Sulfide solid electrolyte and battery comprising the same

Abstract

A sulfide solid electrolyte contains lithium (Li) element, phosphorus (P) element, sulfur (S) element, and halogen (X) element, and has peaks at 2θ = 24.9°±0.3°, 29.2°±0.3°, and 30.6°±0.4° in an X-ray diffraction pattern. In the X-ray diffraction pattern, it is appropriate that the half-value width of each peak observed at 2θ = 24.9°±0.3°, 29.2°±0.3°, and 30.6°±0.4° is 0.1° or more. The halogen (X) element is also appropriate to contain at least iodine (I) element.

Description

Technical Field

[0001] This invention relates to sulfide solid electrolytes and batteries containing them. Background Technology

[0002] In recent years, secondary batteries have attracted attention as a countermeasure to prevent global warming by reducing carbon dioxide emissions. Among them, solid-state batteries are expected to be practical due to their combination of safety and high energy density. Various technologies related to solid electrolytes have been proposed to improve the performance of solid-state batteries.

[0003] One of the required characteristics of solid electrolytes is high flexibility, which, from the perspective of reducing the resistance of solid-state batteries by increasing the contact between the solid electrolyte and the active material, can be cited as an example. However, some solid electrolytes lack flexibility. Therefore, to improve flexibility, Patent Document 1 proposes a sulfide solid electrolyte, which is composed of the formula Li... 8.29 Sn 0.60 P2S 10.30 I 0.09 It indicates that the crystal phase has diffraction peaks at diffraction angles 2θ of 19.80°±0.50°, 20.10°±0.50°, 26.60°±0.50° and 29.30°±0.50° in the X-ray diffraction pattern.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2022-191963 Summary of the Invention

[0007] However, the solid electrolyte described in this literature has room for further improvement in terms of flexibility.

[0008] Therefore, the objective of this invention is to provide a solid electrolyte with higher flexibility than the aforementioned prior art.

[0009] This invention provides a sulfide solid electrolyte comprising lithium (Li), phosphorus (P), sulfur (S), and halogen (X).

[0010] The sulfide solid electrolyte exhibits peaks at 2θ = 24.9° ± 0.3°, 29.2° ± 0.3°, and 30.6° ± 0.4° in the X-ray diffraction pattern. Attached Figure Description

[0011] Figure 1 This is a diagram showing the X-ray diffraction pattern of the sulfide solid electrolyte obtained in Example 1.

[0012] Figure 2 This is a diagram showing the X-ray diffraction pattern of the sulfide solid electrolyte obtained in Example 2.

[0013] Figure 3 This is a diagram showing the X-ray diffraction pattern of the sulfide solid electrolyte obtained in Comparative Example 1.

[0014] Figure 4 This is a perspective view of a deformation rate measuring device used to determine the deformation rate of a sulfide solid electrolyte relative to compression.

[0015] Figure 5 yes Figure 4 An exploded perspective view of the device shown.

[0016] Figure 6 It means Figure 4 A three-dimensional diagram showing the state of the device during the assembly process.

[0017] Figure 7 It means Figure 4 A three-dimensional diagram showing the state of the device during the assembly process.

[0018] Figure 8 This is a three-dimensional diagram showing the assembled deformation rate measuring device. Detailed Implementation

[0019] The present invention will now be described based on its preferred embodiments. The present invention relates to sulfide solid electrolytes. The sulfide solid electrolyte of the present invention has lithium-ion conductivity. The sulfide solid electrolyte of the present invention comprises lithium (Li), phosphorus (P), sulfur (S), and a halogen (X) element as its constituent elements. Examples of halogen (X) elements include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The halogen (X) element can be one of these elements, or a combination of two or more. As an example of the sulfide solid electrolyte of the present invention, an electrolyte with the formula Li... a PS b X c (A solid electrolyte containing a crystalline phase with a sulfide-germanium sulfide-type crystal structure, where "X" represents one or more halogen elements. Details regarding subscripts a, b, and c are described later.) The sulfide solid electrolyte containing the crystalline phase with a sulfide-germanium sulfide-type crystal structure exhibits excellent ionic conductivity and is therefore preferred. Details regarding the sulfide solid electrolyte containing the crystalline phase with a sulfide-germanium sulfide-type crystal structure are described later.

[0020] One characteristic of the sulfide solid electrolyte of the present invention is that diffraction peaks are observed at specific diffraction angles in the X-ray diffraction pattern measured using CuKα1 rays. Specifically, the sulfide solid electrolyte of the present invention preferably has diffraction peaks at least 2θ = 24.9° ± 0.3°, 29.2° ± 0.3°, and 30.6° ± 0.4° in the XRD pattern. The sulfide solid electrolyte of the present invention having diffraction peaks at these positions exhibits high flexibility relative to compression and is easily deformed under compression. Furthermore, it is less prone to springback when the compressive force is released. As a result, the contact between the solid electrolyte of the present invention and the active material becomes excellent. Therefore, the internal resistance of the battery containing the solid electrolyte of the present invention is lower. Consequently, the rate performance of the battery containing the solid electrolyte of the present invention becomes superior.

