Positive electrode mixture, lithium ion battery, and production method for positive electrode mixture

Abstract

This positive electrode mixture comprises: a conductive auxiliary agent which is a carbon material; a sulfur-based active material; and a solid electrolyte, wherein in elemental analysis using energy dispersive X-ray spectroscopy of an electron microscope image, the mapping overlap rate between carbon and phosphorus is 60% or more, and in powder X-ray diffraction using CuKα rays, there is a diffraction peak A at 2θ=25.7±0.5° and a diffraction peak B at 2θ=30.2±0.5°, and the half-value width of diffraction peak A is 0.190 or less.

Description

Positive electrode mixture, lithium ion battery, and method for manufacturing the positive electrode mixture

[0001] The present invention relates to a positive electrode composite, a lithium ion battery, and a method for manufacturing the positive electrode composite. Specifically, the present invention relates to a positive electrode composite, a lithium ion battery, and a method for manufacturing the positive electrode composite that can exhibit excellent reversible discharge capacity.

[0002] In sulfur-based positive electrode composites used in lithium-ion batteries and the like, sulfur is mixed with a conductive additive and a solid electrolyte to form a composite, which allows the insulating sulfur to react sufficiently (Patent Documents 1 and 2).

[0003] JP 2013-258079 A JP 2022-90295 A

[0004] However, it has been found that there is room for further improvement in the cathode composites according to conventional techniques such as those disclosed in Patent Documents 1 and 2, in terms of further increasing the reversible discharge capacity when used in lithium ion batteries, etc. One object of the present invention is to provide a cathode composite, a lithium ion battery, and a method for manufacturing the cathode composite, which are capable of exhibiting excellent reversible discharge capacity.

[0005] As a result of extensive research, the present inventors have found that a specific positive electrode mixture can exhibit excellent reversible discharge capacity, and have thus completed the present invention.

[0006] According to the present invention, the following positive electrode mixtures and the like can be provided. 1. A positive electrode mixture comprising a conductive additive which is a carbon material, a sulfur-based active material, and a solid electrolyte, wherein in elemental analysis of electron microscope images by energy dispersive X-ray spectroscopy, the overlap rate of carbon and phosphorus mapping is 60% or more, and in powder X-ray diffraction using CuKα radiation, the mixture has a diffraction peak A at 2θ = 25.7 ± 0.5° and a diffraction peak B at 2θ = 30.2 ± 0.5°, and the half-width of diffraction peak A is 0.190 or less. 2. The positive electrode mixture according to 1, wherein the solid electrolyte contains lithium atoms, phosphorus atoms, and sulfur atoms, and further contains one or more atoms selected from halogen atoms. 3. The positive electrode mixture according to 1 or 2, wherein the solid electrolyte contains lithium atoms, phosphorus atoms, and sulfur atoms, and further contains two or more atoms selected from halogen atoms. 4. The cathode mixture according to any one of 1 to 3, wherein the solid electrolyte contains lithium atoms, phosphorus atoms, and sulfur atoms, and further contains two or more atoms selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms. 5. The cathode mixture according to any one of 1 to 4, wherein the solid electrolyte contains lithium atoms, phosphorus atoms, and sulfur atoms, and further contains chlorine atoms and bromine atoms. 6. The cathode mixture according to any one of 1 to 5, wherein the cathode mixture is obtained by a production method including a first mixing step of adding a solid electrolyte to a sulfur-based active material and mixing them to obtain a first mixture, and a second mixing step of adding a further solid electrolyte to the first mixture and mixing them to obtain a second mixture, wherein the solid electrolyte added in the second mixing step contains solid electrolyte α, and wherein the solid electrolyte α has a diffraction peak A at 25.7±0.5° and a diffraction peak B at 30.2±0.5° in powder X-ray diffraction using CuKα radiation. 7. The cathode mixture according to 6, wherein the mixing in the second mixing step is performed with lower energy than in the first mixing step. 8. 8. The cathode composite according to claim 6 or 7, wherein the first mixing step is performed under conditions that cause the solid electrolyte α added in the first mixing step to become amorphous, and the second mixing step is performed under conditions that do not cause the crystallinity of the solid electrolyte α added in the second mixing step to disappear. 9. A lithium ion battery comprising the cathode composite according to any one of claims 1 to 8.10. A method for producing a cathode composite, comprising: a first mixing step of adding a solid electrolyte to a sulfur-based active material and mixing the mixture to obtain a first mixture; and a second mixing step of adding a further solid electrolyte to the first mixture and mixing the mixture to obtain a second mixture, wherein the solid electrolyte added in the second mixing step comprises solid electrolyte α, and the solid electrolyte α has a diffraction peak A at 25.7±0.5° and a diffraction peak B at 30.2±0.5° in powder X-ray diffraction using CuKα radiation. 11. A method for producing a cathode composite according to 10, wherein the second mixing step is performed with lower energy than the first mixing step. 12. A method for producing a cathode composite according to 10 or 11, wherein the first mixing step is performed under conditions that cause the solid electrolyte added in the first mixing step to become amorphous, and the second mixing step is performed under conditions that do not cause the crystallinity of the solid electrolyte α added in the second mixing step to be lost. 13. 13. The method for producing a cathode composite according to any one of 10 to 12, wherein the amount of the solid electrolyte α added in the second mixing step is 50 to 100 parts by mass when the total amount of the solid electrolytes added in the second mixing step is 100 parts by mass. 14. The method for producing a cathode composite according to any one of 10 to 13, wherein the half width of the diffraction peak A in the second mixture is 0.190 or less.

[0007] According to the present invention, it is possible to provide a positive electrode composite that can exhibit excellent reversible discharge capacity, a lithium ion battery, and a method for producing the positive electrode composite.

[0008] 1A and 1B are diagrams showing the results of SEM-EDS analysis of Example 1, where (a) shows the image before image processing (before smoothing, compression, and binarization), and (b) shows the image after image processing. C indicates carbon mapping, and P indicates phosphorus mapping. 1B are diagrams showing the results of SEM-EDS analysis of Example 2, where (a) shows the image before image processing (before smoothing, compression, and binarization), and (b) shows the image after image processing. C indicates carbon mapping, and P indicates phosphorus mapping. 1C are diagrams showing the results of SEM-EDS analysis of Comparative Example 1, where (a) shows the image before image processing (before smoothing, compression, and binarization), and (b) shows the image after image processing. C indicates carbon mapping, and P indicates phosphorus mapping. 1C are diagrams showing the results of SEM-EDS analysis of Comparative Example 2, where (a) shows the image before image processing (before smoothing, compression, and binarization), and (b) shows the image after image processing. C indicates carbon mapping, and P indicates phosphorus mapping. FIG. 1 is a diagram showing the results of powder X-ray diffraction (XRD) of the positive electrode composite powder of Example 1. FIG. 2 is a diagram showing the results of powder X-ray diffraction (XRD) of the positive electrode composite powder of Example 2. FIG. 3 is a diagram showing the results of powder X-ray diffraction (XRD) of the positive electrode composite powder of Example 3. FIG. 4 is a diagram showing the results of powder X-ray diffraction (XRD) of the positive electrode composite powder of Example 4. FIG. 5 is a diagram showing the results of powder X-ray diffraction (XRD) of the positive electrode composite powder of Comparative Example 1. FIG. 6 is a diagram showing the results of powder X-ray diffraction (XRD) of the positive electrode composite powder of Reference Example 1.

