Solid electrolyte and method for manufacturing the same

Abstract

The solid electrolyte contains lithium (Li) element, phosphorus (P) element, sulfur (S) element, and element X (X represents at least one halogen element). When peak separation is performed on the diffraction pattern in at least any one of the ranges of 2θ = 25.6 ± 0.8°, 30.2 ± 0.8°, and 31.6 ± 0.8° in the X-ray diffraction pattern measured by an X-ray diffraction apparatus (XRD) using CuKα1 ray and CuKα2 ray, peaks P1 and P2 are present. Peaks P1 and P2 respectively originate from different phases.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte and a method for manufacturing the same. Background Art

[0002] In recent years, solid electrolytes have received attention as alternatives to electrolytes used in many liquid batteries. A solid-state battery using a solid electrolyte is expected to be put into practical use as a battery having higher safety and higher energy density than a liquid battery using a flammable organic solvent.

[0003] As the prior art related to solid electrolytes, for example, the solid electrolyte described in Patent Document 1 is known. Regarding such a solid electrolyte, in recent years, research for obtaining more excellent performance has been prevalent. For example, various studies have been conducted on solid electrolytes having high ionic conductivity.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: US2016 / 156064A1

[0007] Patent Document 2: EP3026749A1 Summary of the Invention

[0008] An object of the present invention is to provide a solid electrolyte having more excellent ionic conductivity.

[0009] The present invention provides a solid electrolyte containing a lithium (Li) element, a phosphorus (P) element, a sulfur (S) element, and an X element (X represents at least one halogen element),

[0010] When peak separation is performed on a diffraction pattern in at least any one of the ranges of 2θ = 25.6 ± 0.8°, 30.2 ± 0.8°, and 31.6 ± 0.8° in an X-ray diffraction pattern (XRD) measured by an X-ray diffraction apparatus using CuKα1 radiation and CuKα2 radiation, it has a peak P1 and a peak P2,

[0011] The peak P1 and the peak P2 respectively originate from different phases.

[0012] In addition, the present invention provides a method for manufacturing a solid electrolyte, which includes the following steps:

[0013] A step of obtaining a raw material composition by mixing a lithium (Li) element source, a phosphorus (P) element source, a sulfur (S) element source, and a halogen (X) element source; and

[0014] A step of calcining the raw material composition at a temperature higher than 500°C and lower than 700°C. Brief Description of the Drawings

[0015] Figure 1 In Figure 1 Figure (a) shows an example of an X-ray diffraction pattern measured by an X-ray diffractometer for an existing solid electrolyte composed of a single phase; Figure 1 Figure (b) is a figure obtained by separating the X-ray diffraction pattern shown in Figure 1 Figure (a) into two peaks.

[0016] Figure 2 In Figure 2 Figure (a) shows an example of an X-ray diffraction pattern measured by an X-ray diffractometer for the solid electrolyte of the present invention; Figure 2 Figure (b) is a figure obtained by separating the X-ray diffraction pattern shown in Figure 2 Figure (a) into two peaks.

[0017] Figure 3 is a figure showing the X-ray diffraction patterns of the solid electrolytes obtained in Example 2 and Comparative Example 2.

[0018] Figure 4 is a figure showing the X-ray diffraction patterns of the solid electrolytes obtained in Example 3 and Comparative Example 3. DETAILED DESCRIPTION

[0019] The present invention will be described below based on preferred embodiments. The solid electrolyte of the present invention is a solid electrolyte containing at least lithium (Li), phosphorus (P), sulfur (S), and halogen (X) elements.

[0020] The X element contained in the solid electrolyte of the present invention is at least one halogen element. More specifically, at least one element selected from chlorine (Cl), bromine (Br), and iodine (I) elements can be used. The X element can be one of these elements, or a combination of two or more.

[0021] From the viewpoint of improving the lithium ion conductivity of the solid electrolyte of the present invention, the solid electrolyte preferably contains at least Cl element as the X element. In particular, when only Cl element is contained as the X element, it is preferable because it is easy to obtain a solid electrolyte containing two or more different phases described below.

