Positive electrode mixture

Abstract

This positive electrode mixture contains a carbon material, a sulfur-based active material, and a sulfide solid electrolyte. In X-ray powder diffraction using CuKα radiation, the positive electrode mixture has a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 30.0 ± 0.5°, and contains at least lithium atoms and phosphorus atoms, and the molar ratio (Li / P) of the lithium atoms to the phosphorus atoms is 0.60 ≤ Li / P ≤ 5.20.

Description

Positive electrode mixture

[0001] The present invention relates to a positive electrode mixture used in lithium ion secondary batteries and the like.

[0002] Lithium-ion batteries require large battery capacity. To improve battery capacity, the use of sulfur in the positive electrode has been investigated due to its large theoretical capacity. However, sulfur has low electronic and ionic conductivity, so when sulfur is used in the positive electrode, it is necessary to ensure the electronic and ionic conductivity within the positive electrode.

[0003] To address the above-mentioned issues, a positive electrode composite material comprising a mixture of sulfur, diphosphorus pentasulfide, conductive carbon, and lithium halide has been investigated (see, for example, Patent Document 1). Also, a positive electrode composite material comprising a mixture of sulfur, carbon nanotubes, and a solid electrolyte 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-type crystal structure (hereinafter sometimes referred to as argyrodite-type solid electrolytes) have been considered for use in cathode composites due to their high ionic conductivity (Non-Patent Document 1). However, lithium-ion batteries using argyrodite-type solid electrolytes as cathode composites have had insufficient rate characteristics. One of the objectives of the present invention is to provide a cathode composite that can be used to obtain lithium-ion batteries with good rate characteristics.

[0007] The inventors have found that the rate characteristics can be improved by using a component containing a specific atom together with an argyrodite-type solid electrolyte in the preparation of a positive electrode composite, and have completed the present invention.

[0008] According to the present invention, the following positive electrode mixtures and the like are provided. 1. A positive electrode mixture comprising a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, which has a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 30.0 ± 0.5° in powder X-ray diffraction using CuKα radiation, and which contains at least lithium atoms and phosphorus atoms, wherein the molar ratio of the lithium atoms to the phosphorus atoms (Li / P) is 0.60 ≦ Li / P ≦ 5.20. 2. The positive electrode mixture according to 1, which contains a reaction product of phosphorus sulfide and lithium sulfide in addition to the sulfide solid electrolyte. 3. The positive electrode mixture according to 1 or 2, which further contains at least one halogen atom of chlorine atoms and bromine atoms. 4. The positive electrode mixture according to 3, wherein the molar ratio of the halogen atoms to the phosphorus atoms (Ha / P) is 0.20 or more and 1.80 or less. 5. The cathode mixture according to 3 or 4, which contains chlorine atoms and bromine atoms. 6. A lithium ion battery, which contains the cathode mixture according to any one of 1 to 5. 7. A method for producing a cathode mixture, comprising a step of mechanically mixing a material containing a carbon material, a sulfur-based active material, phosphorus sulfide, and lithium sulfide, or a composite of two or more materials selected from a carbon material, a sulfur-based active material, phosphorus sulfide, and lithium sulfide, and which contains phosphorus atoms and lithium atoms, with a sulfide solid electrolyte having an argyrodite-type crystal structure. 8. The production method according to 7, which includes a step of combining the carbon material and the sulfur-based active material to form composite A. 9. The production method according to 8, which includes a step of combining the phosphorus sulfide with the composite A. 10. The production method according to 9, in which the phosphorus sulfide is combined in a molten state. 11. 12. The manufacturing method according to 7, comprising the steps of: forming the carbon material and the sulfur-based active material into composite A; mechanically mixing the phosphorus sulfide and the lithium sulfide to form an LPS composition; and mechanically mixing the composite A, the LPS composition, and the sulfide solid electrolyte. 12. The manufacturing method according to 11, wherein the molar ratio of lithium atoms to phosphorus atoms (Li / P) in the positive electrode mixture is adjusted to 0.60≦Li / P≦5.20 by adjusting the amount of the LPS composition added.13. The manufacturing method according to 7, comprising the steps of: forming composite A from the carbon material and the sulfur-based active material; combining composite A with the phosphorus sulfide in a molten state to form composite B; combining composite B with the lithium sulfide to form composite C; and mechanically mixing composite C with the sulfide solid electrolyte. 14. The manufacturing method according to 13, wherein the molar ratio of lithium atoms to phosphorus atoms (Li / P) in the positive electrode mixture is adjusted to 0.60≦Li / P≦5.20 by adjusting the amounts of the phosphorus sulfide and the lithium sulfide added. 15. The manufacturing method according to 13, wherein the phosphorus sulfide is diphosphorus pentasulfide, and the mixing ratio of diphosphorus pentasulfide and lithium sulfide (Li. ２ S:P ２ S ５ 15. The method according to any one of 7 to 14, wherein the ratio of the hydroxyl group to the hydroxyl group is 10 mol% to 90 mol%:90 mol% to 10 mol%.

[0009] According to the present invention, it is possible to provide a positive electrode mixture that can provide a lithium ion battery with good rate characteristics.

[0010] 1 shows XRD patterns of the positive electrode composites obtained in Examples 1 to 4. 2 shows XRD patterns of the positive electrode composites obtained in Examples 5 to 8. 3 shows XRD patterns of the positive electrode composites obtained in Examples 9 to 12. 4 shows XRD patterns of the positive electrode composites obtained in Comparative Examples 1 to 4.

