Positive electrode mixture

Abstract

A positive electrode mixture comprising: a conductive additive that is a carbon material; a sulfur-based active material; and a solid electrolyte, wherein the solid electrolyte has diffraction peaks at 2θ = 25.7 ± 0.5° and 30.2 ± 0.5° in powder X-ray diffraction using CuKα radiation, and comprises an anion A having an ionic radius of 1.75 Å to 2.00 Å, and at least one of an anion B having an ionic radius of less than 1.75 Å and an anion C having an ionic radius of greater than 2.00 Å.

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 a positive electrode using sulfur-based active materials, they are compounded with ion-conducting materials (such as solid electrolytes) and conductive additives (such as carbon materials). As a solid electrolyte used in compounding, sulfide solid electrolytes having an argyrodite-type crystal structure (called argyrodite-type solid electrolytes) are being considered because of their high ionic conductivity (see, for example, Patent Documents 1 and 2).

[0003] International Publication No. 2024 / 034499, International Publication No. 2022 / 090757

[0004] In cathodes using sulfur-based active materials (sulfur cathodes), cycle characteristics such as capacity retention rate were insufficient. One of the objectives of the present invention is to provide a cathode composite material that can improve capacity retention rate.

[0005] One possible reason for the poor cycle performance is the large volume change during charging and discharging in the sulfur cathode. This volume change can cause interfacial delamination between the sulfur-based active material and the solid electrolyte. In particular, argyrodite-type solid electrolytes are harder than other solid electrolytes, making them more susceptible to interfacial delamination between the sulfur-based active material and the solid electrolyte, resulting in poor cycle performance. The inventors of this invention have discovered that by including two or more anions of different sizes in the argyrodite-type solid electrolyte, the cycle performance can be improved compared to conventional methods, thus completing the present invention.

[0006] The present invention provides the following positive electrode composite materials, etc. 1. A positive electrode composite material comprising a conductive additive which is a carbon material, a sulfur-based active material, and a solid electrolyte, wherein the solid electrolyte has diffraction peaks at 2θ = 25.7 ± 0.5° and 30.2 ± 0.5° in powder X-ray diffraction using CuKα rays, and comprises anion A having an ionic radius of 1.75 Å or more and 2.00 Å or less, and at least one of anion B having an ionic radius of less than 1.75 Å and anion C having an ionic radius greater than 2.00 Å. 2. The anion A is Cl － and Br － A positive electrode composite material according to 1, wherein one or more are selected from the following. 3. The anion B is OH － and O ２－ A positive electrode composite material according to 1 or 2, wherein one or more are selected from the following. 4. The anion C is I － The positive electrode composite material described in any of 1 to 3. 5. The anion A is Cl － and Br － 1. A positive electrode composite material according to any one of 1 to 4. 6. A positive electrode composite material according to any one of 1 to 5, wherein the molar ratio of anion A to the sum of anions A to C in the solid electrolyte (A / (A+B+C)) is 0.50 or more. 7. A lithium-ion battery comprising the positive electrode composite material according to any one of 1 to 6. 8. A method for producing a positive electrode composite material, comprising the step of mechanically mixing a composite powder comprising a conductive additive which is a carbon material, a sulfur-based active material, and a solid electrolyte, wherein the solid electrolyte has diffraction peaks at 2θ = 25.7±0.5° and 30.2±0.5° in powder X-ray diffraction using CuKα rays, and comprises anion A having an ionic radius of 1.75 Å or more and 2.00 Å or less, and at least one of anion B having an ionic radius of less than 1.75 Å and anion C having an ionic radius greater than 2.00 Å.

[0007] According to the present invention, it is possible to provide a positive electrode composite material that can improve capacity retention.

[0008] [Positive Electrode Composite Material] The positive electrode composite material according to an embodiment of the present invention includes a conductive auxiliary agent that is a carbon material, a sulfur-based active material, and a solid electrolyte, and the solid electrolyte satisfies the following requirements A and B. Requirement A: In powder X-ray diffraction using CuKα rays, it has diffraction peaks at 2θ = 25.7 ± 0.5° and 30.2 ± 0.5°. Requirement B: It includes an anion A with an ionic radius of 1.75 Å or more and 2.00 Å or less, and at least one of an anion B with an ionic radius of less than 1.75 Å and an anion C with an ionic radius of more than 2.00 Å.

[0009] The above requirement A stipulates that the solid electrolyte includes an alditolite-type crystal structure. The above requirement B stipulates that the solid electrolyte includes two or more types of anions with different ionic radii. In this embodiment, by combining predetermined anions with different sizes, strain can be introduced into the crystal lattice of the alditolite-type crystal. As a result, it is presumed that the hardness of the alditolite-type solid electrolyte is improved, and the ion conduction path is maintained even when the volume of the positive electrode changes. Hereinafter, the constituent members of the positive electrode composite material will be described.