[0022] One of the characteristics of the solid electrolyte of the present invention is that it contains two or more different phases. The two or more different phases are all crystalline phases. As a result of the research by the present inventors, the solid electrolyte of the present invention exhibits more excellent ionic conductivity than before because it contains two or more different phases. The reason is not yet fully understood, but the present inventors believe that the following reasons may be involved. Of course, the scope of the present invention is not limited by this theory. It is considered that the two or more different phases are all crystalline phases and exist in one grain. Although the multiple crystal phases existing in one grain all contain Li element, P element, S element and X element, their compositions are different from each other. And it is speculated that the reason may be that since at least one of the multiple crystal phases existing in one grain becomes a high ionic conductivity phase, the ionic conductivity of the solid electrolyte as a whole is improved. Or it is speculated that the reason may be that since the interfacial resistance between the multiple crystal phases existing in one grain is small, the ionic conductivity of the solid electrolyte as a whole is improved.

[0023] It is possible to confirm that the solid electrolyte of the present invention contains two or more different phases based on the X-ray diffraction pattern measured by an X-ray diffractometer (XRD). Specifically, based on the X-ray diffraction pattern using X-rays with two different wavelengths as the XRD ray source, it is possible to confirm the inclusion of two or more different phases. It is convenient to use CuKα1 ray and CuKα2 ray as the X-ray sources with two different wavelengths. The wavelength of CuKα1 ray is 0.1540562 nm, and the wavelength of CuKα2 is 0.1544390 nm. The intensity ratio of CuKα1 ray to CuKα2 ray is theoretically about 2:1. Therefore, when the solid electrolyte to be measured by XRD is composed of a single phase, when the solid electrolyte is irradiated with CuKα1 ray and CuKα2 ray simultaneously, the obtained X-ray diffraction pattern is as Figure 1 shown in (a) of, and the diffraction lines from the CuKα1 ray and the diffraction lines from the CuKα2 ray are superimposed with an intensity ratio of 2:1.

[0024] If the superimposed diffraction pattern as shown in Figure 1 (a) of is subjected to peak separation mathematically by the least squares method, it will be separated into peaks P1 and P2 having peaks at the same positions as shown in Figure 1 (b) of. In the present invention, a peak refers to a peak formed by superimposing the diffraction lines from the CuKα1 ray and the diffraction lines from the CuKα2 ray with an intensity ratio of 2:1.

[0025] It should be noted that as described in the examples below, the diffraction intensity data actually obtained by XRD are discrete (for example Figure 2(The step size of the horizontal axis 2θ shown in (b) is 0.02°). Therefore, strictly speaking, the positions of the peaks of the two peaks P1 and P2 separated mathematically by the above least squares method are not the same, and sometimes there are some deviations in the positions of the peaks. That is, theoretically, the peak positions of the separated peaks are the same, but sometimes there are some differences in the peak positions of the peaks separated mathematically. For this reason, in this specification, when the absolute value of the difference in the peak positions of the two separated peaks P1 and P2 (denoted as Δ2θ) is 0.04° or less, the peak positions of the two peaks are regarded as the same.)

[0026] On the other hand, when the solid electrolyte of the present invention is irradiated with CuKα1 rays and CuKα2 rays at the same time, the following situation occurs. It should be noted that, for the sake of convenience of explanation, in the following description, the case where the solid electrolyte of the present invention contains two different crystal phases is taken as an example.)

[0027] When the two different crystal phases are the A1 phase and the A2 phase, when the solid electrolyte of the present invention containing the A1 phase and the A2 phase is irradiated with CuKα1 rays and CuKα2 rays at the same time, as shown in Figure 2 (a) of, for the A1 phase, diffracted rays P 11 derived from the CuKα1 rays and diffracted rays P 12 derived from the CuKα2 rays are observed at an intensity ratio of 2:1; and for the A2 phase, diffracted rays P 21 derived from the CuKα1 rays and diffracted rays P 22 derived from the CuKα2 rays are observed at an intensity ratio of 2:1. That is, four diffracted rays P 11 , P 12 , P 21 and P 22 superimposed diffraction pattern are observed.)

