surface area to 30 m 2 / g or more. However, the sulfide solid electrolyte powder according to this embodiment can have a specific surface area of about 10 to 15 m 2 / g.

[0082] As the vessel of the bead mill used for fine pulverization, conventionally known ones can be used. For example, those made of alumina (Al2O3), zirconia (ZrO2), zirconia-reinforced alumina, etc. can be mentioned. Examples of the types of beads for fine pulverization include alumina beads, zirconia beads, glass beads, etc. From the viewpoint of wear resistance, zirconia beads, alumina beads, etc. are preferable.

[0083] When using zirconia beads, from the viewpoint of enhancing fracture toughness, it is preferably yttria-stabilized zirconia.

[0084] When using alumina beads, from the viewpoint of enhancing fracture toughness, high-purity alumina beads are preferable. 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, the wear resistance of the beads can be enhanced, and contamination derived from the beads can be suppressed, which is preferable.

[0085] The purity of the alumina beads is preferably 99.9% or more, more preferably 99.93% or more, still more preferably 99.95% or more, particularly preferably 99.99% or more, and the higher the better.

[0086] 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, still more preferably 2000 HV10 or more, and particularly preferably 2100 HV10 or more. Further, from the viewpoint of suppressing wear of the grinding chamber (vessel) and the rotor, the Vickers hardness is preferably 2300 HV10 or less.

[0087] The purity of the alumina beads can be measured by measuring the amount of impurities by ICP emission spectroscopy and subtracting the total amount of the impurities from 100%. The Vickers hardness of the alumina beads can be measured by pressing a pyramidal indenter made of diamond against the test piece, observing the resulting indentation with a microscope, and measuring the length of the diagonal.

[0088] In addition, as a fine grinding method, although fine powder with a small D50 can be obtained by adopting dry grinding or other grinding methods other than the bead mill, without excessively increasing the BET specific surface area with respect to the strain value, [(strain value - 0.001) / specific surface area (m 2 / g)] × 100, wet grinding using a bead mill is preferred from the viewpoint of easily realizing a range of 0.010 to 0.070.

[0089] In the wet grinding method, the coarse grind of the sulfide solid electrolyte may be dispersed or dissolved in a dispersion medium to form a slurry, and then grinding may be performed. Further, additives such as a dispersant may be further added to the slurry in addition to the sulfide solid electrolyte solvent.

[0090] The dispersion medium is not particularly limited, but since the sulfide solid electrolyte has a property of easily deteriorating by reacting with moisture, a non-aqueous solvent is preferred.

[0091] The type of non-aqueous organic solvent is not particularly limited. For example, hydrocarbon solvents, organic solvents containing a hydroxy group, organic solvents containing an ether group, organic solvents containing a carbonyl group, organic solvents containing an ester group, organic solvents containing an amino group, organic solvents containing a formyl group, organic solvents containing a carboxy group, organic solvents containing an amide group, organic solvents containing a benzene ring, organic solvents containing a mercapto group, organic solvents containing a thioether group, organic solvents containing a thioester group, organic solvents containing a disulfide group, halogenated alkyls, etc. may be mentioned.

[0092] Examples of hydrocarbon solvents include cyclohexane, heptane, octane, and toluene. From the viewpoint of a low saturated water concentration, cyclohexane, heptane, and octane are preferred. Also, from the viewpoint of adjusting the water concentration, it is also preferable to use a mixed solvent in which these hydrocarbon solvents are mixed with toluene, dibutyl ether, or the like.

[0093] From the viewpoint of preventing a decrease in lithium ion conductivity associated with the reaction between the sulfide solid electrolyte and water during the fine pulverization of the coarsely pulverized product of the sulfide solid electrolyte, it is preferable that the water concentration in the above dispersion medium is low. The water concentration of the above dispersion medium may be, for example, 170 mass ppm or less, 150 mass ppm or less, 120 mass ppm or less, 100 mass ppm or less, etc.

[0094] When a dispersant is used as an additive, for example, ether compounds, ester compounds, nitrile compounds, etc. may be mentioned.

[0095] Moreover, the content of the coarsely pulverized product of the sulfide solid electrolyte in the slurry is preferably 5 to 35% by mass, more preferably 10 to 33% by mass, and even more preferably 20 to 30% by mass. Here, from the viewpoints of pulverization efficiency and ease of handling of the slurry, the above content is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and also preferably 35% by mass or less, more preferably 33% by mass or less, and even more preferably 30% by mass or less.

