Positive electrode mixture

Abstract

This positive electrode mixture contains a conductive auxiliary agent which is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte. A relaxation time T1 derived by 7Li-NMR is longer than 0.23 s and shorter than 0.41 s.

Description

Cathode composite material

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

[0002] All-solid-state lithium-ion batteries using solid electrolytes are expected to be highly safe lithium-ion batteries because they have the advantage of being less prone to electrolyte leakage and ignition. Sulfur-based active materials, which are expected to be high-capacity active materials, have low electronic and ionic conductivity. Therefore, when manufacturing positive electrodes using sulfur-based active materials, composite materials with ion-conductive materials (such as solid electrolytes) and conductive additives (such as carbon materials) are being considered (see, for example, Patent Document 1 and Non-Patent Document 1).

[0003] International Publication No. 2022 / 090757

[0004] Batteries & Supercaps 2021, 4, 183-194

[0005] The state of the solid electrolyte changes depending on the compounding conditions. Under conventional compounding conditions, there were problems such as insufficient capacity (rate characteristics) at high rates when used in lithium-ion batteries. One of the objectives of the present invention is to provide a cathode composite material that can improve rate characteristics.

[0006] The inventors have identified a relaxation time T that represents the mobility of lithium ions in the cathode composite material. １ We discovered that the rate characteristics improve when the value is within a predetermined range, and thus completed the present invention.

[0007] According to the present invention, the following positive electrode composite materials are provided: 1. A conductive additive which is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, ７ Relaxation time T derived from Li-NMR １is a positive electrode composite material that is longer than 0.23 s and shorter than 0.41 s. 2. The positive electrode composite material according to 1, which has diffraction peaks at 2θ = 25.6 ± 0.5° and 30.1 ± 0.5° in powder X-ray diffraction using CuKα rays. 3. The positive electrode composite material according to 1 or 2, which contains at least one or more halogen atoms. 4. The positive electrode composite material according to any one of 1 to 3, which contains two or more halogen atoms. 5. The positive electrode composite material according to any one of 1 to 4, which contains at least Cl and Br as halogen atoms. 6. The conductive assistant is the positive electrode composite material according to any one of 1 to 5, which contains activated carbon with a BET specific surface area of 100 m ２ / g or more. 7. The positive electrode composite material according to any one of 1 to 6, wherein the sulfur-based active material contains elemental sulfur. 8. The positive electrode composite material according to 6, wherein the sulfur-based active material is impregnated in the pores of the carbon material. 9. The positive electrode composite material according to any one of 1 to 8, wherein the total of the carbon material, the sulfur-based active material, and the sulfide solid electrolyte is 95% by mass or more based on the total amount of the positive electrode composite material. 10. A lithium ion battery containing the positive electrode composite material according to any one of 1 to 9. 11. Mechanically mix a composite powder containing a conductive assistant that is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, ７ The relaxation time T derived by Li-NMR １ is adjusted to a range longer than 0.23 s and shorter than 0.41 s, and a method for manufacturing a positive electrode composite material is provided. 12. The method for manufacturing a positive electrode composite material according to 11, wherein the sulfide solid electrolyte has diffraction peaks at 2θ = 25.6 ± 0.5° and 30.1 ± 0.5° in powder X-ray diffraction using CuKα rays.

[0008] According to the present invention, a positive electrode composite material capable of improving rate characteristics can be provided.

[0009] [Positive electrode composite material] The positive electrode composite material according to an embodiment of the present invention contains a conductive assistant that is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, ７ The relaxation time T derived by Li-NMR １ is longer than 0.23 s and shorter than 0.41 s. By controlling the relaxation time T １ the rate characteristics of the lithium ion battery can be improved. The relaxation time T １This can be controlled, for example, by adjusting the impact force and time when compounding conductive additives, sulfur-based active materials, and sulfide solid electrolytes. Relaxation time T １ The derivation method will be explained in the examples. Relaxation time T １ This is an indicator that represents the mobility of lithium ions in a solid material, and is generally T １ The shorter the distance, the higher the mobility is considered to be. The following describes the components of the positive electrode composite material.