[0021] As described above, the sulfide solid electrolyte of the present invention exhibits diffraction peaks during XRD analysis, thus demonstrating crystallinity. In particular, a lower crystallinity of the sulfide solid electrolyte of the present invention results in higher flexibility relative to compression, which is therefore preferable. Generally, the crystallinity of a substance can be evaluated by the half-width at half-maximum (WHM) of the diffraction peaks observed during XRD analysis of that substance. Specifically, a larger WHM indicates lower crystallinity. From this perspective, the WHM of each peak observed in the XRD pattern of the sulfide solid electrolyte of the present invention at 2θ = 24.9° ± 0.3°, 29.2° ± 0.3°, and 30.6° ± 0.4° is preferably 0.1° or more, more preferably 0.12° or more, and even more preferably 0.15° or more.

[0022] Furthermore, since the sulfide solid electrolyte of the present invention requires a certain degree of crystallinity, the half-width of each peak observed in the XRD pattern at 2θ = 24.9° ± 0.3°, 29.2° ± 0.3°, and 30.6° ± 0.4° is preferably 1.5° or less, more preferably 1.4° or less, and even more preferably 1.3° or less.

[0023] The inventors' research results indicate that, in order to observe diffraction peaks at the aforementioned positions during XRD analysis of the sulfide solid electrolyte of the present invention, it is advantageous that the sulfide solid electrolyte of the present invention comprises a crystal phase having a sulfogermanite-type crystal structure, and at least contains iodine (I) as a halogen (X) element. In particular, it is shown that the sulfide solid electrolyte of the present invention comprises a phase with the compositional formula Li a PS b I c(Details regarding subscripts a, b, and c will be described later.) The crystal phase indicated is advantageous. However, this does not mean that the sulfide solid electrolyte of the present invention contains only element I as element X. The sulfide solid electrolyte of the present invention is permitted to contain halogen elements other than element I as element X. For example, the sulfide solid electrolyte of the present invention may contain element I and one or more halogen elements other than element I as element X. Specifically, the sulfide solid electrolyte of the present invention may be composed of the formula Li a PS b Cl x I y It can also be represented by the composition formula Li a PS b Cl x Br y I z This means that, as element X, it can contain elements I and Cl, or as element X, it can contain elements I, Cl, and Br.

[0024] The sulfide solid electrolyte of the present invention exhibits diffraction peaks in its XRD pattern at 2θ = 24.9° ± 0.3°, 25.6° ± 0.3°, 29.2° ± 0.3°, 29.9° ± 0.3°, and 30.6 ± 0.4°. These diffraction peaks observed at these locations originate from a crystal phase with a sulfide-germanium-type crystal structure. Furthermore, in the present invention, a diffraction peak can also be observed in the XRD pattern at 17.6° ± 0.3°. It can be considered that the diffraction peaks observed at the aforementioned locations occur when element I is included as element X. It should be noted that the aforementioned diffraction peaks can be in the range of ± 0.2° or ± 0.1°.

[0025] Regarding the sulfide solid electrolyte of the present invention, from the viewpoint of imparting flexibility to the sulfide solid electrolyte, the strain of each crystal phase derived from the diffraction peaks observed in the X-ray diffraction pattern at 2θ = 24.9° ± 0.3°, 29.2° ± 0.3°, and 30.6° ± 0.4° is preferably 0.3% or more, more preferably 0.35% or more, and even more preferably 0.40% or more. When the sulfide solid electrolyte of the present invention comprises multiple crystal phases, it is sufficient if the strain of at least one crystal phase satisfies the aforementioned condition; preferably, the strain of all crystal phases satisfies the aforementioned condition.

[0026] In the sulfide solid electrolyte of the present invention, there exists a composition of Li a PS b Cl c The crystal phase represented is not a problem, but it is preferable that the presence of that crystal phase is rare. From this point of view, Li a PS b Cl cThe height of the representative diffraction peak in the crystal phase shown, observed at 2θ = 25.6° ± 0.3°, is denoted as I. A , will Li a PS b I c The height of the representative diffraction peak in the crystal phase shown, observed at 2θ = 24.9° ± 0.3°, is denoted as I. B At that time, I A Compared to I B The ratio is I A / I B The value is preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.3 or less.

[0027] to I A / I B There are no special restrictions on the lower limit of the value; for example, it can be above 0.01, above 0.02, or above 0.03.

[0028] In XRD analysis, the sulfide solid electrolyte of the present invention sometimes exhibits diffraction peaks originating from other crystal phases, in addition to those originating from the crystalline phase having a sulfide-germanium-type crystal structure. Examples of such diffraction peaks include those originating from the raw materials used to manufacture the sulfide solid electrolyte. Examples of peaks originating from these raw materials include those originating from lithium sulfide (Li₂S).

[0029] In the case where the sulfide solid electrolyte of the present invention has a crystal phase with a sulfide-germanium sulfide-type crystal structure, as described above, from the viewpoint of improving lithium-ion conductivity, the sulfide solid electrolyte preferably has a compositional formula (I): Li a PS b X c In this case, X preferably contains at least iodine.