[0096] The solid content concentration in the slurry is preferably 5 to 35% by mass, more preferably 10 to 33% by mass, and even more preferably 20 to 30% by mass. Here, from the viewpoints of pulverization efficiency and ease of handling of the slurry, the solid content concentration is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and preferably 35% by mass or less, more preferably 33% by mass or less, and even more preferably 30% by mass or less.

[0097] When performing fine pulverization by a bead mill, the diameter of the fine pulverization beads is preferably 0.1 to 1 mm, more preferably 0.2 to 0.8 mm, and even more preferably 0.3 to 0.5 mm. Here, from the viewpoint of obtaining a sulfide solid electrolyte powder having good lithium ion conductivity, the diameter is preferably 0.1 mm or more, more preferably 0.2 mm or more, and even more preferably 0.3 mm or more. Also, from the viewpoint of obtaining a finely pulverized product having a desired small particle size, the diameter is preferably 1 mm or less, more preferably 0.8 mm or less, and even more preferably 0.5 mm or less.

[0098] A drying step may be further performed on the sulfide solid electrolyte powder obtained in Step 4. By drying, even when a dispersion medium or an additive remains in the sulfide solid electrolyte powder, they can be removed. As the drying method, a conventionally known method can be adopted. For example, it can be carried out using a hot plate, a drying furnace, an electric furnace, etc.

[0099] The temperature in the drying step is not particularly limited, and for example, 50 to 300 °C can be mentioned. Also, when fine pulverization is performed using a dispersion medium, heating may be performed at a temperature equal to or higher than the boiling point of the dispersion medium to carry out drying. The time in the drying step is not particularly limited, and for example, 10 minutes to 24 hours can be mentioned. Also, the drying step may be carried out under reduced pressure, for example, the absolute pressure may be 50 kPa or less.

[0100] <Electrode binder> The sulfide solid electrolyte powder according to this embodiment may be used as an electrode binder. That is, the electrode binder according to this embodiment contains the sulfide solid electrolyte powder described in the above <sulfide solid electrolyte powder>, and the preferred embodiments of the sulfide solid electrolyte powder are the same as the preferred embodiments described in the above <sulfide solid electrolyte powder>.

[0101] The electrode binder according to this embodiment is preferably used in a lithium-ion secondary battery and is formed by applying pressure to the sulfide solid electrolyte powder together with the active material. That is, when the electrode binder according to this embodiment is a negative electrode binder, it contains at least a negative electrode active material and a sulfide solid electrolyte powder, and when it is a positive electrode binder, it contains at least a positive electrode active material and a sulfide solid electrolyte powder.

[0102] Conventionally known materials can be used as the active material contained in the electrode binder. For example, as the positive electrode active material, there is no particular limitation as long as the absorption and release of lithium ions, the desorption and insertion (intercalation) of lithium ions, or the doping and dedoping of the counter anion of the lithium ions can proceed reversibly. Specifically, lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, composite metal oxides, polyanion olivine type positive electrodes, etc. can be mentioned.

[0103] The negative electrode active material is also not particularly limited as long as the absorption and release of lithium ions, the desorption and insertion (intercalation) of lithium ions, or the doping and dedoping of the counter anion of the lithium ions can proceed reversibly. Specifically, carbon-based materials such as lithium metal, graphite, hard carbon, and soft carbon, metals that can form alloys with lithium such as aluminum, silicon, and tin, amorphous oxides such as silicon oxide and tin oxide, and lithium titanate, etc. can be mentioned.

[0104] <Solid electrolyte layer> The sulfide solid electrolyte powder according to this embodiment may be used for the solid electrolyte layer. That is, the solid electrolyte layer according to this embodiment contains the sulfide solid electrolyte powder described in the above <sulfide solid electrolyte powder>, and the preferred embodiments of the sulfide solid electrolyte powder are also the same as the preferred embodiments described in the above <sulfide solid electrolyte powder>.

[0105] The solid electrolyte layer according to this embodiment is preferably used for a lithium-ion secondary battery. In addition, the solid electrolyte layer according to this embodiment may contain a binder as necessary.

[0106] The content of the sulfide solid electrolyte powder in the solid electrolyte layer according to this embodiment is not particularly limited and may be appropriately determined according to the performance of the target battery. For example, with respect to the entire solid electrolyte layer, the content of the sulfide solid electrolyte powder is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0107] Examples of the binder that can be contained in the solid electrolyte layer include butadiene rubber (BR), acrylate butadiene rubber (ABR), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and the like. The content of the binder in the solid electrolyte layer may be the same as in the prior art.

