Positive electrode mixture

Abstract

A positive electrode mixture comprising: a conductive auxiliary agent which is a carbon material; a sulfur-based active material; and a sulfide solid electrolyte, and containing at least lithium atoms, phosphorus atoms, and halogen atoms, wherein the molar ratio (Li / P) of lithium atoms to phosphorus atoms is 0.60-5.20, the molar ratio (Ha / P) of halogen atoms to phosphorus atoms is 0.45 or more, and the ratio (I30.0 / I29.3) of the maximum intensity (I30.0) at 2θ=30.0°±0.34° to the maximum intensity (I29.3) at 2θ=29.3°±0.34° in an X-ray diffraction pattern obtained by powder X-ray diffraction using CuKα rays is 0.75 or more.

Description

Cathode composite material

[0001] This invention relates to a positive electrode composite material used in lithium-ion secondary batteries and the like.

[0002] Lithium-ion batteries require a large battery capacity. To improve battery capacity, methods using sulfur as the positive electrode are being considered due to its high theoretical capacity. However, since sulfur has low electronic and ionic conductivity, it is necessary to ensure sufficient electronic and ionic conductivity within the positive electrode when using sulfur.

[0003] To address the above issues, a cathode composite material comprising sulfur, phosphorus pentasulfide, conductive carbon, and lithium halide has been investigated (see, for example, Patent Document 1). In addition, a cathode composite material comprising sulfur, carbon nanotubes, and a solid electrolyte mixed in a polar solvent has been investigated (see, for example, Non-Patent Document 1).

[0004] International Publication No. 2021 / 251031

[0005] ACS Energy Lett. 2023, 8, 10, 3971-3979

[0006] Sulfide solid electrolytes having an argyrodite crystal structure (hereinafter sometimes referred to as argyrodite-type solid electrolytes) have high ionic conductivity and are therefore being considered for use in cathode composite materials (Non-Patent Literature 1). However, lithium-ion batteries using argyrodite-type solid electrolytes as cathode composite materials have had insufficient rate characteristics. One of the objectives of the present invention is to provide a cathode composite material that can produce lithium-ion batteries with good rate characteristics.

[0007] In the preparation of cathode composite materials, we discovered that the rate characteristics can be improved by using components containing specific elements along with the sulfide solid electrolyte. Furthermore, we found that the rate characteristics are specifically improved by adding lithium halide.

[0008] The present invention provides the following positive electrode composite material, etc. 1. A conductive additive which is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, comprising at least lithium atoms, phosphorus atoms, and halogen atoms, wherein the molar ratio of lithium atoms to phosphorus atoms (Li / P) is 0.60 to 5.20, and the molar ratio of halogen atoms to phosphorus atoms (Ha / P) is 0.45 or more, and the maximum intensity (I) at 2θ = 29.3° ± 0.34° in the X-ray diffraction pattern obtained by powder X-ray diffraction using CuKα rays. ２９．３ Maximum intensity (I) at 2θ = 30.0° ± 0.34° for ) ３０．０ ) ratio (I ３０．０ / I ２９．３1. A positive electrode mixture in which the ratio of halogen atoms to halogen atoms is 0.75 or higher. 2. The positive electrode mixture according to 1, wherein the halogen atom is an iodine atom. 3. The positive electrode mixture according to 1 or 2, wherein the halogen atom is three or more types. 4. A positive electrode mixture comprising a conductive additive which is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, and containing at least a lithium atom, a phosphorus atom, and three or more types of halogen atoms. 5. The positive electrode mixture according to 3 or 4, wherein the halogen atoms are a chlorine atom, a bromine atom, and an iodine atom. 6. The positive electrode mixture according to 5, wherein the molar ratio of the iodine atom to the total halogen atoms is 0.10 to 0.50. 7. The positive electrode mixture according to any one of 1 to 6, wherein the molar ratio of the halogen atoms to the phosphorus atom (Ha / P) is 1.60 or lower. 8. The positive electrode mixture according to any one of 1 to 7, wherein the sulfide solid electrolyte has an argyrodite crystal structure. 9. 10. A positive electrode composite material according to any one of 1 to 8, wherein the sulfur-based active material is elemental sulfur. 11. A lithium-ion battery comprising the positive electrode composite material according to any one of 1 to 9. 11. A method for producing a positive electrode composite material, comprising the step of mixing a conductive additive which is a carbon material, a sulfur-based active material, a sulfide solid electrolyte, phosphorus sulfide, lithium sulfide, and lithium halide. 12. The method for producing the positive electrode composite material according to 11, comprising the steps of forming composite B with the conductive additive, the sulfur-based active material, and the phosphorus sulfide, and forming composite B with the sulfide solid electrolyte, lithium sulfide, and lithium halide. 13. The method for producing the positive electrode composite material according to 12, comprising the steps of forming composite A with the conductive additive and the sulfur-based active material, and forming composite B with composite A and the phosphorus sulfide. 14. The method for producing the positive electrode composite material according to any one of 11 to 13, comprising the step of compounding the phosphorus sulfide in a molten state. 15. The manufacturing method according to 12, comprising the steps of: forming a composite C with composite B, lithium sulfide, and lithium halide; and forming a composite with composite C and the sulfide solid electrolyte. 16. The manufacturing method according to any one of 11 to 15, wherein the molar ratio of lithium atoms to phosphorus atoms (Li / P) is adjusted to 0.60 to 5.20, and the molar ratio of halogen atoms to phosphorus atoms (Ha / P) is adjusted to 0.45 or more. 17. The manufacturing method according to any one of 11 to 16, wherein the sulfide solid electrolyte has an argyrodite type crystal structure.18. The manufacturing method according to 17, wherein the sulfide solid electrolyte contains chlorine atoms and bromine atoms as constituent elements. 19. The manufacturing method according to any one of 11 to 18, wherein the sulfur-based active material is sulfur. 20. The manufacturing method according to any one of 11 to 19, wherein the lithium halide is lithium iodide. 21. The manufacturing method according to any one of 11 to 20, wherein the phosphorus sulfide is diphosphorus pentasulfide.