[0010] (Conductive additive) A carbon material is used as the conductive additive. Carbon materials have high electronic conductivity and are lighter than other conductive materials, so the power density and capacity per unit weight of the battery can be increased. The carbon material is preferably porous carbon with pores.

[0011] The carbon materials are not particularly limited, but examples include carbon blacks such as Ketjenblack, acetylene black, Denka black, thermal black, and channel black; mesoporous carbon; activated carbon; amorphous carbon; carbon nanotubes; vapor-grown carbon fibers (VGCF); carbon nanohorns; fullerenes; carbon fibers; natural graphite; artificial graphite; graphene; graphene oxide; and reduced graphene oxide. These materials may be used individually or in combination of two or more. Composite materials of these materials can also be used.

[0012] In one embodiment, the BET specific surface area of ​​the carbon material is 50 m². ２ / g or more, 6000m ２ The concentration is less than / g. This allows for the formation of a broad contact interface between the carbon material and the sulfur-based active material, thereby improving the utilization rate of the sulfur-based active material. The BET specific surface area is 70 m². ２ Preferably, the amount is 100 m / g or more, and more preferably 100 m ２ / g or more, 1000m ２ / g or more, 1500m ２ / g or more is preferable. Also, 5500m ２ Preferably less than / g, and more preferably 5000m ２ Preferably less than / g

[0013] Furthermore, the pore volume of the carbon material is 0.5 cm³. ３ / g or more, 6cm３ The concentration is less than / g. This allows sulfur-based active materials to be impregnated into the pores of the carbon material, further improving the battery capacity. The pore volume is 0.7 cm³. ３ Preferably, it is 1.0 cm or more. ３ A value of 5.5 cm or more is preferable. ３ Preferably less than / g, and moreover 5.0 cm ３ Preferably less than / g

[0014] In this invention, the BET specific surface area and pore volume can be determined using nitrogen adsorption isotherms obtained by adsorbing nitrogen gas onto a carbon material at liquid nitrogen temperature. Specifically, the BET specific surface area can be calculated using the Brunauer-Emmett-Teller (BET) multipoint method with respect to the nitrogen adsorption isotherms. The pore volume can be determined using the Barrett-Joyner-Halenda (BJH) method with respect to the nitrogen adsorption isotherms. As a measuring device, for example, the specific surface area and pore distribution analyzer (Autosorb-3) manufactured by Quantachrome can be used for measurement.

[0015] (Sulfur-based active material) There are no particular limitations on sulfur-based active materials, but sulfur, lithium sulfide (Li ２ S), Lithium polysulfide (Li ２ S ｎ : n satisfies 1 < n ≤ 8. ), Titanium sulfide (TiS ２ ), molybdenum sulfide (MoS ２ ), iron sulfide (FeS, FeS ２ ), copper sulfide (CuS), nickel sulfide (Ni ３ S ２ Examples include sulfur-containing polymer compounds, etc. Among these, sulfur (elemental sulfur) is preferred. There are no particular limitations on the sulfur, but high purity is preferred. Specifically, a purity of 95% by mass or higher is preferred, more preferably 96% by mass or higher, and particularly preferably 97% by mass or higher. Examples of sulfur crystal systems include α-sulfur (orthorhombic), β (monoclinic), γ (monoclinic), amorphous sulfur, etc. These can be used individually or in combination of two or more.

[0016] During a battery reaction, some or all of the sulfur-based active material transforms into discharge products. Therefore, in one embodiment of the electrode material, discharge products of the sulfur-based active material are present. For example, as a sulfur discharge product, Li in a completely discharged state... ２ Li as S and its intermediate stage lithium polysulfide ２ S ２ Li ２ S ４ Li ２ S ６ Li ２ S ８ These are some examples.

[0017] (Sulfide Solid Electrolyte) A sulfide solid electrolyte is a solid electrolyte that contains at least a sulfur atom and exhibits ionic conductivity due to the contained metal atoms. In this embodiment, the solid electrolyte contains a lithium atom, a phosphorus atom, and a halogen atom, and has ionic conductivity due to the lithium atom. The ionic conductivity is, for example, 1.0 × 10⁻⁶. －３ It is preferable that the concentration is S / cm or higher. The sulfide solid electrolyte preferably has an argyrodite-type crystalline structure. Details of the sulfide solid electrolyte will be explained in the manufacturing method described later.