[0108] The thickness of the solid electrolyte layer is not particularly limited and may be appropriately determined according to 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 with increased mechanical strength, strong resistance to stresses such as vibration and bending, and high reliability, the above thickness is preferably 10 μm or more, and more preferably 15 μm or more. Also, from the viewpoint of enhancing the ionic conductivity between the positive and negative electrodes and increasing the energy density of the battery, the above thickness is preferably 50 μm or less, and more preferably 20 μm or less.

[0109] The method for 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 form a slurry, which is then coated in a layer (sheet) form, dried, and optionally pressed to form the solid electrolyte layer. If necessary, a debinding treatment may be performed by applying heat. By adjusting the coating amount and the like of the slurry, the thickness of the solid electrolyte layer can be easily adjusted.

[0110] In addition, instead of the wet forming as described above, the solid electrolyte layer may be formed by dry pressing solid electrolyte powder or the like on the surface of the object (such as the positive electrode, negative electrode, etc.) on which the solid electrolyte layer is to be formed. Alternatively, a solid electrolyte layer may 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 industrially and stably form a strong solid electrolyte layer on the surface of the object to be formed with the solid electrolyte layer, it is preferable to form the solid electrolyte layer on the surface of the object by wet forming using a liquid medium.

[0111] <Lithium-ion secondary battery> The sulfide solid electrolyte powder according to the present embodiment may 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 preferred embodiments are the same.

[0112] The lithium-ion secondary battery according to the present embodiment includes a solid electrolyte layer, a positive electrode layer, and a negative electrode layer. The above sulfide solid electrolyte powder may be included in one or more of the above solid electrolyte layer, positive electrode layer, and negative electrode layer, or may be included in two or more, or even all. For the configurations of the solid electrolyte layer, positive electrode layer, and negative electrode layer other than the above sulfide solid electrolyte powder, conventionally known materials can be adopted.

Examples

[0113] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. Also, Examples 1 to 8 are examples, and Example 9 is a comparative example.

[0114] <Test Example> (Example 1) Under a dry nitrogen atmosphere, Li 5.4 PS 4.4 Cl 0.8 Br 0.8 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 so as to have the following composition, placed in a heat-resistant container, melted at 750°C for 1 hour under an atmosphere of a gas containing sulfur element, and then cooled to room temperature at 5°C / second to obtain a sulfide solid electrolyte. The gas containing sulfur element used 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 sulfur gas in the mixed gas was 10% by volume. The obtained sulfide solid electrolyte was roughly pulverized with a cutter mill and adjusted so that the average particle size (D50) was 10 to 20 μm, and then a roughly pulverized product of the sulfide solid electrolyte was obtained by passing through a 100 μm mesh. Next, 200 g of the roughly pulverized product obtained above was placed in a 1.0 L carbon container and put into an electric furnace with a divided heating area and cooling area. In the above heating area, while flowing N2 gas at 10 L / min, the above roughly pulverized product was heated at 430°C for 15 minutes. Subsequently, it was moved to the above cooling area at room temperature and cooled while flowing N2 gas at 20 L / min to obtain a non-aggregated powder. The powder obtained above was added to 385 g of dehydrated dibutyl ether to obtain a slurry (slurry solid content concentration: 30% by mass). 550 g of the slurry and 468 g of zirconia beads (manufactured by Nichato Co., Ltd., YTZ-0.3) with a diameter of 0.3 mm were put into a zirconia sample container (vessel), set in a Labo Starmini LMZ015 manufactured by Asizawa Fine Tech Co., Ltd., and wet pulverization was performed with a bead mill. Thereafter, it was heated and dried above the boiling point of the solvent under a nitrogen atmosphere to obtain a sulfide solid electrolyte powder.

[0115] (Examples 2 to 5) The sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that the peripheral speed and pulverization time among the wet pulverization conditions using a bead mill were appropriately changed so that the specific surface area of the resulting sulfide solid electrolyte powder became the value described in Table 1.

[0116] (Examples 6, 7) During wet pulverization using a bead mill, instead of zirconia beads, high-purity Al2O3 beads (diameter 0.3 mm, Daimyo Chemical, TB-03, purity 99.99% or more) were used, and the sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that the peripheral speed and pulverization time among the wet pulverization conditions using a bead mill were appropriately changed so that the specific surface area of the resulting sulfide solid electrolyte powder became the value described in Table 1.