[0009] According to the present invention, it is possible to provide a cathode composite material that can be used to obtain a lithium-ion battery with good rate characteristics.

[0010] This is the XRD pattern of the cathode composite obtained in Example 1. This is the XRD pattern of the cathode composite obtained in Example 2. This is the XRD pattern of the cathode composite obtained in Comparative Example 1. This is the XRD pattern of the cathode composite obtained in Comparative Example 2. This is the XRD pattern of the cathode composite obtained in Comparative Example 3. This is the XRD pattern of the cathode composite obtained in Comparative Example 4. This is the XRD pattern of the cathode composite obtained in Comparative Example 5.

[0011] [Positive Electrode Composition Material] A positive electrode composition material according to one aspect of the present invention comprises a conductive additive which is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, and contains at least lithium atoms, phosphorus atoms, and halogen atoms as constituent elements. It also satisfies the following requirements (A) to (C). (A) The molar ratio of lithium atoms to phosphorus atoms (Li / P) is 0.60 to 5.20. (B) The molar ratio of halogen atoms to phosphorus atoms (Ha / P) is 0.45 or more. (C) The maximum intensity (I) at 2θ = 29.3° ± 0.34° in the X-ray diffraction pattern obtained by powder X-ray diffraction using CuKα rays. ２９．３ Maximum intensity (I) at 2θ = 30.0° ± 0.34° for ) ３０．０ ) ratio (I ３０．０ / I ２９．３ The value is 0.75 or higher.

[0012] By satisfying requirements (A) to (C), a cathode composite material can be obtained that yields a lithium-ion battery with good rate characteristics. Requirement (A) is assumed to relate to interface formation ability, requirement (B) to the redox reactivity of the sulfur-based active material, and requirement (C) to the ionic conductivity of the cathode composite material.

[0013] Regarding the above requirements (A) and (B), for example, when the sulfide solid electrolyte is an argyrodite-type solid electrolyte, this indicates that, in addition to lithium atoms and phosphorus atoms derived from the argyrodite-type solid electrolyte, the mixture further contains lithium atoms, phosphorus atoms and halogen atoms. In a typical argyrodite-type solid electrolyte, the molar ratio (Li / P) is greater than 5.20. In the present embodiment, for example, when producing the positive electrode mixture, a compound containing lithium atoms, phosphorus atoms, halogen atoms and sulfur atoms (e.g., phosphorus sulfide, lithium sulfide and lithium halide) is added to the argyrodite-type solid electrolyte, so the molar ratio (Li / P) of the positive electrode mixture is different from the molar ratios (Li / P and Ha / P) of the argyrodite-type solid electrolyte.

[0014] Regarding the above requirement (C), for example, when the sulfide solid electrolyte is an argyrodite-type solid electrolyte, a diffraction peak of the solid electrolyte is observed at 2θ=30.0°±0.34°, and a diffraction peak of a decomposition product is observed at 2θ=29.3±0.34°. The ratio (I ３０．０ / I ２９．３ ) being large means that the sulfide solid electrolyte exists in the positive electrode mixture without being decomposed. The constituent members of the positive electrode mixture will be described below.

[0015] (Carbon material) The carbon material is used as a conductive aid. Since the carbon material has high electron conductivity and is lighter than other conductive materials, it can increase the output density and capacity per unit weight of the battery. The carbon material is preferably porous carbon having pores.

[0016] The carbon material is not particularly limited, and examples thereof include carbon blacks such as Ketjenblack, acetylene black, Denka black, thermal black and channel black, as well as mesoporous carbon, activated carbon, amorphous carbon, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon nanohorns, fullerene, carbon fiber, natural graphite, artificial graphite, graphene, graphene oxide, reduced graphene oxide, and the like. These may be used alone, or two or more thereof may be used in combination. Composite materials of these may also be used.

[0017] In one embodiment, the BET specific surface area of ​​the carbon material is 50 m². ２ / g to 6000m ２ This is / g. This allows for the formation of a broad contact interface between the carbon material and the sulfur-based active material, thereby improving the utilization rate of the sulfur-based active material. The BET specific surface area is preferably 70 m². ２ / g to 5500m ２ / g, more preferably 100m ２ / g to 5000m ２ / g, and more preferably 1000m ２ / g to 5000m ２ The value is / g, and is particularly preferably 1500m ２ / g to 5000m ２ It is / g.

[0018] Furthermore, the pore volume of the carbon material is 0.5 cm³. ３ / g to 6cm ３ This is per gram. This allows sulfur-based active material to be impregnated into the pores of the carbon material, further improving the battery capacity. The pore volume is 0.7 cm³. ３ / g ~ 5.5cm ３ / g is preferred, and moreover, 1.0 cm ３ / g ~ 5.0cm ３ / g is preferred.