[0018] [Method for Manufacturing the Positive Electrode Compound] The positive electrode compound of the present invention can be manufactured by mechanically mixing raw materials, for example, a conductive additive, a sulfur-based active material, and a sulfide solid electrolyte. The conductive additive and sulfur-based active material can be those described in the section on positive electrode compound. As the sulfide solid electrolyte, for example, a sulfide solid electrolyte containing an argyrodite-type crystal structure (argyrodite-type solid electrolyte) is used. Here, as the argyrodite-type crystal structure, for example, Li ７ PS ６ Crystal structure; Li ７ PS ６ Composition formula Li has a structural framework ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ Crystal structure represented by (x is -0.6 to 0.6, y is 0.1 to 0.6); Li ７－ｘ－２ｙPS ６－ｘ－ｙ Cl ｘ Crystal structure shown by (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5); Li ７－ｘ PS ６－ｘ Ha ｘ Examples of crystal structures include those represented by (Ha is Cl or Br, and x is preferably 0.2 to 1.8).

[0019] X-ray diffraction measurements using CuKα rays confirm that the sulfide solid electrolyte contains an argyrodite-type crystal structure by exhibiting diffraction peaks at 2θ = 25.6 ± 0.5° and 30.1 ± 0.5°. The argyrodite-type solid electrolyte may also exhibit a diffraction peak at 2θ = 31.3° ± 0.5°.

[0020] The method for producing argyrodite-type solid electrolytes is not particularly limited, and known methods can be employed. As starting materials, two or more compounds or elements containing lithium atoms, phosphorus atoms, sulfur atoms, chlorine atoms, bromine atoms, etc. as constituent elements can be used in combination, and there are no particular restrictions as long as they exhibit ionic conductivity due to the metal atoms they contain.

[0021] Examples of raw materials containing lithium (Li) include lithium sulfide (Li ２ S), Lithium oxide (Li ２ O), Lithium carbonate (Li ２ CO ３ Examples include lithium compounds such as ) and elemental lithium metal. Among these, lithium compounds are preferred, and lithium sulfide is more preferred.

[0022] Examples of raw materials containing phosphorus (P) and sulfur (S) include diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) such as phosphorus sulfide, sodium phosphate (Na ３ PO ４Examples include phosphorus compounds such as ), elemental phosphorus, and elemental sulfur. Among these, phosphorus sulfide is preferred, and diphosphorus pentasulfide is more preferred. Phosphorus compounds such as diphosphorus pentasulfide, elemental phosphorus, and elemental sulfur can be used without particular limitation as long as they are industrially manufactured and sold.

[0023] Examples of halogen-containing raw materials 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 Phosphorus halides such as ) are preferred. Among them, lithium halides such as LiCl, LiBr, LiI, and PBr ３ Lithium halides such as LiCl, LiBr, and LiI are preferred, and LiCl and LiBr are even more preferred.

[0024] The raw materials used preferably include lithium sulfide, diphosphorus pentasulfide, and lithium halides. It is also preferable to include lithium sulfide, diphosphorus pentasulfide, and two or more types of lithium halides. In particular, it is preferable to include lithium sulfide, diphosphorus pentasulfide, lithium chloride, and lithium bromide. A preferred combination of raw materials is lithium sulfide, diphosphorus pentasulfide, lithium chloride, and lithium bromide. In this case, the molar ratio of the raw materials is preferably lithium sulfide: diphosphorus pentasulfide: total of the two types of lithium halides = 30-60:10-25:15-50.

[0025] An intermediate is obtained by applying mechanical stress to the above raw materials. Examples of means for applying mechanical stress include grinders such as planetary ball mills, vibratory mills, and rolling mills, as well as kneaders. An argyrodite-type solid electrolyte is obtained by heat treatment of the intermediate. The heat treatment temperature is preferably 350 to 650°C, more preferably 360 to 500°C, and even more preferably 380 to 450°C.

