Sulfide solid electrolyte powder and electrode mixture

Abstract

The present invention relates to a sulfide solid electrolyte powder that has a crystal phase, wherein a value that is 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.

Description

Sulfide solid electrolyte powder and electrode mixture

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

[0002] Lithium-ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers. Conventionally, liquid electrolytes have been used in lithium-ion secondary batteries, but all-solid-state lithium-ion batteries (hereinafter also referred to as solid-state batteries), which use solid electrolytes as the electrolyte for lithium-ion secondary batteries, have been attracting attention due to their potential for improved safety and high-speed charging and discharging.

[0003] Solid electrolytes are broadly classified into sulfide solid electrolytes and oxide solid electrolytes. Among them, sulfide solid electrolytes exhibit high ionic conductivity because they contain sulfide ions with high polarizability. １０ GeP ２ S １２ LGPS type crystals such as Li ６ P.S. ５ Argyrodite-type crystals such as Cl, Li ７ P ３ S １１ LPS crystallized glass and the like are known.

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

[0005] International Publication No. 2021 / 085239

[0006] To achieve such high confinement pressure, a large confinement jig is required, and even if an all-solid-state battery is obtained under high confinement pressure, the volume changes with repeated charge-discharge cycles, making it difficult to maintain good interfacial contact, resulting in a decrease in battery capacity.

[0007] Therefore, an object of the present invention is to provide a sulfide solid electrolyte powder that can maintain good interfacial contact with an active material even under low confining pressure when used in an all-solid-state battery, and an electrode mixture containing the same.

[0008] Patent Document 1 discloses a solid electrolyte containing a crystalline phase having an argyrodite-type crystal structure, and discloses that the lattice distortion of the compound having this crystalline phase is less than 0.10%, and that the smaller the lattice distortion, the more improved the lithium ion conductivity. In response to this, the present inventors conducted extensive research and found that the above-mentioned problem can be solved by imparting a certain degree of distortion to the crystalline phase constituting a sulfide solid electrolyte powder, and by ensuring that the lattice distortion has a certain relationship with the specific surface area, thereby completing the present invention.

[0009] That is, the present invention relates to the following: [1] A sulfide solid electrolyte powder having a crystalline phase, wherein the ratio of [(strain value - 0.001) / specific surface area (m ２ / g) × 100 is 0.010 to 0.070, and the crystalline phase has an argyrodite-type crystal structure. [2] The sulfide solid electrolyte powder according to [1] above, further comprising an amorphous phase, and the content of the amorphous phase is 5 mass% or more. [3] The sulfide solid electrolyte powder according to [1] above or [2] above, wherein the argyrodite-type crystal structure contains two or more halogen elements as constituent elements. [4] The sulfide solid electrolyte powder according to [3] above, wherein the halogen element includes Br, and the content ratio of the Br to the halogen element is 0.1 to 0.9. [5] The argyrodite-type crystal structure is formed by adding Li ａ MZ ｂ Ha ｃ

[0013] In the composition formula, M is at least one element selected from Na, K, and elements present as divalent to pentavalent cations in the crystal structure, Z is at least one element selected from elements present 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, and the composition formula satisfies the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2. [6] The sulfide solid electrolyte powder according to any one of [1] to [5], having a composite elastic modulus of 5 to 20 GPa. [7] An electrode mixture comprising the sulfide solid electrolyte powder according to any one of [1] to [6].

[0010] According to the present invention, a sulfide solid electrolyte powder can be obtained that can maintain good interfacial contact with an active material even under low confining pressure when used in an all-solid-state battery. Therefore, an all-solid-state battery can be manufactured without using a large confining jig, and an all-solid-state battery can be obtained in which deterioration of battery characteristics during repeated charge-discharge cycles is suppressed.

[0011] FIG. 1 is a flow diagram showing a method for producing a sulfide solid electrolyte powder according to this embodiment.

[0012] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified as desired without departing from the gist of the present invention. Furthermore, the term "to" indicating a numerical range is used to mean that the numerical values ​​before and after it are included as the lower and upper limits. Furthermore, in this specification, "mass %" and "mass ppm" are synonymous with "weight %" and "weight ppm," respectively.

[0013] <Sulfide Solid Electrolyte Powder> The sulfide solid electrolyte powder according to this embodiment has a crystalline phase, and the crystalline phase has an argyrodite-type crystal structure. The sulfide solid electrolyte powder has a specific surface area (m ２ / g)]×100 satisfies 0.010 to 0.070.

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

[0015] Although the reason for this is unclear, the above-mentioned disordered crystal structure makes it easier for the coordinates of each atom in the crystal structure of the sulfide solid electrolyte powder to shift in accordance with the volumetric change of the active material that occurs during charging and discharging. As a result, it is believed that good interfacial contact between the active material and the sulfide solid electrolyte powder can be maintained. It can be said that the disordered crystal structure, which makes it easier for the coordinates of each atom to shift, absorbs the volumetric change of the active material, i.e., widens the elastic deformation range.

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

[0017] Specifically, the strain value is determined by analyzing the XRD pattern using the Williamson-Hall method.

[0018] The strain value of the sulfide solid electrolyte powder according to this embodiment is preferably large from the viewpoint of maintaining good interfacial contact. Furthermore, it has been found that when the sulfide solid electrolyte is pulverized to reduce the particle size of the sulfide solid electrolyte powder and increase the specific surface area, a positive correlation is observed between the specific surface area and the strain value. That is, the larger the specific surface area, the larger the strain value. On the other hand, the larger the specific surface area of ​​the sulfide solid electrolyte powder, the lower the ionic conductivity tends to be. Therefore, simply increasing the strain value is not enough to obtain good battery characteristics.