[0019] In this invention, the BET specific surface area and pore volume can be determined using nitrogen adsorption isotherms obtained by adsorbing nitrogen gas onto a carbon material at liquid nitrogen temperature. Specifically, the BET specific surface area can be calculated using the Brunauer-Emmett-Teller (BET) multipoint method with respect to the nitrogen adsorption isotherms. The pore volume can be determined using the Barrett-Joyner-Halenda (BJH) method with respect to the nitrogen adsorption isotherms. As a measuring device, for example, the specific surface area and pore distribution analyzer (Autosorb-3) manufactured by Quantachrome can be used for measurement.

[0020] (Sulfur-based active material) There are no particular limitations on sulfur-based active materials, 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 Examples include sulfur-containing polymer compounds, etc. Among these, sulfur (elemental sulfur) is preferred. There are no particular limitations on the sulfur, but high purity is preferred. Specifically, a purity of 95% by mass or higher is preferred, more preferably 96% by mass or higher, and particularly preferably 97% by mass or higher. Examples of sulfur crystal systems include α-sulfur (orthorhombic), β (monoclinic), γ (monoclinic), amorphous sulfur, etc. These can be used individually or in combination of two or more.

[0021] During a battery reaction, some or all of the sulfur-based active material transforms into discharge products. Therefore, in one embodiment of the electrode material, discharge products of the sulfur-based active material are present. For example, as a sulfur discharge product, Li in a completely discharged state... ２ Li as S and its intermediate stage lithium polysulfide ２ S ２ Li ２ S ４ Li ２ S ６ Li ２ S ８ These are some examples.

[0022] (Sulfide Solid Electrolytes) As sulfide solid electrolytes, for example, glass ceramics or sulfide solid electrolytes having the following crystal structure can be used. The crystal structure that a crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms and phosphorus atoms may have is Li ３ PS ４ Crystal structure, Li ４ P ２ S ６ Crystal structure, Li ７ PS ６ Crystal structure, Li ７ P ３ S １１ Examples include crystal structures, and crystal structures having peaks near 2θ = 20.2° and 23.6° (for example, Japanese Patent Publication No. 2013-16423).

[0023] Furthermore, the crystal structure that a crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms may have is Li ４－ｘ Ge １－ｘ P ｘ S ４ The thio-LISICON Region II type crystal structure (see Kanno et al., Journal of The Electrochemical Society, 148(7) A742-746 (2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ Examples include the thio-LISICON Region II type and similar crystal structures (see Solid State Ionics, 177 (2006), 2721-2725). Here, "thio-LISICON Region II type crystal structure" refers to Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-Lisicon Region II type crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ This indicates that the crystal structure is similar to that of the thio-LISICON Region II system.

[0024] In one embodiment, the sulfide solid electrolyte includes an argyrodite-type crystal structure. An example of an argyrodite-type crystal structure is Li ７ PS ６ Crystal structure; Li ７ PS ６ Composition formula Li has a structural framework ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ Crystal structure represented by (x is -0.6 to 0.6, y is 0.1 to 0.6); Li ７－ｘ－２ｙ PS ６－ｘ－ｙ Cl ｘCrystal structure shown by (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5); Li ７－ｘ PS ６－ｘ Ha ｘ Examples of crystal structures include those represented by (Ha is Cl or Br, and x is preferably 0.2 to 1.8).

[0025] X-ray diffraction measurements using CuKα rays show diffraction peaks at 2θ = 25.6 ± 0.5° and 30.0 ± 0.5°, confirming that the sulfide solid electrolyte contains an argyrodite-type crystal structure.

[0026] In the positive electrode composite material of this embodiment, the molar ratio of lithium atoms to phosphorus atoms (Li / P) is 0.60 to 5.20. This ensures an appropriate molar ratio of lithium atoms to phosphorus atoms in the positive electrode composite material, allowing the ion-conducting material to form a strong interface with the carbon material and sulfur-based active material, thereby improving the battery's rate characteristics. The molar ratio (Li / P) may also be 1.00 to 5.00, 1.90 to 4.75, 2.30 to 4.75, or 3.00 to 4.75.

[0027] In the positive electrode composite material of this embodiment, the molar ratio of halogen atoms to phosphorus atoms (Ha / P) is 0.45 or higher. This is expected to result in an appropriate molar ratio of halogen atoms to phosphorus atoms in the positive electrode composite material, thereby improving the rate characteristics. The molar ratio (Ha / P) is preferably 0.50 to 1.60, and particularly preferably 0.52 to 1.40.

[0028] The molar ratios (Li / P) and (Ha / P) of the positive electrode composite material can be measured, for example, by an ICP emission spectrometer. Furthermore, the molar ratios of the positive electrode composite material can be adjusted, for example, by the mixing ratio of the raw materials, such as sulfide solid electrolyte, phosphorus pentasulfide, lithium sulfide, and lithium halide.

[0029] Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. The positive electrode composite material preferably contains iodine atoms. In one embodiment, the molar ratio of iodine atoms to the total number of halogen atoms (iodine / halogen) is 0.01 to 0.80, 0.10 to 0.50, or 0.20 to 0.30.

[0030] In one embodiment, the positive electrode mixture contains three or more halogen atoms. Preferably, the positive electrode mixture contains chlorine, bromine, and iodine atoms. This further improves ionic conductivity and rate characteristics.