[0011] [Cathode Composite] A cathode composite according to one embodiment of the present invention includes a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, and satisfies the following requirements (A) and (B): (A) In powder X-ray diffraction using CuKα radiation, the cathode composite has a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 30.0 ± 0.5°; (B) The cathode composite contains at least lithium atoms and phosphorus atoms, and the molar ratio of the lithium atoms to the phosphorus atoms (Li / P) is 0.60 ≦ Li / P ≦ 5.20.

[0012] The requirement (A) indicates that the positive electrode composite contains a sulfide solid electrolyte having an argyrodite-type crystal structure. The argyrodite-type solid electrolyte may further have a diffraction peak at 2θ=31.3°±0.5°.

[0013] Requirement (B) above indicates that lithium atoms and phosphorus atoms are contained in addition to the lithium atoms and phosphorus atoms derived from the argyrodite-type solid electrolyte. In a typical argyrodite-type solid electrolyte, the molar ratio (Li / P) is greater than 5.2. In this embodiment, for example, during production of the positive electrode composite, an LPS composition containing lithium atoms, phosphorus atoms, and sulfur atoms (e.g., a mixture or reaction product of phosphorus sulfide and lithium sulfide) is added to the argyrodite-type solid electrolyte, and therefore the molar ratio (Li / P) of the positive electrode composite differs from the molar ratio (Li / P) of the argyrodite-type solid electrolyte.

[0014] In this embodiment, an argyrodite-type solid electrolyte and an LPS composition are used in combination as the ion-conductive material. It is considered important to form a strong interface with the carbon material and sulfur-based active material while maintaining the highly ion-conductive argyrodite-type crystal structure. When the molar ratio (Li / P) of the positive electrode composite is 0.60≦Li / P≦5.20, the ion-conductive material forms a strong interface with the carbon material and sulfur-based active material, which is considered to result in improved rate characteristics of the battery. The components of the positive electrode composite are described below.

[0015] (Carbon material) Carbon material is used as a conductive additive. Carbon material has high electronic conductivity and is lighter than other conductive materials, so it can increase the power 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, 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), carbon nanohorns, fullerenes, carbon fibers, 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.

[0017] In one embodiment, the BET specific surface area of ​​the carbon material is 50 m ２ / g or more, 6000m２ This allows a wide contact interface between the carbon material and the sulfur-based active material to be formed, improving the utilization rate of the sulfur-based active material. ２ / g or more is preferable, and 100m ２ / g or more, 1000m ２ / g or more, 1500m ２ / g or more is preferable. ２ / g or less, and more preferably 5000m ２ / g or less is preferred.

[0018] In addition, the pore volume of the carbon material is 0.5 cm ３ / g or more, 6cm ３ This allows the sulfur-based active material to be impregnated into the pores of the carbon material, further improving the battery capacity. ３ / g or more, and more preferably 1.0 cm ３ / g or more is preferable. ３ / g or less, and more preferably 5.0 cm ３ / g or less is preferred.

[0019] In the present invention, the BET specific surface area and pore volume can be determined using a nitrogen adsorption isotherm obtained by adsorbing nitrogen gas onto a carbon material at liquid nitrogen temperature. Specifically, the BET specific surface area can be calculated by the Brenauer-Emmet-Teller (BET) multipoint method using the nitrogen adsorption isotherm. Furthermore, the pore volume can be determined by the Barrett-Joyner-Halenda (BJH) method using the nitrogen adsorption isotherm. As a measuring device, for example, a specific surface area / pore distribution measuring device (Autosorb-3) manufactured by Quantachrome can be used for the measurement.

[0020] (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. Among these, sulfur (elemental sulfur) is preferred. There are no particular limitations on the sulfur, but sulfur with 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.

[0021] The sulfur-based active material is partially or entirely converted into discharge products during the battery reaction. Therefore, in one embodiment, discharge products of the sulfur-based active material are present in the electrode material. For example, the discharge products of sulfur include Li in a fully discharged state. ２ S and its intermediate stage lithium polysulfide Li ２ S ２ , Li ２ S ４ , Li ２ S ６ , Li ２ S ８ etc.

[0022] (Sulfide Solid Electrolyte) The sulfide solid electrolyte has an argyrodite-type crystal structure. Examples of the argyrodite-type crystal structure include Li ７ P.S. ６ Crystal structure; Li ７ P.S. ６ The structural skeleton of the composition formula Li ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ (x is -0.6 to 0.6, y is 0.1 to 0.6); Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ (0.8≦x≦1.7, 0<y≦−0.25x+0.5); Li ７－ｘ P.S. ６－ｘ Ha ｘ(Ha is Cl or Br, and x is preferably 0.2 to 1.8).

[0023] In X-ray diffraction measurement using CuKα rays, it can be confirmed that the sulfide solid electrolyte has an argyrodite-type crystal structure by having diffraction peaks at 2θ=25.6±0.5° and 30.0±0.5°.

[0024] In the positive electrode composite of this embodiment, the molar ratio of lithium atoms to phosphorus atoms (Li / P) is 0.60 or more and 5.20 or less. This is thought to result in an appropriate molar ratio of lithium atoms to phosphorus atoms in the positive electrode composite, allowing the ion-conductive material to form a strong interface with the carbon material and the sulfur-based active material, thereby improving the rate characteristics of the battery. The molar ratio (Li / P) may be 1.00 or more, 1.90 or more, 2.30 or more, or 3.00 or more. The molar ratio (Li / P) may also be 5.00 or less or 4.75 or less. In one embodiment, the molar ratio (Li / P) is 1.00 or more and 5.00 or less, 1.90 or more and 4.75 or less, 2.30 or more and 4.75 or less, or 3.00 or more and 4.75 or less.