[0019] Therefore, the inventors conducted further studies and came to the conclusion that if the strain value of a sulfide solid electrolyte powder could be made larger than that of conventional sulfide solid electrolyte powders for the same specific surface area, the problems of the present invention could be solved while maintaining good ionic conductivity. As a result of further studies, the inventors found that the problems of the present invention could be solved and good battery characteristics could be achieved when the strain value and the specific surface area satisfy a certain relationship, and actually obtained a sulfide solid electrolyte that satisfies such characteristics.

[0020] Specifically, [(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 an approximate value of the strain value of the sulfide solid electrolyte before being pulverized into powder, and is a value arrived at by the inventors through their studies.

[0021] In order to increase the strain value of sulfide solid electrolyte powder, conventional pulverization methods are used, but if the pulverization conditions are stricter or the pulverization is carried out for a long time, the specific surface area becomes too large due to excessive pulverization. As a result, the ionic conductivity decreases, and good battery characteristics cannot be achieved. In this case, [(strain value - 0.001) / specific surface area (m ２ / g) × 100 is less than 0.010.

[0022] In contrast to this, the present invention has been conceived by sequentially applying the following steps to the sulfide solid electrolyte: coarse pulverization, heat treatment, and wet pulverization using a bead mill, and has found that this allows the strain value of the resulting sulfide solid electrolyte powder to be increased even if the increase in specific surface area due to pulverization is smaller than in the past, i.e., even if the pulverization is not as advanced as in the past.

[0023] The sulfide solid electrolyte powder according to this embodiment has a [(strain 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. From the viewpoint of more effectively obtaining the effects of the present invention, the value is preferably 0.015 or more, and more preferably 0.020 or more. On the other hand, there is no particular upper limit to the value, but from the viewpoint of maintaining the crystal structure and maintaining ionic conductivity, the upper limit is set to 0.070 or less. From the above viewpoint, the value is preferably 0.060 or less, and more preferably 0.050 or less.

[0024] The strain value of the sulfide solid electrolyte powder is [(strain value - 0.001) / specific surface area (m ２ / g)] × 100 is not particularly limited as long as it is within the range of 0.010 to 0.070. The strain value is, for example, preferably 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 under low confining pressure, the strain value is preferably 0.0020 or more, more preferably 0.0030 or more, and even more preferably 0.0040 or more. Furthermore, from the viewpoint of maintaining high ionic conductivity, the strain 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 calculated as follows: [(strain value - 0.001) / specific surface area (m ２ / g) × 100 is within the range of 0.010 to 0.070. ２ / g is preferred, and 7 to 30m ２ / g is more preferable, and 13 to 20m ２ From the viewpoint of forming more interfaces with the active material and further improving the battery characteristics, the specific surface area is preferably 4 m / g. ２ / g or more is preferable, and 7m ２ / g or more is more preferable, and 13m ２ From the viewpoint of suppressing the decrease in ionic conductivity due to the reduction in size, the specific surface area is preferably 35 m / g or more. ２ / g or less is preferable, and 30m ２ / g or less is more preferable, and 20m ２The specific surface area in this specification is referred to as the BET specific surface area, which is a value determined by the nitrogen adsorption BET multipoint method.

[0026] The sulfide solid electrolyte powder according to this embodiment has a crystalline phase having an argyrodite-type crystalline structure. Here, the argyrodite-type crystalline structure has the composition formula Ag ８ GeS ６ The sulfide solid electrolyte powder according to the present 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 preferably contains a halogen (Ha) element as a constituent element, more preferably two or more kinds of Ha elements, more preferably at least one element selected from the group consisting of Cl, Br, and I, and even more preferably two or more kinds of elements.

[0028] The argyrodite-type crystal structure in this embodiment more preferably contains at least one of Cl and Br as the Ha element, and even more preferably contains Cl and Br.

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

[0030] The argyrodite-type crystal structure preferably has the above structure, but the composition formula is Li ａ MZ ｂ Ha ｃand it is preferable that the relationships 5≦a≦7, 4≦b≦6 and 1<c≦2 are satisfied.

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

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

[0033] From the viewpoint of the oxidation-reduction potential of the element, it is preferable that the M mainly contains P. Specifically, "M mainly contains P" means that the ratio of the P content (at %) to the M content (atoms %, hereinafter referred to as "at %) in the argyrodite-type crystal structure is 0.6 or more, and this ratio is preferably 0.6 to 1. This ratio is more preferably 0.7 or more, and even more preferably 0.8 or more. Furthermore, there is no particular limitation on the upper limit of this ratio, and it may be 1, 0.98 or less, 0.97 or less, or 0.95 or less.

[0034] The M may contain, in addition to P, at least one element selected from Na, K, Mg, and Ca. As a raw material for forming an argyrodite-type crystal structure, lithium sulfide (Li ２ In some cases, a mixture containing lithium sulfide (LiOH) may be preferably used. Here, it is widely known that lithium sulfide is produced from lithium hydroxide (LiOH), which may contain at least one element selected from the group consisting of Na, K, Mg, and Ca (hereinafter also referred to as "R") as an impurity. That is, M may contain R derived from such impurities in the raw materials.

[0035] Reducing the content of R derived from impurities may require high-purity raw materials, which may increase manufacturing costs. The ratio of the R content (at %) to the M content (at %) is preferably 0.001 to 0.4, more preferably 0.01 to 0.3. From the viewpoint of reducing manufacturing costs, the ratio is preferably 0.001 or more, more preferably 0.01 or more, and even more preferably 0.02 or more. Furthermore, from the viewpoint of suppressing a decrease in lithium ion conductivity, the ratio is preferably 0.4 or less, more preferably 0.3 or less.