[0031] [Other embodiments of the positive electrode composite material] Another embodiment of the positive electrode composite material of the present invention comprises a conductive additive which is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, and contains at least lithium atoms, phosphorus atoms, and three or more types of halogen atoms as constituent elements. This results in a positive electrode composite material that can be used to obtain a lithium-ion battery with good rate characteristics.

[0032] Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. In one embodiment, the positive electrode mixture preferably contains chlorine atoms, bromine atoms, and iodine atoms. The conductive additive, sulfur-based active material, and sulfide solid electrolyte, which are carbon materials, are the same as those in the positive electrode mixture of the other embodiment described above.

[0033] One method for incorporating three or more halogen atoms into a positive electrode composite is to use, for example, a sulfide solid electrolyte containing two types of halogen atoms as constituent elements and lithium halide containing halogen atoms different from these halogens. For example, an argyrodite-type solid electrolyte containing chlorine and bromine atoms as constituent elements and lithium iodide can be used as raw materials.

[0034] [Method for Manufacturing the Positive Electrode Compound] The positive electrode compound of the present invention can be obtained by a manufacturing method that includes the step of mixing, for example, a conductive additive which is a carbon material, a sulfur-based active material, a sulfide solid electrolyte, phosphorus sulfide, lithium sulfide, and lithium halide.

[0035] For the carbon material, sulfur-based active material, and sulfide solid electrolyte, those described for the positive electrode mixture can be used. The method for producing the sulfide solid electrolyte is not particularly limited, and a known method can be employed. As an example, a method for producing an argyrodite-type solid electrolyte will be described. As starting materials, a combination of two or more compounds or simple substances containing lithium atoms, phosphorus atoms, sulfur atoms, chlorine atoms, bromine atoms, and the like as constituent elements can be used, and any material that exhibits ionic conductivity attributable to the contained metal atoms can be employed without particular limitation.

[0036] Examples of raw materials containing lithium (Li) include lithium sulfide (Li ２ S), lithium oxide (Li ２ O), lithium carbonate (Li ２ CO ３ ), other lithium compounds, and simple substance lithium metal, among others. Among these, lithium compounds are preferable, and lithium sulfide is more preferable.

[0037] Examples of raw materials containing phosphorus (P) and sulfur (S) include phosphorus trisulfide (P ２ S ３ ), phosphorus pentasulfide (P ２ S ５ ), other phosphorus sulfides, sodium phosphate (Na ３ PO ４ ), other phosphorus compounds, simple substance phosphorus, and simple substance sulfur, among others. Among these, phosphorus sulfides are preferable, and phosphorus pentasulfide is more preferable. Any industrially produced and commercially available phosphorus compound such as phosphorus pentasulfide, simple substance phosphorus, or simple substance sulfur can be used without particular limitation.

[0038] Preferable examples of halogen-containing raw materials include lithium halides such as lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI); and phosphorus halides such as phosphorus pentachloride (PCl ５ ), phosphorus trichloride (PCl ３ ), phosphorus pentabromide (PBr ５ ), and phosphorus tribromide (PBr ３ ). Among these, preferred are lithium halides such as LiCl, LiBr, and LiI, and PBr ３Lithium halides such as LiCl, LiBr, and LiI are preferred, and LiCl and LiBr are even more preferred.

[0039] Preferably, the combination of raw materials used includes a lithium-containing compound, a phosphorus sulfide, and a lithium halide; more preferably, lithium sulfide, phosphorus sulfide, and lithium halide; and particularly preferably, lithium sulfide, diphosphorus pentasulfide, lithium chloride, and lithium bromide. The molar ratio of the raw materials used is preferably, for example, lithium sulfide: diphosphorus pentasulfide: total of the two types of lithium halides = 30-60:10-25:15-50.

[0040] An intermediate is obtained by applying mechanical stress to the above raw materials. Examples of means for applying mechanical stress include grinders such as planetary ball mills, vibratory mills, and rolling mills, as well as kneaders. An argyrodite-type solid electrolyte is obtained by heat treatment of the intermediate. The heat treatment temperature is preferably 350°C to 650°C, more preferably 360°C to 500°C, and even more preferably 380°C to 450°C.

[0041] In another method for producing argyrodite-type solid electrolytes, the above raw materials are roughly mixed and then dispersed in a solvent (such as a mixed solvent of dehydrated toluene and dehydrated isobutyronitrile) to prepare a slurry. This slurry is then mixed and pulverized using a mixing mill or similar device. After that, the solvent is removed, and the mixture is heated in an electric furnace at 400°C to 430°C, followed by slow cooling to obtain the raw material sulfide solid electrolyte. Under a nitrogen atmosphere, the raw material sulfide solid electrolyte is dispersed in a solvent (such as dehydrated toluene), and then atomized using a planetary ball mill to obtain another slurry. This slurry is dried to remove the solvent and obtain the argyrodite-type solid electrolyte.

[0042] X-ray diffraction measurements using CuKα rays show diffraction peaks at 2θ = 25.6 ± 0.5° and 30.0 ± 0.5°, confirming that the sulfide solid electrolyte contains an argyrodite-type crystal structure.

[0043] As for phosphorus sulfide, diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S５ Examples include the following. The phosphorus sulfide may have a dimer or polysulfide structure, or it may be a mixture. Phosphorus pentasulfide is preferred.

[0044] Examples of lithium halides include lithium fluoride, lithium chloride, lithium bromide, and lithium iodide.

