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

Abstract

This positive electrode mixture contains elemental sulfur, a solid electrolyte, a conductive auxiliary agent, and an organic compound which is capable of suppressing vaporization of elemental sulfur.

Description

Positive electrode mixture, lithium ion battery, positive electrode mixture composition, and method for producing positive electrode mixture

[0001] The present invention relates to a cathode composite, a lithium ion battery, a cathode composite composition, and a method for producing the cathode composite. Specifically, the present invention relates to a cathode composite, a lithium ion battery, a cathode composite composition, and a method for producing the cathode composite that can suppress sulfur vaporization.

[0002] As a cathode composite material used in lithium ion batteries and the like, a sulfur-based cathode composite material having a high theoretical capacity is known (Patent Document 1).

[0003] International Publication No. 2012 / 086196

[0004] When preparing a cathode sheet using a sulfur-based cathode composite, the composite must be dispersed in a solvent, applied, and then dried. However, the sulfur vaporizes during the drying process, which reduces the proportion of sulfur in the cathode composite and may result in a decrease in the capacity per composite.

[0005] An object of the present invention is to provide a positive electrode mixture, a lithium ion battery, a composition for a positive electrode mixture, and a method for producing the positive electrode mixture, which are capable of suppressing sulfur vaporization.

[0006] As a result of extensive research, the inventors have discovered that sulfur evaporation can be suppressed by a cathode mixture containing a specific component, and have thus completed the present invention. According to the present invention, the following cathode mixtures and the like can be provided. 1. A cathode mixture containing elemental sulfur, a solid electrolyte, a conductive additive, and an organic compound capable of suppressing the evaporation of elemental sulfur. 2. The cathode mixture according to 1, wherein the organic compound contains N (nitrogen atom) and has an unshared electron pair. 3. The cathode mixture according to 1 or 2, wherein the organic compound is an amine. 4. The cathode mixture according to any one of 1 to 3, wherein the organic compound is an aliphatic amine. 5. The cathode mixture according to any one of 1 to 4, wherein the organic compound has a tertiary amino group. 6. The cathode mixture according to any one of 1 to 5, wherein the organic compound is tetramethylethylenediamine. 7. The cathode mixture according to any one of 1 to 6, wherein the solid electrolyte is a sulfide solid electrolyte. 8. A lithium ion battery comprising the cathode mixture according to any one of 1 to 7. 9. 10. A cathode composite composition comprising elemental sulfur, a solid electrolyte, a conductive additive, an organic compound capable of suppressing evaporation of the elemental sulfur, and a solvent. 10. A method for producing a cathode composite, comprising heating the cathode composite composition according to 10.9.

[0007] According to the present invention, it is possible to provide a positive electrode mixture capable of suppressing sulfur vaporization, a lithium ion battery, a composition for a positive electrode mixture, and a method for producing the positive electrode mixture.

[0008] FIG. 10 is a diagram showing the results of evolved gas analysis.

[0009] The cathode composite, lithium ion battery, cathode composite composition, and cathode composite manufacturing method 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 The cathode composite according to this embodiment includes elemental sulfur, a solid electrolyte, a conductive additive, and an organic compound capable of suppressing the evaporation of elemental sulfur (hereinafter, sometimes referred to as "organic compound α"). The cathode composite according to this embodiment has the effect of suppressing the evaporation of sulfur. Furthermore, by suppressing the evaporation of sulfur, the decrease in sulfur contained in the cathode composite can be suppressed. Furthermore, by suppressing the evaporation of sulfur, corrosion of manufacturing equipment (particularly metal members) due to sulfur-containing gas can be suppressed.

[0011] As described above, when preparing a positive electrode sheet using a sulfur-based positive electrode composite, it is necessary to disperse the positive electrode composite in a solvent, apply the dispersion, and then perform a drying operation. In this embodiment, sulfur in the positive electrode composite is captured by the organic compound α, and therefore, evaporation of sulfur can be suppressed when the solvent is dried by heating or the like.