[0028] When the diffraction pattern in which the diffracted rays shown in Figure 2 (a) are superimposed is separated into two peaks from a mathematical peak by the least squares method, as shown in Figure 2 (b) of, it is separated into two peaks P1 and P2 having peaks at different positions. In this specification, peak P1 is the result of the superposition of diffracted rays P 11 and P 12 , and peak P2 is the result of the superposition of diffracted rays P 21 and P 22 . It should be noted that when there are two peaks as in P1 in Figure 2 (b), the peak with the highest intensity is taken as the peak.)

[0029] As described above, when an arbitrary diffraction pattern obtained by irradiating a solid electrolyte with both CuKα1 radiation and CuKα2 radiation is separated into two peaks, if the peak top positions of the two separated peaks are different, it can be determined that the solid electrolyte contains two or more different crystal phases.

[0030] From the perspective of further improving the ionic conductivity of the solid electrolyte, preferably, in the X-ray diffraction pattern measured by XRD using CuKα1 radiation and CuKα2 radiation, when the diffraction pattern in at least any one of the ranges of 2θ = 25.6 ± 0.8° (hereinafter this range will also be referred to as the "first range"), 30.2 ± 0.8° (hereinafter this range will also be referred to as the "second range"), and 31.6 ± 0.8° (hereinafter this range will also be referred to as the "third range") is subjected to peak separation, there are peak P1 and peak P2, and peak P1 and peak P2 respectively originate from different phases. In particular, from the perspective of further improving the ionic conductivity of the solid electrolyte, preferably, when the diffraction pattern in at least two angular ranges from the first range to the third range is subjected to peak separation, there are peak P1 and peak P2 respectively originating from different phases; more preferably, when the diffraction pattern in all of the first range to the third range is subjected to peak separation, there are peak P1 and peak P2 respectively originating from different phases.

[0031] It should be noted that the solid electrolyte of the present invention may sometimes observe a diffraction pattern at an angle other than the above first range to third range. When comparing by intensity, the diffraction patterns observed in the first range to third range are very strong, so the diffraction patterns observed in these ranges are used as the object for peak separation.

[0032] As described above, the solid electrolyte of the present invention is a substance containing two or more different phases. These phases have different lattice constants due to different compositions. As a result, as described above, when the operation of separating the diffraction pattern of XRD into multiple peaks is performed, multiple peaks with different peak top positions can be obtained. When two or more peaks originating from different phases are sequentially set as P1 and P2 in ascending order of angle, when the angular difference Δ2θ (= 2θ2 - 2θ1) between the angle 2θ1 at the peak top position of P1 and the angle 2θ2 at the peak top position of P2 is 0.04° or more, the ionic conductivity of the solid electrolyte is further improved, and thus it is preferred. From the perspective of making this advantage more significant, the angular difference Δ2θ is more preferably 0.10° or more, and even more preferably 0.11° or more. On the other hand, the upper limit value of the angular difference Δ2θ is preferably 1.6° or less.

[0033] When separating the diffraction patterns of the first to third ranges into two peaks P1 and P2, sometimes the intensity of peak P1 is higher than that of peak P2, and sometimes vice versa. From the perspective of further improving the lithium-ion conductivity of the solid electrolyte, the ratio I1 / I2 of the intensity I1 of peak P1 to the intensity I2 of peak P2 is preferably 0.8 or less, more preferably 0.4 or less. The intensities I1 and I2 of peaks P1 and P2 mentioned in this specification are parameters obtained by the least squares method during peak separation of the diffraction pattern. It should be noted that in the case of multiple peaks, it is preferred that the intensity of the highest peak among the multiple peaks satisfies the aforementioned conditions.

[0034] On the other hand, when performing XRD measurement on a mixture of a solid electrolyte composed of a first phase with a single composition and a solid electrolyte composed of a second phase with a single composition, if the diffraction pattern obtained by the measurement is subjected to peak separation processing, multiple peaks with different peak top positions can be obtained. However, this mixture does not become a substance with high lithium-ion conductivity. The reason is that when using a mixture, it is impossible to reduce the interfacial resistance between the two phases. That is, the solid electrolyte of the present invention is a solid electrolyte composed of a single substance (in other words, not a mixture) and having two or more different crystal phases. It should be noted that this does not prevent the solid electrolyte of the present invention from being used in combination with other solid electrolytes at all.