[0045] Phosphorus sulfide, lithium sulfide, and lithium halides can be used without any particular limitations, provided they are industrially manufactured and sold.

[0046] In one embodiment, the sulfide solid electrolyte has an argyrodite-type crystal structure. It also contains chlorine and bromine atoms as constituent elements. Furthermore, the lithium halide is lithium iodide.

[0047] In the manufacturing method of this embodiment, a material containing a carbon material, a sulfur-based active material, phosphorus sulfide, lithium sulfide, and lithium halide, or a composite material consisting of two or more selected from the carbon material, sulfur-based active material, phosphorus sulfide, lithium sulfide, and lithium halide, and containing phosphorus atoms, lithium atoms, and halogen atoms, is mechanically mixed. An example of the mechanical mixing means is the same as that for the production of the argyrodite-type solid electrolyte described above. The mixture and / or reactants of phosphorus sulfide, lithium sulfide, and lithium halide are pulverized and mixed under strong mechanical stress so that a portion of the sulfide solid electrolyte reacts with the mixture and / or reactants to form an ion conductor, and the crystalline structure of the sulfide solid electrolyte remains.

[0048] The subject of mechanical mixing may be a mixture of carbon material, sulfur-based active material, phosphorus sulfide, lithium sulfide, lithium halide, and sulfide solid electrolyte. Alternatively, a composite consisting of two or more selected from carbon material, sulfur-based active material, phosphorus sulfide, lithium sulfide, and lithium halide may be prepared in advance, and a mixture of the material containing the composite and the sulfide solid electrolyte may be prepared. In the material containing the composite, the phosphorus atom, lithium atom, and halogen atom are derived, for example, from phosphorus sulfide, lithium sulfide, and lithium halide. For example, a mixture may be prepared by first forming a composite of carbon material and sulfur-based active material (hereinafter sometimes referred to as composite A), and then mixing composite A with phosphorus sulfide, lithium sulfide, lithium halide, and sulfide solid electrolyte. Alternatively, a mixture may be prepared by forming a composite of composite A and phosphorus sulfide (hereinafter sometimes referred to as composite B), and then mixing composite B with lithium sulfide, lithium halide, and sulfide solid electrolyte. Alternatively, a mixture may be formed by combining Complex B, lithium sulfide, and lithium halide to form a complex (hereinafter sometimes referred to as Complex C), and mixing Complex C with a sulfide solid electrolyte. Furthermore, instead of phosphorus sulfide and lithium sulfide, a pre-mechanically mixed complex (reactant) of phosphorus sulfide and lithium sulfide may be used.

[0049] In the manufacturing method of this embodiment, mechanical mixing may be performed two or more times. For example, composite A, phosphorus sulfide, lithium sulfide, and lithium halide may be mechanically mixed, and then a sulfide solid electrolyte may be added and mechanically mixed. Alternatively, composite B, lithium sulfide, and lithium halide may be mechanically mixed, and then a sulfide solid electrolyte may be added and mechanically mixed.

[0050] Composite A can be obtained, for example, by heating and melting a sulfur-based active material and impregnating it into the pores of a carbon material. Melting the sulfur-based active material promotes impregnation into the pores. Furthermore, the sulfur-based active material can be highly dispersed in the carbon material.

[0051] The heating temperature can be appropriately set according to the sulfur-based active material used. For example, if the sulfur-based active material is sulfur, the temperature should be above the melting point of sulfur (approximately 115°C). Preferably, it should be 130°C or higher, and more preferably 150°C or higher. Heating may be carried out in two or more stages.

[0052] Furthermore, composite A can also be prepared by impregnating the pores of a carbon material with a sulfur-based active material through mechanical mixing. Various mills, such as the planetary ball mills mentioned above, can be used for mechanical mixing.

[0053] In the manufacturing method of this embodiment, it is preferable to have a step of compounding phosphorus sulfide into composite A beforehand. This makes the interface between composite A and the ion conductor stronger. It also suppresses the decomposition of the sulfide solid electrolyte. Examples of methods for compounding phosphorus sulfide into composite A beforehand include mixing phosphorus sulfide into composite A in a molten state or mechanically mixing composite A and phosphorus sulfide. Mixing phosphorus sulfide in a molten state is preferred for compounding because it makes the interface between composite A and the ion conductor stronger.

[0054] In one embodiment, the raw materials may or may not contain components other than carbon material, sulfur-based active material, mixture or complex of phosphorus sulfide, lithium sulfide and lithium halide, and sulfide solid electrolyte. Other components are not particularly limited, but examples include binders, solvents, and dispersants.

[0055] In the raw materials for the positive electrode composite, the content of carbon material, sulfur-based active material, mixture or composite of phosphorus sulfide, lithium sulfide, and lithium halide, and sulfide solid electrolyte is not particularly limited. For example, the content of sulfur-based active material is 60 to 1000 parts by mass per 100 parts by mass of sulfide solid electrolyte. The content of carbon material is 20 to 500 parts by mass per 100 parts by mass of sulfide solid electrolyte. The content of phosphorus sulfide, lithium sulfide, and lithium halide is adjusted so that the molar ratio of lithium atoms to phosphorus atoms (Li / P) is 0.60 to 5.20, and the molar ratio of halogen atoms to phosphorus atoms (Ha / P) is 0.45 to 1.60. The content of phosphorus sulfide is 15 to 230 parts by mass per 100 parts by mass of sulfide solid electrolyte. Preferably, it is 25 to 180 parts by mass. The lithium sulfide content is 20 to 100 parts by mass per 100 parts by mass of the sulfide solid electrolyte. Preferably, it is 30 to 70 parts by mass. The lithium halide content is 10 to 80 parts by mass per 100 parts by mass of the sulfide solid electrolyte. Preferably, it is 15 to 50 parts by mass.