[0012] The organic compound α is not particularly limited as long as it is an organic compound capable of suppressing the evaporation of elemental sulfur. Like N (nitrogen atom), S (sulfur atom), which constitutes elemental sulfur, has covalent bonding properties and is prone to negative charge. However, unlike N, S is a third-period element, and therefore can utilize vacant 3d orbitals, making it easy to accept negative charges. Examples of the organic compound α include organic compounds capable of interacting with S (sulfur atom). Without being bound by theory, it is believed that, for example, in an organic compound containing an electronegative element, its lone electron pair interacts with the vacant orbital of S (sulfur atom). As a result of such interaction, the evaporation of elemental sulfur is suppressed. In one embodiment, the organic compound α is a compound having a lone electron pair. In one embodiment, the organic compound α is a compound containing one or more selected from the group consisting of N (nitrogen atom), O (oxygen atom), and halogen atoms.

[0013] In one embodiment, the organic compound α is a compound containing N (nitrogen atom) and having an unshared electron pair. In one embodiment, the organic compound α is an amine (also referred to as an "amine compound"), a nitrile (also referred to as a "nitrile compound"), or an amide (also referred to as an "amide compound"). These compounds can effectively suppress the evaporation of elemental sulfur by bonding with elemental sulfur through a nucleophilic reaction or a reaction similar to the Willgerodt reaction. In one embodiment, the organic compound α has a tertiary amino group. By having the tertiary amino group in the organic compound α, the evaporation of elemental sulfur can be more effectively suppressed. The number of tertiary amino groups in the organic compound α may be one or two or more. It is preferable that the organic compound α has two or more tertiary amino groups.

[0014] Examples of the amine include aliphatic amines, alicyclic amines, heterocyclic amines, and aromatic amines, and these can be used alone or in combination.

[0015] More specifically, typical preferred aliphatic amines include aliphatic tertiary diamines such as N,N,N',N'-tetramethyldiaminomethane, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, N,N,N',N'-tetramethyldiaminopropane, N,N,N',N'-tetraethyldiaminopropane, N,N,N',N'-tetramethyldiaminobutane, N,N,N',N'-tetramethyldiaminopentane, and N,N,N',N'-tetramethyldiaminohexane. In the examples given in this specification, for example, diaminobutane includes, unless otherwise specified, isomers relating to the position of the amino group, such as 1,2-bis(dimethylamino)butane, 1,3-bis(dimethylamino)butane, and 1,4-bis(dimethylamino)butane, as well as all isomers of butane, such as linear and branched isomers. The number of carbon atoms in the aliphatic amine is preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more, with the upper limit being preferably 10 or less, more preferably 8 or less, and even more preferably 7 or less. The number of carbon atoms in the hydrocarbon group of the aliphatic hydrocarbon group in the aliphatic tertiary amine is preferably 2 or more, and the upper limit being preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0016] Typical preferred examples of the alicyclic amine include alicyclic tertiary diamines such as N,N,N',N'-tetramethyl-cyclohexanediamine and bis(ethylmethylamino)cyclohexane, and typical preferred examples of the heterocyclic amine include heterocyclic tertiary diamines such as N,N-dimethylpiperazine and bismethylpiperidylpropane. The number of carbon atoms in the alicyclic amine and heterocyclic amine is preferably 3 or more, more preferably 4 or more, and the upper limit is preferably 16 or less, more preferably 14 or less.