[0117] (Example 8) Under a dry nitrogen atmosphere, Li 5.4 PS 4.4 Cl 0.8 Br 0.8 Instead of the composition of, Li 5.4 PS 4.4 Cl 1.6 The raw materials were mixed so as to have the composition of, and the sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that the peripheral speed and pulverization time among the wet pulverization conditions using a bead mill were appropriately changed so that the specific surface area of the resulting sulfide solid electrolyte powder became the value described in Table 1.

[0118] (Example 9) Under a dry nitrogen atmosphere, Li 5.4 PS 4.4 Cl 0.8 Br 0.8 To obtain a composition of, lithium sulfide powder (manufactured by Sigma, purity 99.98%), diphosphorus 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 and mixed in a mortar, and then further mixed using a planetary ball mill (manufactured by Ito Seisakusho, LP-M2) to obtain a sulfide precursor. Subsequently, the sulfide precursor powder was calcined by heat treatment at 400 °C for 5 hours in a dry nitrogen gas atmosphere, and then cooled to room temperature at a rate of 1 °C / second to obtain a coarsely pulverized product of the sulfide solid electrolyte. In the subsequent procedure, the same method as in Example 1 was adopted except that the peripheral speed and pulverization time among the wet pulverization conditions by a bead mill were appropriately changed so that the specific surface area of the obtained sulfide solid electrolyte powder became the value described in Table 1, and a sulfide solid electrolyte powder was obtained.

[0119] <Evaluation> [Lithium ion conductivity] The sulfide solid electrolyte powder was made into a compact at a pressure of 380 MPa and used as a measurement sample. Using an alternating current impedance measuring device (Potentiostat / Galvanostat VSP manufactured by Bio-Logic Sciences Instruments), the measurement was carried out under the following conditions. Measurement frequency: 100 Hz to 1 MHz Measurement voltage: 100 mV Measurement temperature: 25 °C From the obtained Nyquist plot, the lithium ion conductivity at 25 °C was determined. The results are shown in Table 1.

[0120] [Crystal structure, crystallinity, strain value, crystallite size] The sulfide solid electrolyte powder was measured by X-ray diffraction (XRD), and it was confirmed that all of the obtained sulfide solid electrolytes contained a crystal phase having an argyrodite-type crystal structure. For XRD measurement, Si powder was mixed as an internal standard with the sulfide solid electrolyte powder for each example, and X-ray diffraction measurement (Rigaku, SmartLab) was performed using an airtight holder. For the obtained XRD patterns, refinement of the crystal structure by the Rietveld method was carried out using RIETAN-FP software. The analysis judged the structure with the lowest Rwp value as the crystal structure for each example. The Rwp value is the reliability factor Rwp (R-weighted pattern), which is a general standard for the entire analysis range in the fitting of structure refinement by the Rietveld analysis. A lower Rwp value is better, and in this analysis, all the lowest Rwp values were less than 10%. From this, the crystallinity (mass%) of the argyrodite-type crystals in the sulfide solid electrolyte powder, that is, the ratio of the crystal phase to the total of the crystal phase and the amorphous phase was determined. The results are shown in Table 1.

[0121] In addition, for the results obtained from the above analysis, analysis using the Williamson-Hall method was performed to obtain the strain value and the crystallite size. The method of obtaining was as follows: each peak value (2θ) and the full width at half maximum (β) were extracted and converted to 2sinθ / λ1 and βcosθ / λ1, respectively. Here, λ1 = 1.5405, which is the wavelength of the CuKα1 line / Å, was used. Using the obtained 2sinθ / λ1 and βcosθ / λ1 as the X-axis and Y-axis, respectively, only the peaks derived from the argyrodite-type crystal structure were plotted. The slope value of the linear approximation straight line of the obtained plot was taken as the strain value, and the reciprocal of the intercept value with the Y-axis was taken as the crystallite size to obtain each value. The results are shown in Table 1.

[0122] The XRD measurement conditions are as follows. X-ray source: CuKα ray (λ = 1.5418 Å (CuKα1 ray wavelength 1.5405 Å, CuKα2 ray wavelength 1.5443 Å, intensity ratio Kα2 / Kα1 = 0.497)), tube voltage: 45 kV, tube current: 200 mA, scanning angle: 10 - 120°, scanning speed: 5° / min, step number: 0.01° / step.

[0123] [BET Specific Surface Area] The BET specific surface area (specific surface area, m 2 / g) was measured by the nitrogen adsorption BET multi-point method. The results are shown in Table 1.