[0035] As described above, the solid electrolyte of the present invention is a solid electrolyte containing Li element, P element, S element, and X element. As an example of this solid electrolyte, but not limited to, Li2S-P2S5-LiX (X is at least one halogen element) etc. can be cited.

[0036] From the perspective of improving the lithium-ion conductivity of the solid electrolyte, the solid electrolyte containing the above elements particularly preferably contains a compound represented by the composition formula Li a PS b X c (X is at least one halogen element. a represents a number of 3.0 or more and 6.0 or less. b represents a number of 3.5 or more and 4.8 or less. c represents a number of 0.1 or more and 3.0 or less.)

[0037] In the aforementioned composition formula, a representing the molar ratio of the Li element is preferably a number of 3.0 or more and 6.0 or less, more preferably 3.2 or more and 5.8 or less, and further preferably 3.4 or more and 5.4 or less. It should be noted that a can also be less than 5.4.

[0038] In the aforementioned composition formula, b representing the molar ratio of the S element is preferably a number of 3.5 or more and 4.8 or less, more preferably 3.8 or more and 4.6 or less, and further preferably 4.0 or more and 4.4 or less. It should be noted that b can also be less than 4.4.

[0039] In the above compositional formula, c is preferably a number of 0.1 or more and 3.0 or less, more preferably a number of 0.2 or more and 2.5 or less, and still more preferably a number of 0.4 or more and 2.0 or less. The lithium ion conductivity of the compound within this range is sufficiently high.

[0040] In the solid electrolyte of the present invention, from the perspective of further improving the lithium ion conductivity, the molar ratio of element X to element P, i.e., the value of X / P, is particularly preferably greater than 1.0. From this perspective, the value of X / P is preferably 1.2 or more, and more preferably 1.6 or more. From the perspective of preferably stably maintaining the argyrodite structure, X / P is preferably 2.0 or less.

[0041] In the present invention, the compound obtained in such a manner that the feed amount becomes Li a PS b X c may contain elements other than Li element, P element, S element, and X element. For example, there is a possibility that a part of the Li element can be replaced with other alkali metal elements, a part of the P element can be replaced with other nitrogen group elements, and a part of the S element can be replaced with other chalcogen elements.

[0042] From the perspective of being able to improve the lithium ion conductivity of the solid electrolyte, the solid electrolyte of the present invention particularly preferably contains a crystal phase having an argyrodite-type crystal structure. The argyrodite-type crystal structure refers to the crystal structure possessed by a group of compounds derived from minerals represented by the chemical formula Ag8GeS6. Whether the solid electrolyte of the present invention has a crystal phase of the argyrodite-type crystal structure can be confirmed by measurement based on XRD or the like. For example, in the diffraction pattern measured by XRD using CuKα1 radiation, the crystal phase of the argyrodite-type crystal structure shows characteristic diffraction peaks at 2θ = 15.3° ± 1.0°, 17.7° ± 1.0°, 25.6° ± 1.0°, 30.2° ± 1.0°, 31.6° ± 1.0°, and 44.7° ± 1.0°. In addition, depending on the types of elements constituting the solid electrolyte, sometimes based on the aforementioned diffraction peaks, characteristic diffraction peaks are also shown at 2θ = 47.2° ± 1.0°, 51.7° ± 1.0°, 58.3° ± 1.0°, 60.7° ± 1.0°, 61.5° ± 1.0°, 70.4° ± 1.0°, and 72.6° ± 1.0°. The diffraction peaks derived from the argyrodite-type crystal structure can be identified using, for example, the data with PDF number 00-034-0688.

