Solid electrolyte, and electrode mixtures, solid electrolyte layers, and batteries using solid electrolytes.

Abstract

This solid electrolyte contains elemental lithium (Li), an element M (M is composed of at least one element that is selected from among silicon (Si), antimony (Sb), tin (Sn) and germanium (Ge)), elemental sulfur (S) and iodine (I). The X-ray diffraction pattern of this solid electrolyte has a diffraction peak A within the range where 2θ is from 24.0° to 24.8°, a diffraction peak B within the range where 2θ is from 28.2° to 29.0°, and a diffraction peak C within the range where 2θ is from 29.5° to 30.3°. If Ia is the peak intensity of the diffraction peak A and Id is the peak intensity of a diffraction peak D that is within the range where 2θ is from 25.3° to 25.9°, Id / Ia is 0.05 or less.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte. The present invention also relates to an electrode binder using the solid electrolyte, a solid electrolyte layer, and a battery.

Background Art

[0002] Since a solid battery does not use a flammable organic solvent, simplification of a safety device can be achieved, and moreover, not only can it be excellent in manufacturing cost and productivity, but it also has a feature that high voltage can be achieved by stacking in series in a cell. As one of the solid electrolytes used in a solid battery, Patent Document 1 proposes a lithium sulfur silver germanium ore represented by Li + (12-n-x) B n+ X 2- 6-x Y - x B is an element selected from the group consisting of P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, and Ta. X n+ is an element selected from the group consisting of S, Se, and Te. Y 2- is selected from the group consisting of Cl, Br, I, F, CN, OCN, SCN, and N3. -

[0003] Non-Patent Document 1 describes a thioantimonate lithium compound represented by Li 6+x M x Sb 1-x S5I (M = Si, Ge, Sn) and having an alditol type crystal structure. Non-Patent Document 2 describes a thioantimonate lithium compound represented by Li 6+x Sb 1-x Si x S5I and having an alditol type crystal structure.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] [Non-Patent Document 1] J. Am. Chem. Soc., 2019, 141, 19002-19013 [Non-Patent Document 2] ACS Sustainable Chem. Eng., 2021, 9, 1, 120-128 [Overview of the Initiative]

[0006] To improve the performance of solid-state batteries, solid electrolytes with high ionic conductivity are required. However, the solid electrolytes described in Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2 mentioned above had room for improvement in terms of ionic conductivity. Therefore, the object of the present invention is to provide a solid electrolyte having good ionic conductivity.

[0007] The present invention contains lithium (Li), M (where M is at least one of silicon (Si), antimony (Sb), tin (Sn), and germanium (Ge)), sulfur (S), and iodine (I). In the X-ray diffraction pattern measured by an X-ray diffractometer (XRD) using CuKα as a source, diffraction peak A is present in the range of 2θ = 24.0° to 24.8°, diffraction peak B is present in the range of 2θ = 28.2° to 29.0°, and diffraction peak C is present in the range of 2θ = 29.5° to 30.3°. The present invention provides a solid electrolyte in which, when the peak intensity of diffraction peak A is denoted as Ia, and the peak intensity of diffraction peak D located in the range of 2θ = 25.3° to 25.9° is denoted as Id, the relationship between Ia and Id satisfies the following equation (1). Id / Ia ≤ 0.05 (1) [Brief explanation of the drawing]

[0008] [Figure 1]FIG. 1 is a diagram showing an X-ray diffraction pattern of the solid electrolyte obtained in Example 1. [Figure 2] FIG. 2 is a diagram showing an X-ray diffraction pattern of the solid electrolyte obtained in Example 2. [Figure 3] FIG. 3 is a diagram showing an X-ray diffraction pattern of the solid electrolyte obtained in Example 3. [Figure 4] FIG. 4 is a diagram showing an X-ray diffraction pattern of the solid electrolyte obtained in Example 4. [Figure 5] FIG. 5 is a diagram showing an X-ray diffraction pattern of the solid electrolyte obtained in Example 5. [Figure 6] FIG. 6 is a diagram showing an X-ray diffraction pattern of the solid electrolyte obtained in Example 6. [Figure 7] FIG. 7 is a diagram showing an X-ray diffraction pattern of the solid electrolyte obtained in Comparative Example 2. [Figure 8] FIG. 8 is a diagram showing an X-ray diffraction pattern of the solid electrolyte obtained in Comparative Example 4. [Figure 9] FIG. 9 is a diagram showing the first charge-discharge characteristics of an all-solid-state battery using the solid electrolyte obtained in Example 1 for the positive electrode layer. [Figure 10] FIG. 10 is a diagram showing the first charge-discharge characteristics of an all-solid-state battery using the solid electrolyte obtained in Comparative Example 3 for the positive electrode layer.