[0026] In another method for producing argyrodite-type solid electrolytes, the above raw materials are roughly mixed and then dispersed in a solvent (such as a mixed solvent of dehydrated toluene and dehydrated isobutyronitrile) to prepare a slurry. This slurry is then mixed and pulverized using a mixing mill such as a bead mill. After that, the solvent is removed, and the mixture is heated in an electric furnace at 400-430°C and then slowly cooled to obtain the raw material sulfide solid electrolyte. Under a nitrogen atmosphere, the raw material sulfide solid electrolyte is dispersed in a solvent (such as dehydrated toluene), and pulverized using a planetary ball mill to obtain another slurry. This slurry is dried to remove the solvent and obtain the argyrodite-type solid electrolyte.

[0027] In the manufacturing method of this embodiment, raw materials including a conductive additive which is a carbon material, a sulfur-based active material, and an argyrodite-type solid electrolyte are mechanically mixed. An example of the mechanical mixing means is the same as that used in the production of sulfide solid electrolytes described above. By grinding and mixing while controlling mechanical stress, processing time, etc., the relaxation time T of the positive electrode mixture is achieved. １ Make it longer than 0.23s and shorter than 0.41s.

[0028] The raw materials for the positive electrode composite may be a mixture of a carbon material, a sulfur-based active material, and a sulfide solid electrolyte, or, for example, a mixture in which the carbon material and sulfur-based active material are pre-composited and the sulfide solid electrolyte is mixed with the composite. In one embodiment, the raw materials may or may not contain components other than the carbon material, sulfur-based active material, and sulfide solid electrolyte. Other components are not particularly limited, but examples include binders, solvents, and dispersants.

[0029] In the raw materials for the cathode composite, the content of carbon material, sulfur-based active material, and sulfide solid electrolyte is not particularly limited. For example, the content of sulfur-based active material is 40 to 350 parts by mass, preferably 50 to 120 parts by mass, and particularly preferably 60 to 80 parts by mass, per 100 parts by mass of sulfide solid electrolyte. The content of carbon material is 10 to 300 parts by mass, preferably 20 to 50 parts by mass, and particularly preferably 25 to 35 parts by mass, per 100 parts by mass of sulfide solid electrolyte.

[0030] In one embodiment, 50% or more by mass of the cathode composite raw materials, 60% or more by mass, 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, 99% or more by mass, 99.5% or more by mass, or substantially 100% by mass is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte. In the case of "substantially 100% by mass", unavoidable impurities may be included.

[0031] By grinding and mixing the cathode composite material raw materials while controlling mechanical stress, processing time, etc., the relaxation time T of the cathode composite material is controlled. １ The relaxation time T should be longer than 0.23 s and shorter than 0.41 s. １ As can be seen from the examples and comparative examples, this can be controlled by adjusting the impact force and time during compounding. Conventionally, under the conditions used when a planetary ball mill (manufactured by Fritsch: model number P-7), which is a common condition (rotation speed 370 rpm, 20 hours), the mixing (impact) strength and total energy amount were insufficient (Comparative Example 1). For example, under the compounding conditions of the present embodiment, the relaxation time T １ By controlling this, the rate characteristics can be improved. For example, when using a planetary ball mill, increasing the rotational speed compared to conventional methods will improve the relaxation time T. １ The relaxation time T tends to be shorter. The larger the crushed media, the longer the relaxation time T. １ The relaxation time T tends to be shorter. The longer the processing time, the longer the relaxation time T. １ The relaxation time T of the positive electrode composite material tends to be shorter. １ The relaxation time T may be 0.25 s or more or 0.30 s or more, and may be 0.39 s or less or 0.37 s or less. It may also be 0.25 to 0.39 s, 0.28 to 0.37 s, or 0.30 to 0.37 s. For example, even when using other devices such as a rolling mill, the relaxation time T can be adjusted by adjusting the rotation speed, the size of the grinding media, and the processing time. １ It can be controlled.

[0032] In one embodiment, a sulfur-based active material is heated and melted to impregnate the pores of a carbon material. Melting the sulfur-based active material promotes impregnation into the pores. Furthermore, the sulfur-based active material can be highly dispersed in the carbon material.

[0033] The heating temperature can be appropriately set according to the sulfur-based active material used. For example, if the sulfur-based active material is sulfur, the temperature should be above the melting point of sulfur (approximately 115°C). Preferably, it should be 130°C or higher, and more preferably 150°C or higher. Heating may be carried out in two or more stages.