[0025] In one embodiment, the molar ratio (Ha / P) of halogen atoms to phosphorus atoms in the positive electrode composite is 0.20 or more and 1.80 or less. It is presumed that a molar ratio (Ha / P) of 0.02 or more and 1.80 or less makes the molar ratio of halogen atoms to phosphorus atoms in the positive electrode composite appropriate, thereby further improving the rate characteristics. The molar ratio (Ha / P) is preferably 0.24 or more, and particularly preferably 0.30 or more. The molar ratio (Ha / P) is preferably 1.60 or less, and particularly preferably 1.40 or less. In one embodiment, the molar ratio (Ha / P) is 0.24 or more and 1.60 or less, or 0.30 or more and 1.40 or less.

[0026] The molar ratios (Li / P) and (Ha / P) of the positive electrode composite can be measured, for example, by an ICP optical emission spectrometer. The molar ratios of the positive electrode composite can be adjusted, for example, by the mixing ratio of the raw materials, the sulfide solid electrolyte and phosphorus sulfide.

[0027] Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. The positive electrode composite preferably contains at least one of chlorine atoms and bromine atoms. In one embodiment, the positive electrode composite contains two or more types of halogen atoms. The positive electrode composite preferably contains chlorine atoms and bromine atoms. This further improves ionic conductivity and rate characteristics.

[0028] [Method for producing positive electrode composite] The positive electrode composite of the present invention is obtained by a production method including a step of mechanically mixing a material containing a carbon material, a sulfur-based active material, phosphorus sulfide, and lithium sulfide, or a composite of two or more selected from a carbon material, a sulfur-based active material, phosphorus sulfide, and lithium sulfide, and containing phosphorus atoms and lithium atoms, with a sulfide solid electrolyte having an argyrodite-type crystal structure.

[0029] The carbon material and sulfur-based active material can be those described in the positive electrode composite. An argyrodite-type solid electrolyte is used as the sulfide solid electrolyte. The method for producing the argyrodite-type solid electrolyte is not particularly limited, and known methods can be used. As starting materials, a combination of two or more compounds or simple substances containing lithium atoms, phosphorus atoms, sulfur atoms, chlorine atoms, bromine atoms, etc. as constituent elements can be used, and any starting material can be used without particular limitation as long as it exhibits ionic conductivity due to the contained metal atoms. In one embodiment, the argyrodite-type solid electrolyte does not contain oxygen atoms as a constituent element.

[0030] 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.

[0031] 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.

[0032] Examples of raw materials containing halogen include lithium halides such as lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), and phosphorus pentachloride (PCl ５ ), phosphorus trichloride (PCl ３ ), phosphorus pentabromide (PBr ５ ), phosphorus tribromide (PBr ３ Among them, lithium halides such as LiCl, LiBr, and LiI, PBr ３ is preferred, and lithium halides such as LiCl, LiBr, and LiI are more preferred, with LiCl and LiBr being more preferred.

[0033] The combination of raw materials used is preferably lithium sulfide, diphosphorus pentasulfide, lithium chloride, and lithium bromide, and in this case, the molar ratio of the raw materials used is preferably lithium sulfide:diphosphorus pentasulfide:total of two lithium halides=30-60:10-25:15-50.

[0034] The raw materials are subjected to mechanical stress to form an intermediate. Examples of means for applying mechanical stress include a grinder such as a planetary ball mill, a vibration mill, or a tumbling mill, and a kneader. The intermediate is heat-treated to obtain an argyrodite-type solid electrolyte. The heat treatment temperature is preferably 350 to 650°C, more preferably 360 to 500°C, and even more preferably 380 to 450°C.

[0035] In another method for producing an argyrodite-type solid electrolyte, the above-mentioned raw materials are roughly mixed and then dispersed in a solvent (e.g., a mixed solvent of dehydrated toluene and dehydrated isobutyronitrile) to prepare a slurry. This slurry is mixed and pulverized using a mixer / pulverizer such as a bead mill. The solvent is then removed, and the mixture is heated to 400 to 430°C in an electric furnace and slowly cooled to obtain a raw sulfide solid electrolyte. The raw sulfide solid electrolyte is dispersed in a solvent (e.g., dehydrated toluene) in a nitrogen atmosphere and atomized using a planetary ball mill to obtain a slurry again. This slurry is dried to remove the solvent, thereby obtaining an argyrodite-type solid electrolyte.

[0036] In X-ray diffraction measurement using CuKα rays, it can be confirmed that the sulfide solid electrolyte has an argyrodite-type crystal structure by having diffraction peaks at 2θ=25.6±0.5° and 30.0±0.5°.

[0037] The phosphorus sulfide includes diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and the like. The phosphorus sulfide may have a dimer or polysulfide structure, or may be a mixture. The phosphorus sulfide is preferably diphosphorus pentasulfide. Phosphorus sulfide and lithium sulfide can be used without any particular limitation as long as they are industrially produced and commercially available.

