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

Abstract

A positive electrode mix containing a sulfur-based active substance and a solid electrolyte, having a diffraction peak A at 2θ=15.1±0.8° and a diffraction peak B at 29.8±0.8° when subjected powder x-ray diffraction using CuKα radiation, and containing P and B as constituent elements.

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 the sulfur-based positive electrode composite used in lithium ion batteries, the insulating sulfur can be sufficiently reacted by compounding sulfur with a conductive additive and a solid electrolyte. ６ P.S. ５ On the other hand, although it is not used for sulfur-based positive electrode composites, Li ２ S-P ２ S ５ -LiBH ４ A solid electrolyte has been reported (Non-Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2020-161288

[0004] A. Sakuda et al., ACS OMEGA 3 (2018) 5453-5458

[0005] The present inventors have used Li as a solid electrolyte for a sulfur-based positive electrode composite. ２ S-P ２ S ５ -LiBH ４ However, the cathode composites produced by conventional methods did not provide sufficient reversible discharge capacity. One object of the present invention is to provide a cathode composite, a lithium ion battery, and a method for producing the cathode composite that can exhibit excellent reversible discharge capacity.

[0006] Li ２ S-P ２ S ５ -LiBH ４ However, the inventors continued their research. As a result, when a cathode mixture that did not provide sufficient reversible discharge capacity was analyzed by powder X-ray diffraction (XRD), it was found that Li ２ S-P ２ S ５ -LiBH４ It was found that the characteristic peak disappeared. It was also found that the disappearance of this peak was due to the mixing operation during the production of the positive electrode composite. Based on this finding, the present inventors further conducted extensive research and found that Li ２ S-P ２ S ５ -LiBH ４ It has been found that a specific positive electrode mixture produced by a specific method has excellent reversible discharge capacity even when using Li. ２ S-P ２ S ５ -LiBH ４ It was also found that the characteristic peaks were retained.

[0007] According to the present invention, the following positive electrode composites and the like can be provided. 1. A positive electrode composite comprising a sulfur-based active material and a solid electrolyte, having a diffraction peak A at 2θ=15.1±0.8° and a diffraction peak B at 2θ=29.8±0.8° in powder X-ray diffraction using CuKα radiation, and containing P and B as elements. 2. The positive electrode composite according to 1, in which the half-width of the diffraction peak A is 0.5° or more. 3. The positive electrode composite according to 1 or 2, which comprises a conductive additive that is a carbon material, and in elemental analysis of an electron microscope image by energy dispersive X-ray spectroscopy, the overlap rate of mapping of carbon and phosphorus is 45% or more. 4. 4. The cathode mixture according to any one of 1 to 3, which is obtained by a production 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, wherein the solid electrolyte added in the second mixing step includes solid electrolyte α, and the solid electrolyte α has a diffraction peak A at 2θ = 15.1 ± 0.8° and a diffraction peak B at 2θ = 29.8 ± 0.8° in powder X-ray diffraction using CuKα radiation, and contains P and B as elements. 5. The cathode mixture according to 4, wherein the second mixing step is performed with lower energy than the first mixing step. 6. The cathode mixture according to 4 or 5, 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. 7. A lithium ion battery comprising the cathode mixture according to any one of 1 to 6. 8. A method for producing a cathode mixture, comprising: 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 comprises solid electrolyte α, and the solid electrolyte α has a diffraction peak A at 2θ = 15.1 ± 0.8° and a diffraction peak B at 2θ = 29.8 ± 0.8° in powder X-ray diffraction using CuKα rays, and contains P and B as elements. 9. A method for producing a cathode mixture according to 8, wherein the second mixing step involves mixing with less energy than the first mixing step.10. The method for producing a cathode composite according to 8 or 9, 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 be lost. 11. The method for producing a cathode composite according to any of 8 to 10, wherein the proportion of the solid electrolyte α added in the second mixing step is 50 to 100 parts by mass when the solid electrolyte α contained in the produced cathode composite is taken as 100 parts by mass. 12. The method for producing a cathode composite according to any of 8 to 11, wherein the amount of the solid electrolyte α added in the first mixing step is 0 to 50 parts by mass when the total amount of the solid electrolytes added in the first mixing step is taken as 100 parts by mass. 13. 13. The method for producing a positive electrode composite according to any one of 8 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.

[0008] 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.