[0036] The above range does not in any way preclude intentionally incorporating R into the argyrodite-type crystal structure or incorporating R in a larger amount than the above range. For example, in the above composition formula showing the argyrodite-type crystal structure, when Z contains O, the above R may contain at least one element selected from Al, Ca, Mg, Na and K, and the element may be M. ｎ＋ It is preferable that M is present at the Li site as ｎ＋ represents a monovalent to trivalent cation. In this case, it is more preferable that R contains Al. In this case, the content (at %) of R relative to the content (at %) of M may be higher than the above range.

[0037] In the above composition formula, Z represents at least one element selected from elements present as divalent anions in the crystal structure, such as S, O, Se, and Te. Among these, from the viewpoint of lithium ion conductivity, it is preferable that Z primarily contains S. Specifically, "Z primarily contains S" means that the ratio of the S content (at %) to the Z content (at %) in the crystal structure is 0.6 or more, and this ratio is preferably 0.6 to 1. This ratio is more preferably 0.7 or more, and even more preferably 0.8 or more. Furthermore, the upper limit of this ratio is not particularly limited, and may be 1, 0.98 or less, 0.95 or less, or 0.9 or less.

[0038] In addition, when S is contained as the above Z, a part of S may be Ha or BH in addition to the above O, Se, and Te. ４ , CN, etc.

[0039] In the above composition formula, the halogen element represented by Ha is preferably at least one element selected from the group consisting of F, Cl, Br, and I. From the viewpoint of easiness in forming an argyrodite-type crystal structure, the above Ha preferably contains at least one of Cl and Br, more preferably contains Br, and even more preferably Br alone or a mixture of Cl and Br. Furthermore, from the viewpoint of further improving lithium ion conductivity, the Ha is preferably a mixture of Cl and Br.

[0040] When Ha contains Cl and Br, where x (at%) is the Cl content in the argyrodite-type crystal structure and y (at%) is the Br content, the ratio (x / y) is preferably 0.1 to 10, more preferably 0.3 to 3, and even more preferably 0.5 to 1.6. Here, the ratio is preferably 0.1 or greater, more preferably 0.3 or greater, and even more preferably 0.5 or greater, and is preferably 10 or less, more preferably 3 or less, and even more preferably 1.6 or less. When the ratio (x / y) satisfies the above range, the interaction between lithium ions and halide ions is weakened, and lithium ion conductivity is likely to be improved. This is thought to be due to the mixed anion effect, which weakens the interaction between cations and anions by mixing bromide ions, which have a larger ionic radius than chloride ions. Furthermore, the cycle characteristics of lithium ion secondary batteries are likely 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 ｃ２When expressed as above, c1 is preferably 0.1 to 1.5, more preferably 0.3 to 1.4, and even more preferably 0.5 to 1.3. Here, c1 is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, and is preferably 1.5 or less, more preferably 1.4 or less, and even more preferably 1.3 or less. Furthermore, c2 is preferably 0.1 to 1.9, more preferably 0.3 to 1.6, and even more preferably 0.5 to 1.4. Here, c2 is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, and is preferably 1.9 or less, more preferably 1.6 or less, and even more preferably 1.4 or less. When c1 and c2 each satisfy the above ranges, the proportion of halide ions in the crystal is optimized, and a stable argyrodite-type crystal is obtained while reducing the interaction between anions and lithium ions in the crystal structure. This tends to improve the lithium ion conductivity of the sulfide solid electrolyte powder. Furthermore, when c1 and c2 satisfy the above ranges, the cycle characteristics of the lithium ion secondary battery are likely to be improved. ａ MZ ｂ Cl ｃ１ Br ｃ２ In the composition formula represented by the formula (I), it is preferable that a, b, and (c1+c2) satisfy the same relationship as a, b, and c described below.

[0042] The above Li ａ MZ ｂ Ha ｃ The ratios of the elements in the composition formula represented by the formula preferably satisfy the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2, more preferably satisfy the relationships 5<a<7, 4<b<6, and 1<c<2, even more preferably satisfy the relationships 5.1<a<6.3, 4<b<5.3, and 1.4≦c≦1.9, and even more preferably satisfy the relationships 5.2<a<6.2, 4.1<b<5.2, and 1.5≦c≦1.8.

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

[0044] The argyrodite-type crystal structure is, for example, a cubic crystal (e.g., F-43m), but crystals with reduced symmetry such as hexagonal, tetragonal, orthorhombic, monoclinic, and even less symmetrical crystals such as triclinic may also exist.

[0045] The sulfide solid electrolyte powder according to this embodiment contains a crystalline phase, and the content (crystallinity) of the crystalline phase is preferably 50 to 100% by mass, more preferably 60 to 99% by mass, even more preferably 65 to 95% by mass, and even more preferably 70 to 90% by mass. From the viewpoint of ensuring lithium ion conductivity, the content is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more. On the other hand, the content may be 100% by mass, i.e., it may consist of only the crystalline phase. However, from the viewpoint of obtaining the effect of expanding the elastic deformation region due to the presence of an amorphous phase, the content is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less.