[0017] Typical preferred examples of aromatic amines include aromatic tertiary diamines such as N,N-dimethylphenylenediamine, N,N,N',N'-tetramethylphenylenediamine, N,N,N',N'-tetramethyldiaminodiphenylmethane, N,N,N',N'-tetramethylnaphthalenediamine, etc. The number of carbon atoms in the aromatic amine is preferably 6 or more, more preferably 7 or more, and even more preferably 8 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

[0018] In one embodiment, the amine may be substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxyl group, a hydroxyl group, or a cyano group, or with a halogen atom. While the above specific examples mainly use diamines, the present invention is not limited thereto. For example, polyamines having three or more amino groups, such as N,N,N',N'',N''-pentamethyldiethylenetriamine, N,N'-bis[(dimethylamino)ethyl]-N,N'-dimethylethylenediamine, and hexamethylenetetramine, can also be used. In one embodiment, the organic compound α is an aliphatic tertiary diamine having tertiary amino groups at both ends. Preferred examples of such aliphatic tertiary diamines include tetramethylethylenediamine, tetraethylethylenediamine, tetramethyldiaminopropane, and tetraethyldiaminopropane.

[0019] The nitrile is not particularly limited, and examples thereof include R(CN) ｎ In the formula, R is, for example, an alkyl group having from 1 to 10 carbon atoms, an alkoxyl group having from 1 to 10 carbon atoms, or a group having an aromatic ring having from 6 to 18 ring carbon atoms. n is 1 or 2. Specific examples of the nitrile include acetonitrile, methoxyacetonitrile, propionitrile, methoxypropionitrile, 3-chloropropionitrile, benzonitrile, 4-fluorobenzonitrile, tertiary butyronitrile, isobutyronitrile, cyclohexylnitrile, capronitrile, isocapronitrile, malononitrile, fumaronitrile, and isovaleronitrile.

[0020] In one embodiment, the organic compound α is a compound containing an O (oxygen atom). Examples of compounds containing an O (oxygen atom) include esters, ethers, and ketones.

[0021] In one embodiment, the organic compound α is a compound containing a halogen atom. Examples of halogen atoms include a chlorine atom, a fluorine atom, a bromine atom, and an iodine atom. Specific examples of compounds containing a halogen atom include alkyl halides and aryl halides. The alkyl group in the alkyl halide may have, for example, 1 to 10 carbon atoms. The aryl group in the aryl halide may have, for example, 6 to 18 ring carbon atoms.

[0022] The organic compound α may be an organic compound other than the compounds described above. Examples of such organic compounds include organometallic compounds, organophosphorus compounds, and olefins. The organic compounds α described above may be used alone or in combination.

[0023] The solid electrolyte is not particularly limited, but 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, and in addition to sulfur atoms, preferably contains lithium atoms and phosphorus atoms, more preferably contains lithium atoms, phosphorus atoms, and halogen atoms, and has ionic conductivity due to lithium atoms. The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

[0024] (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 S５ - 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.

[0025] 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 65 to 85:15 to 35, more preferably 70 to 80:20 to 30, and even more preferably 72 to 78:22 to 28. ２ S-P ２ S５ In the case of -LiI-LiBr, the total content of lithium sulfide and diphosphorus pentasulfide is preferably 60 to 95 mol%, more preferably 65 to 90 mol%, and even more preferably 70 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%.

[0026] When the amorphous sulfide solid electrolyte contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, the compounding ratio (molar ratio) of these atoms is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.6, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.05 to 0.5, and even more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.08 to 0.4. Furthermore, when bromine and iodine are used in combination as halogen atoms, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine atoms, and iodine atoms 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. By setting the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, it becomes easier to obtain a solid electrolyte having a thiolisiconregion II type crystal structure described below and having higher ionic conductivity.

[0027] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 to 200 μm. ５０) is the particle size at which 50% of the total particle size is reached when the particle size distribution integral curve is drawn and the integral is calculated from the smallest particle size, and the volume distribution is an average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device.

[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] The crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms may have a crystal structure such as Li ４－ｘ Ge 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－ｘ Ge １－ｘ P ｘ S ４ Examples of the thio-lisicon region II crystal structure include those having a crystal structure similar to the thio-lisicon region II type (see Solid State Ionics, 177 (2006), 2721-2725). ４－ｘ Ge １－ｘ Pｘ S ４ Thio-LISICON Region II crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ This indicates that the thio-LISICON region II type has a similar crystal structure to the thio-LISICON region II type.