[0009] The cathode composite, lithium ion battery, and method for producing the cathode composite of the present invention are described in detail below. In this specification, "x to y" represents a numerical range of "x or more and y or less." The upper and lower limits of the numerical ranges can be combined in any combination.

[0010] 1. Cathode Composite A cathode composite according to one embodiment of the present invention comprises a conductive additive that is a carbon material, a sulfur-based active material, and a solid electrolyte, and in elemental analysis of electron microscope images by energy dispersive X-ray spectroscopy, the carbon and phosphorus mapping overlap rate is 60% or more, and in powder X-ray diffraction using CuKα radiation, the diffraction peak A has a diffraction peak A at 2θ = 25.7 ± 0.5° and a diffraction peak B at 2θ = 30.2 ± 0.5°, and the half-width of the diffraction peak A is 0.190 or less. The cathode composite of this embodiment exhibits the effect of exhibiting excellent reversible discharge capacity.

[0011] (Conductive Aid) An electron-conductive carbon material can be used as the conductive aid. Carbon materials have high conductivity and are lighter than other conductive materials, which allows the battery's power density and capacity per weight to be increased. The conductive aid is preferably a carbon material having micropores. Examples of carbon materials include, but are not limited to, carbon blacks such as ketjen black, acetylene black, denka black, thermal black, and channel black; mesoporous carbon; activated carbon; amorphous carbon; carbon nanotubes; vapor-grown carbon fiber (VGCF); and carbon nanohorns. Examples of conductive carbon materials include fullerenes, carbon fibers, natural graphite, artificial graphite, graphene, graphene oxide, and reduced graphene oxide. These materials may be used alone or in combination of two or more. A composite of these materials may also be used.

[0012] (Sulfur-based active material) The sulfur-based active material is not particularly limited, but sulfur, lithium sulfide (Li ２ S), lithium polysulfide (Li ２ S ｎ : n satisfies 1<n≦8.), titanium sulfide (TiS ２ ), molybdenum sulfide (MoS ２ ), iron sulfide (FeS, FeS ２ ), copper sulfide (CuS), nickel sulfide (Ni ３ S ２ ), sulfur-containing polymer compounds, etc. The sulfur is not particularly limited, but a high purity is preferred. Specifically, the purity is preferably 95% by mass or more, more preferably 96% by mass or more, and particularly preferably 97% by mass or more. Examples of the crystal system of sulfur include α sulfur (orthorhombic system), β (monoclinic system), γ (monoclinic system), amorphous sulfur, etc. These can be used alone or in combination of two or more types.

[0013] (Solid Electrolyte) In one embodiment, the positive electrode composite includes, as the solid electrolyte, a solid electrolyte (also referred to as "solid electrolyte α") having a diffraction peak A at 2θ = 25.7 ± 0.5° and a diffraction peak B at 2θ = 30.2 ± 0.5° in powder X-ray diffraction using CuKα radiation.

[0014] In one embodiment, the solid electrolyte α is an argyrodite-type solid electrolyte. The argyrodite-type crystal structure is, for example, Li ７ P.S. ６ Crystal structure; Li ７ P.S. ６ The structural skeleton of the composition formula Li ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ (x is −0.6 to 0.6, y is 0.1 to 0.6); Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ (0.8≦x≦1.7, 0<y≦−0.25x+0.5); Li ７－ｘ P.S. ６－ｘ Ha ｘ (Ha is Cl or Br, and x is preferably 0.2 to 1.8).

[0015] In one embodiment, the solid electrolyte α contains lithium atoms, phosphorus atoms, and sulfur atoms, and further contains one or more atoms selected from halogen atoms. Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. Among these, chlorine atoms, bromine atoms, and iodine atoms are preferred, and chlorine atoms and bromine atoms are particularly preferred. In one embodiment, the solid electrolyte α contains lithium atoms, phosphorus atoms, and sulfur atoms, and further contains one or more atoms (for example, one type) selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms. In one embodiment, the molar ratio (Li:P:S:Ha) of lithium atoms (Li), phosphorus atoms (P), sulfur atoms (S), and halogen atoms (Ha) in the solid electrolyte α is 5.0-6.0:1.0:4.0-5.0:1.0-2.0.

[0016] In one embodiment, the solid electrolyte α includes lithium atoms, phosphorus atoms, and sulfur atoms, and further includes two or more atoms selected from halogen atoms. Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. Among these, chlorine atoms, bromine atoms, and iodine atoms are preferred, with chlorine atoms and bromine atoms being particularly preferred. In one embodiment, the solid electrolyte α includes lithium atoms, phosphorus atoms, and sulfur atoms, and further includes two or more atoms (e.g., two atoms) selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms. In one embodiment, the solid electrolyte α includes lithium atoms, phosphorus atoms, and sulfur atoms, and further includes chlorine atoms and bromine atoms. In one embodiment, the molar ratio (Li:P:S:Cl+Br) of lithium atoms (Li), phosphorus atoms (P), sulfur atoms (S), chlorine atoms (Cl), and bromine atoms (Br) in the solid electrolyte α is preferably 5.0-6.0:1.0:4.0-5.0:1.0-2.0. The molar ratio of chlorine atoms (Cl) to the total halogens (Cl+Br) is preferably greater than 0.25 and less than 1.0, and more preferably greater than 0.5 and less than 0.8.

[0017] The method for producing the solid electrolyte α is not particularly limited. For example, the method for producing an argyrodite-type solid electrolyte is not particularly limited, and known methods can be used. As starting materials, a combination of two or more compounds or simple substances containing lithium atoms, phosphorus atoms, sulfur atoms, chlorine atoms, bromine atoms, etc. as constituent elements can be used, and any starting material can be used without particular limitation as long as it exhibits ionic conductivity due to the contained metal atoms.

[0018] Examples of raw materials containing lithium (Li) include lithium sulfide (Li ２ S), lithium oxide (Li ２ O), lithium carbonate (Li ２ CO ３ Among these, lithium compounds are preferred, and lithium sulfide is more preferred.

[0019] Examples of raw materials containing phosphorus (P) and sulfur (S) include diphosphorus trisulfide (P ２ S３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides, sodium phosphate (Na ３ P.O. ４ Examples of suitable phosphorus compounds include phosphorus compounds such as phosphorus pentasulfide, phosphorus elemental compounds, and sulfur elemental compounds. Among these, phosphorus sulfide is preferred, and diphosphorus pentasulfide is more preferred. Phosphorus compounds such as diphosphorus pentasulfide, phosphorus elemental compounds, and sulfur elemental compounds can be used without any particular limitation as long as they are industrially produced and commercially available.

[0020] Examples of raw materials containing halogen include lithium halides such as lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), and phosphorus pentachloride (PCl ５ ), phosphorus trichloride (PCl ３ ), phosphorus pentabromide (PBr ５ ), phosphorus tribromide (PBr ３ Among them, lithium halides such as LiCl, LiBr, and LiI, PBr ３ is preferred, and lithium halides such as LiCl, LiBr, and LiI are more preferred, with LiCl and LiBr being more preferred.