[0034] In one embodiment, a method is used in which a sulfur-based active material is impregnated into the pores of a carbon material by mechanical mixing. Various mills, such as the planetary ball mill described above, can be used for mechanical mixing.

[0035] In one embodiment, the cathode composite material exhibits diffraction peaks at 2θ = 25.6 ± 0.5° and 30.1 ± 0.5° in powder X-ray diffraction using CuKα rays. The presence of these diffraction peaks in the cathode composite material indicates the presence of an argyrodite-type solid electrolyte. The presence of the argyrodite-type solid electrolyte even after composite formation allows for the maintenance of high lithium-ion conductivity.

[0036] In one embodiment, the positive electrode mixture contains at least one halogen atom. Alternatively, the positive electrode mixture contains two or more halogen atoms. Furthermore, the positive electrode mixture contains at least Cl and Br as halogen atoms.

[0037] The positive electrode composite material of the present invention can be suitably used, for example, as a constituent material of a secondary battery. For example, it can be used as the positive electrode of a lithium-ion battery. A lithium-ion battery according to one embodiment of the present invention includes the positive electrode composite material of the present invention described above. For example, by using a solid electrolyte, an all-solid-state lithium-ion battery can be manufactured. By using the positive electrode composite material of the present invention, an all-solid-state lithium-ion battery with good rate characteristics can be manufactured. A lithium-ion battery mainly consists of a positive electrode layer, a negative electrode layer, and an electrolyte layer. The negative electrode layer and the electrolyte layer can be manufactured by known methods. For example, the sulfide solid electrolyte described above can be used for the electrolyte layer. In addition to the positive electrode layer, negative electrode layer, and electrolyte layer, it is preferable that a current collector is used, and known current collectors can also be used.

[0038] Hereinafter, the present invention will be specifically described based on examples. The present invention is not limited to the examples. The measurement conditions for X-ray diffraction and ionic conductivity of the solid electrolyte are as follows.

[0039] ・ X-ray diffraction measurement The solid electrolyte was filled into a groove with a diameter of 20 mm and a depth of 0.2 mm, and leveled with glass to make a sample. This sample was sealed with a Kapton film for XRD and measured without exposure to air. The XRD measurement was carried out using a powder X-ray diffractometer D2 PHASER manufactured by BRUKER Corporation under the following measurement conditions. Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα line (1.5418 Å) Optical system: Converging method Slit configuration: Solar slit 4° (both on the incident side and the light-receiving side), divergence slit 1 mm, Kβ filter (Ni plate 0.5%), air scatter screen 3 mm were used) Detector: Semiconductor detector Measurement range: 2θ = 10 - 60° Step width, scan speed: 0.05°, 0.05° / second

[0040] ・ Ionic conductivity From the solid electrolyte, circular pellets with a diameter of 10 mm (cross-sectional area S: 0.785 cm ２ ), and a height (L) of 0.1 - 0.3 cm were formed as samples. Electrode terminals were taken from the top and bottom of the sample, and measured at 25°C by the alternating current impedance method (frequency range: 5 MHz - 0.5 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. At the point near the right end of the arc observed in the high-frequency side region where -Z'' (Ω) is minimum, the real part Z' (Ω) at this point 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) σ = 1 / ρ

[0041] [Preparation of positive electrode composite material] Example 1 (1) Preparation of composite powder A Activated carbon (MSC-30 manufactured by Kansai Thermal Chemical Co., Ltd.) and sulfur were put into a glass bottle in a mass ratio of 3:7 and sealed in a SUS tube container. It was heated in an electric furnace at 150°C for 6 hours and at 300°C for 2.75 hours to obtain composite powder A of activated carbon and sulfur.