[0030] In composition formula (I), 'a', representing the molar ratio of Li, is preferably 3.0 or more, more preferably 4.0 or more, and particularly preferably 5.0 or more. Furthermore, 'a' is preferably 6.5 or less, more preferably 5.9 or less, and particularly preferably 5.6 or less. By setting 'a' to this range, the cubic argyroclase-type crystal structure near room temperature (25°C) becomes more stable, thereby enabling the sufficient introduction of lithium-ion holes into the structure, and consequently, effectively improving lithium-ion conductivity.

[0031] In composition (I), b is preferably 3.5 or more, more preferably 4.0 or more, and particularly preferably 4.2 or more. Furthermore, b is preferably 5.5 or less, more preferably 4.9 or less, and particularly preferably 4.7 or less. By making b within the aforementioned range, the sulfide-germanium ore-type crystal structure near room temperature (25°C) becomes more stable, and lithium-ion conductivity is effectively increased.

[0032] In composition (I), c is preferably 0.1 or more, more preferably 1.0 or more, even more preferably 1.1 or more, and particularly preferably 1.4 or more. Additionally, c is preferably 2.5 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0033] In the case where the sulfide solid electrolyte of the present invention has a crystal phase with a sulfide-germanium ore-type crystal structure, the sulfide solid electrolyte can be composed of formula (II): Li 7-d PS 6-d X d In this case, X preferably contains at least iodine. The composition shown in formula (II) is the stoichiometric composition of the silver-germanium sulfide-type crystal phase.

[0034] In composition (II), d is preferably 0.4 or more, more preferably 0.8 or more, and particularly preferably 1.2 or more. Furthermore, d is preferably 2.2 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0035] In the case where the sulfide solid electrolyte of the present invention has a crystal phase with a sulfide-germanium ore-type crystal structure, the sulfide solid electrolyte can be composed of formula (III): Li 7-d-2e PS 6-d-e X d In this case, X preferably contains at least iodine. A sulforaphane-germanium ore-type crystal phase having the composition shown in formula (III) is generated, for example, by reacting a sulforaphane-germanium ore-type crystal phase having the composition shown in formula (II) with P2S5 (phosphorus pentasulfide).

[0036] In composition formula (III), e represents the deviation of the Li2S composition from the stoichiometric composition shown in composition formula (II). e is preferably -0.9 or more, more preferably -0.6 or more, and particularly preferably -0.3 or more. In addition, e is preferably (-d+2) or less, more preferably (-d+1.6) or less, and particularly preferably (-d+1.0) or less.

[0037] In the sulfide solid electrolyte of the present invention, the atomic ratio of all X elements to P elements, X / P, is preferably 1.0 or more, more preferably 1.1 or more, even more preferably 1.2 or more, and still more preferably 1.4 or more. Furthermore, the atomic ratio X / P is preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.2 or less. By making the atomic ratio X / P within the above range, lithium-ion conductivity is further improved. The atomic ratio X / P can be determined, for example, by high-frequency inductively coupled plasma atomic emission spectrometry (ICP emission spectrometry) or SEM-EDS analysis.

[0038] The sulfide solid electrolyte of the present invention is preferably an aggregate of particles. In this case, from the viewpoints of suppressing the increase in resistance caused by the increase in surface area and facilitating mixing with active materials, the volumetric cumulative particle size D at a cumulative volume of 50% is determined based on the laser diffraction scattering particle size distribution method. 50 Preferably, the particle size is 0.1 μm or more, more preferably 0.4 μm or more, and even more preferably 0.6 μm or more. Furthermore, from the viewpoint of suppressing adhesion, aggregation, and particle size growth caused by heating, the volumetric cumulative particle size D... 50 Preferably, it is 100 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and particularly preferably 1 μm or less.

[0039] The sulfide solid electrolyte of the present invention exhibits lithium-ion conductivity in a solid state. The lithium-ion conductivity of the solid electrolyte of the present invention is preferably 1.0 mS / cm or higher at room temperature, i.e., 25°C, more preferably 1.2 mS / cm or higher, more preferably 1.3 mS / cm or higher, and particularly preferably 1.5 mS / cm or higher. The lithium-ion conductivity can be measured using the method described in the examples below.

[0040] The sulfide solid electrolyte of the present invention can be used in the form of an electrode mixture comprising the sulfide and an active material. Alternatively, the sulfide solid electrolyte of the present invention can also be used in the form of a solid electrolyte layer containing the sulfide.

[0041] By using the sulfide solid electrolyte of the present invention, a solid-state battery can be manufactured, for example, having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the aforementioned positive electrode layer and the aforementioned negative electrode layer, and containing the sulfide solid electrolyte of the present invention.

[0042] Next, a suitable method for manufacturing the sulfide solid electrolyte of the present invention will be described. The sulfide solid electrolyte of the present invention can be suitably obtained by mechanically grinding a raw material composition. The aforementioned raw material composition is a mixture of raw materials comprising the elements described above that constitute the solid electrolyte. The raw material composition comprises one or more compounds containing at least one element selected from Li, P, S, and X.