[0021] The combination of raw materials used is preferably lithium sulfide, diphosphorus pentasulfide, lithium chloride, and lithium bromide, and in this case, the molar ratio of the raw materials used is preferably lithium sulfide:diphosphorus pentasulfide:total of two lithium halides=30-60:10-25:15-50.

[0022] The above raw materials are subjected to mechanical stress to form an intermediate. Here, "applying mechanical stress" means mechanically applying shear force, impact force, or the like. Examples of means for applying mechanical stress include grinders such as planetary ball mills, vibration mills, and tumbling mills, and kneaders. The intermediate is heat-treated to obtain a crystalline solid electrolyte α (argyrodite-type solid electrolyte). The heat treatment temperature is preferably 350 to 650°C, more preferably 360 to 500°C, and even more preferably 380 to 450°C.

[0023] In one embodiment, the above raw materials are roughly mixed and then dispersed in a solvent (e.g., a mixed solvent of dehydrated toluene and dehydrated isobutyronitrile) to prepare a slurry. This slurry is mixed and pulverized using a mixer / pulverizer such as a bead mill. The solvent is then removed, and the mixture is heated to 400 to 430°C in an electric furnace and slowly cooled to obtain a raw sulfide solid electrolyte. The raw sulfide solid electrolyte is dispersed in a solvent (e.g., dehydrated toluene) in a nitrogen atmosphere and atomized using a planetary ball mill to obtain a slurry again. This slurry is dried to remove the solvent, thereby obtaining solid electrolyte α.

[0024] In one embodiment, the positive electrode composite includes, as the solid electrolyte, a solid electrolyte α and a solid electrolyte other than the solid electrolyte α.

[0025] (Solid Electrolytes Other Than Solid Electrolyte α) The solid electrolyte other than the solid electrolyte α is not particularly limited, and examples thereof include sulfide solid electrolytes. The sulfide solid electrolyte is a solid electrolyte that contains at least sulfur atoms and exhibits ionic conductivity due to the contained metal atoms. In addition to sulfur atoms, it preferably contains lithium atoms and phosphorus atoms, more preferably lithium atoms, phosphorus atoms, and halogen atoms, and has ionic conductivity due to lithium atoms. The solid electrolyte may contain metal atoms (e.g., lithium atoms) that contribute to the expression of ionic conductivity, or may not yet contain metal atoms that contribute to the expression of ionic conductivity. A solid electrolyte that does not yet contain metal atoms that contribute to the expression of ionic conductivity may contain metal atoms that contribute to the expression of ionic conductivity, for example, depending on the progress of the electrode reaction. Therefore, a substance that exhibits ionic conductivity by containing metal atoms that contribute to the expression of ionic conductivity is also a solid electrolyte. Examples of such substances (solid electrolytes) include phosphorus sulfide and boron sulfide. Examples of phosphorus sulfide include phosphorus trisulfide (P ４ S ３ ), diphosphorus pentasulfide (P ２ S ５ ), phosphorus heptasulfide (P ４ S ７ ), tetraphosphorus pentasulfide (P ４ S ５) and the like. The phosphorus sulfide may have a dimer or polysulfide structure, or may be a mixture. Particularly preferred is diphosphorus pentasulfide, which is expected to react with lithium to form a sulfide solid electrolyte exhibiting high ionic conductivity. In one embodiment, the solid electrolyte contains lithium atoms, phosphorus atoms, sulfur atoms, bromine atoms, and iodine atoms. In this case, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine atoms, and iodine atoms is not particularly limited, but is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.02 to 0.25: 0.02 to 0.25, more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.03 to 0.2: 0.03 to 0.2, and even more preferably 1.35 to 1.45: 1.4 to 1.7: 0.3 to 0.45: 0.04 to 0.18: 0.04 to 0.18. The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

[0026] (Amorphous sulfide solid electrolyte) The amorphous sulfide solid electrolyte can be used without any particular limitation as long as it contains at least sulfur atoms and exhibits ionic conductivity due to the contained metal atoms. Representative examples include Li ２ S-P ２ S ５ a solid electrolyte containing sulfur atoms, lithium atoms, and phosphorus atoms, which is composed of lithium sulfide and phosphorus sulfide such as Li; ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ -LiI-LiBr, etc., a solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide; ２ S-P ２S ５ -Li ２ O-LiI, Li ２ S-SiS ２ -P ２ S ５ In order to obtain higher ionic conductivity, a solid electrolyte such as Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as LiI-LiBr, is preferred. The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0027] The amorphous sulfide solid electrolyte contains at least Li ２ S-P ２ S ５ When Li ２ S and P ２ S ５ From the viewpoint of obtaining high chemical stability and higher ionic conductivity, the molar ratio of Li to Li is preferably 30 to 85:15 to 70, more preferably 40 to 80:20 to 60, and even more preferably 45 to 78:22 to 55. ２ S-P ２ S ５ In the case of -LiI-LiBr, the total content of lithium sulfide and diphosphorus pentasulfide is preferably 30 to 95 mol%, more preferably 35 to 90 mol%, and even more preferably 40 to 85 mol%. The ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, even more preferably 40 to 80 mol%, and particularly preferably 50 to 70 mol%.

[0028] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte may be, for example, a so-called glass ceramic obtained by heating the amorphous sulfide solid electrolyte to a temperature equal to or higher than the crystallization temperature, and a sulfide solid electrolyte having the following crystal structure may be used. Examples of crystal structures that the crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, and phosphorus atoms may have include Li ３ P.S. ４ Crystal structure, Li ４ P ２ S ６ Crystal structure, Li ７ P.S. ６ Crystal structure, Li ７ P ３ S １１ Examples of such structures include a crystal structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP 2013-16423 A).

[0029] In addition, a crystalline structure that the crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms may have is a thiolicon region II type crystalline structure. Here, the "thiolicon region II type crystalline structure" refers to a structure in which Li ４－ xGe １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure (Kanno et al., Journal of the Electrochemical Society, 148(7)A742-746(2001)), Li ４－ xGe １－ｘ P ｘ S ４ Examples include a crystal structure similar to the thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725).

[0030] In X-ray diffraction measurement using CuKα radiation, Li ３ P.S. ４ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.5°, 18.3°, 26.1°, 27.3°, and 30.0°. ４ P２ S ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=16.9°, 27.1°, and 32.5°. ７ P.S. ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=15.3°, 25.2°, 29.6°, and 31.0°. ７ P ３ S １１ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, and Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II crystal structure appear, for example, at 2θ=20.1°, 23.9°, and 29.5°, and Li ４－ｘ Ge １－ｘ P ｘ S ４ Diffraction peaks of a crystal structure similar to thio-lisicon region II type appear, for example, at 2θ = 20.2° and 23.6°. These peak positions may vary within a range of ±0.5°. The solid electrolyte may have the thio-lisicon region II type crystal structure, or may have it as the main crystal. In this specification, "having it as the main crystal" means that the proportion of the target crystal structure in the crystal structure is 80% or more, preferably 90% or more, and more preferably 95% or more.

[0031] Among the above crystal structures, the crystal structure of the crystalline sulfide solid electrolyte is Li ３ P.S. ４ The crystalline structure, thioliconregion type II crystalline structure, is preferred.