[0046] The crystalline phase in this embodiment may have a crystalline phase having a crystal structure other than the argyrodite type, but the proportion of the crystalline phase having the argyrodite type crystal structure relative to the entire crystalline phase is preferably 50 mass % or more, more preferably 80 mass % or more, and the higher the better. The crystalline phase that may have a crystalline structure other than the argyrodite type crystal structure is, for example, Li ７ P ３ S １１Crystal phases having a crystal structure containing Li, P, and S elements, called LPS systems, such as Li １０ GeP ２ S １２ Examples of such a crystal phase include a crystalline phase having a crystal structure containing Li, Ge, P, and S elements, which is called an LGPS system, such as a crystalline phase having a thiolicon-type crystal structure, and a crystalline phase containing an oxide.

[0047] The sulfide solid electrolyte powder according to this embodiment may contain an amorphous phase. The presence of the amorphous phase is preferable because it expands the elastic deformation region. The composition of the amorphous phase is generally the same as that of the crystalline phase. Details of the elastic deformation region will be described below.

[0048] The content of the amorphous phase in the sulfide solid electrolyte powder is preferably 5% by mass or more, more preferably 5 to 50% by mass, even more preferably 10 to 40% by mass, and even more preferably 15 to 30% by mass. From the viewpoint of further enhancing the effects of the presence of the amorphous phase, the content is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, from the viewpoint of maintaining ionic conductivity, the content is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. The crystal structure and content of the crystalline phase in the sulfide solid electrolyte powder can be determined by analyzing the XRD pattern. The content of the amorphous phase can be determined by analyzing the XRD pattern and subtracting the content from the proportion of all crystalline phases, leaving a remainder.

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

[0050] Generally, crystalline solid electrolytes have a small elastic deformation region and cannot absorb the volume change of the active material that occurs during charge and discharge. Therefore, it is necessary to fabricate all-solid-state batteries at high confinement pressures to maintain the contact interface between the solid electrolyte and the active material. However, even when high confinement pressures are used, repeated charge and discharge cycles gradually cause the solid electrolyte material to undergo plastic deformation, resulting in a deterioration in cycle characteristics. In contrast, the sulfide solid electrolyte powder according to this embodiment is thought to have an expanded elastic deformation region due to the disturbance of the crystalline structure, i.e., distortion. Furthermore, the inclusion of an amorphous phase is thought to further expand the elastic deformation region. As a result, even when an all-solid-state battery is fabricated at low confinement pressures, the contact interface between the solid electrolyte and the active material is maintained, resulting in good battery characteristics and further suppressing a deterioration in cycle characteristics.

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

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

[0053] The BET specific surface area and particle size D50 of the sulfide solid electrolyte powder can be adjusted by the pulverization method and pulverization conditions when pulverizing the sulfide solid electrolyte to obtain the sulfide solid electrolyte powder. Pulverization using a bead mill is an example of a pulverization method for the sulfide solid electrolyte. It has been found that this method allows the strain value to be increased to a desired level without reducing the particle size D50 too much.

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

[0055] From the viewpoint of obtaining good battery characteristics when used in a lithium ion secondary battery, 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. The upper limit of the lithium ion conductivity is not particularly limited, but is, for example, 15 mS / cm.

[0056] The lithium ion conductivity in this specification is a value determined by applying a pressure of 380 MPa to a sulfide solid electrolyte powder to form a compact, and measuring the compact using an AC impedance measuring device. The AC impedance measurement conditions are a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C.

[0057] The sulfide solid electrolyte powder according to the present embodiment is suitably used in an all-solid-state lithium ion secondary battery by treating it by a conventionally known method as desired, and then applying pressure together with a positive electrode active material or a negative electrode active material to form a positive electrode layer or a negative electrode layer, which is an electrode mixture, or by applying pressure together with an additive such as a binder as needed to form a solid electrolyte layer.

[0058] <Method for producing sulfide solid electrolyte powder> The method for producing a sulfide solid electrolyte powder according to this embodiment includes the following steps in order, as shown in Fig. 1 : Step 1: Step of preparing a sulfide solid electrolyte; Step 2: Step S1: Step of coarsely pulverizing the sulfide solid electrolyte to obtain a coarsely pulverized sulfide solid electrolyte; Step 3: Step S2: Step of heat-treating the coarsely pulverized product while suppressing aggregation to obtain a powder; Step 4: Step S3: Step of finely pulverizing the heat-treated powder to obtain a sulfide solid electrolyte powder.

[0059] Each step will be explained below 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 one may be used. When synthesizing the sulfide solid electrolyte, a conventionally known method may be used, but a melting method is preferred from the viewpoint of obtaining a sulfide solid electrolyte with a high distortion value.

[0061] When synthesizing a sulfide solid electrolyte, it is preferable to include, for example, a step of obtaining a raw material mixture, a step of reacting the raw material mixture, and a step of crystallizing or amorphizing the raw material mixture.

[0062] The reaction in the step of reacting the raw material mixture may be a thermal reaction or a mechanochemical reaction. Furthermore, when the sulfide solid electrolyte is obtained by the thermal reaction, a separate crystallization or amorphization step does not need to be included. In the case of the melting method, the raw materials are mixed as needed, then heated and melted, and then cooled and solidified to obtain the sulfide solid electrolyte.

[0063] The raw materials vary depending on the composition of the desired crystalline or amorphous phase, but raw materials containing, for example, Li, P, S, and Ha can be used. Conventionally known raw materials can be used for each of the raw materials. Conventionally known conditions can be used for the mixing and reaction of the raw materials. For example, in the case of a melting method, conventionally known conditions can be used for the heating temperature during heat melting, the time during heat melting or cooling and solidifying, the atmosphere, pressure, dew point, etc. Also, an intermediate obtained by reacting the raw materials before melting can be used, and melt synthesis can be performed from there.