MODE FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, the present invention will be described based on its preferred embodiments. The present invention relates to a solid electrolyte. The solid electrolyte of the present invention has ion conductivity, and preferably has lithium ion conductivity. The solid electrolyte of the present invention is a sulfide solid electrolyte containing S element as its constituent element, and specifically contains Li element, M element (M is at least one element selected from Si, Sb, Sn, and Ge), S element, and I element. The solid electrolyte of the present invention may contain other elements in addition to the elements described above as constituent elements. For example, some of the Li element may be replaced with other alkali metal elements, some of the S element may be replaced with other chalcogen elements, and some of the I element may be replaced with other halogen (Ha) elements.

[0010] As solid electrolytes, for example, sulfide solid electrolytes such as Li6PS5I, Li6PS5Br, and Li6PS5Cl, as described in Patent Document 1 mentioned above, are known. The solid electrolyte of the present invention uses element M instead of element P in these sulfide solid electrolytes. By using element M instead of element P, the solid electrolyte of the present invention exhibits higher ionic conductivity than the sulfide solid electrolytes known to date. It is preferable that the solid electrolyte of the present invention does not contain element P.

[0011] From the viewpoint of the solid electrolyte of the present invention exhibiting even higher lithium conductivity, it is preferable that the M element contains at least Sb. From a similar viewpoint, it is preferable that the solid electrolyte of the present invention contains at least Sb as the M element and also contains other M elements. Examples of M elements other than Sb include at least one of Si and Sn. In particular, it is preferable that the solid electrolyte of the present invention contains at least Si and Sb, or at least Sn and Sb, as the M element. The inclusion of Sn as the M element can improve the atmospheric stability of the solid electrolyte.

[0012] From the viewpoint of obtaining better ionic conductivity, the solid electrolyte of the present invention preferably has a ratio of the number of moles of Sb to the total number of moles of all M elements within a predetermined range. The ratio is preferably, for example, 25 mol% or more, preferably 45 mol% or more, more preferably 55 mol% or more, and even more preferably 65 mol% or more. On the other hand, the ratio is preferably, for example, 75 mol% or less, more preferably 73 mol% or less, and even more preferably 70 mol% or less.

[0013] The solid electrolyte of the present invention may contain elements other than element I, such as Ha. This makes it possible to enhance the ionic conductivity of the solid electrolyte of the present invention. Examples of Ha elements other than element I include chlorine (Cl) and bromine (Br), and the solid electrolyte of the present invention may contain at least one of these elements.

[0014] When the solid electrolyte of the present invention contains elements other than element I (Ha), the content (moles) of elements other than element I per mole of element I is preferably, for example, 1 or less, more preferably 0.6 or less, and even more preferably 0.4 or less. Furthermore, from the viewpoint of obtaining better ionic conductivity, the content (moles) of elements other than element I per mole of element I is preferably, for example, 0.05 or more, and even more preferably 0.2 or more.

[0015] The solid electrolyte of the present invention exhibits high ionic conductivity in its X-ray diffraction pattern, as measured by an X-ray diffractometer (XRD) using CuKα as a source. This pattern shows diffraction peak A in the range of 2θ = 24.0° to 24.8°, diffraction peak B in the range of 2θ = 28.2° to 29.0°, and diffraction peak C in the range of 2θ = 29.5° to 30.3°. When the peak intensities of diffraction peaks A, B, and C are denoted as Ia, Ib, and Ic, respectively, it is preferable from the viewpoint of further increasing the ionic conductivity of the solid electrolyte that Ia > Ib and Ia > Ic are satisfied. Ib and Ic may satisfy Ib ≥ Ic, Ib ≤ Ic, or Ib = Ic. In this specification, peak intensity refers to the peak height in the X-ray diffraction pattern.