[0032] In one embodiment, 1 to 100 mass %, 5 to 95 mass %, or 15 to 85 mass % of the solid electrolyte contained in the cathode composite produced by the method for producing a cathode composite according to this aspect is solid electrolyte α.

[0033] In one embodiment, the positive electrode composite may or may not contain components other than the sulfur-based active material, the solid electrolyte, and the conductive additive. The other components are not particularly limited, and examples thereof include a binder, a solvent, a dispersant, and the like.

[0034] In the positive electrode mixture, the contents of the sulfur-based active material, solid electrolyte, and conductive additive are not particularly limited. In one embodiment, the content of the sulfur-based active material is 40 to 350 parts by mass per 100 parts by mass of the solid electrolyte. In one embodiment, the content of the conductive additive is 10 to 300 parts by mass per 100 parts by mass of the solid electrolyte. In one embodiment, the mass ratio of the sulfur-based active material to the conductive additive (sulfur-based active material:conductive additive) is 10:90 to 95:5 or 20 to 90:80 to 10. In one embodiment, the ratio of the content of the solid electrolyte to the content of the sulfur-based active material and conductive additive (solid electrolyte:sulfur-based active material + conductive additive) is 10:90 to 90:10, 15 to 70:85 to 30, or 20 to 60:80 to 40. In one embodiment, the positive electrode composite comprises 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, 99.5% by mass or more, or substantially 100% by mass of the conductive additive, sulfur-based active material, and solid electrolyte. Note that "substantially 100% by mass" may contain inevitable impurities.

[0035] (Overlap Rate of Carbon and Phosphorus Mapping) As described above, in elemental analysis of electron microscope images by energy dispersive X-ray spectroscopy, the positive electrode composite has an overlap rate of carbon and phosphorus mapping of 60% or more. The overlap rate is preferably 70% or more, 80% or more, 90% or more, or even 95% or more. The higher the overlap rate of 60% or more, the more thoroughly the components in the positive electrode composite (e.g., solid electrolyte, conductive additive, sulfur-based active material, etc.) are mixed. From the viewpoint of the composite structure, it is possible to ensure conductivity to a larger portion of the sulfur-based active material, and the effect of increasing the active material utilization rate can be expected. The overlap rate of carbon and phosphorus mapping is a value measured by the method described in the examples.

[0036] (Powder X-ray Diffraction) As described above, the positive electrode composite has a diffraction peak A at 2θ = 25.7 ± 0.5° and a diffraction peak B at 2θ = 30.2 ± 0.5° in powder X-ray diffraction using CuKα radiation. These diffraction peaks A and B are derived from the solid electrolyte α.

[0037] Furthermore, the positive electrode composite has a half-width of the diffraction peak A of 0.190° or less. In one embodiment, the half-width of the diffraction peak A is 0.190° or less, 0.180° or less, 0.170° or less, 0.160° or less, 0.150° or less, 0.140° or less, 0.130° or less, 0.120° or less, 0.110° or less, 0.100° or less, 0.090° or less, or 0.080° or less. This enables the formation of a good ion conduction path. The lower limit of the half-width of the diffraction peak A is not particularly limited and may be, for example, 0.070° or more or 0.075° or more. The half-width of the diffraction peak A is a value measured by the method described in the examples.

[0038] In one embodiment, the positive electrode composite is obtained by a manufacturing method including a first mixing step of adding a solid electrolyte to a sulfur-based active material and mixing the mixture to obtain a first mixture, and a second mixing step of adding a further solid electrolyte to the first mixture and mixing the mixture to obtain a second mixture, wherein the solid electrolyte added in the second mixing step includes solid electrolyte α. In this embodiment, it is preferable that the second mixing step is performed with less energy than the first mixing step. In this embodiment, it is preferable that the first mixing step is performed under conditions that promote amorphization of the solid electrolyte added in the first mixing step, and that the second mixing step is performed under conditions that do not cause the crystallinity of the solid electrolyte added in the second mixing step to disappear. Note that the description of "2. Method for manufacturing positive electrode composite" is used to cite the manufacturing method in this embodiment.

[0039] 2. Manufacturing Method of Cathode Composite A manufacturing method of a cathode composite according to one aspect of the present invention includes a first mixing step of adding a solid electrolyte to a sulfur-based active material and mixing the resulting mixture to obtain a first mixture, and a second mixing step of adding a further solid electrolyte to the first mixture and mixing the resulting mixture to obtain a second mixture, wherein the solid electrolyte added in the second mixing step includes solid electrolyte α, and wherein the solid electrolyte α has a diffraction peak A at 25.7±0.5° and a diffraction peak B at 30.2±0.5° in powder X-ray diffraction using CuKα radiation. According to the manufacturing method of the cathode composite according to this aspect, the cathode composite according to one aspect of the present invention can be suitably manufactured.

[0040] (First Mixing Step) In the first mixing step, a solid electrolyte is added to a sulfur-based active material and mixed to obtain a first mixture. The solid electrolyte added in the first mixing step is not particularly limited, and examples thereof include solid electrolyte α and solid electrolytes other than solid electrolyte α. For solid electrolyte α and solid electrolytes other than solid electrolyte α, the explanation given in "1. Positive Electrode Composite" is applicable. In one embodiment, the solid electrolyte added in the first mixing step includes a solid electrolyte other than solid electrolyte α.

[0041] In one embodiment, when the total amount of the solid electrolytes added in the first mixing step is 100 parts by mass, the amount of solid electrolyte α added in the first mixing step is 0 to 50 parts by mass, 0 to 50 parts by mass, 0 to 40 parts by mass, 0 to 30 parts by mass, 0 to 20 parts by mass, 0 to 10 parts by mass, 0 to 5 parts by mass, or 0 parts by mass.

[0042] (Second Mixing Step) In the second mixing step, a second mixture (cathode composite) is obtained by adding a further solid electrolyte to the first mixture and mixing the resulting mixture. The solid electrolyte added in the second mixing step includes solid electrolyte α. In the second mixing step, a solid electrolyte other than solid electrolyte α may be added together with solid electrolyte α.

[0043] In one embodiment, when the total amount of the solid electrolytes added in the second mixing step is 100 parts by mass, the amount of solid electrolyte α added in the second mixing step is 50 to 100 parts by mass, 60 to 100 parts by mass, 70 to 100 parts by mass, 80 to 100 parts by mass, 90 to 100 parts by mass, 95 to 100 parts by mass, or 100 parts by mass.

[0044] In one embodiment, when the solid electrolyte α contained in the cathode composite produced by the method for producing a cathode composite according to the present aspect is taken as 100 parts by mass, the proportion of the solid electrolyte α added in the second mixing step is 50 to 100 parts by mass, 60 to 100 parts by mass, 70 to 100 parts by mass, 80 to 100 parts by mass, 90 to 100 parts by mass, 95 to 100 parts by mass, or 100 parts by mass.

[0045] In one embodiment, the second mixing step is performed with a lower energy level than the first mixing step. In other words, in one embodiment, the energy levels of the first and second mixing steps satisfy the condition that the energy level of the first mixing step is higher than the energy level of the second mixing step.