[0038] In the manufacturing method of this embodiment, a material containing a carbon material, a sulfur-based active material, phosphorus sulfide, and lithium sulfide, or a composite of two or more selected from a carbon material, a sulfur-based active material, phosphorus sulfide, and lithium sulfide, and a material containing phosphorus atoms and lithium atoms, are mechanically mixed. Examples of mechanical mixing methods are the same as those used in the production of the argyrodite-type solid electrolyte described above. The mixture and / or reactant of phosphorus sulfide and lithium sulfide are pulverized and mixed under strong mechanical stress so that a portion of the argyrodite-type solid electrolyte reacts to form an ionic conductor, while the argyrodite-type crystal structure remains.

[0039] The mechanical mixing may be a mixture obtained by simply mixing a carbon material, a sulfur-based active material, phosphorus sulfide, lithium sulfide, and an argyrodite-type solid electrolyte. Alternatively, a mixture may be obtained by first preparing a composite consisting of two or more materials selected from a carbon material, a sulfur-based active material, phosphorus sulfide, and lithium sulfide, and then mixing a material containing the composite with an argyrodite-type solid electrolyte. In the material containing the composite, the phosphorus atoms and lithium atoms are derived from, for example, phosphorus sulfide and lithium sulfide. For example, a mixture may be obtained by first forming a composite (hereinafter sometimes referred to as composite A) of a carbon material and a sulfur-based active material, and then mixing phosphorus sulfide, lithium sulfide, and an argyrodite-type solid electrolyte with composite A. Alternatively, a mixture may be obtained by forming a composite (hereinafter sometimes referred to as composite B) of composite A and phosphorus sulfide, and then mixing lithium sulfide and an argyrodite-type solid electrolyte with composite B. Alternatively, a mixture may be obtained by forming a composite (hereinafter sometimes referred to as composite C) of composite B and lithium sulfide, and then mixing an argyrodite-type solid electrolyte with composite C. In place of phosphorus sulfide and lithium sulfide, a complex (reactant) in which phosphorus sulfide and lithium sulfide are mechanically mixed in advance may be used.

[0040] In the production method of this embodiment, mechanical mixing may be performed two or more times. For example, the composite A, phosphorus sulfide, and lithium sulfide may be mechanically mixed, and then the argyrodite-type solid electrolyte may be added and mechanically mixed. Alternatively, the composite B and lithium sulfide may be mechanically mixed, and then the argyrodite-type solid electrolyte may be added and mechanically mixed.

[0041] The 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 can promote impregnation into the pores. Furthermore, the sulfur-based active material can be highly dispersed in the carbon material.

[0042] The heating temperature can be appropriately set depending on the sulfur-based active material used. For example, when the sulfur-based active material is sulfur, the heating temperature is equal to or higher than the melting point of sulfur (about 115°C). The heating temperature is preferably equal to or higher than 130°C, and more preferably equal to or higher than 150°C. The heating may be performed in two or more stages.

[0043] Alternatively, the composite A can be prepared by mechanically mixing the sulfur-based active material into the pores of the carbon material using various mills such as the planetary ball mill described above.

[0044] The manufacturing method of this embodiment preferably includes a step of previously compounding phosphorus sulfide with composite A. This can further strengthen the interface between composite A and the ionic conductor. Also, decomposition of the argyrodite-type solid electrolyte can be suppressed. Examples of a method for previously compounding phosphorus sulfide with composite A include a method of mixing phosphorus sulfide in a molten state with composite A and a method of mechanically mixing composite A and phosphorus sulfide. The method of mixing phosphorus sulfide in a molten state is preferred for compounding, as it can further strengthen the interface between composite A and the ionic conductor.

[0045] In this embodiment, a preferred production method includes the steps of: forming the carbon material and the sulfur-based active material into composite A; mechanically mixing the phosphorus sulfide and lithium sulfide to form an LPS composition; and mechanically mixing the composite A, the LPS composition, and the sulfide solid electrolyte. Also preferred is a production method including the steps of forming the carbon material and the sulfur-based active material into composite A; complexing composite A with the phosphorus sulfide in a molten state to form composite B; complexing composite B with the lithium sulfide to form composite C; and mechanically mixing composite C with the sulfide solid electrolyte.

[0046] In one embodiment, the raw materials may or may not contain components other than the carbon material, the sulfur-based active material, the mixture or composite of phosphorus sulfide and lithium sulfide, and the argyrodite-type solid electrolyte. The other components are not particularly limited, and examples thereof include a binder, a solvent, and a dispersant.

[0047] In the raw materials of the positive electrode composite, the contents of the carbon material, sulfur-based active material, mixture or composite of phosphorus sulfide and lithium sulfide, and sulfide solid electrolyte are not particularly limited. For example, the content of the sulfur-based active material is 60 to 1000 parts by mass per 100 parts by mass of the sulfide solid electrolyte. The content of the carbon material is 20 to 500 parts by mass per 100 parts by mass of the sulfide solid electrolyte. The contents of the phosphorus sulfide and lithium sulfide (LPS composition) are adjusted so that the molar ratio of lithium atoms to phosphorus atoms (Li / P) is 0.60 or more and 5.20 or less. For example, the molar ratio (Li ２ S:P ２ S ５ ) is 75:25 (the composition of the LPS composition is Li ３ P.S. ４ In the case where the sulfide solid electrolyte is used, the amount of the sulfide solid electrolyte is 10 to 900 parts by mass per 100 parts by mass of the sulfide solid electrolyte.

[0048] In one embodiment, 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 positive electrode composite raw material is a mixture or composite of a carbon material, a sulfur-based active material, phosphorus sulfide and lithium sulfide, and an argyrodite-type solid electrolyte. Note that "substantially 100% by mass" may contain inevitable impurities.