[0016] In the solid electrolyte of the present invention, when the peak intensity of diffraction peak D located in the range of 2θ = 25.3° to 25.9° is denoted as Id, and the peak intensity of diffraction peak A described above is denoted as Ia, it is preferable from the viewpoint of further improving the ionic conductivity of the solid electrolyte that Id with respect to Ia satisfies the following formula (1). Id / Ia ≤ 0.05 (1)

[0017] The diffraction peak D mentioned above is attributed to lithium iodide (LiI). As stated above, the solid electrolyte of the present invention contains lithium and iodine as constituent elements. The fact that Id / Ia is less than or equal to the above value means that the amount of lithium iodide contained in the solid electrolyte is small. In other words, when lithium iodide is contained in the solid electrolyte of the present invention, it is preferable from the viewpoint of improving ionic conductivity to keep the amount as small as possible. From this viewpoint, it is even more preferable that Id / Ia ≤ 0.03 is satisfied, and even more preferable that Id / Ia ≤ 0.01 is satisfied. Most preferably, Id / Ia = 0 is satisfied, that is, no diffraction peak D is observed in the XRD diffraction pattern.

[0018] From the viewpoint of exhibiting high ionic conductivity, it is preferable that the solid electrolyte of the present invention be crystalline, and from this viewpoint, it is preferable that it contains a crystalline phase having an argyrodite-type crystal structure. In particular, it is preferable that it contains a crystalline phase having a cubic argyrodite-type crystal structure, as this further enhances ionic conductivity. Whether or not the solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure can be determined based on the X-ray diffraction pattern obtained by X-ray diffraction. The crystalline phase with an argyrodite-type crystal structure exhibits characteristic diffraction peaks at 2θ = 17.1°±1.0°, 24.4°±1.0°, 28.6°±1.0°, 29.9°±1.0°, and 42.8°±1.0°. Furthermore, depending on the element species constituting the solid electrolyte, characteristic diffraction peaks may be observed at 2θ = 45.6°±1.0°, 49.9°±1.0°, 56.3°±1.0°, 59.3°±1.0°, 65.0°±1.0°, and 67.8°±1.0°, in addition to the aforementioned diffraction peaks. For identifying diffraction peaks originating from the argyrodite crystal structure, the data in PDF number 01-077-5737 can be used.

[0019] Here, the statement that a solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure means that the solid electrolyte contains at least one crystalline phase having an argyrodite-type crystal structure. In the present invention, it is preferable that the solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure as the main phase. The "main phase" refers to the phase that accounts for the largest proportion of the total amount of all crystalline phases constituting the solid electrolyte. Therefore, the content of the crystalline phase having an argyrodite-type crystal structure in the solid electrolyte is preferably, for example, 60% by mass or more, and more preferably 70% by mass or more, 80% by mass or more, or 90% by mass or more, relative to all crystalline phases constituting the solid electrolyte. The proportion of the crystalline phase can be confirmed, for example, by XRD.

[0020] The solid electrolyte of the present invention may consist of a single phase composed of a crystalline phase having an argyrodite-type crystal structure, or it may be a mixed phase containing a crystalline phase having an argyrodite-type crystal structure and other crystalline phases. Examples of other crystalline phases include other solid electrolyte materials, Li2S, Li3PS4, Li4P2S6, etc., but are not limited to these. As mentioned above, it is preferable that the solid electrolyte of the present invention contains as little LiI crystalline phase as possible from the viewpoint of improving ionic conductivity, and even if such crystalline phase is included, it is preferable that it is within the range that satisfies formula (1) described above.

[0021] The solid electrolyte of the present invention has the compositional formula Li 6+x MS 5+y I Z Ha α It is preferable that the composition of the solid electrolyte be expressed as follows (where Ha represents at least one halogen element other than iodine), from the viewpoint of further improving ionic conductivity. By adjusting the composition of the solid electrolyte in this way, the formation of a LiI crystalline phase becomes less likely, and as a result, the ionic conductivity of the solid electrolyte is improved. In the above compositional formula, it is preferable that x, y, z, and α satisfy the following formulas (3) to (6). -1.0 ≤ x ≤ 1.5 (3) -0.5 ≤ y ≤ 0.5 (4) 0.5 ≤ z ≤ 1.1 (5) 0 ≤ α ≤ 0.5 (6)

[0022] From the viewpoint of further suppressing the formation of the LiI crystalline phase, it is preferable that x, y, z, and α satisfy the following equations (3') to (6'). -0.5 ≤ x ≤ 1.0 (3') -0.3 ≤ y ≤ 0.3 (4') 0.8 ≤ z ≤ 1.1 (5') 0.0 ≤ α ≤ 0.4 (6')