[0056] In one embodiment, 50% or more by mass of the cathode composite material raw materials, 60% or more by mass, 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, 99% or more by mass, 99.5% or more by mass, or substantially 100% by mass is a mixture or composite of carbon material, sulfur-based active material, phosphorus sulfide, lithium sulfide, and lithium halide, and a sulfide solid electrolyte. In the case of "substantially 100% by mass", unavoidable impurities may be included.

[0057] The positive electrode composite material of the present invention can be suitably used, for example, as a constituent material of a secondary battery. For example, it can be used as the positive electrode of a lithium-ion battery. A lithium-ion battery according to one embodiment of the present invention includes the positive electrode composite material of the present invention described above. For example, by using a solid electrolyte, an all-solid-state lithium-ion battery can be manufactured. By using the positive electrode composite material of the present invention, an all-solid-state lithium-ion battery can be manufactured that has good cycle characteristics and rate characteristics, and low initial irreversible capacity. A lithium-ion battery mainly consists of a positive electrode layer, a negative electrode layer, and an electrolyte layer. The negative electrode layer and the electrolyte layer can be manufactured by known methods. For example, the sulfide solid electrolyte described above can be used for the electrolyte layer. In addition to the positive electrode layer, negative electrode layer, and electrolyte layer, it is preferable that a current collector is used, and known current collectors can also be used.

[0058] The present invention will be described in detail below based on examples. The present invention is not limited to these examples.

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

[0060] (2) Preparation of composite powder B The powder of composite A obtained in (1) above and phosphorus pentasulfide (made by Italmatch, melting point 286-290°C) were placed in a Tammann tube with an inner diameter of 12 mm in a mass ratio of 0.7143:0.2857 and sealed inside a SUS tube container. It was heated in an electric furnace at 350°C for 6 hours to obtain composite powder B.

[0061] (3) Preparation of solid electrolyte A Under a nitrogen atmosphere, lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ ), lithium bromide (LiBr) and lithium chloride (LiCl), in molar ratio (Li ２ S:P ２ S ５The raw material mixture was prepared by weighing LiBr:LiCl in a ratio of 47.5:12.5:15.0:25.0 and roughly mixing them. The raw material mixture was dispersed in a mixed solvent of dehydrated toluene and 2% by mass of dehydrated isobutyronitrile relative to the raw material mixture to obtain a slurry of approximately 10% by mass. 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 the mixture. After removing the solvent from the obtained mixture, it was heated in an electric furnace at 400-430°C for 2 hours. Subsequently, the raw material sulfide solid electrolyte was obtained by slow cooling. Under a nitrogen atmosphere, the raw material sulfide solid electrolyte was dispersed in dehydrated toluene and placed together with 0.3 mm diameter zirconia balls in a zirconia pot of a planetary ball mill device (Fritsch: model P-7), and the inside of the pot was made into an inert atmosphere. A slurry containing a finely particulated sulfide solid electrolyte was obtained by processing in a planetary ball mill at a rotation speed of 150 rpm for 2 hours. After transferring the slurry to a nitrogen-purged Schlenk bottle, it was dried at room temperature for 1 hour using a vacuum pump, and then heated to 80°C to 100°C to further remove the solvent contained in the finely particulate sulfide solid electrolyte (vacuum drying) to obtain solid electrolyte A. XRD measurements showed diffraction peaks at 2θ = 25.5°, 30.0°, and 31.3°, confirming that solid electrolyte A has an argyrodite-type crystal structure. The ionic conductivity was 4.7 × 10⁻¹⁵. －３ The value was S / cm.

[0062] (4) Preparation of Cathode Compound 0.8537 g of composite powder B, 0.0975 g of lithium sulfide, and 0.0488 g of lithium iodide were placed in a 45 mL zirconia pot together with 10 zirconia balls with a diameter of 10 mm and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was heated at a rotation speed of 370 rpm for 20 hours at room temperature to obtain composite powder C. 0.7380 g of the obtained composite powder C and 0.1620 g of solid electrolyte A were placed in a 45 mL zirconia pot together with 10 zirconia balls with a diameter of 10 mm and sealed. Using a planetary ball mill, the mixture was heated at a rotation speed of 370 rpm for 20 hours at room temperature to obtain a powdered cathode compound.

[0063] Example 2 A cathode composite powder was obtained in the same manner as in Example 1 (4), except that the mixing time of composite powder B, lithium sulfide, and lithium iodide was changed from 20 hours to 40 hours.

[0064] Comparative Example 1: 0.4500 g of composite powder A, obtained in the same manner as in Example 1, and 0.4500 g of solid electrolyte A were placed in a 45 mL zirconia pot along with 10 zirconia balls with a diameter of 10 mm, and the pot was sealed. A positive electrode composite was obtained by mixing using a planetary ball mill (Fritsch, model P-7) at a rotation speed of 370 rpm for 20 hours at room temperature.