[0049] In one embodiment, the LPS composition is not limited to a mixture or reactant of phosphorus sulfide and lithium sulfide. The LPS composition includes lithium atoms, phosphorus atoms, and sulfur atoms. In one embodiment, the LPS composition consists solely of lithium atoms, phosphorus atoms, and sulfur atoms. In this case, the LPS composition may contain atoms derived from unavoidable impurities. The LPS composition may be a single compound or a mixture of two or more compounds. When the LPS composition is a reactant of two or more compounds, a portion of the LPS composition may contain unreacted compounds.

[0050] As the starting material for the LPS composition, two or more compounds or simple substances containing lithium atoms, phosphorus atoms, and sulfur atoms as constituent elements can be used in combination. Examples of the raw material containing lithium atoms 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.

[0051] Examples of raw materials containing phosphorus atoms and sulfur atoms include phosphorus sulfide and sodium phosphate (Na ３ P.O. ４ Among these, phosphorus sulfide is preferred, and diphosphorus pentasulfide is more preferred.

[0052] The LPS composition can be prepared by, for example, mechanically mixing (mechanical milling) the above starting materials. Examples of mechanical mixing methods include the planetary ball mill described above. The mixing ratio of lithium sulfide and diphosphorus pentasulfide in the raw materials (Li ２ S:P ２ S ５ ) is preferably 10 mol% to 90 mol%:90 mol% to 10 mol%. ２ S:P ２ S ５ ) may be 65 mol% to 85 mol%: 15 mol% to 35 mol%, 70 mol% to 80 mol%: 20 mol% to 30 mol%, 72 mol% to 78 mol%: 22 mol% to 28 mol%, or 75 mol%: 25 mol%. ２ S:P ２ S ５ ) is 75 mol %:25 mol %, the composition of the LPS composition is Li ３ P.S. ４ is.

[0053] The cathode composite of the present invention can be suitably used, for example, as a constituent material of a secondary battery. For example, it can be used for the positive electrode of a lithium ion battery. A lithium ion battery according to one embodiment of the present invention includes the cathode composite of the present invention described above. For example, by using a solid electrolyte as the electrolyte, an all-solid-state lithium ion battery can be manufactured. By using the cathode composite of the present invention, an all-solid-state lithium ion battery having good cycle characteristics and rate characteristics and a small initial irreversible capacity can be manufactured. A lithium ion battery mainly consists of a cathode layer, an anode layer, and an electrolyte layer. The anode layer and 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 cathode layer, anode layer, and electrolyte layer, it is preferable to use a current collector, and known current collectors can also be used.

[0054] The present invention will be described in detail below based on examples. The present invention is not limited to these examples. The ionic conductivity and X-ray diffraction measurements of the solid electrolyte were carried out as follows. (1) Ion Conductivity: A 10 mm diameter (cross-sectional area S: 0.785 cm) solid electrolyte was cut. ２ ), and a height (L) of 0.1 to 0.5 cm were molded into a circular pellet to prepare a sample. Electrode terminals were attached to the top and bottom of the sample, and measurements were made at 25°C using the AC impedance method (frequency range: 1 MHz to 1 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high-frequency region was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following formula: R = ρ (L / S)

[0055] (2) X-ray diffraction (XRD) measurement: The positive electrode 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 a sample. This sample was sealed with a Kapton film for XRD and measured without being exposed to air. XRD measurement was performed using a powder X-ray diffraction measurement device D2 PHASER manufactured by BRUKER Co., Ltd. under the following measurement conditions.

[0056] Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: Concentration method Slit configuration: Soller slit 4° (both incident and receiving sides), divergence slit 1 mm, Kβ filter (Ni plate 0.5%), air scatter screen 3 mm Detector: Semiconductor detector Measurement range: 2θ = 10-60° Step width, scan speed: 0.05°, 0.05° / sec

[0057] [Preparation of Positive Electrode Composite] Example 1 (1) Preparation of Composite Powder A Activated carbon (MSC-30 manufactured by Kansai Coke Chemical Industry Co., Ltd.) and sulfur were placed in a glass bottle in a weight 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.

[0058] (2) Preparation of Solid Electrolyte A: Lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ ), lithium bromide (LiBr) and lithium chloride (LiCl) in a molar ratio (Li ２ S:P ２ S ５The raw material mixture was roughly mixed to obtain a raw material mixture. 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. A bead mill was operated at a peripheral speed of 12 m / s and a flow rate of 500 mL / min, and the slurry was introduced into the mill and circulated for 1 hour to obtain a mixture. After removing the solvent from the obtained mixture, the mixture was heated in an electric furnace at 400 to 430 °C for 2 hours. The mixture was then slowly cooled to obtain a raw material sulfide solid electrolyte. Under a nitrogen atmosphere, the raw material sulfide solid electrolyte was dispersed in dehydrated toluene and placed in a zirconia pot of a planetary ball mill (manufactured by Fritsch: model number P-7) together with 0.3 mm diameter zirconia balls, and the pot was filled with an inert atmosphere. The planetary ball mill was rotated at 150 rpm for 2 hours to obtain a slurry containing a finely divided sulfide solid electrolyte. The slurry was transferred to a nitrogen-purged Schlenk flask and dried at room temperature for 1 hour using a vacuum pump. It was then heated to 80°C to 100°C, and the solvent contained in the finely divided sulfide solid electrolyte was removed (vacuum drying) to obtain solid electrolyte A. XRD analysis revealed 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 －３ S / cm.