[0043] The aforementioned compounds may be, for example, compounds containing Li, compounds containing S, compounds containing P, and compounds containing X.

[0044] Furthermore, the aforementioned compounds may contain at least two of the elements selected from Li, P, S, and X. For example, the aforementioned compounds may include: compounds containing Li and X, compounds containing P and S, compounds containing Li and S, compounds containing P and X, and compounds containing S and X.

[0045] As compounds containing Li and X elements, lithium halides such as lithium iodide and lithium chloride can be used.

[0046] Phosphorus sulfides, such as phosphorus trisulfide (P2S3) and phosphorus pentasulfide (P2S5), can be used as compounds containing P and S elements.

[0047] Lithium sulfide (Li2S) can be used as a compound containing both Li and S elements.

[0048] Phosphorus halides such as PX3 and P2X5 can be used as compounds containing P and X elements.

[0049] As compounds containing both sulfur (S) and x (X) elements, for example, SX2, SX4, SX6, and S2X can be used. 10 Isohalated sulfur.

[0050] From the perspective of being able to successfully synthesize sulfide solid electrolytes with high flexibility relative to compression, the aforementioned raw material composition particularly preferably includes lithium sulfide, phosphorus sulfide, and lithium halides such as lithium iodide and lithium chloride as the aforementioned compounds.

[0051] In preparing the aforementioned raw material composition, from the viewpoint of obtaining a sulfide solid electrolyte with high flexibility relative to compression and from the viewpoint of being able to suppress the generation of hydrogen sulfide from the sulfide solid electrolyte, it is preferable to mix each compound in an amount that is the composition shown in any of the above compositional formulas (I) to (III).

[0052] The above compounds are mixed to prepare a raw material composition. For example, a grinder, paint mixer, planetary ball mill, ball mill, bead mill, homogenizer, etc., can be used for mixing. The amount of each raw material added during mixing is appropriately adjusted to meet the composition of the target sulfide solid electrolyte.

[0053] As a subsequent mixing operation, mechanical grinding is performed to react the components contained in the raw material composition, thereby obtaining the target sulfide solid electrolyte. By obtaining the sulfide solid electrolyte in this way, excessive increase in the crystallinity of the sulfide solid electrolyte can be effectively suppressed. Therefore, in this manufacturing method, it is preferable not to perform the operation of increasing the crystallinity of the sulfide solid electrolyte, that is, to generate the sulfide solid electrolyte by calcining the raw material composition.

[0054] When obtaining sulfide solid electrolytes by mechanical grinding, a planetary ball mill is preferred. When a planetary ball mill is used, the container filled with the raw material composition rotates and revolves at high speed, thus generating appropriate impact energy between the balls, which serve as the grinding medium, and the raw material composition, allowing for the successful acquisition of low-crystallinity sulfide solid electrolytes.

[0055] As conditions for using a planetary ball mill for mechanical grinding, methods such as adjusting the revolution and / or rotation speed of the device, the diameter of the balls, the material and the ratio of the ball volume to the volume of the mixing container, and the mixing time can be cited.

[0056] For example, the raw material composition is treated at a rotation speed of 200 rpm or more, preferably 300 rpm or more, and even more preferably 350 rpm or more for at least 25 hours, more preferably 35 hours or more, and even more preferably 45 hours or more.

[0057] The spheres used as the pulverizing medium are preferably made of ZrO2, Al2O3, Si3N4 (silicon nitride), or WC (tungsten carbide). The diameter of the spheres is preferably 0.2 mm or more and 10 mm or less.

[0058] The resulting sulfide solid electrolyte can be used alone or in combination with other solid electrolytes. Specifically, when the sulfide solid electrolyte is formed from Li, P, S, and I elements, it can be mixed with a sulfide solid electrolyte formed from Li, P, S, and Cl elements.

[0059] As another method for manufacturing sulfide solid electrolytes, a solid-phase reaction involving heating and sintering the raw material composition can also be suitably employed. In this method, the raw material composition is fed into a firing process to allow a solid-phase reaction to occur, resulting in a crystalline sintered product. The firing atmosphere can be, for example, an inert gas atmosphere such as argon or nitrogen, or a hydrogen sulfide atmosphere. From the viewpoint of adjusting the proportion of sulfur in the solid electrolyte, an inert gas atmosphere is preferred. The firing time is not a critical time; it is simply the time required to obtain a sintered product with the desired composition. Specifically, a firing time that sufficiently allows for the solid-phase reaction of the raw material composition to occur is preferred. The firing time can, for example, be 30 minutes or more, 2 hours or more, or 3 hours or more. On the other hand, the firing time can, for example, be 10 hours or less, or 5 hours or less.