[0065] Comparative Example 2 0.6300 g of composite powder B and 0.2700 g of solid electrolyte A, obtained in the same manner as in Example 1, were placed in a 45 mL zirconia pot along with 10 zirconia balls with a diameter of 10 mm, and sealed. A positive electrode composite was obtained by mixing using a planetary ball mill (Fritsch, model P-7) at a rotation speed of 370 rpm for 20 hours at room temperature.

[0066] Comparative Example 3: In Example 1 (4), without adding lithium sulfide, 0.8537 g of composite powder B and 0.1463 g of lithium iodide were mixed in a planetary ball mill to obtain composite powder E. A cathode composite material was obtained in the same manner as in Example 1, except that composite powder E was used instead of composite powder C.

[0067] Comparative Example 4: In Example 1 (4), without adding lithium iodide, 0.8537 g of composite powder B and 0.1463 g of lithium sulfide were mixed in a planetary ball mill to obtain composite powder F. A cathode composite material was obtained in the same manner as in Example 1, except that composite powder F was used instead of composite powder C.

[0068] Comparative Example 5: A cathode composite material was obtained in the same manner as in Comparative Example 4, except that the mixing time of composite powder B and lithium sulfide was 40 hours.

[0069] [Evaluation of Cathode Compound] The molar ratio of each element in the cathode compound was calculated from the blending amounts of lithium sulfide, diphosphorus pentasulfide, lithium iodide, and solid electrolyte A, which are the raw materials. The molar ratio of lithium element to phosphorus element (Li / P) and the molar ratio of halogen element to phosphorus element (Ha / P) were calculated.

[0070] - The X-ray diffraction cathode composite was filled into a groove with a diameter of 20 mm and a depth of 0.2 mm, and leveled with glass to prepare the sample. This sample was sealed with Kapton film for XRD and measured without exposure to air. The XRD measurement was performed using a BRUKER Corporation D2 PHASER powder X-ray diffraction analyzer under the following measurement conditions.

[0071] Tube voltage: 30kV Tube current: 10mA X-ray wavelength: Cu-Kα line (1.5418Å) Optical system: Focused method Slit configuration: Solar slit 4° (both incident and receiving sides), divergent slit 1mm, Kβ filter (Ni plate 0.5%), air scatter screen 3mm Detector: Semiconductor detector Measurement range: 2θ = 10⁻⁶⁰ degrees Step width, scan speed: 0.05 degrees, 0.05 degrees / second

[0072] I is the maximum value of intensity within the range of 2θ = 30.0 ± 0.34°. ３０．０ I is the maximum value of the intensity in the range of 2θ = 29.3 ± 0.34°. ２９．３ Let I be the ratio of the two. ３０．０ / I ２９．３ The result was calculated.

[0073] [Preparation of Lithium-ion Battery] (1) Preparation of Negative Electrode Mixture Lithium titanate (Ishihara Sangyo Co., Ltd. "LT-112"), conductive additive (Denka Co., Ltd. "Li-100", powdered acetylene black), and solid electrolyte A were weighed in a mass ratio of 60:5:35 and mixed in a mortar for 5 minutes to obtain negative electrode mixture (also called "LTO (lithium titanate) negative electrode mixture").

[0074] (2) Preparation of Solid Electrolyte B 0.4127 g of lithium sulfide, 0.6655 g of phosphorus pentasulfide, 0.2137 g of lithium iodide, and 0.2080 g of lithium bromide, along with 10 zirconia balls with a diameter of 10 mm, were placed in a 45 ml zirconia pot and sealed. Using a planetary ball mill (Fritsch, model 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 Solid Electrolyte B.

[0075] (3) Preparation of Lithium-ion Battery A solid electrolyte layer (a layer of solid electrolyte B) was formed by placing 100 mg of solid electrolyte B into a 10 mm diameter Macol cylinder and pressurizing it. Next, 10 mg of the positive electrode composite powder prepared in the examples and comparative examples was placed on one pressurized surface of the solid electrolyte layer and pressurized again. Next, 166 mg of LTO negative electrode composite material was placed on the other pressurized surface of the solid electrolyte layer (the pressurized surface opposite to the positive electrode) and pressurized. A lithium-ion battery was then prepared by placing a 9 mm diameter, 0.1 mm thick Li foil on top of that and pressurizing it again.

[0076] [Evaluation of Battery Characteristics] (1) Charge and Discharge Tests Constant current charge and discharge tests were performed on lithium-ion batteries using the positive electrode composite materials of each example and comparative example. The voltage range for the constant current charge and discharge tests was set to -0.4 to 1.3V, and the current value was set as shown in Table 1 based on the C rate determined based on the theoretical capacity of sulfur of 1672 mAh / g. For charging, CC-CV charging was performed, which involves constant current charging followed by constant voltage charging with a termination condition of 0.02C, and for discharging, constant current discharge (CC discharge) was performed. The composition, molar ratio, and XRD intensity ratio (I) of the positive electrode composite material were evaluated. ３０．０ / I ２９．３ The discharge capacity at ) and 1C is shown in Table 2.

[0077]

[0078]

[0079] P ２ S ５ Li ２ In the examples using both S and LiI, exceptionally high rate characteristics were obtained. Comparative Example 1, which simply used an argyrodite-type solid electrolyte, is thought to have had insufficient interface formation and therefore insufficient characteristics.