[0059] (3) Preparation of LPS Composition A: 0.5746 g of lithium sulfide, 0.9254 g of diphosphorus pentasulfide, and ten zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. The contents were mixed (mechanically milled) for 40 hours at a rotation speed of 370 rpm using a planetary ball mill (manufactured by Fritsch, model number P-7) to obtain LPS Composition A.

[0060] (4) Preparation of Positive Electrode Composite Material: 0.4500 g of composite powder A, 0.0900 g of LPS composition A, and 0.3600 g of solid electrolyte A were placed in a 45 mL zirconia pot together with ten 10 mm diameter zirconia balls and sealed. The mixture was mixed using a planetary ball mill (manufactured by Fritsch, model number P-7) at a rotation speed of 370 rpm for 20 hours at room temperature to obtain a powder of the positive electrode composite material.

[0061] Example 2 A positive electrode mixture was obtained in the same manner as in Example 1(4), except that 0.4500 g of composite powder A, 0.1800 g of LPS composition A, and 0.2700 g of solid electrolyte A were used.

[0062] Example 3 A positive electrode mixture was obtained in the same manner as in Example 1(4), except that 0.4500 g of composite powder A, 0.2700 g of LPS composition A, and 0.1800 g of solid electrolyte A were used.

[0063] Example 4 A positive electrode mixture was obtained in the same manner as in Example 1(4), except that 0.4500 g of composite powder A, 0.3600 g of LPS composition A, and 0.0900 g of solid electrolyte A were used.

[0064] Example 5 (1) Preparation of Composite Powder B Activated carbon (MSC-30SSS manufactured by Kansai Thermal Chemical Industries, Ltd.) and sulfur were placed in a glass bottle in a weight 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 B of activated carbon and sulfur.

[0065] (2) Preparation of Composite Powder C: Composite powder B obtained in (1) above and diphosphorus pentasulfide (manufactured by Italmatch, melting point 286-290°C) were placed in a Tammann tube with an inner diameter of 12 mm in a weight ratio of 0.7143:0.2857, and the mixture was sealed in an SUS tube. The mixture was heated in an electric furnace at 350°C for 6 hours to obtain composite powder C.

[0066] (3) Preparation of Positive Electrode Composite Material 0.9459 g of composite powder C and 0.0541 g of lithium sulfide were placed in a 45 mL zirconia pot along with ten 10 mm diameter zirconia balls and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), the mixture was rotated at 370 rpm for 20 hours at room temperature to obtain composite powder D. 0.6660 g of composite powder D and 0.2340 g of solid electrolyte A were placed in a 45 mL zirconia pot along with ten 10 mm diameter zirconia balls and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), the mixture was rotated at 370 rpm for 20 hours at room temperature to obtain a positive electrode composite.

[0067] Example 6 A positive electrode composite was obtained in the same manner as in Example 5 (3), except that in Example 5 (3), the blending amount of composite powder C was changed to 0.8974 g, the blending amount of lithium sulfide was changed to 0.1026 g, the blending amount of the obtained composite powder D was changed to 0.7020 g, and the blending amount of solid electrolyte A was changed to 0.1980 g.

[0068] Example 7 A positive electrode composite was obtained in the same manner as in Example 5 (3), except that in Example 5 (3), the blending amount of composite powder C was changed to 0.8750 g, the blending amount of lithium sulfide was changed to 0.1250 g, the blending amount of the obtained composite powder D was changed to 0.7200 g, and the blending amount of solid electrolyte A was changed to 0.1800 g.

[0069] Example 8 A positive electrode composite was obtained in the same manner as in Example 5 (3), except that in Example 5 (3), the blending amount of composite powder C was changed to 0.8537 g, the blending amount of lithium sulfide was changed to 0.1463 g, the blending amount of the obtained composite powder D was changed to 0.7380 g, and the blending amount of solid electrolyte A was changed to 0.1620 g.

[0070] Example 9 A positive electrode composite was obtained in the same manner as in Example 5(3), except that the mixing time in the planetary ball mill when mixing composite powder C and lithium sulfide was 40 hours.

[0071] Example 10 A positive electrode mixture was obtained in the same manner as in Example 6, except that the mixing time in the planetary ball mill when mixing mixed powder C and lithium sulfide was 40 hours.

[0072] Example 11 A positive electrode mixture was obtained in the same manner as in Example 7, except that the mixing time in the planetary ball mill when mixing mixed powder C and lithium sulfide was 40 hours.

[0073] Example 12 A positive electrode mixture was obtained in the same manner as in Example 8, except that the mixing time in the planetary ball mill when mixing mixed powder C and lithium sulfide was 40 hours.

[0074] Example 13 (1) Preparation of LPS Composition B 0.2058 g of lithium sulfide, 0.9942 g of diphosphorus pentasulfide, and ten zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. The contents were mixed (mechanically milled) for 20 hours at a rotation speed of 370 rpm using a planetary ball mill (manufactured by Fritsch, model number P-7) to obtain LPS Composition B.

[0075] (2) Preparation of Positive Electrode Composite Material: 0.4500 g of composite powder A, 0.0900 g of LPS composition B, and 0.3600 g of solid electrolyte A were placed in a 45 mL zirconia pot together with ten 10 mm diameter zirconia balls and sealed. The mixture was mixed using a planetary ball mill (manufactured by Fritsch, model number P-7) at a rotation speed of 370 rpm for 20 hours at room temperature to obtain a powder of the positive electrode composite material.