[0009] 1 is a diagram showing the results of powder X-ray diffraction (XRD) of the positive electrode composite powder. It is a diagram 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. Furthermore, C indicates carbon mapping, and P indicates phosphorus mapping. It is a diagram 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. Furthermore, C indicates carbon mapping, and P indicates phosphorus mapping.

[0010] 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.

[0011] 1. Cathode Composite A cathode composite according to one embodiment of the present invention includes a sulfur-based active material and a solid electrolyte, and in powder X-ray diffraction using CuKα radiation, has a diffraction peak A at 2θ = 15.1 ± 0.8° and a diffraction peak B at 2θ = 29.8 ± 0.8°, and contains P and B as elements. The cathode composite of this embodiment exhibits the effect of exhibiting excellent reversible discharge capacity.

[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 α) In one embodiment, the positive electrode composite includes a solid electrolyte (also referred to as "solid electrolyte α") that has a diffraction peak A at 2θ = 15.1 ± 0.8° and a diffraction peak B at 2θ = 29.8 ± 0.8° in powder X-ray diffraction using CuKα radiation, and contains P and B as elements. In one embodiment, the solid electrolyte α is an argyrodite-type solid electrolyte. In one embodiment, the solid electrolyte α contains P, B, Li, and S as elements. Here, the solid electrolyte α contains B as BH ４ It may include as.

[0014] The method for producing the solid electrolyte α is not particularly limited. As a starting material, two or more compounds or simple substances containing lithium, phosphorus, sulfur, boron, or the like as constituent elements can be used in combination, and any starting material can be used without particular limitation as long as it exhibits ionic conductivity due to the contained metal atoms.

[0015] 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.

[0016] Examples of raw materials containing phosphorus (P) and sulfur (S) include diphosphorus trisulfide (P ２ S ３ ), 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.

[0017] As a raw material containing boron (B), lithium borohydride (LiBH ４ ), sodium borohydride, lithium tetraborate, lithium metaborate, etc. Among these, lithium borohydride is preferred.

[0018] The combination of raw materials used is preferably lithium sulfide, diphosphorus pentasulfide, and lithium borohydride. The molar ratio of lithium sulfide to diphosphorus pentasulfide in the raw materials is preferably 65 to 85:15 to 35, more preferably 70 to 80:20 to 30, even more preferably 72 to 78:22 to 28, and particularly preferably 75:25. The amount of lithium borohydride blended is preferably 25 mol% or more and 95 mol% or less, more preferably 30 mol% or more and 85 mol% or less, based on the total of lithium sulfide, diphosphorus pentasulfide, and lithium borohydride.

[0019] The raw materials are subjected to mechanical stress to form the solid electrolyte α. Here, "applying mechanical stress" means mechanically applying shear force, impact force, etc. Examples of means for applying mechanical stress include a pulverizer such as a planetary ball mill, a vibration mill, or a tumbling mill, and a kneader.

[0020] The order of mixing is not particularly limited. For example, when lithium sulfide, diphosphorus pentasulfide, and lithium borohydride are used as raw materials, the three compounds may be mixed and treated in the above-mentioned apparatus. Alternatively, a mixture of lithium sulfide and diphosphorus pentasulfide may be treated in advance, and then lithium borohydride may be added to the resulting treated product and mixed. The solid electrolyte α may also be produced by the method described in Non-Patent Document 1, for example.

[0021] 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.

[0022] (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, the sulfide solid electrolyte preferably contains lithium atoms and phosphorus atoms, and more preferably contains lithium atoms, phosphorus atoms, and halogen atoms, and has ionic conductivity due to lithium atoms. 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.

[0023] (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 ２ S 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.

[0024] 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 ５In 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%.

[0025] (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).

[0026] 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 ４Examples include a crystal structure similar to the thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725).

[0027] 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 P ２ 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.

[0028] The crystal structure of the crystalline sulfide solid electrolyte also includes an argyrodite-type crystal structure. 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).

[0029] Among the above crystal structures, the crystal structure of the crystalline sulfide solid electrolyte is Li ３ P.S. ４ The crystal structure, the thiolicon region II crystal structure, and the argyrodite crystal structure are preferred.

[0030] In one embodiment, 20 to 100 mass %, 25 to 95 mass %, or 30 to 90 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.

[0031] (Powder X-ray Diffraction) As described above, the positive electrode composite has a diffraction peak A at 2θ = 15.1 ± 0.8° and a diffraction peak B at 2θ = 29.8 ± 0.8° in powder X-ray diffraction using CuKα radiation. These diffraction peaks A and B are derived from the solid electrolyte α.