[0023] In the above compositional formula, when the element M is Si and Sb, the solid electrolyte of the present invention is composed of Li 6+x+x’ Si x’ S 1-x’ S 5+y I Z Ha α It is preferable that the composition of the solid electrolyte be expressed as follows (where Ha represents at least one halogen element other than iodine(I)): from the viewpoint of further improving ionic conductivity. By adjusting the composition of the solid electrolyte in this way, the formation of a LiI crystalline phase becomes less likely, and as a result, the ionic conductivity of the solid electrolyte is improved. In the above compositional formula, it is preferable that x, x', y, z, and α satisfy the following formulas (7) to (10). 0 ≤ x + x' ≤ 1.5 (7) -0.5 ≤ y ≤ 0.5 (8) 0.5 ≤ z ≤ 1.1 (9) 0 ≤ α ≤ 0.5 (10)

[0024] In the above compositional formula, z+a, which represents the total amount of element I and element Ha, is preferably 0.8 or more, more preferably 0.9 or more, and even more preferably 0.95 or more. On the other hand, z+a is preferably 1.6 or less, more preferably 1.4 or less, even more preferably 1.2 or less, even more preferably 1.1 or less, and even more preferably 1.05 or less.

[0025] From the viewpoint of further suppressing the formation of the LiI crystalline phase, it is preferable that x, x', y, z, and α satisfy the following equations (7') to (10'). 0.5 ≤ x + x' ≤ 1.0 (7') -0.3 ≤ y ≤ 0.3 (8') 0.8 ≤ z ≤ 1.1 (9') 0 ≤ α ≤ 0.4 (10')

[0026] In equations (7) and (7') above, it is preferable that x' be between 0.5 and 0.7, and more preferably between 0.6 and 0.7, from the viewpoint of improving the ionic conductivity of the solid electrolyte.

[0027] The solid electrolyte of the present invention is preferably in the form of powder particles, and its particle size is specified by the cumulative volume particle size D at 50% of the cumulative volume as measured by laser diffraction scattering particle size distribution analysis. 50 For example, the particle size D is preferably 0.1 μm or larger. 50 By having a value greater than or equal to the aforementioned value, it is possible to suppress an excessive increase in the surface area of ​​the solid electrolyte particles, thereby suppressing an increase in resistance. Furthermore, mixing with the active material becomes easier. On the other hand, particle size D 50 For example, the particle size D is preferably 150 μm or less, more preferably 50 μm or less, even more preferably 10 μm or less, even more preferably 7 μm or less, and even more preferably 5 μm or less. 50 When this value is less than or equal to the aforementioned value, solid electrolyte particles can easily penetrate the gaps between the active materials, increasing the number of contact points and the contact area. This allows for further improvement of ionic conductivity.

[0028] Next, a preferred method for producing the solid electrolyte of the present invention will be described. The solid electrolyte of the present invention can be obtained, for example, by using lithium sulfide (Li2S) powder, sulfide powder of element M or element M as raw materials, sulfur (S) powder, and lithium iodide (LiI) powder, mixing these powders, and calcining the mixed powder. The amount of each powder used is adjusted so that the desired solid electrolyte has the desired composition consisting of Li, M, S, and I elements. If the solid electrolyte of the present invention contains an element other than element I, such as Cl or Br, then, for example, lithium chloride powder or lithium bromide powder may be used further.

[0029] Among the aforementioned raw materials, there are compounds that are extremely unstable in the atmosphere and readily react with moisture to decompose, generating hydrogen sulfide gas or undergoing oxidation. Therefore, it is preferable to manufacture the solid electrolyte in a glove box purged with an inert gas atmosphere. This suppresses the formation of sulfur deficiencies in the resulting solid electrolyte and lowers its electronic conductivity.

[0030] For mixing the raw material powders, it is preferable to use a ball mill, bead mill, homogenizer, etc. Mechanical alloying can also be used for mixing the raw material powders. In this case, increasing the energy applied during mixing allows the raw material powders to be uniformly mixed at the atomic level, and a more uniform solid electrolyte can be obtained by calcining the resulting mixed powder. However, when the energy applied during mixing is increased, the media placed in the mixing container along with the raw material powders may wear down, potentially introducing impurities and negatively affecting the properties of the resulting solid electrolyte. From this perspective, it is preferable to avoid applying excessively high energy during mixing.

[0031] The mixed powder obtained by mixing the raw material powders is preferably dried as needed, then crushed and classified, and calcined in an inert gas atmosphere or under hydrogen sulfide (H2S) gas flow. Setting the calcination temperature to preferably 350°C or higher can suppress sulfur deficiency. Furthermore, setting the calcination temperature to 350°C or higher can suppress the retention of unreacted raw material powder, such as lithium iodide, in the solid electrolyte, thereby suppressing a decrease in ionic conductivity.