[0076] Example 14 A positive electrode composite was obtained in the same manner as in Example 13 (2), except that 0.4500 g of composite powder A, 0.1800 g of LPS composition B, and 0.2700 g of solid electrolyte A were used.

[0077] Comparative Example 1 A positive electrode mixture was obtained in the same manner as in Example 1(4), except that 0.4500 g of composite powder A and 0.4500 g of solid electrolyte A were used.

[0078] Comparative Example 2 A positive electrode mixture was obtained in the same manner as in Example 1(4), except that 0.4500 g of composite powder A and 0.4500 g of LPS composition A were used.

[0079] Comparative Example 3 A positive electrode mixture was obtained in the same manner as in Example 1(4), except that 0.4500 g of composite powder B, 0.3600 g of diphosphorus pentasulfide, and 0.0900 g of solid electrolyte A were used.

[0080] Comparative Example 4 A positive electrode mixture was obtained in the same manner as in Example 1(4), except that 0.4500 g of composite powder B and 0.4500 g of LPS composition B were used.

[0081] [Evaluation of Positive Electrode Composite] The molar ratio of lithium atoms to phosphorus atoms (Li / P) and the molar ratio of halogen atoms to phosphorus atoms (Ha / P:Ha = Cl + Br) were calculated from the blend amounts of the raw materials lithium sulfide, diphosphorus pentasulfide, and solid electrolyte A. Table 1 shows the blending amounts, molar ratios, and presence or absence of diffraction peaks A and B of the positive electrode composite.

[0082]

[0083] In Table 1, ◯ means that diffraction peak A (2θ=25.6±0.5°) and diffraction peak B (30.0±0.5°) are present, and × means that diffraction peaks A and B are absent. XRD patterns of the positive electrode composites of Examples 1 to 4 are shown in FIG. 1. XRD patterns of the positive electrode composites of Examples 5 to 8 are shown in FIG. 2. XRD patterns of the positive electrode composites of Examples 9 to 12 are shown in FIG. 3. XRD patterns of the positive electrode composites of Comparative Examples 1 to 4 are shown in FIG. 4. The presence or absence of diffraction peak A (2θ=25.6±0.5°) and diffraction peak B (2θ=30.0±0.5°) was determined by the following method.

[0084] (1) Method for determining the presence or absence of diffraction peaks (a) Diffraction peak A In the XRD pattern, the average value of the X-ray intensity (counts) at 2θ=(25.6°-0.5°)±0.1° (i.e., 2θ=25.1°±0.1°) and 2θ=(25.6°+0.5°)±0.1° (i.e., 2θ=26.1°±0.1°) was calculated by multiplying the average value of the X-ray intensity (counts) by the background (BG) intensity I ｂｇ The maximum value of the X-ray intensity (counts) at 2θ = 25.6° ± 0.5° was defined as the peak intensity I ｐｅａｋ When the ratio (I ｐｅａｋ / I ｂｇ When the ratio (I) of the diffraction peak A is 1.027 or more, it is determined that the diffraction peak A exists. ｐｅａｋ / I ｂｇ ) is preferably 1.030 or more, more preferably 1.035 or more.

[0085] (b) Diffraction Peak B In the XRD pattern, the average of the X-ray intensities (counts) at 2θ = (30.0° - 0.5°) ± 0.1° (i.e., 2θ = 29.5° ± 0.1°) and 2θ = (30.0° + 0.5°) ± 0.1° (i.e., 2θ = 30.5° ± 0.1°) was calculated by dividing the average of the X-ray intensities (counts) by the background (BG) intensity I ｂｇ The maximum value of the X-ray intensity (counts) at 2θ = 30.0° ± 0.5° was defined as the peak intensity I ｐｅａｋ When the ratio (I ｐｅａｋ / I ｂｇ When the ratio (I) of the diffraction peak B is 1.065 or more, it is determined that the diffraction peak B is present. ｐｅａｋ / I ｂｇ ) is preferably 1.070 or more, and more preferably 1.075 or more. ｐｅａｋ / I ｂｇ ) are shown in Table 2.

[0086]

[0087] [Preparation of lithium ion batteries] (1) Preparation of solid electrolyte B 0.4398 g of lithium sulfide, 0.7084 g of diphosphorus pentasulfide, 0.2133 g of lithium iodide, 0.1384 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 milling) for 40 hours at a rotation speed of 370 rpm. The obtained powder was heated at 195 ° C. for 3 hours to obtain solid electrolyte B.

[0088] (2) Preparation of Negative Electrode Composite Lithium titanate ("LT-112" manufactured by Ishihara Sangyo Kaisha), a conductive additive ("Li-100" manufactured by Denka Co., Ltd., powdered acetylene black), and solid electrolyte A were weighed out to a mass ratio of 60:5:35 and mixed in a mortar for 5 minutes to obtain a negative electrode composite (also referred to as "LTO (lithium titanate) negative electrode composite").

[0089] (3) Preparation of Lithium-Ion Battery: 100 mg of solid electrolyte B was placed in a 10 mm diameter Macol cylinder and pressure-molded to form a solid electrolyte layer (layer of solid electrolyte B). Next, 10 mg of the positive electrode composite powder prepared in Examples 1 to 4 and Comparative Examples 1 to 3 was placed on one pressure surface of the solid electrolyte layer and pressure-molded again. Next, 166 mg of LTO negative electrode composite was placed on the other pressure surface of the solid electrolyte layer (the pressure surface opposite the positive electrode) and pressure-molded. A Li foil with a diameter of 9 mm and a thickness of 0.1 mm was placed on top of it and pressure-molded again to prepare a lithium-ion battery.