[0032] In one embodiment, the positive electrode composite has a half-width of the diffraction peak A of 0.5° or more. The half-width of the diffraction peak A is preferably 0.6° or more, more preferably 0.7° or more. This allows for good compaction properties and the formation of a strong interface with the active material. In one embodiment, the positive electrode composite has a half-width of the diffraction peak A of 0.5 to 3.0°, 0.6 to 2.5°, or 0.7 to 2.0°. The half-width of the diffraction peak A is a value measured by the method described in the examples.

[0033] (Conductive additive) In one embodiment, the positive electrode composite contains a conductive additive. Examples of the conductive additive include a carbon material. In one embodiment, the positive electrode composite contains a conductive additive that is a carbon material, and in elemental analysis of electron microscope images using energy dispersive X-ray spectroscopy, the overlap rate between carbon and phosphorus mapping is 45% or more. The overlap rate is preferably 55% or more, more preferably 60% or more. When the overlap rate is 45% or more, the components in the positive electrode composite (e.g., solid electrolyte, conductive additive, sulfur-based active material, etc.) are sufficiently mixed. From the viewpoint of the composite structure, conductivity to a larger portion of the sulfur-based active material can be ensured, and an effect of increasing the active material utilization rate can be expected.

[0034] The conductive additive may be any material having electron conductivity, and is preferably a carbon material. The conductive additive preferably has a plurality of pores. A carbon material having pores is particularly preferred. Carbon materials have high conductivity and are lighter than other conductive materials, so that the output density and capacity per unit weight of the battery can be increased.

[0035] The carbon material is not particularly limited, but examples thereof include carbon black 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 fullerene, carbon fiber, natural graphite, artificial graphite, graphene, graphene oxide, and reduced graphene oxide. These may be used alone or in combination of two or more. Composites of these may also be used.

[0036] 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.

[0037] 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.

[0038] In one embodiment, the positive electrode composite includes 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. The solid electrolyte added in the second mixing step is obtained by a manufacturing method including solid electrolyte α, and the solid electrolyte α has a diffraction peak A at 2θ = 15.1 ± 0.8° and a diffraction peak B at 2θ = 29.8 ± 0.8° in powder X-ray diffraction using CuKα radiation, and contains P and B as elements. In this embodiment, the second mixing step is preferably performed with a lower energy than the first mixing step. In this embodiment, the first mixing step is preferably performed under conditions that promote amorphization of the solid electrolyte added in the first mixing step, and the second mixing step is preferably 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 the solid electrolyte α has a diffraction peak A at 2θ = 15.1 ± 0.8° and a diffraction peak B at 2θ = 29.8 ± 0.8° in powder X-ray diffraction using CuKα radiation, and contains P and B as elements. 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 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.

[0051] 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.

[0052] 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."

[0053] 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 in which a negative electrode active material and a solid electrolyte are mixed.

[0054] 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, Sn ２ 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.

[0055] 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.

[0056] 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.

[0057] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0058] 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.

[0059] (2) Preparation of Solid Electrolyte A 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 10 zirconia balls having 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 milled) for 40 hours at a rotation speed of 370 rpm. The resulting powder was then heat-treated at 195 ° C. for 3 hours to obtain a solid electrolyte A.

[0060] (3) Preparation of solid electrolyte α 0.3830 g of lithium sulfide, 0.6170 g of diphosphorus pentasulfide, 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) at a rotation speed of 370 rpm for 40 hours to obtain a powder. Next, 0.8053 g of the obtained powder, 0.1947 g of lithium borohydride, and 100 g of zirconia balls with a diameter of 4 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) at a rotation speed of 510 rpm for 15 hours to obtain a solid electrolyte α (powder).

[0061] (4) Preparation of Positive Electrode Composite Powder First Mixing Step 0.9 g of composite powder A and 0.18 g of solid electrolyte A were placed in a 45 mL zirconia pot together with 10 zirconia balls having a diameter of 10 mm 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 at room temperature (25 ° C.; the same applies below) to obtain composite powder B.

[0062] Second Mixing Step: 0.54 g of composite powder B and 0.36 g of solid electrolyte α 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 using a tumbling mill ("Small Ball Mill Stand", manufactured by Asahi Rika Seisakusho, Model AV-1) at a rotation speed of 600 rpm for 1 hour at room temperature to obtain a positive electrode composite powder.