[0042] (2) Preparation of solid electrolyte A Under a nitrogen atmosphere, lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S５ ), lithium bromide (LiBr) and lithium chloride (LiCl) were metered so that the molar ratio (Li ２ S:P ２ S ５ :LiBr:LiCl) was 47.5:12.5:15.0:25.0, and they were roughly mixed to form a raw material mixture. In dehydrated toluene, the raw material mixture was dispersed in a mixed solvent containing 2% by mass of dehydrated isobutyronitrile with respect to the raw material mixture to form a slurry of about 10% by mass. The bead mill was operated under the conditions of a peripheral speed of 12 m / s and a flow rate of 500 mL / min, the slurry was charged into the mill, and circulated for 1 hour to obtain a mixture. After removing the solvent of the obtained mixture, it was heated in an electric furnace at 400 - 430 °C for 2 hours. Then, by gradually cooling, solid electrolyte A was obtained. As a result of XRD measurement, since diffraction peaks were present at 2θ = 25.6°, 30.1°, and 31.3°, it was confirmed that solid electrolyte A had an alditolite-type crystal structure. The ionic conductivity was 8.0×10 －３ S / cm.

[0043] (3) Preparation of the positive electrode composite material 0.4500 g of composite powder A and 0.4500 g of solid electrolyte A were put into a 45 mL zirconia pot together with 10 zirconia balls with a diameter of 10 mm and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P - 7), they were mixed at a rotation speed of 700 rpm for 20 hours under room temperature conditions to obtain the powder of the positive electrode composite material.

[0044] Example 2 In Example 1(3), a positive electrode composite material was obtained in the same manner as in Example 1, except that the rotation speed was set to 510 rpm.

[0045] Example 3 (1) Preparation of composite powder A Composite powder A was obtained in the same manner as in Example 1.

[0046] (2) Preparation of solid electrolyte B Under a nitrogen atmosphere, lithium sulfide (Li ２ S), phosphorus pentasulfide (P ２ S ５ ), lithium bromide (LiBr) and lithium chloride (LiCl) were metered so that the molar ratio (Li ２ S:P ２ S ５The raw material mixture was prepared by weighing LiBr:LiCl in a ratio of 47.5:12.5:15.0:25.0 and roughly mixing them. The raw material mixture was dispersed in a mixed solvent of dehydrated toluene and 2% by mass of dehydrated isobutyronitrile relative to the raw material mixture to obtain a slurry of approximately 10% by mass. The bead mill was operated at a peripheral speed of 12 m / s and a flow rate of 500 mL / min, and the slurry was introduced into the mill and circulated for 1 hour to obtain the mixture. After removing the solvent from the obtained mixture, it was heated in an electric furnace at 400-430°C for 2 hours. Subsequently, the raw material sulfide solid electrolyte was obtained by slow cooling. Under a nitrogen atmosphere, the raw material sulfide solid electrolyte was dispersed in dehydrated toluene and placed together with 0.3 mm diameter zirconia balls in a zirconia pot of a planetary ball mill device (Fritsch: model P-7), and the inside of the pot was made into an inert atmosphere. A slurry containing a finely particulated sulfide solid electrolyte was obtained by processing in a planetary ball mill at a rotation speed of 150 rpm for 2 hours. After transferring the slurry to a nitrogen-purged Schlenk bottle, it was dried at room temperature for 1 hour using a vacuum pump, and then heated to 80°C to 100°C to further remove the solvent contained in the finely particulated sulfide solid electrolyte (vacuum drying) to obtain solid electrolyte B. XRD measurements showed diffraction peaks at 2θ = 25.5°, 30.0°, and 31.3°, confirming that solid electrolyte B has an argyrodite-type crystal structure. The ionic conductivity was 4.7 × 10⁻⁶. －３ The value was S / cm.

[0047] (3) Preparation of the cathode composite material 0.4500 g of composite powder A and 0.4500 g of solid electrolyte B were placed in a 45 mL zirconia pot together with 10 zirconia balls with a diameter of 10 mm and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was mixed at a rotation speed of 700 rpm for 20 hours at room temperature to obtain the cathode composite material powder.

[0048] Example 4 A positive electrode composite material was obtained in the same manner as in Example 3 (3), except that the rotational speed was set to 510 rpm.

[0049] Comparative Example 1 A positive electrode composite material was obtained in the same manner as in Example 1 (3), except that the rotation speed was set to 370 rpm.