[0046] In one embodiment, the first mixing step is performed under conditions that promote amorphization of the solid electrolyte added in the first mixing step, and the second mixing step is performed under conditions that prevent the crystallinity of the solid electrolyte α added in the second mixing step. For example, the first mixing step can be performed under conditions that may cause a decrease in the intensity of the crystalline peak of the solid electrolyte added in the first mixing step, an increase in the half-width of the peak, or even the disappearance of the peak. On the other hand, the second mixing step can be performed under conditions that prevent the disappearance of the crystalline peak of the solid electrolyte α added in the second mixing step, preferably under conditions that cause only a small change in the intensity or half-width of the crystalline peak. Here, "small change" may mean, for example, that the rate of change is smaller than the rate of change in the first mixing step.

[0047] Examples of mixing devices used in the first mixing step include planetary ball mills, tumbling mills, bead mills, Filmix mixers, Nauta mixers, tornado mixers, twin-screw extruders, multi-screw rollers, and solid-phase shear mixers. The mixing devices used in the second mixing step can be those exemplified for the first mixing step. In this case, when selecting a mixing device and setting operating conditions, it is preferable that the energy required for the mixing process be greater than that required for the first mixing step. The devices used in the first and second mixing steps may be the same or different. When using the same device, for example, the processing time or integrated power can be set to be greater than that required for the second mixing step, or, in the case of devices that utilize rotational power, such as planetary ball mills and tumbling mills, the rotation speed can be set to be greater than that required for the first mixing step. In one embodiment, a planetary ball mill is used in the first mixing step. In one embodiment, a tumbling mill is used in the second mixing step.

[0048] In one embodiment, the sulfur-based active material subjected to the first mixing step is pre-composited with a conductive additive (preferably a carbon material). For example, prior to the first mixing step, the sulfur-based active material can be composited with the conductive additive by heating the sulfur-based active material together with the conductive additive. The heating temperature is not particularly limited and may be, for example, a temperature exceeding 120°C, such as 150°C or higher, 170°C or higher, 200°C or higher, 150°C or higher, 200°C or higher, 250°C or higher, or 300°C or higher. The upper limit is, for example, 350°C or lower. In one embodiment, the mass ratio of the sulfur-based active material to the conductive additive (sulfur-based active material:conductive additive) is 10:90 to 95:5 or 20 to 90:80 to 10.

[0049] In one embodiment, in the cathode composite produced by the cathode composite production method according to the present aspect, the ratio of the total mass of the solid electrolyte to the total mass of the sulfur-based active material and the conductive additive (solid electrolyte:sulfur-based active material+conductive additive) is 10:90 to 90:10, 15 to 70:85 to 30, or 20 to 60:80 to 40.

[0050] In one embodiment, the half-width of the diffraction peak A in the second mixture is 0.190° or less. Regarding this half-width, the explanation given in "1. Positive electrode composite" is incorporated herein. The half-width of the diffraction peak A measured for the solid electrolyte α alone before being mixed with other raw materials may be, for example, approximately 0.010 to 0.150°. While the half-width of the solid electrolyte α may increase during the mixing operation, it is preferable to perform mixing so that the half-width of the diffraction peak A in the second mixture is maintained at 0.190° or less.

[0051] In one embodiment, the cathode composite produced by the method for producing a cathode composite according to this aspect is the cathode composite according to the aspect of the present invention described above, and the description of the cathode composite according to the aspect of the present invention is incorporated herein by reference.

[0052] 3. Lithium-ion battery A lithium-ion battery according to an aspect of the present invention includes the positive electrode composite according to an aspect of the present invention. The lithium-ion battery of this aspect exhibits an excellent reversible discharge capacity.

[0053] The positive electrode composite can be used as the positive electrode layer of a lithium-ion battery. In this case, other components of the lithium-ion battery known in the art can be used, and the negative electrode layer can be selected so that the negative electrode active material does not contain lithium ions. The negative electrode active material contained in the negative electrode layer of the lithium-ion battery can be a "negative electrode active material containing lithium ions." Alternatively, the negative electrode active material contained in the negative electrode layer of the lithium-ion battery can be a "negative electrode active material that supplies lithium ions to the positive electrode."

[0054] The negative electrode of the lithium ion battery is not particularly limited as long as it is one that can be used in ordinary batteries. The negative electrode may be made of a negative electrode mixture that is a mixture of a negative electrode active material and a solid electrolyte.

[0055] As the negative electrode active material, commercially available materials can be used. For example, carbon materials, Sn metal, In metal, Si metal, alloys of these metals, etc. can be used. Specifically, natural graphite, various graphites, metal powders of Si, Sn, Al, Sb, Zn, Bi, etc., SiAl, Sn ５ Cu ６ , Sn ２ Co, Sn２ Examples include metal alloys such as Fe, amorphous alloys, and plated alloys. There are no particular restrictions on the particle size, but particles with an average particle size of several μm to 80 μm are preferably used.

[0056] The electrolyte layer is not particularly limited, and known electrolytes can be used. For example, oxide-based solid electrolytes, sulfide-based solid electrolytes, and polymer-based electrolytes are preferred, and sulfide-based solid electrolytes are more preferred from the viewpoint of ionic conductivity. The sulfide-based solid electrolyte is preferably the one used in the above-mentioned positive electrode composite.

[0057] The method for producing a lithium ion battery is not particularly limited, and examples thereof include a method in which a sheet is formed by forming a positive electrode layer made of the positive electrode composite according to one embodiment of the present invention on a positive electrode current collector, forming a solid electrolyte layer on the sheet, and laminating the sheet on which the negative electrode layer is formed on a previously formed negative electrode current collector, followed by pressing.

[0058] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0059] 1. Preparation of Positive Electrode Composite Material (Example 1) (1) Preparation of Composite Powder A Activated carbon (MSC-30 manufactured by Kansai Thermal Chemical Industries, Ltd.) and sulfur were placed in a glass bottle in a mass ratio of 3:7, and the bottle was sealed in an SUS tubular container. The mixture was heated in an electric furnace at 150°C for 6 hours and then at 300°C for 2.75 hours to obtain composite powder A of activated carbon and sulfur.

[0060] (2) Preparation of Solid Electrolyte A Under a nitrogen atmosphere, 0.4127 g of lithium sulfide, 0.6655 g of diphosphorus pentasulfide, 0.2137 g of lithium iodide, 0.2080 g of lithium bromide, and ten zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), the mixture was mixed (mechanical milling) for 40 hours at a rotation speed of 370 rpm to obtain a powder. The obtained powder was heated at 195 ° C. for 3 hours to obtain a solid electrolyte A.

