Positive electrode mixture

Abstract

This positive electrode mixture contains a carbon material, a sulfur-based active material, and an ion conductor containing lithium atoms, phosphorus atoms and halogen atoms, and has diffraction peaks at 2θ = 29.3 ± 0.5° and 2θ = 34.0 ± 0.5° according to X-ray powder diffraction using CuKα radiation.

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, positive electrode composites that are mixtures of sulfur, a conductive additive, a solid electrolyte, and an ion-conductive material such as diphosphorus pentasulfide have been investigated (see, for example, Patent Documents 1 to 3).

[0004] International Publication No. 2021 / 251031 Patent No. 7006510 Patent No. 6531886

[0005] When a sulfide solid electrolyte is used as the ion-conducting material, the cycle characteristics and rate characteristics are insufficient. Furthermore, when diphosphorus pentasulfide is used as the ion-conducting material, the initial irreversible capacity is large and the rate characteristics are insufficient. One object of the present invention is to provide a positive electrode composite that can be used to obtain a lithium-ion battery with good cycle characteristics and rate characteristics and a small initial irreversible capacity.

[0006] The present inventors have found that by using a combination of phosphorus sulfide and a predetermined sulfide solid electrolyte in the preparation of a positive electrode composite, a positive electrode composite can be obtained that has good cycle characteristics and rate characteristics and can improve the initial irreversible capacity, and have completed the present invention.

[0007] 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 an ion conductor containing lithium atoms, phosphorus atoms, and halogen atoms, the positive electrode mixture having diffraction peaks at 2θ=29.3±0.5° and 2θ=34.0±0.5° in powder X-ray diffraction using CuKα radiation. 2. The positive electrode mixture according to 1, wherein the ion conductor comprises a reaction product of a sulfide solid electrolyte and phosphorus sulfide. 3. The positive electrode mixture according to 1 or 2, wherein the molar ratio of the lithium atoms to the phosphorus atoms (Li / P) is 0.20 or more and 5.20 or less. 4. The positive electrode mixture according to any one of 1 to 3, wherein the molar ratio of the halogen atoms to the phosphorus atoms (Ha / P) is 0.02 or more and 1.80 or less. 5. The positive electrode mixture according to any one of 1 to 4, wherein the halogen atoms include at least one of chlorine atoms and bromine atoms. 6. The cathode mixture according to any one of 2 to 5, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure. 7. The cathode mixture according to any one of 1 to 6, wherein the sulfur-based active material contains sulfur, and the carbon material contains porous carbon, with at least a portion of the sulfur impregnated into the pores of the porous carbon. 8. A lithium ion battery comprising the cathode mixture according to any one of 1 to 7. 9. A method for producing a cathode mixture, comprising mechanically mixing raw materials comprising a carbon material, a sulfur-based active material, a sulfide solid electrolyte containing lithium atoms, phosphorus atoms, and halogen atoms, and phosphorus sulfide. 10. The method for producing a cathode mixture according to 9, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure.

[0008] According to the present invention, it is possible to provide a positive electrode mixture that can provide a lithium ion battery having good cycle characteristics and rate characteristics and a small initial irreversible capacity.

[0009] 1 shows XRD patterns of the positive electrode composites obtained in Examples 1 to 4. 1 shows XRD patterns of the positive electrode composites obtained in Comparative Examples 1 and 2.

[0010] [Positive Electrode Composite] A positive electrode composite according to one embodiment of the present invention includes a carbon material, a sulfur-based active material, and an ionic conductor containing lithium atoms, phosphorus atoms, and halogen atoms. The ionic conductor containing lithium atoms, phosphorus atoms, and halogen atoms is, for example, a reaction product of a sulfide solid electrolyte having an argyrodite-type crystal structure and phosphorus sulfide. The ionic conductor can be identified by powder X-ray diffraction using CuKα radiation, which shows diffraction peaks at 2θ = 29.3 ± 0.5 ° and 34.0 ± 0.5 °. The crystals identified by these diffraction peaks are believed to suggest that a good interface formed by the ionic conductor is formed between the carbon material and the sulfur-based active material in the positive electrode composite.