[0060] The sulfide solid electrolyte of the present invention can be used as a material constituting a solid electrolyte layer, a positive electrode layer, or a negative electrode layer. Specifically, the sulfide solid electrolyte of the present invention can be used in batteries having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive and negative electrode layers. That is, the sulfide solid electrolyte of the present invention can be used in solid-state batteries. More specifically, it can be used in lithium solid-state batteries. Lithium solid-state batteries can be primary batteries or, alternatively, secondary batteries. There are no particular limitations on the shape of the battery; for example, laminated, cylindrical, and prismatic shapes can be used. The term "solid-state battery" includes, in addition to solid-state batteries that completely do not contain liquid or gel-like substances as electrolytes, schemes that contain, for example, 50% or less, 30% or less, or 10% or less of liquid or gel-like substances as electrolytes.

[0061] When the solid electrolyte layer contains the sulfide solid electrolyte of the present invention, the solid electrolyte layer can be manufactured, for example, by methods such as: dripping a slurry containing the sulfide solid electrolyte, binder, and solvent onto a substrate and then grinding it with a scraper or the like; cutting it with an air knife after the substrate has come into contact with the slurry; or forming a coating film by screen printing or the like, and then removing the solvent by heating and drying. Alternatively, it can be manufactured by pressing the powdered sulfide solid electrolyte into a pressed powder and then processing it appropriately.

[0062] To balance the prevention of short circuits and volumetric capacity density, the thickness of the solid electrolyte layer is typically 5 μm or more and 300 μm or less, and more preferably 10 μm or more and 100 μm or less.

[0063] The sulfide solid electrolyte of the present invention can also be used with active materials to form an electrode mixture. Typically, the proportion of the sulfide solid electrolyte in the electrode mixture is 10% by mass or more and 50% by mass or less. The electrode mixture may also contain other materials such as conductive materials as needed. As described above, the sulfide solid electrolyte of the present invention has high flexibility relative to compression, thus resulting in good adhesion to the active material. Therefore, solid-state batteries manufactured using electrode mixtures containing the sulfide solid electrolyte of the present invention have lower internal resistance.

[0064] Electrode mixtures, binders, and solvents are mixed to form a paste, which is then applied to current collectors such as aluminum foil and dried to produce positive and negative electrodes.

[0065] As the cathode material constituting the cathode layer, cathode materials used as cathode active materials in lithium-ion batteries can be appropriately used. Examples include lithium-containing cathode active materials, specifically spinel-type lithium transition metal oxides and lithium metal oxides with layered structures. By using high-voltage cathode materials, energy density can be increased. In addition to the cathode active material, the cathode material may also contain conductive materials, or other materials.

[0066] As the negative electrode material constituting the negative electrode layer, a negative electrode material used as the negative electrode active material in lithium-ion batteries can be appropriately used. The sulfide solid electrolyte of the present invention is electrochemically stable; therefore, lithium metal can be used, or at a low potential comparable to lithium metal (approximately 0.1V vs. Li). + Materials that are charged and discharged under Li (Li) conditions, namely carbon-based materials such as graphite, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon), can be used as anode materials. This significantly improves the energy density of solid-state batteries. Alternatively, silicon or tin, which are expected to be high-capacity materials, can be used as active materials. Regarding anode materials, in addition to the active material, conductive materials or other materials may also be included.

[0067] Regarding the above embodiments, the present invention further discloses the following sulfide solid electrolyte and battery.

[0068] [1] A sulfide solid electrolyte comprising lithium (Li), phosphorus (P), sulfur (S) and halogen (X) elements,

[0069] The sulfide solid electrolyte exhibits peaks at 2θ = 24.9° ± 0.3°, 29.2° ± 0.3°, and 30.6° ± 0.4° in the X-ray diffraction pattern.

[0070] [2] According to the sulfide solid electrolyte described in [1], the half-width of each peak observed in the X-ray diffraction pattern at 2θ = 24.9° ± 0.3°, 29.2° ± 0.3° and 30.6° ± 0.4° is independently greater than 0.1°.

[0071] [3] The sulfide solid electrolyte according to [1] or [2], wherein the halogen (X) element contains at least the iodine (I) element.

[0072] [4] A sulfide solid electrolyte according to any one of [1] to [3], wherein the halogen (X) element comprises iodine (I) and chlorine (Cl),

[0073] The X-ray diffraction pattern shows peaks at 2θ = 24.9°±0.3°, 25.6°±0.3°, 29.2°±0.3°, 29.9°±0.3° and 30.6±0.4°.

[0074] [5] The sulfide solid electrolyte according to any one of [1] to [4], wherein the strain of the crystal phases derived from the diffraction peaks observed in the X-ray diffraction pattern at 2θ = 24.9° ± 0.3°, 29.2° ± 0.3° and 30.6° ± 0.4° is each independently greater than 0.3%.

[0075] [6] The sulfide solid electrolyte according to any one of [1] to [5], wherein the height I of the peak observed at 2θ = 25.6° ± 0.3° is A The height I relative to the peak observed at 2θ = 24.9° ± 0.3° B It is above 0.01 and below 0.5.

[0076] [7] The sulfide solid electrolyte according to any one of [1] to [6] has a crystal phase with a sulfide-germanium mineral-type crystal structure.

[0077] [8] A battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer.

[0078] The battery contains a sulfide solid electrolyte as described in any one of [1] to [7].