[0032] In particular, when hydrogen sulfide gas is used as the firing atmosphere, the sulfur gas produced by the decomposition of hydrogen sulfide during firing can increase the sulfur partial pressure of the atmosphere. As a result, even if the firing temperature is set high, sulfur deficiencies are less likely to occur in the resulting solid electrolyte, and the emergence of electronic conductivity can be suppressed. Therefore, when hydrogen sulfide gas is used as the firing atmosphere, the firing temperature is preferably, for example, 350°C to 650°C, more preferably 450°C to 600°C, and even more preferably 450°C to 500°C.

[0033] On the other hand, when firing under an inert gas atmosphere, setting a high firing temperature may easily lead to the formation of sulfur deficiencies in the resulting solid electrolyte. From this viewpoint, the firing temperature when firing under an inert gas atmosphere is preferably, for example, 350°C to 550°C, more preferably 350°C to 500°C, and even more preferably 400°C to 450°C.

[0034] Normally, it is preferable to use hydrogen sulfide gas as the firing atmosphere and fire at 450°C or higher in order to completely react the raw material powder and eliminate any unreacted phases, especially the unreacted lithium iodide phase. However, when using raw material powders with small particle sizes and consequently high reactivity, the reaction can be promoted even at low temperatures, so firing may be carried out in an inert gas atmosphere.

[0035] Regardless of the firing atmosphere, the firing time is preferably set to 1 to 10 hours, more preferably to 2 to 8 hours, and even more preferably to 3 to 6 hours. The heating rate during firing is preferably 250°C / h or less, from the viewpoint of eliminating unreacted phases, particularly unreacted lithium iodide phases, caused by uneven heating. Taking into account the viewpoint of maintaining firing efficiency, it is preferable to have a rate of 50°C / h to 200°C / h, and particularly 80°C / h to 150°C / h.

[0036] The solid electrolyte obtained in this way has lithium ion conductivity in the solid state. The lithium ion conductivity of the solid electrolyte is preferably 1.0 mS / cm or higher, more preferably 1.5 mS / cm or higher, and even more preferably 2.0 mS / cm or higher, at room temperature, i.e., 25°C. The lithium ion conductivity can be measured using the method described in the examples below.

[0037] The 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 solid electrolyte of the present invention can be used in a battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer. In other words, the solid electrolyte of the present invention can be used in so-called solid batteries. More specifically, it can be used in lithium solid batteries. The lithium solid battery may be a primary battery or a secondary battery. There are no particular restrictions on the shape of the battery, and shapes such as laminated, cylindrical, and prismatic can be adopted. The term "solid battery" includes not only solid batteries that do not contain any liquid or gel-like substances as an electrolyte, but also embodiments that contain, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of a liquid or gel-like substance as an electrolyte.

[0038] When the solid electrolyte layer contains the solid electrolyte of the present invention, the solid electrolyte layer can be manufactured by, for example, dropping a slurry consisting of a sulfide solid electrolyte, a binder, and a solvent onto a substrate and scraping it off with a doctor blade, cutting it with an air knife after bringing the substrate and slurry into contact, forming a coating film by screen printing, and then removing the solvent by heating and drying. Alternatively, the powdered sulfide solid electrolyte can be compacted into a powder by pressing or the like, and then processed as appropriate. The thickness of the solid electrolyte layer is typically preferably between 5 μm and 300 μm, and more preferably between 10 μm and 100 μm, considering the balance between preventing short circuits and maintaining volumetric capacity density.

[0039] The solid electrolyte of the present invention may be used together with the active material to constitute the electrode mixture. The proportion of the solid electrolyte in the electrode mixture is typically 10% by mass or more and 50% by mass or less. The electrode mixture may contain other materials such as conductive additives and binders as needed. A positive electrode layer and a negative electrode layer can be produced by mixing the electrode mixture with a solvent to make a paste, applying it to a current collector such as aluminum foil, and drying it.

[0040] As the positive electrode material constituting the positive electrode layer, any positive electrode material used as the positive electrode active material in lithium-ion batteries can be used as appropriate. For example, lithium-containing positive electrode active materials, specifically spinel-type lithium transition metal oxides and lithium metal oxides with a layered structure, can be used. By using a high-voltage positive electrode material, the energy density can be improved. In addition to the positive electrode active material, the positive electrode material may also contain a conductive material or other materials.