[0011] In this embodiment, the above-mentioned ion conductor is used as the ion-conducting material. By combining phosphorus sulfide with a sulfide solid electrolyte containing lithium atoms and having high lithium ion conductivity, lithium ions accepted during initial discharge can be more reversibly released, which is believed to be the reason for the reduction in initial irreversible capacity and the improvement in rate characteristics. Furthermore, by combining phosphorus sulfide with a sulfide solid electrolyte, which has high interface-forming ability, a strong interface can be formed between the sulfur-based active material and the carbon material, which is also believed to be a factor in the development of the effects of the present invention. The components of the positive electrode composite will be described below.

[0012] (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.

[0013] 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.

[0014] In one embodiment, the BET specific surface area of ​​the carbon material is 50 m ２ / g or more, 6000m ２ 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.

[0015] 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.

[0016] 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.

[0017] (Sulfur-based active material) The sulfur-based active material is not particularly limited, but sulfur, lithium sulfide (Li ２ S), lithium polysulfide (Li ２ Sｎ : 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. are preferred. Of 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.

[0018] 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.

[0019] (Ionic Conductor) When the positive electrode mixture contains a predetermined ionic conductor, a lithium ion battery having good cycle characteristics and rate characteristics and a small initial irreversible capacity can be obtained.

[0020] The ionic conductor can be obtained, for example, by mechanically mixing (mechanical milling) a sulfide solid electrolyte having an argyrodite-type crystal structure with phosphorus sulfide. The ionic conductor has diffraction peaks at 2θ=29.3±0.5° and 2θ=34.0±0.5° in powder X-ray diffraction using CuKα radiation. In one embodiment, the ionic conductor contains phosphorus atoms, lithium atoms, and halogen atoms. The ionic conductor further contains sulfur atoms. In one embodiment, the ionic conductor consists only of phosphorus atoms, sulfur atoms, lithium atoms, and halogen atoms. In this case, the ionic conductor may contain atoms derived from inevitable impurities. A portion of the ionic conductor may contain unreacted sulfide solid electrolyte and phosphorus sulfide remaining.

[0021] The sulfide solid electrolyte is a solid electrolyte that contains at least sulfur atoms and exhibits ionic conductivity due to the contained metal atoms. In this embodiment, the sulfide solid electrolyte contains lithium atoms, phosphorus atoms, and halogen atoms and has ionic conductivity due to the lithium atoms. The ionic conductivity is, for example, 1.0×10 －３ The sulfide solid electrolyte preferably has a specific surface area of ​​1000 nm or more. The sulfide solid electrolyte preferably has an argyrodite-type crystal structure. Details of the sulfide solid electrolyte will be described later in the production method.

[0022] The phosphorus sulfide includes phosphorus trisulfide (P ４ S ３ ), diphosphorus pentasulfide (P ２ S ５ ), phosphorus heptasulfide (P ４ S ７ ), tetraphosphorus pentasulfide (P ４ S ５ The phosphorus sulfide may have a dimer or polysulfide structure, or may be a mixture. Diphosphorus pentasulfide is preferred.

[0023] In one embodiment of the positive electrode composite, the molar ratio of lithium atoms to phosphorus atoms (Li / P) is 0.20 or more and 5.20 or less. In this embodiment, the lithium atoms and phosphorus atoms contained in the positive electrode composite are derived from the sulfide solid electrolyte and phosphorus sulfide, and the molar ratio (Li / P) is related to the mixing ratio of the sulfide solid electrolyte and phosphorus sulfide. Since phosphorus sulfide does not contain lithium atoms, a large molar ratio (Li / P) indicates a large amount of sulfide solid electrolyte. When the molar ratio (Li / P) is 0.20 or more and 5.20 or less, the molar ratio of lithium atoms to phosphorus atoms in the positive electrode composite is appropriate, and it is presumed that the lithium ion conductivity and the ability to release lithium ions in the initial stage are improved. It is also presumed that a good interface is formed. The molar ratio (Li / P) is preferably 0.40 or more, particularly preferably 1.00 or more. The molar ratio (Li / P) is preferably 4.00 or less, particularly preferably 3.50 or less. In one embodiment, the molar ratio (Li / P) is 0.40 or greater and 4.00 or less, or 1.00 or greater and 3.50 or less.