[0064] Step 2 Step 2 is a step of coarsely pulverizing the sulfide solid electrolyte obtained in Step 1 to obtain a coarsely pulverized sulfide solid electrolyte (Step S1). By performing coarse pulverization before carrying out the heat treatment in Step 3 described below, the particle size is made fine to a certain extent. Then, by carrying out the heat treatment in the next Step 3 while suppressing aggregation, a sulfide solid electrolyte powder with high ionic conductivity is obtained. As a result, the load of the subsequent pulverization step is reduced, the decrease in ionic conductivity can be suppressed, and the process load can also be reduced.

[0065] The coarse pulverization method is based on the ratio of (strain value - 0.001) / specific surface area (m ２ Although there are no particular limitations on the method as long as the value expressed by (g / g) × 100 is a desired value, a method other than wet grinding is preferred. For example, coarse grinding using a cutter mill (cut mill) can be used. Alternatively, the coarse powder may be obtained by a method of obtaining the coarse powder directly from a melt of the sulfide solid electrolyte.

[0066] The cutter mill is a method of crushing raw materials by shearing or cutting force using a rotor equipped with cutters that rotates at high speed. By performing coarse crushing using a cutter mill, the ratio of [(strain value - 0.001) / specific surface area (m ２ Therefore, the value expressed by the formula (1) can be increased, and a sulfide solid electrolyte powder that maintains good interfacial contact with the active material even under low confining pressure can be obtained.

[0067] Furthermore, as a coarse pulverization method other than the cutter mill, for example, a planetary ball mill, a jet mill, etc. may be adopted, but in this case, dry pulverization without using a dispersion medium is preferred.

[0068] The coarse pulverization is preferably carried out so that the particle size D50 of the coarsely pulverized sulfide solid electrolyte is 5 to 300 μm, more preferably 10 to 200 μm, and even more preferably 10 to 150 μm. 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. From the viewpoint of powder handling, the particle size D50 is preferably 5 μm or more, and more preferably 10 μm or more.

[0069] Furthermore, after the sulfide solid electrolyte is coarsely pulverized, classification (sieving, etc.) may be carried out as necessary to obtain a coarsely pulverized sulfide solid electrolyte.

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

[0071] By carrying out the heat treatment, the homogeneity is increased and the quality as a solid electrolyte is stabilized, so that high ionic conductivity can be maintained even after fine pulverization in the subsequent step 4.

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

[0073] The heating time in the heat treatment is, for example, preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, even more preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. Here, from the viewpoint of particle homogenization and stabilization of quality, the heat treatment time is preferably 10 minutes or more, more preferably 30 minutes or more, even more preferably 45 minutes or more, and particularly preferably 1 hour or more. Furthermore, from the viewpoint of production costs, the heat treatment time is preferably 10 hours or less, more preferably 9.5 hours or less, and even more preferably 9 hours or less.

[0074] The heat treatment is preferably carried out in an inert atmosphere, such as a nitrogen gas atmosphere, an argon gas atmosphere, or a helium gas atmosphere.

[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, for example, preferably 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 aggregation of the coarsely pulverized material, the 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. Furthermore, from the viewpoint of suppressing scattering of the coarsely pulverized material, the 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.

[0076] In addition to the above inert gases, SO ２ Agglomeration can also be suppressed by performing the heat treatment in an atmosphere with a concentration of, for example, 1 to 1000 ppm by volume.Furthermore, agglomeration can also be suppressed by using a container with a low height and a wide bottom during the heat treatment.

[0077] The dew point during the heat treatment is preferably −20° C. or lower, and although there is no particular lower limit, it is usually about −80° C. The oxygen concentration is preferably 1000 ppm by volume or lower.

[0078] Furthermore, when cooling after heat treatment, agglomeration of the coarsely pulverized material can be suppressed by passing an inert gas through the inert gas. The flow rate of the inert gas in this case is, for example, preferably 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 agglomeration of the coarsely pulverized material, the 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. Furthermore, from the viewpoint of suppressing scattering of the coarsely pulverized material, the 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] The fine pulverization is preferably carried out using a bead mill. A bead mill is a method of grinding materials into fine powder by rotating hard beads in a cylindrical container. By carrying out fine pulverization using this method, the strain value can be increased without excessive pulverization, and the ratio [(strain value - 0.001) / specific surface area (m ２ / g) × 100 can be increased.

[0081] That is, conventional sulfide solid electrolyte powder is crushed to have a specific surface area of ​​15 m ２ / g, the distortion value is 0.0010 or more and less than 0.0020, but the sulfide solid electrolyte powder according to this embodiment can have a distortion value of 0.0020 or more. Also, for example, to obtain a sulfide solid electrolyte powder having a distortion value of about 0.0025 by pulverization, the specific surface area must be 30 m ２ / g or more, the sulfide solid electrolyte powder according to this embodiment has a specific surface area of ​​10 to 15 m ２ / g.

[0082] The vessel of the bead mill used for fine pulverization can be a conventionally known one, for example, an alumina (Al ２ O ３ ) and zirconia (ZrO ２Examples of the types of beads for fine grinding include alumina beads, zirconia beads, and glass beads, with zirconia beads and alumina beads being preferred from the viewpoint of wear resistance.

[0083] When zirconia beads are used, they are preferably yttria-stabilized zirconia from the viewpoint of increasing fracture toughness.

[0084] When alumina beads are used, high-purity alumina beads are preferred from the viewpoint of increasing fracture toughness. 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. Use of such high-purity alumina beads is preferred because it can increase the abrasion resistance of the beads and suppress contamination caused by the beads.