[0061] (3) Preparation of Solid Electrolyte B Lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５), lithium bromide (LiBr) and lithium chloride (LiCl) in a molar ratio of Li ２ S:P ２ S ５ The mixture was roughly mixed to a ratio of 47.5:12.5:15.0:25.0. The mixture was then dispersed in a mixed solvent of dehydrated toluene and dehydrated isobutyronitrile (2 wt % of the raw material) to obtain a slurry of approximately 10 wt %. The mixture was then mixed and pulverized using a bead mill. The bead mill was operated at a peripheral speed of 12 m / s and a flow rate of 500 mL / min, and the slurry was introduced into the mill and circulated for 1 hour to obtain a mixture. After removing the solvent from the resulting mixture, the mixture was heated (400-430 °C) in an electric furnace for 2 hours. The mixture was then slowly cooled to obtain a raw sulfide solid electrolyte. The mixture was then dispersed in dehydrated toluene as a solvent under a nitrogen atmosphere, and placed in a zirconia pot of a planetary ball mill (manufactured by Fritsch: model number P-7) together with 0.3 mm diameter zirconia balls, and the pot was filled with an inert atmosphere. The mixture was processed in a planetary ball mill at a rotation speed of 150 rpm for 2 hours to obtain a slurry containing a finely divided sulfide solid electrolyte. The slurry was transferred to a nitrogen-substituted Schlenk flask, dried at room temperature for 1 hour using a vacuum pump, heated to 80 to 100°C, and the solvent contained in the finely divided sulfide solid electrolyte was removed (vacuum drying) to obtain solid electrolyte B.

[0062] (4) Preparation of Positive Electrode Composite Powder First Mixing Step 0.7778 g of Composite Powder A and 0.2222 g of Solid Electrolyte A were placed in a 45 mL zirconia pot together with ten zirconia balls having a diameter of 10 mm, and the pot was sealed. Mixing was carried out using a planetary ball mill (manufactured by Fritsch, model number P-7) at a rotation speed of 370 rpm for 20 hours to obtain Composite Powder B.

[0063] Second mixing step: 0.81 g of composite powder B and 0.09 g of solid electrolyte B were placed in a 45 mL zirconia pot together with 34 g of zirconia balls with a diameter of 2 mm, and the pot was sealed. Mixing was carried out for 1 hour at a rotation speed of 600 rpm using a tumbling mill ("small ball mill stand," manufactured by Asahi Rika Seisakusho, model AV-1) to obtain a positive electrode composite powder.

[0064] (Example 2) Steps (1) to (3) were carried out in the same manner as in Example 1. (4) Preparation of Positive Electrode Composite Powder First Mixing Step 0.8235 g of composite powder A and 0.1765 g of solid electrolyte A were placed in a 45 mL zirconia pot along with ten 10 mm diameter zirconia balls and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), mixing was carried out at a rotation speed of 370 rpm for 20 hours to obtain composite powder C. Second Mixing Step 0.765 g of composite powder C and 0.135 g of solid electrolyte B were placed in a 45 mL zirconia pot along with 34 g of 2 mm diameter zirconia balls and sealed. Using a tumbling mill ("Small Ball Mill Stand," manufactured by Asahi Rika Seisakusho, model number AV-1), mixing was carried out at a rotation speed of 600 rpm for 1 hour to obtain a positive electrode composite powder.

[0065] (Example 3) Steps up to (1) were carried out in the same manner as in Example 1. (2) Preparation of Positive Electrode Composite Powder Pretreatment Step Composite powder A obtained in (1) above and diphosphorus pentasulfide (manufactured by Italmatch) were placed in a Tammann tube with an inner diameter of 12 mm in a weight ratio of 0.8235:0.1765, and the mixture was sealed in an SUS tube. The mixture was heated in an electric furnace at 350°C for 6 hours to obtain composite powder D. First Mixing Step 1.000 g of composite powder D was placed in a 45 mL zirconia pot together with 10 zirconia balls with a diameter of 10 mm, and the pot was sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), mixing was carried out at a rotation speed of 370 rpm for 20 hours to obtain composite powder E. Second mixing step: 0.765 g of composite powder E and 0.135 g of solid electrolyte B were placed in a 45 mL zirconia pot together with 34 g of zirconia balls with a diameter of 2 mm, and the pot was sealed. Mixing was carried out for 1 hour at a rotation speed of 600 rpm using a tumbling mill ("small ball mill stand," manufactured by Asahi Rika Seisakusho, model AV-1) to obtain a positive electrode composite powder.

[0066] (Example 4) Steps up to (1) were carried out in the same manner as in Example 1. (2) Preparation of Positive Electrode Composite Powder First Mixing Step 0.8235 g of composite powder A and 0.1765 g of diphosphorus pentasulfide were placed in a 45 mL zirconia pot along with ten 10 mm diameter zirconia balls and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), mixing was carried out at a rotation speed of 370 rpm for 20 hours to obtain composite powder F. Second Mixing Step 0.765 g of composite powder F and 0.135 g of solid electrolyte B were placed in a 45 mL zirconia pot along with 34 g of 2 mm diameter zirconia balls and sealed. Using a tumbling mill ("Small Ball Mill Stand", manufactured by Asahi Rika Seisakusho, model number AV-1), mixing was carried out at a rotation speed of 600 rpm for 1 hour to obtain a positive electrode composite powder.

[0067] (Comparative Example 1) (1) to (3) were carried out in the same manner as in Example 1. (4) Preparation of Positive Electrode Composite Powder 0.63 g of composite powder A obtained in the same manner as in Example 1 and 0.27 g of solid electrolyte B obtained in the same manner as in Example 1 were placed in a 45 mL zirconia pot together with ten zirconia balls having a diameter of 10 mm, and the pot was sealed. Mixing was carried out using a planetary ball mill (manufactured by Fritsch, model number P-7) at a rotation speed of 370 rpm for 20 hours to obtain a positive electrode composite powder.

[0068] (Comparative Example 2) Steps (1) to (3) were carried out in the same manner as in Example 1. (4) Preparation of Positive Electrode Composite Powder 0.63 g of composite powder A obtained in the same manner as in Example 1 and 0.27 g of solid electrolyte B obtained in the same manner as in Example 1 were placed in a 45 mL zirconia pot together with 34 g of zirconia balls having a diameter of 2 mm, and the pot was sealed. Mixing was carried out at a rotation speed of 600 rpm for 1 hour using a tumbling mill ("small ball mill stand", manufactured by Asahi Rika Seisakusho, model AV-1) to obtain a positive electrode composite powder.

[0069] 2. Evaluation Methods and Test Methods (1) Energy Dispersive X-ray Spectroscopy (SEM-EDS Analysis) of Electron Microscope Images and Calculation of Carbon and Phosphorus Overlap Rate (1-1) Preparation of Cathode Composite Pellets SEM-EDS analysis was performed on each of the cathode composite powders obtained in the Examples and Comparative Examples. Specifically, 100 mg of solid electrolyte A was placed in a Macol cylinder with a diameter of 10 mm and pressure-molded. 20 mg of the obtained cathode composite powder was placed on the pressure surface and pressure-molded again. Subsequently, 20 mg of the cathode composite powder was placed on the opposite pressure surface and pressure-molded again, and the molded body was extracted from the cylinder to obtain a cathode composite pellet.

[0070] (1-2) SEM-EDS analysis The positive electrode composite pellet was split vertically, and the exposed surface was subjected to ion milling (Hitachi High-Tech Corporation, IM4000) to expose the cross section of the positive electrode composite pellet. The obtained cross section was subjected to SEM-EDS elemental mapping measurement using an SEM (Hitachi High-Tech Corporation, SU8220) and EDS (Bruker, QUANTAX FlatQUAD), and secondary electron images and EDS images of carbon and phosphorus were obtained from 10 fields of view. The observation magnification was 5000x, the acceleration voltage was 10 kV, and the scan area was 1024 × 768. No special image processing was performed for EDS mapping, and an image in which the actual measured intensity was mapped was used. In addition, during the SEM-EDS elemental mapping measurement, the area cross-sectionally processed by ion milling was divided into two equal parts, top and bottom, and each of the two equal parts was divided into five equal parts on the left and right. The central portion of each of the 10 divided regions was subjected to SEM-EDS elemental mapping at a magnification of 5000 times.