[0063] Comparative Example 1 0.45 g of composite powder A obtained in the same manner as in Example 1 and 0.45 g of solid electrolyte α 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 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 at room temperature to obtain a positive electrode composite powder. A charge-discharge test was carried out on the obtained positive electrode composite powder in the same manner as in Example 1. The obtained reversible discharge capacity (discharge capacity in the 2nd cycle) is shown in Table 1.

[0064] 2. Measurement Method and Test Method (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 a Kapton film for XRD and measured without being exposed to air. The XRD measurement was performed using a powder X-ray diffraction measurement device D2 PHASER from BRUKER Co., Ltd. under the following measurement conditions. [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 (Ni plate 0.5%), air scatter screen (3 mm used) Detector: semiconductor detector Measurement range: 2θ = 10-60 deg Step width, scan speed: 0.05 deg, 0.05 deg / sec Note that XRD measurement was also performed on a reference sample (Reference Example 1) consisting only of solid electrolyte α. The results are shown in Figure 1.

[0065] The X-ray diffraction pattern was examined to determine whether or not a diffraction peak A at 2θ = 15.1 ± 0.8° and a diffraction peak B at 2θ = 29.8 ± 0.8° were present, and the half-value width of the diffraction peak A was determined by the following method.

[0066] 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 = 15.1° ± 0.8° in the X-ray diffraction pattern is determined by multiplying the average of the X-ray intensities (counts) at 2θ = (15.1° - 0.8°) ± 0.2, i.e., 2θ = 14.3° ± 0.2°, and 2θ = (15.1° + 0.8°) ± 0.2°, i.e., 2θ = 15.9° ± 0.2°, by the background (BG) intensity I ｂｇ The maximum value of the X-ray intensity (counts) at 2θ = 15.1° ± 0.8° is defined as the peak intensity I ｐｅａｋ When 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.

[0067] Diffraction Peak B Whether or not diffraction peak B exists in the range of 2θ = 29.8 ± 0.8° can be determined by multiplying the average of the X-ray intensities (counts) at 2θ = (29.8° - 0.8°) ± 0.2, i.e., 2θ = 29.0° ± 0.2°, and 2θ = (29.8° + 0.8°) ± 0.2°, i.e., 2θ = 30.6° ± 0.2°, by the background (BG) intensity I ｂｇ The maximum value of the X-ray intensity (counts) at 2θ = 29.8° ± 0.8° 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.

[0068] As a result of the above, in the positive electrode composite of Example 1, the diffraction peak A is ｐｅａｋ / I ｂｇ ) is 1.247, so it is determined to be "present," and the diffraction peak B is ｐｅａｋ / I ｂｇOn the other hand, in the positive electrode composite of Comparative Example 1, the diffraction peak A was determined to be "present" because the ratio (I ｐｅａｋ / I ｂｇ ) is 1.085, so it is determined to be "absent," and the diffraction peak B is ｐｅａｋ / I ｂｇ ) was 1.049, so it was determined to be "not present."

[0069] Calculation of 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 15.1 ± 0.8° 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.

[0070]

[0071] 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.

[0072] As a result, the half-value width of the diffraction peak A in Example 1 was 1.18°.

[0073] (2) Energy Dispersive X-ray Spectroscopy (SEM-EDS Analysis) of Electron Microscope Images and Calculation of Carbon and Phosphorus Overlap Rate 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.

[0074] 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. SEM-EDS elemental mapping measurement was performed on the obtained cross section using an SEM (Hitachi High-Tech Corporation, SU8220) and an 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 x 768. No special image processing was performed for EDS mapping, and an image on 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.

[0075] 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 the carbon and phosphorus EDS images were subjected to smoothing twice using a bilateral filter with d = 15, sigmaColor = 64, and sigmaSpace = 64. The resulting images were compressed to one-third of their original pixel 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 converted to grayscale 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 carbon. The results of the SEM-EDS analysis, including the above image processing, are shown in Figure 2 (Example 1) and Figure 3 (Comparative Example 1). 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 carbon and phosphorus numerical matrices, 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 for one field of view. The average of the overlap rates for all 10 fields of view was taken as the overlap rate of this embodiment (the overlap rate of carbon and phosphorus mapping).

[0076] As a result of the above, the overlap rate of carbon and phosphorus mapping was 70.9% in Example 1. In Comparative Example 1, the overlap rate of carbon and phosphorus mapping was 99.7%.