[0041] As the negative electrode material constituting the negative electrode layer, any negative electrode material used as the negative electrode active material in lithium-ion batteries can be used as appropriate. Since the sulfide solid electrolyte of the present invention is electrochemically stable, it can withstand lithium metal or a low potential comparable to lithium metal (approximately 0.1V vs. Li + Carbon-based materials such as graphite, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon), which are charged and discharged using lithium (Li), can be used as negative electrode materials. This can significantly improve the energy density of solid-state batteries. Furthermore, silicon or tin, which are promising as high-capacity materials, can also be used as active materials. In batteries using conventional electrolytes, the electrolyte and active material react during charging and discharging, causing corrosion on the surface of the active material and resulting in significant deterioration of battery characteristics. In contrast to this, by using the solid electrolyte of the present invention instead of an electrolyte and using silicon or tin as the negative electrode active material, the above-mentioned corrosion reaction does not occur, thus improving the durability of the battery. The negative electrode material may also contain conductive materials in addition to the negative electrode active material, or other materials may be included. [Examples]

[0042] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0043] [Example 1] Lithium sulfide (Li2S) powder, antimony sulfide (Sb2S3) powder, Si powder, S powder, and LiI powder were weighed to a total weight of 2.0 g each, as shown in Table 1 below. These were then ground and mixed in a planetary ball mill for 20 hours to prepare a mixed powder. This mixed powder was filled into a carbon container and placed in a tubular electric furnace. While circulating hydrogen sulfide gas (100% purity) at a rate of 1.0 L / min, the furnace was heated at a heating rate of 100°C / h and calcined at 475°C for 4 hours. The resulting calcined material was crushed in a mortar and sieved through a 53 μm mesh sieve to obtain a solid electrolyte. In the above procedure, the weighing and mixing of the powders, the placement of the mixed powders into the electric furnace, and the removal of the solid electrolyte from the electric furnace, crushing, and sizing were all carried out in a glove box purged with thoroughly dried argon gas (dew point below -60°C).

[0044] [Examples 2 and 3] Each powder was weighed to obtain the composition shown in Table 1 below. Otherwise, a solid electrolyte was obtained in the same manner as in Example 1.

[0045] [Example 4] Lithium sulfide (Li2S) powder, antimony sulfide (Sb2S3) powder, Si powder, S powder, LiI powder, and lithium bromide (LiBr) powder were weighed to obtain the composition shown in Table 1 below. The firing temperature was also as shown in the same table. A solid electrolyte was obtained in the same manner as in Example 1, except for these factors.

[0046] [Examples 5 and 6] Each powder was weighed to obtain the composition shown in Table 1 below. The calcination temperature was also as shown in the same table. A solid electrolyte was obtained in the same manner as in Example 1, except for these factors.

[0047] [Comparative Example 1] Each powder was weighed to obtain the composition shown in Table 2 below. The calcination temperature was also as shown in Table 2. A solid electrolyte was obtained in the same manner as in Example 1, except for these factors.

[0048] [Comparative Example 2] Each powder was weighed to obtain the composition shown in Table 2 below. Otherwise, a solid electrolyte was obtained in the same manner as in Example 1.

[0049] [Comparative Example 3] Lithium sulfide (Li2S) powder, antimony sulfide (Sb2S3) powder, Si powder, S powder, LiI powder, and lithium chloride (LiCl) powder were weighed to obtain the composition shown in Table 2 below. The firing temperature was also as shown in the same table. A solid electrolyte was obtained in the same manner as in Example 1, except for these factors.

[0050] [Comparative Example 4] Each powder was weighed to obtain the composition shown in Table 2 below. The calcination temperature was also as shown in the same table. A solid electrolyte was obtained in the same manner as in Example 1, except for these factors.

[0051] [Rating 1] XRD measurements were performed on the solid electrolytes obtained in the examples and comparative examples. The X-ray diffraction patterns of Examples 1 to 6 and Comparative Examples 2 and 4 are shown in Figures 1 to 8. In addition, the Id / Ia values ​​were calculated based on the XRD measurement results. The results are shown in Tables 1 and 2. XRD measurements were performed using the "Smart Lab" X-ray diffractometer manufactured by Rigaku Corporation. The measurement conditions were: no exposure to air, scanning axis: 2θ / θ, scanning range: 10° to 80°, step size: 0.01°, and scanning speed: 1° / min. The X-ray source used was a CuKα1-ray source utilizing a Johansson crystal. A one-dimensional detector was used for detection. Measurements were performed so that the intensity at 21.3 ± 1.0° was between 100 and 700 counts. Additionally, measurements were performed so that the maximum peak intensity between 10° and 140° was above 1000 counts.