[0043] The solid electrolyte of the present invention is a substance having lithium ion conductivity in a solid state. The lithium ion conductivity of the solid electrolyte of the present invention is preferably 0.5 mS / cm or more, more preferably 1.0 mS / cm or more, still more preferably 1.5 mS / cm or more, and particularly preferably 4.0 mS / cm or more at room temperature, i.e., 25°C. The lithium ion conductivity can be measured by the method described in the examples below.

[0044] The solid electrolyte of the present invention can be suitably manufactured by the method described below. As raw materials, compounds of a Li element source, a P element source, an S element source, and an X element source are used. As the Li element source compound, for example, lithium sulfide (Li2S) can be used. As the P element source compound, for example, diphosphorus pentasulfide (P2S5) can be used. As the S element source compound, when the Li element source compound and / or the P element source compound is a sulfide, this sulfide can be used as the S element source compound. As the X element source compound, compound B (LiX) can be used. These raw materials are mixed so that the Li element, P element, S element, and X element are in a specified molar ratio. Then, the mixed raw material composition is calcined in an inert gas atmosphere or in an atmosphere containing hydrogen sulfide gas.

[0045] Especially when the temperature range described below is adopted as the calcination temperature, by using an inert gas atmosphere, such as a nitrogen atmosphere or an argon atmosphere, as the calcination atmosphere, a solid electrolyte in which multiple crystal phases exist in one crystal grain can be obtained smoothly.

[0046] Especially in this manufacturing method, by adjusting the above-mentioned calcination conditions, a solid electrolyte in which multiple crystal phases exist in one crystal grain can be obtained. Specifically, the research results of the present inventors show that as the calcination temperature, by calcining at a temperature higher than the temperature adopted in the past, for example, the temperature adopted in Patent Document 1, multiple crystal phases can be generated. From this perspective, the calcination temperature is preferably set to exceed 500°C. On the other hand, when the calcination temperature is too high, heterogeneous phases that hinder lithium ion conductivity may be generated. Therefore, the calcination temperature is preferably set to be less than 700°C. From the above perspectives, the calcination temperature is more preferably set to be 540°C or more and 660°C or less, and still more preferably set to be 580°C or more and 620°C or less.

[0047] Regarding the calcination time, on the condition that the calcination temperature is within the above range, it is preferably set to be 1 hour or more and 7 hours or less, more preferably 2 hours or more and 6 hours or less, and still more preferably 3 hours or more and 5 hours or less.

[0048] The calcined product thus obtained is provided to a prescribed pulverization step. When pulverizing the calcined product, either dry pulverization or wet pulverization, or a combination of both, can be performed.

[0049] For dry pulverization, for example, a jet mill, a ball mill, a rod mill, a vibration ball mill, a planetary mill, a disk mill, etc. can be used. On the other hand, for wet pulverization, various media mills can be used. As the media mill, a ball mill, a bead mill, a paint agitator, a homogenizer, etc. can be used.

[0050] When performing wet pulverization, after wet pulverization, the powder of the solid electrolyte is separated from the solvent. To separate the two, it is preferable to perform solid-liquid separation treatment such as natural filtration, centrifugation, pressure filtration, vacuum filtration, etc. on the slurry containing the powder of the solid electrolyte and the organic solvent. Or heat air drying or vacuum drying can also be performed without performing the above operations.

[0051] The solid electrolyte obtained by the above method can be used as a material for 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. That is, the solid electrolyte can be used in a so-called solid-state battery. More specifically, it can be used in a lithium solid-state battery. The lithium solid-state battery can be a primary battery or a secondary battery. The shape of the battery is not particularly limited, and shapes such as a laminate type, a cylindrical type, and a square type can be adopted. The "solid-state battery" includes not only a solid-state battery that completely does not contain a liquid substance or a gel-like substance as an electrolyte, but also a form that contains, for example, 50% by mass or less, 30% by mass or less, 10% by mass or less of a liquid substance or a gel-like substance as an electrolyte.