[0079] Example

[0080] The present invention will now be described in more detail through embodiments. However, the scope of the present invention is not limited to these embodiments. Unless otherwise specified, "%" refers to "mass %".

[0081] [Example 1]

[0082] Lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, and lithium iodide (LiI) powder were weighed separately according to the raw material mass ratios shown in Table 1 below. Heptane was added to these powders to prepare a slurry. This slurry was placed in a zirconia container and placed in a planetary ball mill. Zirconia balls with a diameter of 5 mm were used as the grinding medium. The ball mill was operated at 370 rpm for 50 hours for wet mixing and mechanical grinding. The mixed slurry was then vacuum dried at room temperature to remove the heptane. This yielded the powder of the target sulfide solid electrolyte (D). 50 =10.0μm).

[0083] [Example 2]

[0084] Lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, lithium iodide (LiI) powder, and lithium chloride (LiCl) powder were weighed separately according to the raw material mass ratios shown in Table 1 below. The powders were then pulverized and mixed using a planetary ball mill for 3 hours to prepare a mixed powder. After removing the solvent from the mixed powder, it was placed in an electric furnace. Nitrogen gas was circulated in the furnace at a rate of 1.0 L / min, and the furnace was heated at 500°C for 4 hours at a heating rate of 200°C / h to obtain a calcined product. This calcined product was mixed with heptane to form a slurry, which was then pulverized using a planetary ball mill. The mixed slurry was vacuum dried at room temperature to remove the heptane, yielding the calcined powder. The calcined powder was sieved using a 53 μm mesh sieve, and the calcined product that passed through the sieve was used as the powder of the sulfide solid electrolyte. Weighing, mixing, placing into the electric furnace, removing from the furnace, crushing, and sieving are all carried out in a glove box purged with thoroughly dried Ar gas (dew point below -60°C). This yields a powder of the target sulfide solid electrolyte (D...). 50 =1.6μm).

[0085] [Example 3]

[0086] Lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, and lithium chloride (LiCl) powder were weighed separately in the raw material mass ratios shown in Table 1 below. Otherwise, the same procedure as in Example 2 was followed to obtain the powder of the target sulfide solid electrolyte.

[0087] [Comparative Example 1]

[0088] Lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, and lithium chloride (LiCl) powder were weighed separately in the raw material mass ratios shown in Table 1 below. Otherwise, the same procedure as in Example 2 was followed to obtain the powder of the target sulfide solid electrolyte.

[0089] [evaluate]

[0090] The sulfide solid electrolytes obtained in the examples and comparative examples were subjected to XRD analysis using the method described below (excluding Example 3). The results are shown below. Figures 1-3 Furthermore, the half-width and strain of the crystal phase were measured.

[0091] Furthermore, for the sulfide solid electrolytes obtained in the examples and comparative examples, the deformation rate relative to compression and the elastic recovery rate after release of compression were determined using the method described below.

[0092] Furthermore, the ionic conductivity of the sulfide solid electrolytes obtained in the examples and comparative examples and the characteristics of the solid-state batteries containing the sulfide solid electrolytes were determined using the methods described below. The results are shown in Table 1 below.

[0093] [XRD Measurement]

[0094] XRD measurements were performed using a Smart Lab SE X-ray diffraction apparatus manufactured by Rigaku Corporation. The measurement conditions were set as follows: no atmospheric exposure, scanning axis: 2θ / θ, scanning range: 10° to 120°, step width: 0.02°, and scanning speed: 1° / min.

[0095] The X-ray source is CuKα1 radiation. The tube voltage is set to 40kV and the tube current is set to 80mA.

[0096] [Determination of half-width]

[0097] The XRD results were analyzed using SmartLab Studio II from Rigaku Corporation. For the obtained XRD patterns, peak shapes were fitted using a segmented pseudo-Voigt function, and the background was fitted using B-splines. The half-width (FWHM) of the corresponding peaks was obtained.

[0098] [Determination of strain in crystalline phases]

[0099] The XRD results were analyzed using HighScore Plus from Malvern Panalytical. In Line Profile Analysis mode, the background of the obtained XRD pattern was specified, and peaks were determined based on peak search. Then, a pseudo-Voigt function was used as the profile function, and profile fitting was performed in Default Profile Fit mode. The peaks of the desired crystalline phase were selected, and the strain of each phase was calculated from the slope of the Williamson-Hall curve.

[0100] [Deformation rate relative to compression]

[0101] use Figure 4 The deformation rate measuring device 10 shown is used for measurement.

[0102] Figure 5 An exploded perspective view of the device is shown in the figure. As shown, the deformation rate measuring device 10 includes a sulfide solid electrolyte receiving section 13. The receiving section 13 is cylindrical and can receive the sulfide solid electrolyte within a cylindrical space 13s concentric with the receiving section 13. The space 13s extends through the receiving section 13.

[0103] The deformation rate measuring device 10 also includes a first sealing member 11 and a second sealing member 12.