[0050] Comparative Example 2 In Example 1 (3), 0.4500 g of composite powder A and 0.4500 g of solid electrolyte A were placed in a 45 mL zirconia pot together with 34 g of zirconia balls with a diameter of 2 mm, and the pot was sealed. The mixture was mixed at room temperature for 1 hour at a rotation speed of 600 rpm using a rolling mill ("Small Ball Mill Stand", manufactured by Asahi Rika Seisakusho, model number AV-1). Otherwise, a cathode composite material was obtained in the same manner as in Example 1.

[0051] [Evaluation of cathode composite material] ・Relaxation time T １ Inside the glove box, a 5 mm diameter glass NMR sample tube was filled with the sample, compacted to a height of 10 mm. The tube was then sealed with a resin cap, and the connection was secured with epoxy adhesive (Araldite® Rapid, Huntsman Japan Co., Ltd.). After removing the tube from the glove box, the sample was adjusted using the instrument's sample gauge so that the filled portion was centered in the observation area of ​​the NMR detector. The tube was then placed in the NMR apparatus, and measurements and analysis were performed under the following conditions. The time between removing the glove box and starting measurements was kept within one hour.

[0052] NMR spectrometer: JNM-ECZ400S (manufactured by JEOL Ltd.) NMR detector: 5mmΦ ROYAL probe for solution NMR Observed nuclei: ７ Li Resonance frequency of observed nucleus: 155.4 MHz Measurement method: Inversion recovery method (using the instrument's built-in pulse sequence double_pulse.jpxp) Measurement temperature: 21-23°C Measurement range: -400 to 400 ppm Number of FID acquisition points: 1024 points Waiting time after FID acquisition until next pulse application: 10 seconds Sample rotation: None (stationary) Deuterium lock: None Chemical shift: Using a 1 mol / L deuterium aqueous solution of LiCl beforehand ７Li-NMR spectra were measured, and the chemical shift of the detected signal was set to 0 ppm and used as an external standard. 90° pulse width: Pre-adjusted using a 1 mol / L heavy aqueous solution of LiCl. Resolution adjustment: The resolution adjustment conditions (shim) used when measuring the 1 mol / L heavy aqueous solution of LiCl were applied directly. Analysis method: Using the software "Delta" (manufactured by JEOL Ltd.), a Fourier transform was performed with a window function of sexp (width 10 Hz, shift 0 s), followed by phase adjustment. Then, the regression calculation analysis function was used, with the analysis mode set to Nonlinear Inversion Recovery, and the relaxation time T １ The analysis was performed assuming the presence of one component.

[0053] This measurement method makes it possible to analyze lithium ions that are highly mobile, such as lithium ions in solid electrolytes. The relaxation time T obtained from the measurement １ This is an indicator that represents the mobility of lithium ions in a solid material, and is generally T １ The shorter the distance, the higher the perceived mobility.

[0054] - Evaluation of battery characteristics (1) Preparation of negative electrode composite material Lithium titanate (Ishihara Sangyo Co., Ltd. "LT-112") and conductive additive (Denka Co., Ltd. "Li-100", powdered acetylene black) and Li ２ S-P ２ S ５ -LiCl-LiBr type solid electrolyte B was mixed in a mortar and pestle in a mass ratio of 60:5:35 for 5 minutes to obtain a negative electrode mixture (also called "LTO (lithium titanate) negative electrode mixture").

[0055] (2) Preparation of Solid Electrolyte C 0.4127 g of lithium sulfide, 0.6655 g of phosphorus pentasulfide, 0.2137 g of lithium iodide, 0.2080 g of lithium bromide, and 10 zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was mixed (mechanical milling) at a rotation speed of 370 rpm for 40 hours to obtain a powder. The obtained powder was heated at 195°C for 3 hours to obtain solid electrolyte C.

[0056] (3) Fabrication of a lithium-ion battery A solid electrolyte layer (a layer of solid electrolyte C) was formed by placing 100 mg of solid electrolyte C into a 10 mm diameter Macol cylinder and pressurizing it. Next, 10 mg of positive electrode composite powder was placed on one pressurized surface of the solid electrolyte layer and pressurized again. Then, 166 mg of LTO negative electrode composite was placed on the other pressurized surface of the solid electrolyte layer (the pressurized surface opposite to the positive electrode) and pressurized. A lithium-ion battery was then fabricated by placing a 9 mm diameter, 0.1 mm thick Li foil on top of that and pressurizing it again.