[0024] In one embodiment of the positive electrode composite, the molar ratio of halogen atoms to phosphorus atoms (Ha / P) is 0.02 or more and 1.80 or less. In this embodiment, the phosphorus atoms and halogen atoms contained in the positive electrode composite are derived from the sulfide solid electrolyte and phosphorus sulfide, and the molar ratio (Ha / P) is related to the mixing ratio of the sulfide solid electrolyte and phosphorus sulfide. A large molar ratio (Ha / P) means a large amount of sulfide solid electrolyte. When the molar ratio (Ha / P) is 0.02 or more and 1.80 or less, the molar ratio of halogen atoms to phosphorus atoms in the positive electrode composite is appropriate, and it is presumed that the lithium ion conductivity and the ability to release lithium ions in the initial stage are improved. It is also presumed that a good interface is formed. The molar ratio (Ha / P) is preferably 0.10 or more, particularly preferably 0.15 or more. The molar ratio (Ha / P) is preferably 1.50 or less, particularly preferably 1.20 or less. In one embodiment, the molar ratio (Ha / P) is 0.10 or greater and 1.50 or less, or 0.15 or greater and 1.20 or less.

[0025] 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.

[0026] 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.

[0027] In one embodiment, the sulfur-based active material contains sulfur, the carbon material contains porous carbon, and at least a portion of the sulfur is impregnated into the pores of the porous carbon. This increases the number of contact points between the insulating sulfur and the porous carbon, effectively providing an electron conduction path for the sulfur, resulting in improved battery characteristics. The impregnation of the pores of the porous carbon with sulfur can be confirmed, for example, by X-ray diffraction measurement, specific surface area / pore volume measurement, elemental mapping using SEM / EDS, or the like.

[0028] [Method for Producing Cathode Composite] The cathode composite of the present invention can be produced, for example, by mechanically mixing raw materials including a carbon material, a sulfur-based active material, a sulfide solid electrolyte, and phosphorus sulfide.

[0029] The carbon material, sulfur-based active material, and phosphorus sulfide described in the positive electrode composite can be used. As the sulfide solid electrolyte, for example, a sulfide solid electrolyte having an argyrodite-type crystal structure (argyrodite-type solid electrolyte) can be used. Here, the argyrodite-type crystal structure can be, for example, Li ７ P.S. ６ Crystal structure; Li ７ P.S. ６ The structural skeleton of the composition formula Li ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６(x is -0.6 to 0.6, y is 0.1 to 0.6); Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ (0.8≦x≦1.7, 0<y≦−0.25x+0.5); Li ７－ｘ P.S. ６－ｘ Ha ｘ (Ha is Cl or Br, and x is preferably 0.2 to 1.8).

[0030] In X-ray diffraction measurement using CuKα radiation, the sulfide solid electrolyte can be confirmed to have an argyrodite-type crystal structure by having diffraction peaks at 2θ=25.6±0.5° and 30.0±0.5°. The argyrodite-type solid electrolyte may further have a diffraction peak at 2θ=31.3±0.5°.

[0031] The method for producing the argyrodite-type solid electrolyte is not particularly limited, and known methods can be used. As the starting material, 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.

[0032] 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.