[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 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 that of thio-LISICON Region II type appear, for example, at 2θ=20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0031] 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).

[0032] 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.

[0033] The shape of the crystalline sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) is the average particle size (D ５０ ) and the range of 0.01 μm to 500 μm, or 0.1 to 200 μm, for example, can be exemplified.

[0034] The conductive additive may be any material that has electron conductivity, but 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 the output density and capacity per unit weight of the battery can be increased. The BET specific surface area of ​​the conductive additive is 0.1 m ２ / g or more 6000m２ / g or less is more preferable, and 1m ２ / g or more 5000m ２ / g or less, and more preferably 1m ２ / g or more 4000m ２ / g or less, and most preferably 10m ２ / g or more 4000m ２ The pore volume of the conductive additive is preferably 0.1 cc / g or more and 6.0 cc / g or less. The pores of the conductive additive preferably have an average diameter of 0.1 nm or more and 40 nm or less, more preferably 0.5 nm or more and 40 nm or less, even more preferably 0.5 nm or more and 20 nm or less, and most preferably 0.7 nm or more and 20 nm or less.

[0035] The BET specific surface area, average pore diameter, and pore volume of the conductive additive can be measured using a nitrogen adsorption isotherm obtained by adsorbing nitrogen gas to the conductive additive under liquid nitrogen. Specifically, the BET specific surface area can be determined by the Brenauer-Emmet-Telle (BET) method, and the average pore diameter and pore volume can be determined by the BJH (Barrett-Joyner-Halenda) method. Measurements can be performed using, for example, a specific surface area / pore distribution measuring device (Autosorb-3) manufactured by Quantacrome.

[0036] 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, and carbon nanohorns. Examples of conductive carbon materials include fullerene, carbon fiber, natural graphite, and artificial graphite. These may be used alone or in combination of two or more. Composite materials of these may also be used.

[0037] Mesoporous carbon is a carbon material having two-dimensional or three-dimensional pores, which can be obtained by the production method described in the following documents: S. J. Sang, S. H. Joo, R. Ryoo, et., J. Am. Chem. Soc., 122 (2000) 10712-10713, and T. Yokoi, Y. Sakamoto, O. Terasaki, et., J. Am. Chem. Soc., 128 (2006) 13664-13665.

[0038] In one embodiment, the positive electrode mixture may or may not contain other components in addition to the elemental sulfur, the solid electrolyte, the conductive additive, and the organic compound α. The other components are not particularly limited, and examples thereof include a solvent, a dispersant, a binder, and the like.

[0039] In the positive electrode mixture, the contents of elemental sulfur, solid electrolyte, conductive additive, organic compound α, and other components are not particularly limited. In one embodiment, the content of elemental sulfur is 20 to 80 mass% of the total. In one embodiment, the content of solid electrolyte is 5 to 50 mass% of the total. In one embodiment, the content of conductive additive is 5 to 30 mass% of the total. In one embodiment, the content of organic compound α is 0.1 to 10 mass% with respect to 100 mass% of the solid electrolyte. In one embodiment, the content of other components is 0.1 to 10 mass% of the total. In one embodiment, 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, 90 mass% or more, 95 mass% or more, 99 mass% or more, 99.5 mass% or more, or substantially 100 mass% of the positive electrode mixture are elemental sulfur, solid electrolyte, conductive additive, and organic compound α. Note that "substantially 100 mass%" may include inevitable impurities.

[0040] 2. Lithium-ion battery A lithium-ion battery according to an embodiment of the present invention includes the cathode composite according to the embodiment of the present invention described above. The lithium-ion battery according to an embodiment of the present invention can suppress the evaporation of sulfur during manufacturing.

[0041] 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."

[0042] 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.

[0043] 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, Sn5Cu6, 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.

[0044] 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.