[0077] (3) Reversible Discharge Capacity (Charge / Discharge Test) Preparation of Lithium Ion Battery (All-Solid-State Battery) A lithium ion battery (all-solid-state battery) was prepared using 5 mg of each of the positive electrode composite powders obtained in the Examples and Comparative Examples. Specifically, 100 mg of solid electrolyte A was first pressure-molded in a Macol cylinder with a diameter of 10 mm. Next, 5 mg of the positive electrode composite powder was added to one side of the molded solid electrolyte A, and the resulting mixture was pressure-molded again. Next, three sheets of indium foil and two sheets of lithium foil were alternately stacked on the other side of the molded solid electrolyte A (the side opposite the positive electrode composite), and pressure was applied to obtain an all-solid-state battery.

[0078] Charge / Discharge Test The obtained all-solid-state battery was subjected to a constant current charge / discharge test. In the constant current charge / discharge test, the voltage range was set to 0.8 to 2.2 V and the current value was set to 0.147 mA at the start of discharge.

[0079] As a result, the reversible discharge capacity (discharge capacity at the 2nd cycle) was 1474 mAh / g in Example 1 and 397 mAh / g in Comparative Example 1. Therefore, it can be seen that the reversible discharge capacity of Example 1 is significantly improved compared to Comparative Example 1.

[0080] 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. It contains a sulfur-based active material and a solid electrolyte, In powder X-ray diffraction using CuKα rays, diffraction peak A is observed at 2θ = 15.1 ± 0.8° and diffraction peak B is observed at 29.8 ± 0.8°. Having P and B as elements, Cathode composite material.

2. The positive electrode composite material according to claim 1, wherein the full width at half maximum of the diffraction peak A is 0.5° or more.

3. The cathode composite material according to claim 1 or 2, comprising a conductive additive which is a carbon material, wherein the overlap rate of carbon and phosphorus mapping in elemental analysis by energy-dispersive X-ray spectroscopy of electron microscope images is 45% or more.

4. The manufacturing method comprises a first mixing step of obtaining a first mixture by adding a solid electrolyte to a sulfur-based active material and mixing it, and a second mixing step of obtaining a second mixture by adding a further solid electrolyte to the first mixture and mixing it, wherein the solid electrolyte added in the second mixing step is obtained by a manufacturing method that includes solid electrolyte α. The solid electrolyte α, in powder X-ray diffraction using CuKα rays, has a diffraction peak A at 2θ = 15.1 ± 0.8° and a diffraction peak B at 29.8 ± 0.8°, and contains elements P and B. The positive electrode composite material according to claim 1 or 2.

5. The positive electrode composite material according to claim 4, wherein the mixing process in the second mixing step is performed with less energy than in the first mixing step.

6. The first mixing step is performed under conditions that allow the amorphous formation of the solid electrolyte added in the first mixing step to proceed. The second mixing step is performed under conditions that the crystallinity of the solid electrolyte α added in the second mixing step is not lost. The positive electrode composite material according to claim 4.

7. A lithium-ion battery comprising the positive electrode composite material described in claim 1 or 2.

8. A first mixing step involves adding a solid electrolyte to a sulfur-based active material and mixing it to obtain a first mixture, The process includes a second mixing step of obtaining a second mixture by adding a further solid electrolyte to the first mixture and mixing it, The solid electrolyte added in the second mixing step includes solid electrolyte α, The solid electrolyte α, in powder X-ray diffraction using CuKα rays, has a diffraction peak A at 2θ = 15.1 ± 0.8° and a diffraction peak B at 29.8 ± 0.8°, and contains elements P and B. A method for manufacturing positive electrode composite material.

9. A method for producing a positive electrode composite material according to claim 8, wherein the mixing process in the second mixing step is performed with less energy than in the first mixing step.

10. The first mixing step is performed under conditions that allow the amorphous formation of the solid electrolyte added in the first mixing step to proceed. The second mixing step is performed under conditions that the crystallinity of the solid electrolyte α added in the second mixing step is not lost. A method for producing a positive electrode composite material according to claim 8 or 9.

11. A method for producing a cathode composite material according to claim 8 or 9, wherein, when the solid electrolyte α contained in the manufactured cathode composite material is 100 parts by mass, the proportion of solid electrolyte α added in the second mixing step is 50 to 100 parts by mass.

12. A method for producing a positive electrode composite according to claim 8 or 9, wherein when the total amount of solid electrolyte 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.

13. A method for producing a positive electrode composite according to claim 8 or 9, wherein when the total amount of solid electrolyte 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.