[0080] The XRD patterns of the positive electrode composite materials of the examples and comparative examples are shown in Figures 1 to 7. XRD intensity ratio (I ３０．０ / I ２９．３ ) is thought to represent the degree of decomposition of the argyrodite-type solid electrolyte. The peak around 30.0° is the crystal peak of solid electrolyte A, and the peak around 29.3° is the crystal peak of solid electrolyte A and P ２ S５ Since it is assumed that a crystal peak of the decomposition product is present, the ratio (I ３０．０ / I ２９．３ A larger value indicates that decomposition is suppressed. In the example, compared to Comparative Examples 2 and 3, the intensity in the range of 2θ = 29.3 ± 0.34°, which is the decomposition product, is lower, confirming that the solid electrolyte A remains undecomposed.

[0081] Li ２ In comparative examples 2 and 3 that do not include S, the ratio (I ３０．０ / I ２９．３ Since the amount is small, Li is used to suppress decomposition. ２ It is expected that S is contributing. This suggests that the positive electrode composite material of the example has high ionic conductivity. In addition, in Comparative Example 3, which contains only LiI, the ratio (I ３０．０ / I ２９．３ The ratio is further reduced. From this, it is assumed that the addition of LiI is disadvantageous from the viewpoint of ionic conductivity, but in the example with LiI added, the rate characteristics are improved compared to Comparative Examples 4 and 5 which do not contain LiI. This is assumed to be due to the effect of LiI on promoting the oxidation-reduction reaction of sulfur-based active materials, and the possibility of the emergence of a redox mediator function by undergoing oxidation-reduction itself can be considered.

[0082] The positive electrode composite material of the present invention can be suitably used as the positive electrode of a lithium-ion battery. Furthermore, the lithium-ion battery of the present invention can be suitably used in information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, as well as batteries used in vehicles such as electric vehicles.

[0083] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will find it easy to make many modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and effects of the present invention. Accordingly, many of these modifications fall within the scope of the present invention. All references to the documents described in this specification and the contents of the application on which the priority claim under the Paris Convention of this application is based are incorporated herein by reference.

Claims

1. A conductive additive comprising a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, comprising at least lithium atoms, phosphorus atoms, and halogen atoms, wherein the molar ratio of lithium atoms to phosphorus atoms (Li / P) is 0.60 to 5.20, and the molar ratio of halogen atoms to phosphorus atoms (Ha / P) is 0.45 or more, and the maximum intensity (I) at 2θ = 29.3° ± 0.34° in the X-ray diffraction pattern obtained by powder X-ray diffraction using CuKα rays. ２９．３ Maximum intensity (I) at 2θ = 30.0° ± 0.34° for ) ３０．０ ) ratio (I ３０．０ / I ２９．３ A positive electrode composite material in which the ratio is 0.75 or higher.

2. The positive electrode composite material according to claim 1, wherein the halogen atom contains an iodine atom.

3. The positive electrode composite material according to claim 1 or 2, comprising three or more types of halogen atoms.

4. A positive electrode composite material comprising a conductive additive which is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, and containing at least lithium atoms, phosphorus atoms, and three or more types of halogen atoms.

5. The positive electrode mixture according to claim 3 or 4, wherein the halogen atom is a chlorine atom, a bromine atom, and an iodine atom.

6. The positive electrode composite material according to claim 5, wherein the molar ratio of the iodine atoms to the total halogen atoms is 0.10 to 0.

50.

7. The positive electrode composite material according to any one of claims 1 to 6, wherein the molar ratio of the halogen atoms to the phosphorus atoms (Ha / P) is 1.60 or less.

8. The positive electrode composite material according to any one of claims 1 to 7, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure.

9. The positive electrode mixture according to any one of claims 1 to 8, wherein the sulfur-based active material is elemental sulfur.

10. A lithium-ion battery comprising the positive electrode composite material according to any one of claims 1 to 9.

11. A method for producing a positive electrode composite, comprising the step of mixing a conductive additive which is a carbon material, a sulfur-based active material, a sulfide solid electrolyte, phosphorus sulfide, lithium sulfide, and lithium halide.

12. The manufacturing method according to claim 11, comprising the steps of: forming a composite B with the conductive additive, the sulfur-based active material, and the phosphorus sulfide; and forming a composite with the composite B, a sulfide solid electrolyte, lithium sulfide, and lithium halide.

13. The manufacturing method according to claim 12, comprising the steps of: forming a composite A with the conductive additive and the sulfur-based active material; and forming a composite B with the composite A and the phosphorus sulfide.

14. A manufacturing method according to any one of claims 11 to 13, comprising the step of compounding the phosphorus sulfide in a molten state.

15. The manufacturing method according to claim 12, comprising the steps of: forming a composite C with composite B, lithium sulfide, and lithium halide; and forming a composite with composite C and the sulfide solid electrolyte.

16. The manufacturing method according to any one of claims 11 to 15, wherein the molar ratio of lithium atoms to phosphorus atoms (Li / P) is adjusted to 0.60 to 5.20, and the molar ratio of halogen atoms to phosphorus atoms (Ha / P) is adjusted to 0.45 or more.

17. The manufacturing method according to any one of claims 11 to 16, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure.

18. The manufacturing method according to claim 17, wherein the sulfide solid electrolyte contains chlorine atoms and bromine atoms as constituent elements.

19. The manufacturing method according to any one of claims 11 to 18, wherein the sulfur-based active material is sulfur.

20. The manufacturing method according to any one of claims 11 to 19, wherein the lithium halide is lithium iodide.

21. The manufacturing method according to any one of claims 11 to 20, wherein the phosphorus sulfide is diphosphorus pentasulfide.

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