[0052] When the solid electrolyte layer contains the solid electrolyte of the present invention, the solid electrolyte layer can be manufactured by, for example, the following methods: a method of dropping a slurry composed of a solid electrolyte, a binder, and a solvent onto a substrate and leveling it with a doctor blade or the like; a method of making the substrate contact the slurry and then cutting it with an air knife; a method of forming a coating film by a screen printing method or the like and then removing the solvent by heating and drying; etc. Or the powdered solid electrolyte can be made into a compact by pressing or the like and then appropriately processed for manufacturing. Considering the balance between preventing short circuits and the volume capacity density, the thickness of the solid electrolyte layer is typically preferably 5 μm or more and 300 μm or less, and more preferably 10 μm or more and 100 μm or less.

[0053] The solid electrolyte of the present invention can be used together with an active material to form an 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 a conductive additive and a binder as needed. A paste can be prepared by mixing the electrode mixture with a solvent, and an electrode layer such as a positive electrode layer and / or a negative electrode layer can be prepared by coating the paste on a current collector such as aluminum foil and drying it.

[0054] As the positive electrode material constituting the positive electrode layer, a positive electrode material used as a positive electrode active material of a lithium ion battery can be appropriately used. For example, a lithium-containing positive electrode active material, specifically, spinel-type lithium transition metal oxide and layered-structured lithium metal oxide can be cited. By using a high-voltage positive electrode material as the positive electrode material, an increase in energy density can be achieved. In addition to the positive electrode active material, the positive electrode material may contain a conductive material or other materials.

[0055] As the negative electrode material constituting the negative electrode layer, a negative electrode material used as a negative electrode active material of a lithium ion battery can be appropriately used. Since the solid electrolyte of the present invention is electrochemically stable, a material that can be charged and discharged under the condition of lithium metal or a low potential equivalent to lithium metal (about 0.1V vs Li + / Li) can be used as the negative electrode material, that is, a carbon-based material such as graphite, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon) can be used as the negative electrode material. Thereby, the energy density of the solid-state battery can be significantly increased. In addition, silicon or tin, which is expected to be a high-capacity material, can also be used as an active material. In a battery using a conventional electrolyte, the electrolyte reacts with the active material during charge and discharge, and the battery characteristics deteriorate significantly due to corrosion on the surface of the active material. In contrast, when the solid electrolyte of the present invention is used instead of the electrolyte and silicon or tin is used in the negative electrode active material, since the above corrosion reaction does not occur, an improvement in the durability of the battery can be achieved. Similarly, in addition to the negative electrode active material, the negative electrode material may contain a conductive material or other materials.

[0056] Examples

[0057] 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 "% by mass".

[0058] 〔Example 1〕

[0059] Weigh Li2S powder, P2S5 powder, and LiCl powder in such a way as to form the composition shown in Table 1 below, with the total amount reaching 5 g. Crush and mix these powders using a wet ball mill with heptane to obtain a mixed composition. Roast the mixed composition to obtain a roasted product. The roasting is carried out using a tubular electric furnace. During roasting, introduce nitrogen with a purity of 100% into the electric furnace. Set the roasting temperature to 600 °C and roast for 4 hours.

[0060] Crush the obtained roasted product using a mortar and pestle. Then, crush it using a wet ball mill with heptane.

[0061] Dry the crushed roasted product by vacuum pumping to remove heptane. Screen the dried roasted product using a sieve with a mesh size of 1 mm to obtain the powder of the target solid electrolyte. Confirm that the obtained solid electrolyte has a thiogermanate crystal structure.

[0062] 〔Examples 2 and 3 and Comparative Examples 1 to 3〕

[0063] Mix the powders in such a way as to form the composition shown in the table and adopt the roasting conditions shown in the table. Except for this, perform the same operations as in Example 1 to obtain the powder of the solid electrolyte. Confirm that the obtained solid electrolyte has a thiogermanate crystal structure.

[0064] 〔Evaluation〕

[0065] For the solid electrolytes obtained in the examples and comparative examples, perform XRD measurement according to the following conditions. And for each of the first range to the third range, perform the operation of separating the peaks into two using the following method. The XRD patterns of the solid electrolytes obtained in Examples 2 and 3 and Comparative Examples 2 and 3 are shown in Figure 3 and Figure 4 . In addition, for the solid electrolytes obtained in the examples and comparative examples, measure the lithium ion conductivity by the following method. These results are shown in Table 1 below.