[0010] (Conductive Auxiliary Agent) A carbon material is used as the conductive auxiliary agent. Since the carbon material has high electronic conductivity and is lighter than other conductive materials, the output density and capacity per unit weight of the battery can be increased. The carbon material is preferably porous carbon having pores.

[0011] The carbon material is not particularly limited, and examples include carbon blacks such as Ketjen black, acetylene black, Denka black, thermal black, and channel black, mesoporous carbon, activated carbon, amorphous carbon, carbon nanotubes, vapor-grown carbon fibers (VGCFs), 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. Also, these composite materials can be used.

[0012] In one embodiment, the BET specific surface area of the carbon material is 50 m ２ / g or more and 6000 m ２The 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, 6cm ３ 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, FeS２ ), 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] (Solid Electrolyte) In this embodiment, a solid electrolyte is used that has diffraction peaks at 2θ = 25.7 ± 0.5° and 30.2 ± 0.5° in powder X-ray diffraction using CuKα rays. That is, an argyrodite-type solid electrolyte is used. The argyrodite-type solid electrolyte may further have a diffraction peak at 2θ = 47.9 ± 0.5°. The crystal structure of the argyrodite-type solid electrolyte may include, for example, Li ７－ｘ PS ６－ｘ An ｘ Examples of crystal structures include those represented by (An being the sum of anions A to C, and x being preferably 0.2 to 1.8).

[0018] Furthermore, in this embodiment, a solid electrolyte is used that includes anion A having an ionic radius of 1.75 Å or more and 2.00 Å or less, and at least one of anion B having an ionic radius of less than 1.75 Å and anion C having an ionic radius greater than 2.00 Å. The ionic radii of the anions are the values ​​listed in Table 1 of "Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides" (Acta Cryst. (1976), A32, 751-767). ４ － The ionic radius of is 2.05 Å.

[0019] As for anion A, Cl － , Br － Examples include: Anion A may be only one type, or it may be a combination of two or more types. In one embodiment, anion A is Cl － and Br － It is one or more selected from the following. Among them, as anion A, Cl － and Br － It is preferable to include both.

[0020] As for anion B, OH － , O ２－ F － , N ３－ One example is anion B is OH － and O ２－ It is one or more selected from the options.

[0021] As for Anion C, I － BH ４ － Examples include: In one embodiment, anion C is I － That is the case.

[0022] The method for producing argyrodite-type solid electrolytes is not particularly limited, and known production methods can be referred to. As starting materials, two or more compounds or elements containing lithium atoms, phosphorus atoms, sulfur atoms, anions, or atoms that become anions as constituent elements can be used in combination.

[0023] 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.

[0024] 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 ４ Examples 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 manufactured and sold industrially.

[0025] Examples of raw materials containing anions include raw materials containing halogens. Examples of raw materials containing halogens include lithium halides such as lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), and LiF, 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 LiCl, LiBr, LiI, LiF, and other lithium halides are preferred. Other raw materials containing anions include lithium oxide (Li ２O), lithium hydroxide (LiOH), Li ３ N, LiBH ４ These are some examples.

[0026] In this embodiment, the above raw materials are combined to prepare a solid electrolyte containing anion A and anion B, anion A and anion C, or anion A, anion B, and anion C. In one embodiment, the molar ratio of anion A to the total of anions A to C in the solid electrolyte (A / (A+B+C)) is 0.50 or higher. The molar ratio (A / (A+B+C)) is preferably 0.50 to 0.99, and more preferably 0.60 to 0.95.

[0027] As for the combination of raw materials used, for example, lithium sulfide, diphosphorus pentasulfide, lithium chloride, lithium bromide, and lithium iodide are preferred. In this case, the molar ratio of the raw materials used is preferably lithium sulfide: diphosphorus pentasulfide: total of the three lithium halides = 30-60:10-25:15-50. Lithium sulfide, diphosphorus pentasulfide, lithium chloride, lithium bromide, and lithium hydroxide are also preferred. In this case, the molar ratio of the raw materials used is preferably lithium sulfide: diphosphorus pentasulfide: (total of lithium chloride + lithium bromide + lithium hydroxide) = 30-60:10-25:15-50.

[0028] 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.

[0029] 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.

[0030] The ionic conductivity of a solid electrolyte is, for example, 1.0 × 10⁻⁶ －３ It is preferable that the ratio is S / cm or higher.