[0052] [Rating 2] The lithium-ion conductivity of the solid electrolytes obtained in the examples and comparative examples was measured using the following method. The results are shown in Tables 1 and 2. Each solid electrolyte was subjected to a flow rate of approximately 6 t / cm³ in a glove box purged with thoroughly dried argon gas (dew point below -60°C). 2 Lithium ion conductivity samples were prepared by uniaxial compression molding under a load, consisting of pellets with a diameter of 10 mm and a thickness of approximately 1 mm to 8 mm. Lithium ion conductivity was measured using Solartron Analytical's Solartron 1255B electrochemical measurement system (1280C) and impedance / gain phase analyzer (SI 1260). The measurement conditions were AC impedance method with a temperature of 25°C, a frequency of 100 Hz to 1 MHz, and an amplitude of 100 mV.

[0053] [Rating 3] The positive electrode mixture and negative electrode mixture prepared by the following method, along with the solid electrolyte powder obtained in Example 1 and Comparative Example 3, were used to produce solid batteries, and their battery characteristics (initial charge / discharge capacity) were evaluated using the following method. The results are shown in Table 3 and Figures 9 and 10. (material) LiNi is a layered compound in which Nb oxide is coated on the particle surface as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 O2 (NCM) powder (D 50 A 4.2 μm (D) particle was used as the negative electrode active material. 50 The solid electrolyte used was D (=20μm). 50 Powder with a particle size of approximately 3 μm was used. (Preparation of positive electrode mixture) The positive electrode mixture powder for the positive electrode layer was prepared by mixing positive electrode active material powder, solid electrolyte powder, and carbon nanotubes (Showa Denko Co., Ltd., VGCF®-H) as a conductive material in a mass ratio of 60:37:3 using a mortar and pestle. (Preparation of negative electrode mixture) The negative electrode mixture powder for the negative electrode layer was prepared by mixing the negative electrode active material powder and the solid electrolyte powder in a mortar and pestle in a mass ratio of 50:50.

[0054] (Fabrication of solid-state batteries) A solid electrolyte layer was formed by closing the lower opening of a polypropylene cylindrical container (opening diameter 10.5 mm, height 18 mm) with open top and bottom using a negative electrode (made of stainless steel), placing solid electrolyte powder on top, closing it with a positive electrode (made of stainless steel), and then uniaxially pressing it at 100 MPa. Next, the positive electrode was removed, positive electrode mixture powder was placed on top of the solid electrolyte layer, and the opening was closed again with the positive electrode. The cylindrical container was inverted, the negative electrode was removed, negative electrode mixture powder was placed on top of the solid electrolyte layer, and the opening was closed with the negative electrode. A solid battery cell was fabricated by uniaxially pressing the space between the positive and negative electrodes at 500 MPa, resulting in a stacked positive electrode layer, solid electrolyte layer, and negative electrode layer. The solid battery cell was fabricated in a glove box purged with sufficiently dry argon gas (dew point below -60°C).

[0055] (Battery characteristics evaluation (initial charge / discharge capacity)) Solid-state battery cells were placed in an environmental testing chamber maintained at 25°C, and their characteristics were evaluated by connecting them to a charge / discharge measurement device. The batteries were charged and discharged using a current of 1.5mA (battery capacity: 1.5mAh). The initial charge capacity was obtained by charging to 4.4V at 0.1C using the CC-CV method. Discharge was performed to 3.0V at 0.1C using the CC method to obtain the initial discharge capacity. The initial charge / discharge efficiency (%) was calculated by dividing the initial discharge capacity by the initial charge capacity and multiplying by 100.

[0056] [Table 1]

[0057] [Table 2]

[0058] [Table 3]

[0059] As is clear from the results shown in Tables 1 and 2, no or only slight diffraction peaks originating from LiI were observed in the solid electrolytes obtained in each example. Furthermore, the solid electrolytes obtained in each example had higher lithium ion conductivity than the solid electrolyte obtained in the comparative example.

[0060] As is clear from the results shown in Table 3, the solid-state battery using the solid electrolyte obtained in Example 1 exhibits better battery characteristics, with higher initial discharge capacity and charge / discharge efficiency than the solid-state battery using the solid electrolyte obtained in Comparative Example 3. This is thought to be due to the higher lithium-ion conductivity of the solid electrolyte obtained in Example 1 compared to the solid electrolyte obtained in Comparative Example 3. [Industrial applicability]

[0061] According to the present invention, a solid electrolyte with high ionic conductivity is provided.