[0104] The first closing member 11 has a cylindrical first insertion portion 11a, which has a shape complementary to the shape of the space 13s of the receiving portion 13. The first insertion portion 11a hangs down from the lower surface of the disc-shaped base 11b. A plurality of through holes 11c are formed in the base 11b, extending through the base 11b in the thickness direction. The bolt 14, described later, is inserted into the through holes 11c.

[0105] The second closing member 12 has a cylindrical second insertion portion 12a, which has a shape complementary to the shape of the space 13s of the receiving portion 13. The second insertion portion 12a is erected on the upper surface of the disk-shaped base 12b. A plurality of through holes 12c are formed in the base 12b, extending through the base 12b in the thickness direction. Bolts 14, described later, are inserted into the through holes 12c. The number of through holes 12c is the same as the number of through holes 11c.

[0106] The sum of the height H1 of the first insertion portion 11a of the first closing member 11 and the height H2 of the second insertion portion 12a of the second closing member 12, i.e., H1 + H2, is greater than the height of the storage portion, i.e., the height H3 of the space 13s. It should be noted that in... Figure 5There is shown a state where the height H1 of the first insertion portion 11a is greater than the height H2 of the second insertion portion 12a, but the magnitude relationship between H1 and H2 is not limited thereto; H1 may be less than H2, or H1 may be equal to H2.

[0107] In order to measure the deformation rate of the sulfide solid electrolyte, first, as Figure 6 shown, the second sealing member 12 is placed with the second insertion portion 12a facing upward, and in this state, the second insertion portion 12a is inserted into the space 13s in the receiving portion 13. Thus, a bottomed receiving space S is formed in the space 13s. The receiving space S has a volume obtained by subtracting the volume of the second insertion portion 12a from the volume of the space 13s. The receiving space S is a cylindrical space with a diameter of 10 mm. 100 mg of sulfide solid electrolyte SE is filled into the receiving space S.

[0108] Next, as Figure 7 shown, the first insertion portion 11a of the first sealing member 11 is inserted downward into the receiving space S. When the first insertion portion 11a is completely inserted into the receiving space S, the base end side of the first insertion portion 11a remains exposed. This is because the sum of the height H1 of the first insertion portion 11a and the height H2 of the second insertion portion 12a, i.e., the value of H1+H2, is greater than the height H3 of the space 13s. Therefore, when the first insertion portion 11a is completely inserted into the receiving space S, the sulfide solid electrolyte SE is compressed between the upper end face of the first insertion portion 11a and the upper end face of the second insertion portion 12a.

[0109] Next, four bolts 14 (see Figure 5 ) are inserted through the through holes 11c formed in the first sealing member 11 and the through holes 12c formed in the second sealing member 12, and nuts 15 are screwed onto the bolts 14 and tightened, to assemble the deformation rate measuring device 10. During tightening, a wrench 16 is used as shown in Figure 8 . As described above, the sulfide solid electrolyte SE is compressed between the upper end face of the first insertion portion 11a and the upper end face of the second insertion portion 12a, therefore, the degree of compression of the sulfide solid electrolyte SE can be adjusted by adjusting the tightening degree with the wrench 16. In the present measurement, tightening performed using the wrench 16 is carried out with a torque of 0.1 N·m.

[0110] After tightening each bolt 14 with the above torque, maintaining this state for 1 minute, then the distance D0 between the upper surface of the base 11b of the first sealing member 11 and the lower surface of the base 12b of the second sealing member 12 is measured with a vernier caliper (see Figure 4 ).

[0111] Next, bolt 14 was used to increase the tightening force, and the bolt was tightened with a torque of 10 N·m to further compress the sulfide solid electrolyte SE. After maintaining this state for 1 minute, the distance D1 between the upper surface of base 11b and the lower surface of base 12b was measured using vernier calipers (refer to...). Figure 4 ).

[0112] Based on the obtained values ​​of D1 and D0, the deformation rate (%) of the sulfide solid electrolyte is calculated using the formula [1-D1 / D0×100]. The larger the deformation rate, the greater the flexibility of the sulfide solid electrolyte relative to compression.

[0113] [Elastic recovery rate after compression]

[0114] In the deformation rate measuring device 10 after measuring distance D1, all bolts 14 are removed by loosening the fastening of bolts 14. In this state, the distance D2 between the upper surface of base 11b and the lower surface of base 12b is measured using vernier calipers.

[0115] Based on the values ​​of D2 and D1 obtained in this way, the elastic recovery rate (%) of the sulfide solid electrolyte after release and compression can be calculated using the formula (D2-D1) / D1×100. The larger the value of the elastic recovery rate, the easier it is for the sulfide solid electrolyte to rebound.

[0116] [Ion conductivity]

[0117] In a glove box purged with thoroughly dried Ar gas (dew point below -60°C), an application of approximately 6 t / cm was applied to the solid electrolyte. 2 The lithium-ion conductivity of the samples was determined by uniaxial compression molding under a load, producing granules with a diameter of 10 mm and a thickness of approximately 0.5 mm to 8 mm. The lithium-ion conductivity of the samples was measured using a Solartron 1255B impedance measuring device from TOYO Corporation. Measurements were performed by AC impedance method at a temperature of 25°C and a frequency of 0.1 Hz to 1 MHz.