[0071] (1-3) Calculation of Overlap Rate of Carbon and Phosphorus Mapping The images obtained using the above procedure were processed using OpenCV (4.5.1) in Python (3.9.9). All 10 fields of view of carbon and phosphorus EDS images were subjected to smoothing twice using a bilateral filter with d = 15, sigmaColor = 64, and sigmaSpace = 64. The obtained images were compressed to 1 / 3 of their original size using MaxPooling2D (pool_size = 3, strides = 3) in the neural network open library Keras (2.4.3), and smoothed using a median filter. The smoothed images were grayscaled and binarized with a minimum brightness of 30 for carbon and a maximum brightness of 255 for phosphorus, and a minimum brightness of 40 for phosphorus and a maximum brightness of 255 for phosphorus. The results of the SEM-EDS analysis, including the above image processing, are shown in Figure 1 (Example 1), Figure 2 (Example 2), Figure 3 (Comparative Example 1), and Figure 4 (Comparative Example 2). In these figures, (a) shows the image before processing (before smoothing, compression, and binarization), and (b) shows the image after processing. C indicates carbon mapping, and P indicates phosphorus mapping. Through these processes, the image data was converted into a numerical matrix of 0 if the element was not present and 255 if the element was present. In the numerical matrix of carbon and phosphorus, the total number of pixels where 255 overlapped at the same coordinate was divided by the total number of pixels to calculate the overlap rate of one field of view. The average of the overlap rates of all 10 fields of view was taken as the overlap rate of this embodiment (the overlap rate of carbon and phosphorus mapping).

[0072] (2) XRD Measurement and Peak Half-Width Calculation (2-1) Powder X-ray Diffraction (XRD) of Positive Electrode Composite Powder XRD measurement was performed on each of the positive electrode composite powders obtained in the Examples and Comparative Examples. Specifically, the positive electrode composite powder was filled into a groove with a diameter of 20 mm and a depth of 0.2 mm and leveled with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured without being exposed to air. The XRD measurement was performed under the following measurement conditions using a powder X-ray diffraction measurement device D2 PHASER from BRUKER Co., Ltd. [Measurement conditions] Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα radiation (1.5418 Å) Optical system: focusing method Slit configuration: Soller slit 4° (on both the incident and receiving sides), divergence slit 1 mm, Kβ filter (0.5% Ni plate), and air scatter screen 3 mm were used. Detector: semiconductor detector Measurement range: 2θ = 10-60 deg Step width, scan speed: 0.05 deg, 0.05 deg / sec. XRD measurement was also performed on a reference sample (Reference Example 1) consisting only of solid electrolyte α. The results of Example 1 are shown in FIG. 5, Example 2 in FIG. 6, Example 3 in FIG. 7, Example 4 in FIG. 8, Comparative Example 1 in FIG. 9, and Reference Example 1 in FIG. 10.

[0073] The X-ray diffraction pattern was examined to determine whether or not a diffraction peak A at 25.7±0.5° and a diffraction peak B at 2θ=30.2±0.5° were present, and the half-value width of the diffraction peak A was determined by the following method.

[0074] (2-2) Method for determining whether or not diffraction peak A and diffraction peak B are present Diffraction peak A Whether or not diffraction peak A is present in the range of 2θ = 25.7 ± 0.5° in the X-ray diffraction pattern can be determined by multiplying the average value of the X-ray intensity (counts) at 2θ = (25.7 - 0.5) ± 0.2°, i.e., 2θ = 25.2 ± 0.2°, and at 2θ = (25.7 + 0.5) ± 0.2°, i.e., 2θ = 26.2 ± 0.2°, by the background (BG) intensity I ｂｇ The maximum value of the X-ray intensity (counts) at 2θ=25.7±0.5° is defined as the peak intensity I ｐｅａｋWhen the ratio (I ｐｅａｋ / I ｂｇ If the ratio (I) of the diffraction peak A is 1.100 or more, it is determined that the diffraction peak A exists. ｐｅａｋ / I ｂｇ ) is preferably 1.150 or more, more preferably 1.200 or more.

[0075] Diffraction Peak B Whether or not diffraction peak B exists in the range of 2θ = 30.2 ± 0.5° can be determined by multiplying the average of the X-ray intensities (counts) at 2θ = (30.2 - 0.5) ± 0.2°, i.e., 2θ = 29.7 ± 0.2°, and 2θ = (30.2 + 0.5) ± 0.2°, i.e., 2θ = 30.7 ± 0.2°, in the X-ray diffraction pattern by the background (BG) intensity I ｂｇ The maximum value of the X-ray intensity (counts) at 2θ=30.2±0.5° is defined as the peak intensity I ｐｅａｋ When the ratio (I ｐｅａｋ / I ｂｇ If the ratio (I) of the diffraction peak B is 1.055 or more, it is determined that the diffraction peak B exists. ｐｅａｋ / I ｂｇ ) is preferably 1.070 or more, more preferably 1.100 or more.

[0076] For example, in the positive electrode composite of Example 1, the diffraction peak A is ｐｅａｋ / I ｂｇ ) is 1.489, so it is determined to be "present," and the diffraction peak B is ｐｅａｋ / I ｂｇ ) was 1.843, and therefore it was determined to be "present." In the positive electrode composite of Example 2, the diffraction peak A ｐｅａｋ / I ｂｇ ) is 1.818, so it is determined to be "present," and the diffraction peak B is ｐｅａｋ / I ｂｇ ) was 2.385, and therefore it was determined to be "present." In the positive electrode composite of Example 3, the diffraction peak A ｐｅａｋ / I ｂｇ ) is 1.790, so it is determined to be "present," and the diffraction peak B is ｐｅａｋ / I ｂｇ) was 2.190, and therefore it was determined to be "present." In the positive electrode composite of Example 4, the diffraction peak A ｐｅａｋ / I ｂｇ ) is 1.782, so it is determined to be "present," and the diffraction peak B is ｐｅａｋ / I ｂｇ ) was 2.221, so it was determined to be "present."

[0077] (2-3) Calculation of the half width of diffraction peak A The half width (β) of diffraction peak A was calculated by subtracting the instrument constant (B) specific to the measurement device from the half width (w) obtained by measurement, as follows: β = w - B. w: half width of the peak (diffraction peak A) at 2θ = 25.7 ± 0.5° obtained by measurement. B: instrument constant (a standard material (silicon) was measured in the same way, and B = 0.1269° was obtained from the peak at 2θ = 28.4°). w (half width obtained by measurement) was calculated as follows. A linear baseline was set for the peak shape obtained by XRD measurement, and the difference between the intensity at each point and the baseline was calculated to obtain an XRD curve. The XRD curve was fitted to the equation (f(x) = (1 - α) × L(x) + α × G(x)) consisting of a Lorentzian function L(x) and a Gaussian function G(x), and the parameters A (corrected peak intensity), w, and x were calculated by curve fitting. ０ (2θ of the peak top) and α (the ratio of the Lorentzian function) were determined.