[0045] 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.

[0046] 3. Cathode Composite Composition A cathode composite composition according to one embodiment of the present invention includes elemental sulfur, a solid electrolyte, a conductive additive, an organic compound (organic compound α) capable of suppressing the evaporation of elemental sulfur, and a solvent. The description of the cathode composite according to one embodiment of the present invention applies to the elemental sulfur, solid electrolyte, conductive additive, and organic compound α contained in the cathode composite composition. The solvent is not particularly limited, but examples include fluorine-based solvents, hydrocarbon-based solvents, and thio-based solvents. Specific examples include fluorocarbons, fluorobenzene, trifluoromethylbenzene, bistrifluoromethylbenzene, benzene, toluene, xylene, and thiol. The solids concentration of the cathode composite composition is, for example, 20% by weight to 95% by weight, preferably 30% by weight to 85% by weight.

[0047] 4. Manufacturing Method of Cathode Composite A manufacturing method of a cathode composite according to one aspect of the present invention includes heating the cathode composite composition according to one aspect of the present invention described above. By heating the cathode composite composition, the solvent contained in the cathode composite composition is dried and removed, thereby obtaining a cathode composite. By using the cathode composite composition according to one aspect of the present invention, the effect of suppressing sulfur vaporization can be obtained even when such a drying operation is performed. The heating temperature is not particularly limited, but is, for example, 50 to 200°C. The heating time is not particularly limited, but is, for example, 0.1 to 120 minutes. Heating is preferably performed under reduced pressure or in an inert gas atmosphere. In one embodiment, the cathode composite composition (as a coating liquid) is applied to a substrate (e.g., a cathode current collector) and then heated to dry and remove the solvent, thereby obtaining a cathode composite. The cathode composite obtained in this manner can be in the form of, for example, a sheet, and can form the cathode layer of the lithium-ion battery described above.

[0048] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0049] (Example 1) (1) Preparation of Solid Electrolyte A 15.3 g of lithium sulfide and 24.7 g of diphosphorus pentasulfide were placed in a 1 L reactor equipped with a stirring blade under a nitrogen atmosphere. After the stirring blade was turned on, 400 mL of tetrahydrofuran cooled to −20° C. was added to the vessel. After allowing the vessel to naturally warm to room temperature, stirring was continued for 72 hours. The resulting reaction solution slurry was placed in a glass filter (pore size: 40 to 100 μm) to obtain a solid content, which was then dried at 90° C. to obtain Li. ３ P.S. ４ The obtained Li powder (purity: 90% by mass) was placed in a Schlenk flask (volume: 100 mL) equipped with a stirrer under a nitrogen atmosphere. ３ P.S. ４ 1.70 g of powder, 0.19 g of lithium bromide, and 0.28 g of lithium iodide were added. After rotating the stirrer, 20 mL of the complexing agent tetramethylethylenediamine (TMEDA) was added, and stirring was continued for 12 hours. The resulting electrolyte precursor content was dried under vacuum at room temperature to obtain a powdered electrolyte precursor. The resulting electrolyte precursor was heated under vacuum at 120°C for 2 hours, and then further heated under vacuum at 140°C for 2 hours to obtain solid electrolyte A.

[0050] A portion of the obtained solid electrolyte A was dissolved in methanol, and the obtained methanol solution was analyzed by gas chromatography to measure the content of tetramethylethylenediamine. As a result, the content of the complexing agent in the solid electrolyte was 1.2 mass%.

[0051] (2) Preparation of Cathode Composite A Activated carbon (MSC-30, manufactured by Kansai Ceramic Chemicals) and elemental sulfur were placed in a glass tube in a mass ratio of 30:70 and sealed in a SUS tube 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 a composite powder A of activated carbon and elemental sulfur. 0.45 g of the obtained composite powder A and 0.45 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), the mixture was mixed at room temperature for 20 hours at a rotation speed of 370 rpm to obtain a cathode composite A.