[0118] Characteristics of solid-state batteries

[0119] Using LiCo 0.6 Ni 0.2 Mn 0.2 O2 was used as the positive electrode active material, and graphite (Gr) powder was used as the negative electrode active material. The sulfide solid electrolyte powders obtained in Examples 1, 2, and 3 and Comparative Example 1 were used.

[0120] The positive electrode active material, the sulfide solid electrolyte obtained in Examples 1, 2 and 3 and Comparative Example 1, and conductive carbon as a conductive aid were mixed in a mortar at a mass ratio of 70:27:3 to prepare a positive electrode mixture powder.

[0121] In addition, the negative electrode active material and the solid electrolyte are mixed in a mortar at a mass ratio of 1:1 to prepare a negative electrode mixture powder.

[0122] A polypropylene cylinder (10.5 mm in diameter and 18 mm in height) with openings at both ends was sealed at its lower opening with a positive electrode (SUS). A solid electrolyte was then placed on top of the cylinder, and after sealing with a negative electrode (SUS), it was uniaxially pressed at 10 MPa to form a solid electrolyte layer. Next, the negative electrode was temporarily removed, and a negative electrode powder was placed on the solid electrolyte layer, then sealed again with a negative electrode. Then, the cylinder was inverted, the positive electrode was temporarily removed, and a positive electrode powder was placed on the solid electrolyte layer, then sealed again with a positive electrode, and uniaxially pressed at 60 MPa. This produced a three-layer structure consisting of a positive electrode powder, a solid electrolyte layer, and a negative electrode powder, with an areal capacity of 3 mAh / cm². 2 Solid-state batteries.

[0123] Using the manufactured solid-state battery, a charge-discharge test was performed as follows. Specifically, the battery was placed in an environmental testing chamber set to an ambient temperature of 25°C for charging and discharging, and prepared in a charge-discharge manner, until the battery temperature reached the ambient temperature.

[0124] Next, at 0.1C (0.3mA / cm) 2 After being charged to 4.5V with a constant current and constant potential, it is then charged at 0.1C (0.3mA / cm). 2 Discharge to 2.5V with a constant current and repeat for 3 cycles. Then, charge until the state of charge (SOC) reaches 50%, and measure the charge-movement resistance value before the storage test by impedance measurement.

[0125] The charge-movement resistance of a battery is proportional to the ionic conductivity of the solid electrolyte in the positive electrode layer. Therefore, the value of (charge-movement resistance of the battery) / (resistance of the solid electrolyte) is calculated to evaluate the contactability between the active material and the solid electrolyte. This value indicates how much active material is in contact with the solid electrolyte while maintaining a constant ionic conductivity.

[0126] [Table 1]

[0127]

[0128] As can be clearly seen from the results shown in Table 1, the sulfide solid electrolytes obtained in each embodiment have high flexibility relative to compression and low rebound after release from compression.

[0129] Furthermore, it is known that the solid-state battery containing the sulfide solid electrolyte obtained in each embodiment has sufficient battery characteristics.

[0130] Industrial availability

[0131] As detailed above, according to the present invention, a solid electrolyte with superior flexibility compared to the prior art, good contact with active materials, and low internal resistance can be provided.

Claims

1. A sulfide solid electrolyte comprising lithium (Li), phosphorus (P), sulfur (S) and halogen (X) elements. The sulfide solid electrolyte exhibits peaks at 2θ = 24.9° ± 0.3°, 29.2° ± 0.3°, and 30.6° ± 0.4° in the X-ray diffraction pattern.

2. The sulfide solid electrolyte according to claim 1, wherein, In the X-ray diffraction pattern, the half-widths of each peak observed at 2θ = 24.9° ± 0.3°, 29.2° ± 0.3°, and 30.6° ± 0.4° were all independently greater than 0.1°.

3. The sulfide solid electrolyte according to claim 1, wherein, Halogen (X) elements contain at least iodine (I) elements.

4. The sulfide solid electrolyte according to claim 1, wherein, Halogen (X) elements include iodine (I) and chlorine (Cl). The X-ray diffraction pattern shows peaks at 2θ = 24.9°±0.3°, 25.6°±0.3°, 29.2°±0.3°, 29.9°±0.3° and 30.6±0.4°.

5. The sulfide solid electrolyte according to claim 1, wherein, The strain of the crystalline phases originating from the diffraction peaks observed in the X-ray diffraction pattern at 2θ = 24.9° ± 0.3°, 29.2° ± 0.3°, and 30.6° ± 0.4° is independently greater than 0.3%.

6. The sulfide solid electrolyte according to claim 1, wherein, The peak height I observed at 2θ = 25.6° ± 0.3° A The height I relative to the peak observed at 2θ = 24.9° ± 0.3° B It is above 0.01 and below 0.

5.

7. The sulfide solid electrolyte according to claim 1, having a crystal phase with a sulfogermanium ore-type crystal structure.

8. A battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer. The battery contains a sulfide solid electrolyte as described in any one of claims 1 to 7.

Images