[0066] 〔XRD Measurement〕

[0067] Perform the measurement using the X-ray powder diffractometer "SmartLab SE" of Rigaku Corporation under non-atmospheric exposure conditions. The measurement conditions are as follows.

[0068] · Tube voltage: 40 kV

[0069] · Tube current: 50 mA

[0070] · X-ray: CuKα ray (including CuKα1 ray and CuKα2 ray in an intensity ratio of 2:1)

[0071] · Optical system: Focused beam method

[0072] · Detector: One-dimensional detector

[0073] · Measurement range: 2θ = 10 - 120°

[0074] · Step size: 0.02°

[0075] · Scanning speed: 1° / min

[0076] 〔Peak separation〕

[0077] Separate the diffraction patterns in the 1st to 3rd ranges of the obtained XRD pattern (denoted as I XRD (2θ)) into two peaks P1, P2 and BG representing the background of the diffraction pattern. That is, derive P1, P2 and BG as follows:

[0078] I XRD (2θ) = P1 + P2 + BG

[0079] For peak separation, use the solver function of the software "Microsoft Excel for Office 365" to perform curve fitting based on the least squares method. Here, peaks P1 and P2 are expressed as functions of 2θ by the following equations.

[0080]

[0081]

[0082] In addition, BG is represented by a linear function obtained by connecting two data points at both ends of each target range with a straight line within the 1st to 3rd ranges.

[0083] Here, I1 and I2 are positive constants representing the intensities of peaks P1 and P2 respectively. P 11 and P 12 each represent the diffraction lines from CuKα1 ray and CuKα2 ray that make up peak P1. Similarly, P 21 and P 22 represent the diffraction lines from CuKα1 ray and CuKα2 ray that make up peak P2 respectively. In curve fitting, the diffraction lines P 11 and P 12 as well as P 21 and P 22 are represented using the pseudo-Voigt function as follows, which is a weighted sum of a Lorentz function and a Gaussian function with equal full width at half maximum.

[0084]

[0085]

[0086]

[0087]

[0088] Here, η 11 、η 12 、η 21 、η 22 are each constants between 0 and 1 representing the proportion of the Lorentz component in P 11 、P 12 、P 21 、P 22 .

[0089] In addition, 2θ 11 、2θ 12 、2θ 21 、2θ 22 are each positive constants representing the peak positions of P 11 、P 12 、P 21 、P 22 .

[0090] Furthermore, w 11 、w 12 、w 21 、w 22 are each positive constants representing the peak widths of P 11 、P 12 、P 21 、P 22 .

[0091] That is, the free parameters for deriving P1 and P2 by curve fitting are:

[0092] I1, η 11 、η 12 、θ 11 、θ 12 、w 11 、w 12

[0093] I2, η 21 、η 22 、θ 21 、θ 22 、w 21 、w 22 .

[0094] Among them, from the perspective that the diffraction lines from CuKα1 rays and CuKα2 rays for the same phase must have the same shape, the following restrictions are set:

[0095] η 11 = η 12 、w 11 = w 12 、η 21= η 22 、w 21 = w 22 。

[0096] In addition, for η 11 、η 12 、η 21 、η 22 , set a limit of 0 or more and 1 or less.

[0097] Furthermore, the difference in the positions of the diffraction lines from the CuKα1 ray and the CuKα2 ray within the first to third ranges is theoretically 0.06° or more and 0.08° or less. Therefore, in order to simplify the peak separation, the following limits are also set:

[0098] 2θ 12 = 2θ 11 + 0.07, 2θ 22 = 2θ 21 + 0.07.

[0099] The index of the effectiveness of the least squares method is set to R < 10.

[0100] From the curve fitting, the angular difference Δ2θ between P1 and P2 is:

[0101] Δ2θ = 2θ 21 - 2θ 11 .