[0033] 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. ４Examples 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] In the manufacturing method of this embodiment, raw materials including a carbon material, a sulfur-based active material, an argyrodite-type solid electrolyte, and phosphorus sulfide are mechanically mixed. Examples of mechanical mixing methods are the same as those used in the manufacturing of the sulfide solid electrolyte described above. The raw materials are pulverized and mixed so that strong mechanical stress causes at least a portion of the argyrodite-type solid electrolyte and phosphorus sulfide to react, resulting in diffraction peaks at 2θ = 29.3 ± 0.5° and 2θ = 34.0 ± 0.5° in powder X-ray diffraction using CuKα radiation.

[0039] The raw material for the positive electrode composite may be a mixture of a carbon material, a sulfur-based active material, a sulfide solid electrolyte, and phosphorus sulfide, or may be a mixture of a carbon material and a sulfur-based active material that are first formed into a composite and then mixed with a sulfide solid electrolyte and phosphorus sulfide. In one embodiment, the raw material may or may not contain components other than the carbon material, the sulfur-based active material, the sulfide solid electrolyte, and the phosphorus sulfide. The other components are not particularly limited, and examples thereof include a binder, a solvent, and a dispersant.

[0040] The contents of the carbon material, sulfur-based active material, sulfide solid electrolyte, and phosphorus sulfide in the raw materials for the positive electrode composite are not particularly limited. For example, the content of the sulfur-based active material is 60 to 1,000 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 content of the phosphorus sulfide (e.g., diphosphorus pentasulfide) is 10 to 900 parts by mass per 100 parts by mass of the sulfide solid electrolyte.

[0041] In one embodiment, the positive electrode composite raw material comprises 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, 99.5% by mass or more, or substantially 100% by mass of the carbon material, sulfur-based active material, sulfide solid electrolyte, and phosphorus sulfide. Note that "substantially 100% by mass" may contain inevitable impurities.

[0042] In one embodiment, the sulfur-based active material is heated and melted to be impregnated into the pores of the carbon material. Melting the sulfur-based active material can promote impregnation into the pores and also enable the sulfur-based active material to be highly dispersed in the carbon material.

[0043] 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.

[0044] In one embodiment, the sulfur-based active material is impregnated into the pores of the carbon material by mechanical mixing. For the mechanical mixing, various mills such as the planetary ball mill described above can be used.

[0045] 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.

[0046] 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)

[0047] (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.

[0048] 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

[0049] [Preparation of Positive Electrode Composite] Example 1 (1) Preparation of Composite Powder A 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 A of activated carbon and sulfur.

[0050] (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 ５ The 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.

[0051] (3) Preparation of Positive Electrode Composite Material: 0.4500 g of composite powder A, 0.0900 g of diphosphorus pentasulfide, 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.

[0052] Example 2 A positive electrode composite was obtained in the same manner as in Example 1(3), except that 0.4500 g of composite powder A, 0.1800 g of phosphorus pentasulfide, and 0.2700 g of solid electrolyte A were used.

[0053] Example 3 A positive electrode composite was obtained in the same manner as in Example 1 (3), except that 0.4500 g of composite powder A, 0.2700 g of diphosphorus pentasulfide, and 0.1800 g of solid electrolyte A were used.

[0054] Example 4 A positive electrode composite was obtained in the same manner as in Example 1(3), except that 0.4500 g of composite powder A, 0.3600 g of phosphorus pentasulfide, and 0.0900 g of solid electrolyte A were used.

[0055] Comparative Example 1 A positive electrode composite was obtained in the same manner as in Example 1(3), except that 0.4500 g of composite powder A and 0.4500 g of solid electrolyte A were used.

[0056] Comparative Example 2 A positive electrode composite was obtained in the same manner as in Example 1(3), except that 0.4500 g of composite powder A and 0.4500 g of diphosphorus pentasulfide were used.

[0057] [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 diphosphorus pentasulfide and solid electrolyte A. The blending amounts of the positive electrode composite, molar ratios, and the presence or absence of diffraction peaks A and B are shown in Table 1. In Table 1, ◯ indicates the presence of diffraction peak A (2θ = 29.3 ± 0.5°) and diffraction peak B (2θ = 34.0 ± 0.5°), and × indicates the absence of diffraction peaks A and B.