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

[0086] The Vickers hardness of the alumina beads is preferably 1800 HV10 to 2300 HV10. From the viewpoint of wear resistance, the Vickers hardness is preferably 1800 HV10 or more, more preferably 1900 HV10 or more, even more preferably 2000 HV10 or more, and particularly preferably 2100 HV10 or more. Furthermore, from the viewpoint of suppressing wear of the grinding chamber (vessel) and rotor, the Vickers hardness is preferably 2300 HV10 or less.

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

[0088] Furthermore, fine powder with a small particle size D50 can be obtained by using dry milling or other milling methods other than a bead mill, but the BET specific surface area relative to the strain value should not be too large, and the ratio of [(strain value - 0.001) / specific surface area (m ２ Wet grinding using a bead mill is preferred from the viewpoint that it is easier to achieve a value expressed by [(amount of carbon black) / g)]×100 in the range of 0.010 to 0.070.

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

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

[0091] The type of non-aqueous organic solvent is not particularly limited, and examples thereof include 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, and alkyl halides.

[0092] Examples of hydrocarbon solvents include cyclohexane, heptane, octane, and toluene, and cyclohexane, heptane, and octane are preferred from the viewpoint of low saturated water concentration. Also, from the viewpoint of adjusting the water concentration, it is preferred to mix these hydrocarbon solvents with toluene, dibutyl ether, or the like to form mixed solvents.

[0093] In order to prevent a decrease in lithium ion conductivity due to a reaction between the sulfide solid electrolyte and water during fine pulverization of the coarsely pulverized sulfide solid electrolyte, the water concentration in the dispersion medium is preferably low. The water concentration of the dispersion medium may be, for example, 170 ppm by mass or less, 150 ppm by mass or less, 120 ppm by mass or less, or 100 ppm by mass or less.

[0094] When a dispersant is used as the additive, examples thereof include an ether compound, an ester compound, and a nitrile compound.

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

[0097] When pulverization is performed using a bead mill, the diameter of the pulverizing 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. 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. Furthermore, from the viewpoint of obtaining a finely pulverized product with 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] The sulfide solid electrolyte powder obtained in step 4 may be further subjected to a drying step. By drying, even if a dispersion medium or additive remains in the sulfide solid electrolyte powder, these can be removed. As a drying method, a conventionally known method can be used, and for example, drying can be performed using a hot plate, a drying furnace, an electric furnace, or the like.

[0099] The temperature in the drying step is not particularly limited, but may be, for example, 50 to 300°C. When fine pulverization is performed using a dispersion medium, drying may be performed by heating at a temperature equal to or higher than the boiling point of the dispersion medium. The time for the drying step is also not particularly limited, but may be, for example, 10 minutes to 24 hours. The drying step may also be performed under reduced pressure, for example, at an absolute pressure of 50 kPa or less.

[0100] <Electrode Mix> The sulfide solid electrolyte powder according to this embodiment may be used for an electrode mix. That is, the electrode mix according to this embodiment contains the sulfide solid electrolyte powder described in the above <Sulfide Solid Electrolyte Powder>, and preferred aspects of the sulfide solid electrolyte powder are also the same as the preferred aspects described in the above <Sulfide Solid Electrolyte Powder>.

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

[0102] The active material contained in the electrode mixture may be a conventionally known material. For example, the positive electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions, intercalate and deintercalate lithium ions, or dope and dedope counter anions of the lithium ions. Specific examples include lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, composite metal oxides, and polyanion olivine-type positive electrodes.

[0103] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions, desorb and insert (intercalate) lithium ions, or dope and dedope counter anions of the lithium ions. Specific examples include lithium metal, carbonaceous materials such as graphite, hard carbon, and soft carbon, metals capable of forming alloys with lithium such as aluminum, silicon, and tin, amorphous oxides such as silicon oxide and tin oxide, and lithium titanate.

[0104] <Solid Electrolyte Layer> The sulfide solid electrolyte powder according to this embodiment may be used in a 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 preferred aspects of the sulfide solid electrolyte powder are also the same as the preferred aspects described in the above <Sulfide Solid Electrolyte Powder>.

[0105] The solid electrolyte layer according to this embodiment is preferably used in a lithium ion secondary battery. The solid electrolyte layer according to this embodiment may contain a binder as needed.

[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 depending on the target battery performance. For example, the content of the sulfide solid electrolyte powder is preferably 80 mass % or more, and more preferably 90 mass % or more, of the entire solid electrolyte layer.

[0107] Examples of binders 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), etc. The content of the binder in the solid electrolyte layer may be the same as that of conventional binders.

[0108] The thickness of the solid electrolyte layer is not particularly limited and may be appropriately determined depending on the desired battery performance. For example, the thickness is preferably 10 to 50 μm, more preferably 15 to 20 μm. Here, from the viewpoint of obtaining a solid electrolyte layer that has increased mechanical strength, is resistant to stresses such as vibration and bending, and has high reliability, the thickness is preferably 10 μm or more, more preferably 15 μm or more. Furthermore, from the viewpoint of increasing ionic conductivity between the positive and negative electrodes and increasing the energy density of the battery, the thickness is preferably 50 μm or less, 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 solid electrolyte layer described above are dispersed or dissolved in a liquid medium to form a slurry, which is then applied in a layer (sheet), dried, and optionally pressed to form the solid electrolyte layer. If necessary, heat may be applied to remove the binder. The thickness of the solid electrolyte layer can be easily adjusted by adjusting the amount of the slurry applied, etc.