[0057] (4) Charge and Discharge Tests Constant current charge and discharge tests were performed on lithium-ion batteries using the positive electrode composite materials of each example and comparative example. The voltage range for the constant current charge and discharge tests was set to -0.4 to 1.3V, and the current value was set as shown in Table 1 based on the C rate determined based on the theoretical capacity of sulfur of 1672 mAh / g. For charging, CC-CV charging was performed, which involves constant current charging followed by constant voltage charging with a termination condition of 0.02C. For discharging, constant current discharge (CC discharge) was performed. Composite conditions and relaxation time T of the positive electrode composite material. １ The discharge capacity at 1C is shown in Table 2.

[0058]

[0059]

[0060] In this example, the capacity obtained at a high rate (1C) is high. This represents the relaxation time T, which indicates the mobility of lithium ions in the solid electrolyte contained in the cathode composite material of this example. １ This effect is thought to be due to the adjustment being within a suitable range. As in Comparative Example 1, T １ If the interval is long, the lithium ion conductivity in the solid electrolyte will be insufficient when charging and discharging at a high rate, and sufficient capacity cannot be obtained. On the other hand, as in Comparative Example 2, T １ When the T is short, the lithium ion conductivity in the solid electrolyte appears to be high, but the domain size of the solid electrolyte is large, and the supply of lithium ions to the sulfur-based active material is insufficient, so it is thought that sufficient capacity cannot be obtained. In the example, compounding is performed using a planetary ball mill, but by adjusting the energy applied during compounding, the above-mentioned favorable T can be achieved.１ It is believed that a positive electrode composite material exhibiting this characteristic has been successfully fabricated.

[0061] The positive electrode composite material of the present invention can be suitably used as the positive electrode of a lithium-ion battery. Furthermore, the lithium-ion battery of the present invention can be suitably used in information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, as well as batteries used in vehicles such as electric vehicles.

[0062] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will find it easy to make many modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and effects of the present invention. Therefore, many of these modifications fall within the scope of the present invention. All references to the documents described in this specification and to the application on which the Paris Convention priority claim of this application is based are incorporated herein by reference.

Claims

1. It comprises a conductive additive which is a carbon material, a sulfur-based active material, and a sulfide solid electrolyte. ７ Relaxation time T derived from Li-NMR １ However, the positive electrode composite material has a time interval longer than 0.23 s and shorter than 0.41 s.

2. The positive electrode composite material according to claim 1, wherein in powder X-ray diffraction using CuKα rays, the material has diffraction peaks at 2θ = 25.6 ± 0.5° and 30.1 ± 0.5°.

3. The positive electrode composite material according to claim 1 or 2, comprising at least one halogen atom.

4. A positive electrode composite material according to any one of claims 1 to 3, comprising two or more halogen atoms.

5. A positive electrode composite material according to any one of claims 1 to 4, comprising at least Cl and Br as halogen atoms.

6. The conductive additive has a BET specific surface area of ​​100 m². ２ A positive electrode composite material according to claims 1 to 5, comprising activated carbon of 1g or more.

7. The positive electrode mixture according to any one of claims 1 to 6, wherein the sulfur-based active material contains elemental sulfur.

8. The positive electrode composite material according to claim 6, wherein the sulfur-based active material is impregnated into the pores of the carbon material.

9. The positive electrode mixture according to any one of claims 1 to 8, wherein the total amount of the carbon material, the sulfur-based active material, and the sulfide solid electrolyte is 95% by mass or more of the total amount of the positive electrode mixture.

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

11. A composite powder containing a carbon material conductive additive, a sulfur-based active material, and a sulfide solid electrolyte is mechanically mixed. ７ Relaxation time T derived from Li-NMR １ A method for manufacturing a positive electrode composite, comprising the step of adjusting the interval to a range longer than 0.23 s and shorter than 0.41 s.

12. The method for producing a positive electrode composite according to claim 11, wherein the sulfide solid electrolyte has diffraction peaks at 2θ = 25.6 ± 0.5° and 30.1 ± 0.5° in powder X-ray diffraction using CuKα rays.

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