[0078]

[0079] In curve fitting, a range of approximately ±1.0° from the peak top is appropriately set as the fitting range. Fitting was performed by taking the error between the intensity of the fitting curve calculated by f(x) at each θ and the intensity of the XRD curve, and minimizing the sum of the errors over the entire fitting range. Here, the solver function (GRG nonlinear) of spreadsheet software (Excel, Microsoft) was used.

[0080] In the solid electrolyte α alone (Reference Example 1) before mixing, the half-value width of the diffraction peak A was 0.075°.

[0081] (3) Evaluation of Battery Characteristics (3-1) Preparation of Negative Electrode Composite Lithium titanate ("LT-112" manufactured by Ishihara Sangyo Kaisha), a conductive additive ("Li-100" manufactured by Denka Co., Ltd., powdered acetylene black), and solid electrolyte B were mixed in a mortar in a mass ratio of 60:5:35 for 5 minutes to obtain a negative electrode composite (also referred to as "LTO (lithium titanate) negative electrode composite").

[0082] (3-2) Preparation of Lithium Ion Battery 100 mg of solid electrolyte A was placed in a 10 mm diameter Macol cylinder and pressure molded to form a solid electrolyte layer (layer of solid electrolyte A). Next, 12 mg of positive electrode composite powder was placed on one pressure surface of the solid electrolyte layer and pressure molded again. Next, 166 mg of LTO negative electrode composite was placed on the other pressure surface of the solid electrolyte layer (the pressure surface opposite the positive electrode) and pressure was applied. A Li foil with a diameter of 9 mm and a thickness of 0.1 mm was placed on top of it and pressure was applied again to prepare a lithium ion battery.

[0083] (3-3) Charge / Discharge Test A constant-current charge / discharge test was conducted on the lithium-ion batteries obtained in each Example and Comparative Example. The voltage range for the constant-current charge / discharge test was set to -0.4 to +1.3 V, and the test was conducted at a current value equivalent to 0.05 C of the C rate calculated based on the theoretical sulfur capacity of 1672 mAh / g. Charge was performed using CC-CV charging, in which a constant current charge at 0.05 C was followed by a constant voltage charge at 0.02 C as a termination condition. Discharge was performed using a constant current discharge (CC discharge) at 0.05 C. The test started with discharge under the above conditions, and the capacity obtained in the second cycle of discharge was taken as the reversible discharge capacity. The reversible discharge capacity per unit sulfur mass [mAh / g-s] and the reversible discharge capacity [mAh] of the entire lithium-ion battery were calculated.

[0084] The results are shown in Table 1. In Table 1, "CP overlap rate" means the overlap rate of carbon and phosphorus mapping. In Table 1, when "ARG crystal peak" is "present," it means that both diffraction peaks A and B were determined to be present.

[0085]

[0086] It can be seen from Table 1 that the Examples achieved significantly higher reversible discharge capacities than the Comparative Examples. The Examples achieved both a good mixed state (high overlap rate of carbon and phosphorus mapping) and high crystallinity (small half-width of diffraction peak A), and it is believed that these synergistic effects contributed to the achievement of significantly higher reversible discharge capacities.

[0087] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will readily be able to make numerous modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and advantages of the present invention. Accordingly, these numerous modifications are within the scope of the present invention. The contents of all documents cited in this specification and of the applications from which this application claims priority under the Paris Convention are incorporated by reference in their entirety.

Claims

1. A positive electrode composite comprising a conductive additive which is a carbon material, a sulfur-based active material, and a solid electrolyte, wherein in elemental analysis of electron microscope images by energy dispersive X-ray spectroscopy, the overlap rate of carbon and phosphorus mapping is 60% or more, and in powder X-ray diffraction using CuKα rays, the composite has a diffraction peak A at 2θ=25.7±0.5° and a diffraction peak B at 2θ=30.2±0.5°, and the half-width of diffraction peak A is 0.190 or less.

2. The positive electrode mixture according to claim 1, wherein the solid electrolyte contains lithium atoms, phosphorus atoms, and sulfur atoms, and further contains one or more atoms selected from halogen atoms.

3. The positive electrode mixture according to claim 1 or 2, wherein the solid electrolyte contains lithium atoms, phosphorus atoms, and sulfur atoms, and further contains two or more types of atoms selected from halogen atoms.

4. The positive electrode mixture according to any one of claims 1 to 3, wherein the solid electrolyte contains lithium atoms, phosphorus atoms, and sulfur atoms, and further contains two or more atoms selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms.

5. The positive electrode mixture according to any one of claims 1 to 4, wherein the solid electrolyte contains lithium atoms, phosphorus atoms, and sulfur atoms, and further contains chlorine atoms and bromine atoms.

6. The positive electrode composite according to any one of claims 1 to 5, comprising: a first mixing step of adding a solid electrolyte to a sulfur-based active material and mixing the resulting mixture to obtain a first mixture; and a second mixing step of adding a further solid electrolyte to the first mixture and mixing the resulting mixture to obtain a second mixture, wherein the solid electrolyte added in the second mixing step comprises solid electrolyte α, and wherein the solid electrolyte α has a diffraction peak A at 25.7±0.5° and a diffraction peak B at 30.2±0.5° in powder X-ray diffraction using CuKα radiation.

7. The positive electrode mixture according to claim 6, wherein the second mixing step is performed with less energy than the first mixing step.

8. The cathode composite according to claim 6 or 7, wherein the first mixing step is performed under conditions that promote amorphization of the solid electrolyte added in the first mixing step, and the second mixing step is performed under conditions that do not cause the crystallinity of the solid electrolyte α added in the second mixing step to disappear.

9. A lithium ion battery comprising the positive electrode mixture according to any one of claims 1 to 8.

10. A method for producing a positive electrode composite, comprising: a first mixing step of adding a solid electrolyte to a sulfur-based active material and mixing the resulting mixture to obtain a first mixture; and a second mixing step of adding a further solid electrolyte to the first mixture and mixing the resulting mixture to obtain a second mixture, wherein the solid electrolyte added in the second mixing step comprises solid electrolyte α, and wherein the solid electrolyte α has a diffraction peak A at 25.7±0.5° and a diffraction peak B at 30.2±0.5° in powder X-ray diffraction using CuKα radiation.

11. The method for producing a positive electrode mixture according to claim 10, wherein the second mixing step is performed with less energy than the first mixing step.

12. The method for producing a positive electrode composite according to claim 10 or 11, wherein the first mixing step is performed under conditions that cause the solid electrolyte added in the first mixing step to become amorphous, and the second mixing step is performed under conditions that do not cause the crystallinity of the solid electrolyte α added in the second mixing step to disappear.

13. A method for producing a positive electrode composite according to any one of claims 10 to 12, wherein the amount of solid electrolyte α added in the second mixing step is 50 to 100 parts by mass when the total amount of solid electrolytes added in the second mixing step is 100 parts by mass.

14. The method for producing a positive electrode mixture according to any one of claims 10 to 13, wherein the half-value width of the diffraction peak A in the second mixture is 0.190 or less.

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