[0031] [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 which is a carbon material, a sulfur-based active material, and a solid electrolyte. The conductive additive (carbon material), sulfur-based active material, and solid electrolyte can be those described in the section on positive electrode compound. An example of the mechanical mixing method is the same as that for manufacturing the solid electrolyte described above.

[0032] The raw materials for the positive electrode composite may be a mixture of carbon material, sulfur-based active material, and solid electrolyte, or, for example, a mixture in which carbon material and sulfur-based active material are pre-composited and a solid electrolyte is mixed with the composite. In one embodiment, the raw materials may or may not contain components other than carbon material, sulfur-based active material, and solid electrolyte. Other components are not particularly limited, but examples include binders, solvents, and dispersants.

[0033] In the raw materials for the cathode composite, the content of carbon material, sulfur-based active material, and solid electrolyte is not particularly limited. For example, the content of sulfur-based active material is 40 to 350 parts by mass per 100 parts by mass of sulfide solid electrolyte. The content of carbon material is 10 to 300 parts by mass per 100 parts by mass of sulfide solid electrolyte.

[0034] In one embodiment, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, 99% or more, 99.5% or more, or substantially 100% or more of the cathode composite material raw materials are carbon material, sulfur-based active material, and solid electrolyte. In the case of "substantially 100% or more," unavoidable impurities may be included.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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 cycle 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.

[0039] [Another Aspect of the Positive Electrode Composite Material] In another aspect of the positive electrode composite material of the present invention, in the case of carbon, it contains a conductive auxiliary agent that is a carbon material, a sulfur-based active material, and a solid electrolyte, and the solid electrolyte has diffraction peaks at 2θ = 25.7 ± 0.5° and 30.2 ± 0.5° in powder X-ray diffraction using CuKα rays, and Cl － and Br － One or more anions A selected from, OH － , O ２－ , F － and N ３－ One or more anions B selected from the group consisting of and I － and BH ４ － At least one of one or more anions C selected from. This aspect specifies anions A to C by specific ion species rather than ionic radii. The constituent members, manufacturing methods, etc., are the same as those of the positive electrode composite material of the present invention described above.

[0040] Hereinafter, the present invention will be specifically described based on examples. The present invention is not limited to the examples. [Production of Solid Electrolyte] Production Example 1 (Solid Electrolyte A) Lithium sulfide (Li ２ S), phosphorus pentasulfide (P ２ S ５ ), lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI) were put into a 45 mL zirconia pot together with 1 ten zirconia balls with a diameter of 10 mm so that the molar ratio (Li ２ S:P ２ S ５ :LiBr:LiCl:LiI) was 47.5:12.5:25.0:10.0:5.0, and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P - 7), it was mixed (mechanically milled) at a rotational speed of 450 rpm for 40 hours to obtain a powder. The obtained powder was heated at 430 °C for 2 hours to obtain solid electrolyte A. As a result of XRD measurement, since it had diffraction peaks at 2θ = 25.41°, 29.89°, and 47.65°, it was confirmed that solid electrolyte A had an argyrodite-type crystal structure. The ionic conductivity was 9.1× －３ S / cm.

[0041] Production Example 2 (Solid Electrolyte B) Lithium iodide (LiI) was changed to lithium hydroxide (LiOH), and the molar ratio (Li ２ S:P ２ S ５ :LiBr:LiCl:LiOH) was set to 42.5:12.5:30.0:10.0:5.0. Otherwise, in the same manner as in Production Example 1, Solid Electrolyte B was obtained. As a result of XRD measurement, since diffraction peaks were observed at 2θ = 25.57°, 30.10°, and 47.98°, it was confirmed that Solid Electrolyte B had an alditolite-type crystal structure. The ionic conductivity was 9.9×10 －３ S / cm.

[0042] Production Example 3 (Solid Electrolyte C) The molar ratio (Li ２ S:P ２ S ５ :LiBr:LiCl:LiOH) was set to 47.5:12.5:25.0:12.5:7.5. Otherwise, in the same manner as in Production Example 2, Solid Electrolyte C was obtained. As a result of XRD measurement, since diffraction peaks were observed at 2θ = 25.51°, 30.02°, and 47.90°, it was confirmed that Solid Electrolyte C had an alditolite-type crystal structure. The ionic conductivity was 10.1×10 －３ S / cm.