[0058]

[0059] XRD patterns of the positive electrode composites of the Example and Comparative Example are shown in Figures 1 and 2. It can be seen from Figures 1 and 2 that, unlike Comparative Example 1, diffraction peaks A and B different from the diffraction peaks attributable to solid electrolyte A are observed in the Example. Therefore, the presence of an ionic conductor, which is a reaction product of solid electrolyte A and diphosphorus pentasulfide, can be confirmed in the Example.

[0060] [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.

[0061] (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").

[0062] (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 and 2 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.

[0063] [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 2 at a C rate determined based on the theoretical capacity of sulfur of 1672 mAh / g. For charging, CC-CV charging was performed, 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 discharge.

[0064] The initial irreversible capacity is the difference between the charge and discharge capacities at the first cycle, and is calculated by subtracting the charge capacity from the discharge capacity. The capacity at rate characteristics 1C is the discharge capacity at the eighth cycle. The cycle characteristics were evaluated by the capacity retention rate after 50 cycles. The capacity retention rate was calculated using the following formula: Capacity retention rate (%) = (discharge capacity at 50th cycle / discharge capacity at 10th cycle) × 100 Table 3 shows the composition of the positive electrode composite and the evaluation results of the lithium ion battery.

[0065]

[0066]

[0067] It can be seen that the positive electrode composite of the example has a higher capacity retention rate at the 50th cycle than Comparative Example 1, which uses only solid electrolyte A. It can also be seen that the initial irreversible capacity is smaller and the capacity at 1 C is higher than Comparative Example 2, which uses only diphosphorus pentasulfide. ＋ By combining (reacting) the highly conductive solid electrolyte A, the Li ＋ It is believed that the initial irreversible capacity was reduced and the rate characteristics were improved because the solid electrolyte A was able to release phosphorus pentasulfide more reversibly. It is also believed that the addition of phosphorus pentasulfide, which has a high interface-forming ability, to the solid electrolyte A allowed for the formation of a strong interface between the sulfur and carbon material and the ionic conductor. In particular, Examples 1 and 2, which contained 10 to 20 wt % of phosphorus pentasulfide, exhibited significantly higher rate characteristics.

[0068] 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.

[0069] 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 an ion conductor containing lithium atoms, phosphorus atoms, and halogen atoms, the positive electrode composite having diffraction peaks at 2θ=29.3±0.5° and 2θ=34.0±0.5° in powder X-ray diffraction using CuKα radiation.

2. The cathode mixture of claim 1, wherein the ionic conductor comprises a reaction product of a sulfide solid electrolyte and phosphorus sulfide.

3. The positive electrode mixture according to claim 1 or 2, wherein the molar ratio of the lithium atoms to the phosphorus atoms (Li / P) is 0.20 or more and 5.20 or less.

4. The positive electrode mixture according to any one of claims 1 to 3, wherein the molar ratio of said halogen atoms to said phosphorus atoms (Ha / P) is 0.02 or more and 1.80 or less.

5. The positive electrode mixture according to any one of claims 1 to 4, wherein the halogen atoms include at least one of chlorine atoms and bromine atoms.

6. The positive electrode mixture according to any one of claims 2 to 5, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure.

7. The positive electrode mixture according to any one of claims 1 to 6, wherein the sulfur-based active material contains sulfur, the carbon material contains porous carbon, and at least a portion of the sulfur is impregnated into the pores of the porous carbon.

8. A lithium ion battery comprising the positive electrode mixture according to any one of claims 1 to 7.

9. A method for producing a positive electrode composite, comprising mechanically mixing raw materials including a carbon material, a sulfur-based active material, a sulfide solid electrolyte containing lithium atoms, phosphorus atoms, and halogen atoms, and phosphorus sulfide.

10. The method for producing a positive electrode mixture according to claim 9, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure.

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