[0110] Instead of the wet molding described above, the solid electrolyte layer may be formed by dry press molding of a solid electrolyte powder or the like on the surface of the object (positive electrode, negative electrode, etc.) on which the solid electrolyte layer is to be formed. Alternatively, the solid electrolyte layer may be formed on another substrate and then 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 on which the solid electrolyte layer is to be formed, it is preferable to form the solid electrolyte layer on the surface of the object by wet molding using a liquid medium.

[0111] <Lithium-ion secondary battery> The sulfide solid electrolyte powder according to this embodiment may be used in a lithium-ion secondary battery. That is, the lithium-ion secondary battery according to this embodiment includes the sulfide solid electrolyte described in the above <Sulfide solid electrolyte powder>, and preferred aspects are also the same.

[0112] The lithium ion secondary battery according to this embodiment includes a solid electrolyte layer, a positive electrode layer, and a negative electrode layer. The sulfide solid electrolyte powder may be contained in at least one of the solid electrolyte layer, the positive electrode layer, and the negative electrode layer, or may be contained in two or more of them, or may be contained in all of them. The solid electrolyte layer, the positive electrode layer, and the negative electrode layer, other than the sulfide solid electrolyte powder, may be configured as conventionally known ones.

[0113] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. Examples 1 to 8 are working examples, and Example 9 is a comparative example.

[0114] <Test Examples> (Example 1) Li was dissolved in a dry nitrogen atmosphere. ５．４ P.S. ４．４ Cl ０．８ Br ０．８ 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 out to give a composition of the above, placed in a heat-resistant container, and dissolved at 750°C for 1 hour in an atmosphere of a gas containing sulfur element, followed by cooling to room temperature at a rate of 5°C / sec to obtain a sulfide solid electrolyte. The gas containing sulfur element was a mixture of sulfur gas (Sx (x = 2 to 8)) and nitrogen gas (N ２ A mixed gas of sulfur gas and sulfur dioxide gas (sulfur dioxide gas) was used, and the content of sulfur gas in the mixed gas was 10% by volume. The obtained sulfide solid electrolyte was coarsely pulverized using a cutter mill, adjusted to an average particle size (D50) of 10 to 20 μm, and then passed through a 100 μm mesh to obtain a coarsely pulverized sulfide solid electrolyte. Next, 200 g of the coarsely pulverized product obtained above was placed in a carbon container with a capacity of 1.0 L and placed in an electric furnace with separate heating and cooling areas. In the heating area, N ２ The coarsely pulverized material was heated at 430°C for 15 minutes while gas was being passed through at a rate of 10 L / min. Then, the material was transferred to the cooling area at room temperature and cooled under N ２The mixture was cooled while flowing gas at 20 L / min to obtain a non-agglomerated powder. The powder obtained above was added to 385 g of dehydrated dibutyl ether to obtain a slurry (slurry solids concentration: 30% by mass). 550 g of the slurry and 468 g of 0.3 mm diameter zirconia beads (YTZ-0.3, manufactured by Nikkato Corporation) were placed in a zirconia sample container (vessel), and the container was set in a Labostar Mini LMZ015 manufactured by Ashizawa Finetech Co., Ltd., and wet-pulverized using a bead mill. The mixture was then heated and dried at a temperature above the boiling point of the solvent under a nitrogen atmosphere to obtain a sulfide solid electrolyte powder.

[0115] (Examples 2 to 5) Sulfide solid electrolyte powders were obtained in the same manner as in Example 1, except that the peripheral speed and grinding time among the wet grinding conditions using a bead mill were appropriately changed so that the specific surface area of ​​the resulting sulfide solid electrolyte powder would have the value shown in Table 1.

[0116] (Examples 6 and 7) During wet grinding using a bead mill, high-purity Al was used instead of zirconia beads. ２ O ３ A sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that beads (diameter 0.3 mm, Taimei Chemical, TB-03, purity 99.99% or more) were used and the peripheral speed and grinding time among the wet grinding conditions using a bead mill were appropriately changed so that the specific surface area of ​​the resulting sulfide solid electrolyte powder would have the value shown in Table 1.

[0117] (Example 8) Li ５．４ P.S. ４．４ Cl ０．８ Br ０．８ Instead of the composition of Li ５．４ P.S. ４．４ Cl １．６ and the peripheral speed and grinding time among the wet grinding conditions using a bead mill were appropriately changed so that the specific surface area of ​​the resulting sulfide solid electrolyte powder would have the value shown in Table 1.

[0118] (Example 9) Li ５．４ P.S. ４．４ Cl ０．８ Br ０．８Lithium 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 Co., Ltd., LP-M2) to obtain a sulfide precursor. Next, the sulfide precursor powder was calcined by heat treatment at 400 ° C. for 5 hours under a dry nitrogen gas atmosphere, and then cooled to room temperature at 1 ° C. / second to obtain a coarsely pulverized sulfide solid electrolyte. The subsequent procedure was carried out in the same manner as in Example 1, except that the peripheral speed and pulverization time of the wet pulverization conditions using a bead mill were appropriately changed so that the specific surface area of ​​the resulting sulfide solid electrolyte powder would be the value listed in Table 1. A sulfide solid electrolyte powder was obtained.

[0119] <Evaluation> [Lithium ion conductivity] The sulfide solid electrolyte powder was pressed under a pressure of 380 MPa and used as a measurement sample. Measurement was performed using an AC impedance measuring device (VSP potentiostat / galvanostat, manufactured by Bio-Logic Sciences Instruments) under the following conditions: Measurement frequency: 100 Hz to 1 MHz, Measurement voltage: 100 mV, Measurement temperature: 25°C. The lithium ion conductivity at 25°C was calculated from the obtained Nyquist plot. The results are shown in Table 1.