[0102] [Lithium ion conductivity]

[0103] Inside a glove box replaced with sufficiently dried Ar gas (dew point -60°C or lower), a load of about 6 t / cm 2 was applied to the solid electrolytes obtained in the examples and comparative examples, and uniaxial compression molding was performed to produce samples for measuring lithium ion conductivity composed of pellets with a diameter of 10 mm and a thickness of about 1 mm to 8 mm. The lithium ion conductivity of the samples was measured using Solartron 1255B of Toyo Technica Co., Ltd. The measurement was performed by the AC impedance method under the conditions of a temperature of 25°C and a frequency of 0.1 Hz to 1 MHz.

[0104] [Table 1]

[0105]

[0106] As is clear from the results shown in Table 1, when the diffraction patterns in the 1st to 3rd ranges of the XRD diffraction pattern of the solid electrolytes obtained in each example were subjected to peak separation, two different peaks were observed. From this, it can be seen that there are two different phases in the solid electrolytes obtained in each example. And it is known that the lithium ion conductivity of the solid electrolytes obtained in each example having two different phases is higher than that of the solid electrolyte of the comparative example.

[0107] Industrial applicability

[0108] According to the present invention, a solid electrolyte having higher ion conductivity than before can be provided.

Claims

1. A solid electrolyte comprising lithium (Li), phosphorus (P), sulfur (S), and element X, wherein, X represents at least one halogen element. The solid electrolyte contains a compound represented by the composition formula Li a PS b X c where a represents a number of 3.0 or more and 6.0 or less, b represents a number of 3.5 or more and 4.8 or less, and c represents a number of 0.1 or more and 3.0 or less. When performing peak separation on the diffraction pattern within at least any one of the ranges of 2θ = 25.6 ± 0.8°, 30.2 ± 0.8°, and 31.6 ± 0.8° in the X-ray diffraction pattern measured by an X-ray diffraction apparatus (XRD) using CuKα1 ray and CuKα2 ray, there are peak P1 and peak P2. The peak P1 and peak P2 are represented by the following formula as a function of 2θ. where I1 and I2 are positive constants representing the intensities of peaks P1 and P2, respectively, P 11 and P 12 each represent diffraction lines from CuKα1 and CuKα2 rays that make up peak P1, P 21 and P 22 respectively represent diffraction lines from CuKα1 and CuKα2 rays that make up peak P2. In curve fitting, diffraction lines P 11 and P 12 as well as P 21 and P 22 are represented using the pseudo-Voigt function, which is a weighted sum of a Lorentzian function and a Gaussian function with equal full widths at half maximum. The peak P1 and the peak P2 respectively originate from different phases.

2. The solid electrolyte according to claim 1, wherein, When performing peak separation on the diffraction pattern within the ranges of 2θ = 25.6 ± 0.8°, 30.2 ± 0.8°, and 31.6 ± 0.8° in the X-ray diffraction pattern measured by an X-ray diffraction apparatus (XRD) using CuKα1 ray and CuKα2 ray, there are the peak P1 and the peak P2.

3. The solid electrolyte according to claim 1 or 2, wherein The X element contains at least chlorine (Cl).

4. The solid electrolyte according to claim 1 or 2, wherein The molar ratio (X / P) of the X element to the phosphorus (P) element is greater than 1.

0.

5. The solid electrolyte according to claim 1 or 2, wherein The angular difference Δ2θ between the peak P1 and the peak P2 is 0.04° or more.

6. The solid electrolyte according to claim 1 or 2, which contains a crystal phase having a thiogermanate crystal structure.

7. A method for manufacturing a solid electrolyte, which is a method for manufacturing the solid electrolyte according to any one of claims 1 to 6, and has the following steps: A step of obtaining a raw material composition by mixing a lithium (Li) element source, a phosphorus (P) element source, a sulfur (S) element source, and a halogen (X) element source; and A step of calcining the raw material composition at a temperature of 540°C or higher and 660°C or lower for 2 hours or more and 6 hours or less in an inert gas atmosphere.

8. An electrode mixture, which contains the solid electrolyte according to any one of claims 1 to 6 and an active material.

9. A solid electrolyte layer, which contains the solid electrolyte according to any one of claims 1 to 6.

10. A battery, which has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, and the battery contains the solid electrolyte according to any one of claims 1 to 6.

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