Claims

1. It contains lithium (Li), M (where M is at least one of silicon (Si), antimony (Sb), tin (Sn), and germanium (Ge)), sulfur (S), iodine (I), and halogen (Ha) elements other than iodine (I). In the X-ray diffraction pattern measured by an X-ray diffractometer (XRD) using CuKα as a source, diffraction peak A is present in the range of 2θ = 24.0° to 24.8°, diffraction peak B is present in the range of 2θ = 28.2° to 29.0°, and diffraction peak C is present in the range of 2θ = 29.5° to 30.3°. A solid electrolyte in which, when the peak intensity of diffraction peak A is Ia, and the peak intensity of diffraction peak D located in the range of 2θ = 25.3° to 25.9° is Id, the relationship between Ia and Id satisfies the following equation (1). Id / Ia≦0.05 (1)

2. It contains lithium (Li), M (where M is at least one of silicon (Si), antimony (Sb), tin (Sn), and germanium (Ge)), sulfur (S), and iodine (I), In the X-ray diffraction pattern measured by an X-ray diffractometer (XRD) using CuKα as a source, diffraction peak A is present in the range of 2θ = 24.0° to 24.8°, diffraction peak B is present in the range of 2θ = 28.2° to 29.0°, and diffraction peak C is present in the range of 2θ = 29.5° to 30.3°. When the peak intensity of diffraction peak A is denoted as Ia, and the peak intensity of diffraction peak D located in the range of 2θ = 25.3° to 25.9° is denoted as Id, the solid electrolyte satisfies the following equation (1) for Ia, Id / Ia≦0.05 (1) The solid electrolyte has the compositional formula Li ６＋ｘ MS ５＋ｙ I Ｚ Ha α A solid electrolyte represented as (Ha represents at least one halogen element other than iodine (I)), where x, y, z, and α satisfy the following conditions (3) to (6). -1.0 ≤ x ≤ 1.5 (3) -0.5 ≤ y ≤ 0.5 (4) 0.5 ≤ z ≤ 1.1 (5) ０≦α≦０．５ （６）

3. It contains lithium (Li), M (where M is at least one of silicon (Si), antimony (Sb), tin (Sn), and germanium (Ge)), sulfur (S), and iodine (I), In the X-ray diffraction pattern measured by an X-ray diffractometer (XRD) using CuKα as a source, diffraction peak A is present in the range of 2θ = 24.0° to 24.8°, diffraction peak B is present in the range of 2θ = 28.2° to 29.0°, and diffraction peak C is present in the range of 2θ = 29.5° to 30.3°. When the peak intensity of diffraction peak A is denoted as Ia, and the peak intensity of diffraction peak D located in the range of 2θ = 25.3° to 25.9° is denoted as Id, the solid electrolyte satisfies the following equation (1) for Ia, Id / Ia≦0.05 (1) where the solid electrolyte has a composition formula Li ６＋ｘ＋ｘ’ Si ｘ’ Sb １－ｘ’ S ５＋ｙ I Ｚ Ha α (where Ha represents at least one halogen element other than the iodine (I) element), and x, x', y, z, and α satisfy the following formulas (7) to (10), the solid electrolyte.) 0≦x+x'≦1.5 (7) -0.5 ≤ y ≤ 0.5 (8) 0.5 ≤ z ≤ 1.1 (9) ０≦α≦０．５ （１０）

4. The solid electrolyte according to claim 2 or 3, further containing a halogen (Ha) element other than iodine (I).

5. The solid electrolyte according to claim 1 or 4, wherein the content (moles) of halogen (Ha) elements other than iodine is 1 or less relative to the content (moles) of iodine (I).

6. The solid electrolyte according to any one of claims 1 to 5, wherein the M element comprises Si and Sb.

7. The solid electrolyte according to claim 1, 2, 4, or 5, wherein the M element comprises Sn and Sb.

8. The solid electrolyte according to claim 3, wherein x' is 0.5 or more and 0.7 or less.

9. An electrode mixture comprising a solid electrolyte and an active material according to any one of claims 1 to 8.

10. A solid electrolyte layer containing the solid electrolyte described in any one of claims 1 to 8.

11. A battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the battery contains the solid electrolyte described in any one of claims 1 to 8.

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