[0120] [Crystalline 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 crystalline phase having an argyrodite-type crystal structure. For XRD measurement, Si powder was mixed as an internal standard for the sulfide solid electrolyte powder of each example, and an X-ray diffraction measurement (Rigaku Corporation, SmartLab) was performed using a holder not exposed to the atmosphere. The obtained XRD pattern was refined by the Rietveld method using RIETAN-FP software. The analysis determined the structure with the lowest Rwp value as the crystal structure of each example. The Rwp value is the reliability factor Rwp (R-weighted pattern), which is a general guideline for the entire analysis range in fitting structure refinement by Rietveld analysis. The lower the Rwp value, the better. In this analysis, the lowest Rwp values ​​were all less than 10%. This allowed the crystallinity (mass%) of the argyrodite-type crystals in the sulfide solid electrolyte powder, i.e., the ratio of the crystalline phase to the total of the crystalline phase and the amorphous phase, to be determined. The results are shown in Table 1.

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

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

[0123] [BET specific surface area] The BET specific surface area (specific surface area, m ２ The results are shown in Table 1.

[0124] [Strain value parameter] From the strain value and BET specific surface area obtained above, [(strain value - 0.001) / specific surface area (m ２ The value expressed as: (1 / g) × 100 was calculated. The results are shown in Table 1.

[0125] [Battery Evaluation] Obtained sulfide solid electrolyte powder: LiNi coated with lithium niobate having an average particle size of 7 μm １／３ Co １／３ Mn １／３ O ２ The particles (positive electrode active material):conductive additive:binder were mixed in a ratio of 1.1 g:5.0 g:0.1 g:0.6 g and stirred in a butyl butyrate solution to obtain a slurry. The slurry was applied to an Al foil current collector using a blade method with an applicator, and vacuum dried at 80 °C for 4 hours to obtain a positive electrode sheet. The obtained sheet was punched with a die having a diameter of 10 mm to obtain a positive electrode mixture. Meanwhile, a compact (diameter 10 mm, thickness 1 mm) of the obtained sulfide solid electrolyte powder was prepared, and the positive electrode mixture was placed on the compact and pressed at 500 MPa. After that, a Li-In alloy was attached to the counter electrode. Then, the mixture was constrained at a confining pressure of 10 MPa or 100 MPa to prepare a lithium ion secondary battery (half cell). The half cell has a structure in which the contents are not exposed to the atmosphere.

[0126] The obtained half cell was subjected to a voltage test at 25°C, with a voltage of 4.3 to 2.5 V vs. Li ＋ Charge and discharge were repeated five times in the range of 0.1 C for both charge and discharge. In the sixth cycle, the voltage reached 4.3 V vs. Li at a rate of 0.1 C. ＋ After charging to 1.9V vs. Li at a rate of 1C ＋ The battery was discharged to 0.15 V / Li, and the discharge capacity was determined.

[0127] The ratio of the discharge capacity of the half-cell with a confining pressure of 10 MPa to the discharge capacity of the half-cell with a confining pressure of 100 MPa was determined. The results are shown in Table 1, where the discharge capacity ratios are normalized. Specifically, the discharge capacity ratio of Example 9 is normalized to 1.00. The larger the normalized discharge capacity ratio compared to Example 9, the better the ability to maintain good interfacial contact with the active material, even when the confining pressure is low.

[0128] [Complex Elastic Modulus] The composite elastic modulus of the sulfide solid electrolyte powder obtained in Example 1 was determined. Specifically, 0.1 g of the sulfide solid electrolyte powder was molded into a 10 mm diameter green compact (pellet). This green compact was produced by applying pressure so that the relative density was 90%, and the sample of Example 1 was molded by applying a pressure of 570 MPa. A nanoindentation test was performed on the above pellet using a spherical indenter with an indenter tip radius of 100 μm. As a result, the composite elastic modulus of Example 1 was confirmed to be 11 GPa. Note that all samples were handled and measured in an environment not exposed to the atmosphere.

[0129]

[0130] As shown in Table 1, by obtaining a sulfide solid electrolyte by employing a melting method, and then sequentially subjecting the sulfide solid electrolyte to coarse pulverization using a cutter mill, heat treatment while suppressing aggregation, and fine pulverization using a bead mill, the strain value can be increased without excessively reducing the particle size of the resulting sulfide solid electrolyte powder, and the ratio of [(strain value - 0.001) / specific surface area (m ２ / g)] × 100. As a result, even when a lithium ion battery was assembled under a low confining pressure of 10 MPa, favorable interfacial contact allowed for the realization of favorable battery characteristics even after repeated charge-discharge cycles, without reducing the lithium ion conductivity of the sulfide solid electrolyte powder.

[0131] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 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, wherein [(distortion value - 0.001) / specific surface area (m ２ / g)]×100 is 0.010 to 0.070, and the crystal phase has an argyrodite-type crystal structure.

2. The sulfide solid electrolyte powder according to claim 1, further comprising an amorphous phase, the content of the amorphous phase being 5 mass % or more.

3. The sulfide solid electrolyte powder according to claim 1, wherein the argyrodite-type crystal structure 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, and the content ratio of the Br to the halogen element is 0.1 to 0.

9.

5. The argyrodite type crystal structure is Li ａ M.Z. ｂ Ha ｃ wherein in the composition formula, M is at least one element selected from Na, K, and elements present as divalent to pentavalent cations in the crystal structure, Z is at least one element selected from elements present 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, and the composition formula satisfies the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2. The sulfide solid electrolyte powder according to claim 1, 6. The sulfide solid electrolyte powder according to claim 1, having 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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