[0124] [Strain Value Parameter] From the strain value and BET specific surface area obtained above, the value represented by [(strain value - 0.001) / specific surface area (m 2 / g)]×100 was determined. The results are shown in Table 1.

[0125] [Battery Evaluation] The obtained sulfide solid electrolyte powder: LiNi coated with lithium niobate with an average particle size of 7 μm 1 / 3 Co 1 / 3 Mn 1 / 3 O2 particles (cathode active material): conductive assistant: binder = 1.1 g: 5.0 g: 0.1 g: 0.6 g were mixed in a ratio, and stirred in a butyl butyrate solution to obtain a slurry. The above slurry was coated on an Al foil, which is a current collector, by the blade method using an applicator, and vacuum dried at 80 °C for 4 hours to obtain a cathode sheet. The obtained sheet was punched out with a die having a diameter of 10 mm to obtain a cathode mixture. On the other hand, a pellet (diameter 10 mm, thickness 1 mm) of the obtained sulfide solid electrolyte powder was prepared, the above cathode mixture was placed on the pellet, pressed at 500 MPa, and then a Li-In alloy was bonded to the counter electrode. Then, it was constrained at a constraint pressure of 10 MPa or 100 MPa to fabricate a lithium-ion secondary battery (half cell). Note that the above half cell has a structure in which the inside is not exposed to the atmosphere.

[0126] For the obtained half cell, charge and discharge were repeated 5 cycles in the range of 4.3~2.5 V vs. Li + / Li at 25 °C. The rate was 0.1C for both charge and discharge. In the 6th cycle, after charging to 4.3 V vs. Li + / Li at a rate of 0.1C, discharge was performed to 1.9 V vs. Li + / Li at a rate of 1C, and the discharge capacity at that time was determined.

[0127] The ratio of the discharge capacity of the half-cell with a confinement pressure of 10 MPa to the discharge capacity of the half-cell with a confinement pressure of 100 MPa was determined. The results are shown in Table 1, where the ratio of the discharge capacity is represented in a normalized form. Specifically, it is normalized such that the ratio of the discharge capacity, which is the result of Example 9, becomes 1.00. And the larger the normalized discharge capacity ratio is compared to Example 9, the better the interfacial contact with the active material can be maintained even when the confinement pressure is low.

[0128] [Composite Elastic Modulus] The composite elastic modulus of the sulfide solid electrolyte powder obtained in Example 1 was determined. Specifically, using 0.1 g of the sulfide solid electrolyte powder, a pellet with a diameter of 10 mm was molded. This pellet was produced by applying pressure so that the relative density became 90%, but the sample of Example 1 was molded by applying a pressure of 570 MPa. For the above pellet, a nanoindentation test was conducted using a spherical indenter with a tip radius of 100 μm. As a result, it was confirmed that the composite elastic modulus of Example 1 was 11 GPa. In addition, all handling of the samples was carried out in a non-atmospheric exposure environment and the measurement was performed.

[0129]

Table 1

[0130] As shown in Table 1, by adopting the melting method to obtain the sulfide solid electrolyte, and successively undergoing coarse pulverization by a cutter mill, heat treatment while suppressing aggregation, and fine pulverization by a bead mill, it is possible to increase the strain value without making the particle size of the obtained sulfide solid electrolyte powder excessively small, and it is possible to increase the value represented by [(strain value - 0.001) / specific surface area (m 2 / g)]×100. As a result, even when a lithium-ion battery was assembled at a low confinement pressure of 10 MPa without reducing the lithium-ion conductivity of the sulfide solid electrolyte powder, good battery characteristics could be realized due to good interfacial contact even when the charge-discharge cycle was repeated.

Claims

**Claim 1** A sulfide solid electrolyte powder having a crystalline phase, [((Warp value - 0.001) / Specific surface area (m ２ / g)) × 100] represents a value that is from 0.010 to 0.070, and wherein the strain value is 0.0030 or more and the specific surface area is 20 m2 / g or less, the sulfide solid electrolyte powder. **Claim 2** further having an amorphous phase, The sulfide solid electrolyte powder according to claim 1, wherein the content ratio of the amorphous phase is 5% by mass or more. **Claim 3** The sulfide solid electrolyte powder according to claim 1, wherein the complex elastic modulus is 5 to 20 GPa. **Claim 4** An electrode binder containing the sulfide solid electrolyte powder according to any one of claims 1 to 3.

Images