[0052] <Evaluation Method> Evolved Gas Analysis 5 mg of the obtained cathode composite was packed into a glass tube in a glove box, and the end of the glass tube was sealed. The glass tube filled with the cathode composite was removed from the glove box, attached to an online micro reaction sampler (manufactured by Frontier Labs), and introduced into a pyrolysis apparatus. The gas generated by heating the cathode composite was detected online using a gas chromatograph mass spectrometer (GCMS). The equipment used for the measurement, pyrolysis furnace temperature rise conditions, and GCMS conditions were as follows. <Apparatus used> Pyrolysis apparatus: EGA / PY-3030D (Frontier Labs) Gas chromatograph mass spectrometer: 8890 / 5977B (Agilent) Column: EGA capillary tube (length 2.5 m x inner diameter 0.15 mm) (Frontier Labs) <Pyrolysis furnace temperature rise conditions> 50°C → temperature rise 10°C / min → 600°C (hold for 5 min) <GCMS conditions> Carrier gas (He) flow rate: 1 mL / min Split ratio: 10:1 Injection port temperature: 300°C Oven: 300°C (constant) Ion source temperature: 300°C

[0053] The results of the evolved gas analysis are shown in FIG.

[0054] (Comparative Example 1) (1) Preparation of Solid Electrolyte B 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) at a rotation speed of 370 rpm for 40 hours to obtain a powder. The obtained powder was heated at 195 ° C. for 3 hours to obtain a solid electrolyte B. The obtained solid electrolyte B did not contain tetramethylethylenediamine.

[0055] (2) Preparation of Positive Electrode Composite B A positive electrode composite B was obtained under the same preparation conditions as in "(2) Preparation of Positive Electrode Composite A" in Example 1, except that solid electrolyte B was used as the electrolyte.

[0056] The resulting positive electrode mixture B was subjected to evolved gas analysis in the same manner as in Example 1. The analysis results from 50° C. to 250° C. are shown in FIG.

[0057] <Evaluation> From Figure 1, when the amount of gas generated by elemental sulfur at 200°C is compared between cathode composite A containing an organic compound (tetramethylethylenediamine in this case) capable of suppressing the evaporation of elemental sulfur and cathode composite B which does not contain this, the amount of gas generated by cathode composite A is about ⅛ of that of cathode composite B, confirming that sulfur is less likely to evaporate. Therefore, it is thought that sulfur is less likely to evaporate when cathode composite A is dispersed in a solvent and applied as a material for a positive electrode sheet, and then dried.

[0058] The positive electrode composite of the present invention is suitable for use as a positive electrode for a lithium ion battery. The lithium ion battery of the present invention is also suitable for use in, for example, information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and vehicles such as electric vehicles.

[0059] 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 material comprising elemental sulfur, a solid electrolyte, a conductive additive, and an organic compound capable of suppressing evaporation of the elemental sulfur.

2. The positive electrode mixture according to claim 1 , wherein the organic compound contains N (nitrogen atom) and has an unshared electron pair.

3. The positive electrode mixture according to claim 1 or 2, wherein the organic compound is an amine.

4. The positive electrode mixture according to claim 1 or 2, wherein the organic compound is an aliphatic amine.

5. The positive electrode mixture according to claim 1 or 2, wherein the organic compound has a tertiary amino group.

6. The positive electrode mixture according to claim 1 or 2, wherein the organic compound is tetramethylethylenediamine.

7. The positive electrode mixture according to claim 1 or 2, wherein the solid electrolyte is a sulfide solid electrolyte.

8. A lithium ion battery comprising the positive electrode mixture according to claim 1 or 2.

9. A positive electrode mixture composition comprising: elemental sulfur; a solid electrolyte; a conductive additive; an organic compound capable of suppressing evaporation of the elemental sulfur; and a solvent.

10. A method for producing a positive electrode mixture, comprising heating the positive electrode mixture composition according to claim 9.