[0090] [Evaluation of Battery Characteristics] (1) Charge / Discharge Test A constant current charge / discharge test was performed on the lithium ion batteries using the positive electrode composites of each Example and Comparative Example. The voltage range of the constant current charge / discharge test was set to -0.4 to 1.3 V, and the current value was set as shown in Table 3 at a C rate determined based on the theoretical capacity of sulfur of 1672 mAh / g. Charging was performed by CC-CV charging, in which constant voltage charging was performed with a termination condition of 0.02 C after constant current charging, and constant current discharge (CC discharge) was performed for discharging. The discharge capacity at the 8th cycle (1 C) is shown in Table 1. Note that at all cycles (rates), the discharge capacity of the Examples was greater than that of the Comparative Examples.

[0091]

[0092] It can be seen that the cathode composites of the Examples have higher capacities at high rates such as 1C than Comparative Examples 1, 2, and 4, which used only solid electrolyte A or the LPS composition, and Comparative Example 3, which used diphosphorus pentasulfide and solid electrolyte A. It is believed that the cathode composites of the Examples maintain the highly ionic conductive crystalline structure of solid electrolyte A while coexisting with the LPS composition, improving the interfacial state with sulfur and activated carbon, resulting in improved capacity. The compatibility of maintaining the highly ionic conductive crystalline structure and the interfacial state is achieved by an appropriate composition (0.60≦Li / P≦5.20) and is believed to be achieved by using a component (LPS composition) containing Li, P, and S atoms. When the molar ratio (Li / P) does not satisfy the conditions, as in Comparative Example 3, the crystalline structure is not maintained in the cathode composite, resulting in poor rate performance.

[0093] The positive electrode composite of the present invention can be suitably used for the positive electrode of a lithium ion battery. The lithium ion battery of the present invention can also be suitably used for batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and vehicles such as electric vehicles.

[0094] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will readily be able to make numerous modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and advantages of the present invention. Accordingly, these numerous modifications are within the scope of the present invention. The contents of all documents cited in this specification and of the applications from which this application claims priority under the Paris Convention are incorporated by reference in their entirety.

Claims

1. A positive electrode composite comprising a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, wherein in powder X-ray diffraction using CuKα radiation, the positive electrode composite has a diffraction peak A at 2θ=25.6±0.5° and a diffraction peak B at 2θ=30.0±0.5°, and the positive electrode composite contains at least lithium atoms and phosphorus atoms, and the molar ratio of the lithium atoms to the phosphorus atoms (Li / P) is 0.60≦Li / P≦5.

20.

2. The positive electrode mixture according to claim 1, further comprising a reaction product of phosphorus sulfide and lithium sulfide in addition to the sulfide solid electrolyte.

3. The positive electrode mixture according to claim 1 or 2, further comprising at least one halogen atom selected from the group consisting of chlorine and bromine atoms.

4. The positive electrode mixture according to claim 3, wherein the molar ratio of said halogen atoms to said phosphorus atoms (Ha / P) is 0.20 or more and 1.80 or less.

5. The positive electrode mixture according to claim 3 or 4, which contains chlorine atoms and bromine atoms.

6. A lithium ion battery comprising the positive electrode mixture according to any one of claims 1 to 5.

7. A method for producing a positive electrode composite, comprising a step of mechanically mixing a material containing a carbon material, a sulfur-based active material, a material containing phosphorus sulfide and lithium sulfide, or a composite of two or more materials selected from a carbon material, a sulfur-based active material, phosphorus sulfide and lithium sulfide, and containing phosphorus atoms and lithium atoms, with a sulfide solid electrolyte having an argyrodite-type crystal structure.

8. The method according to claim 7, further comprising the step of forming a composite A by combining the carbon material and the sulfur-based active material.

9. The method of claim 8, further comprising the step of complexing said composite A with said phosphorus sulfide.

10. The method of claim 9, wherein the phosphorus sulfide is compounded in a molten state.

11. The manufacturing method according to claim 7, comprising the steps of: forming composite A from the carbon material and the sulfur-based active material; mechanically mixing the phosphorus sulfide and the lithium sulfide to form an LPS composition; and mechanically mixing composite A, the LPS composition, and the sulfide solid electrolyte.

12. The manufacturing method according to claim 11, wherein the molar ratio of lithium atoms to phosphorus atoms (Li / P) in the positive electrode mixture is adjusted to 0.60≦Li / P≦5.20 by adjusting the amount of the LPS composition added.

13. The manufacturing method according to claim 7, comprising the steps of: forming composite A from the carbon material and the sulfur-based active material; compounding composite A with the phosphorus sulfide in a molten state to form composite B; compounding composite B with the lithium sulfide to form composite C; and mechanically mixing composite C with the sulfide solid electrolyte.

14. The manufacturing method according to claim 13, wherein the molar ratio of lithium atoms to phosphorus atoms (Li / P) in the positive electrode mixture is adjusted to 0.60≦Li / P≦5.20 by adjusting the amounts of the phosphorus sulfide and lithium sulfide added.

15. The phosphorus sulfide is diphosphorus pentasulfide, and the mixing ratio of diphosphorus pentasulfide and lithium sulfide (Li ２ S:P ２ S ５ 15. The method according to any one of claims 7 to 14, wherein the ratio of 10 mol% to 90 mol%:90 mol% to 10 mol%.

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