[0043] Production Example 4 (Solid Electrolyte D) Li ２ S, P ２ S ５ , LiCl and LiBr were put into a 45 mL zirconia pot together with 10 zirconia balls with a diameter of 10 mm so that the molar ratio (Li ２ S:P ２ S ５ :LiBr:LiCl) became 47.5:12.5:25.0:15.0, and the pot was sealed. Thereafter, in the same manner as in Example 1, Solid Electrolyte D was obtained. As a result of XRD measurement, since diffraction peaks were observed at 2θ = 25.48°, 29.99°, and 47.81°, it was confirmed that Solid Electrolyte D had an alditolite-type crystal structure. The ionic conductivity was 10.4×10 －３ S / cm.

[0044] [Evaluation of Solid Electrolyte] The presence of argyrodite-type crystals was confirmed by X-ray diffraction (XRD) measurements. Furthermore, the relative magnitudes of the lattice constants relative to solid electrolyte D were evaluated from the shift of the main peak position. The results are shown in Table 1. The composition of the solid electrolyte (molar ratio of each element to phosphorus (P)) and ionic conductivity are also shown in Table 1.

[0045] - The positive electrode composite material for X-ray diffraction measurement was filled into a groove with a diameter of 20 mm and a depth of 0.2 mm, and leveled with glass to prepare the sample. This sample was sealed with Kapton film for XRD and measured without exposure to air. XRD measurements were performed using a BRUKER Corporation powder X-ray diffraction analyzer D2 PHASER under the following measurement conditions: Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα line (1.5418 Å) Optical system: Focusing method Slit configuration: Solar slit 4° (both incident and receiving sides), diverging 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

[0046] - Ionic conductivity from solid electrolyte, diameter 10 mm (cross-sectional area S: 0.785 cm²) ２ Circular pellets with a height (L) of 0.1 to 0.3 cm were formed as samples. Electrode terminals were taken from the top and bottom of the samples, and measurements were taken at 25°C using the AC impedance method (frequency range: 5 MHz to 0.5 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. Near the right end of the arc observed in the high-frequency region, the real part Z' (Ω) at the point where -Z'' (Ω) is minimized 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

[0047]

[0048] Table 2 shows the ionic radii for anions, taken from Table 1 of Acta Cryst. (1976), A32, 751-767.

[0049]

[0050] OH derived from lithium hydroxide (LiOH) is present in solid electrolytes. － or O ２－ It exists in this state. XRD measurements of the solid electrolyte revealed a shift in the position of the crystal peak, indicating that a change in the lattice constant occurs in accordance with the size of the anionic radius. Furthermore, regarding ionic conductivity, it was confirmed that solid electrolyte D exhibited very high ionic conductivity, while solid electrolytes A to C used in the examples were slightly lower than solid electrolyte D.

[0051] [Preparation of Cathode Compound] Example 1 (1) Preparation of Composite Powder A Activated carbon (MSC-30, manufactured by Kansai Thermal Chemical Co., Ltd.) and sulfur were placed in a glass bottle in a mass ratio of 3:7 and sealed in a SUS tube container. The mixture was heated in an electric furnace at 150°C for 6 hours and at 300°C for 2.75 hours to obtain composite powder A of activated carbon and sulfur.

[0052] (2) Preparation of the cathode composite material 0.5400 g of composite powder A and 0.3600 g of solid electrolyte A were placed in a 45 mL zirconia pot together with 10 zirconia balls with a diameter of 10 mm and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was mixed at a rotation speed of 370 rpm for 20 hours at room temperature to obtain the cathode composite material powder.

[0053] Example 2 A positive electrode composite material was obtained in the same manner as in Example 1, except that solid electrolyte B was used instead of solid electrolyte A.

[0054] Example 3 A positive electrode composite material was obtained in the same manner as in Example 1, except that solid electrolyte C was used instead of solid electrolyte A.

[0055] Comparative Example 1: A positive electrode composite material was obtained in the same manner as in Example 1, except that solid electrolyte D was used instead of solid electrolyte A.

[0056] [Evaluation of positive electrode composite material] ・Capacity retention rate of lithium-ion battery (1) Preparation of negative electrode composite material Lithium titanate (Ishihara Sangyo Co., Ltd. "LT-112"), conductive additive (Denka Co., Ltd. "Li-100", powdered acetylene black), and Li ２ S-P ２ S ５-LiCl-LiBr type solid electrolyte E 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").

[0057] (2) Preparation of Solid Electrolyte F 0.4127 g of lithium sulfide, 0.6655 g of phosphorus pentasulfide, 0.2137 g of lithium iodide, and 0.2080 g of lithium bromide, along with 10 zirconia balls with a diameter of 10 mm, were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was mixed (mechanical milling) at a rotation speed of 370 rpm for 40 hours to obtain a powder. The obtained powder was heated at 195°C for 3 hours to obtain solid electrolyte F.

[0058] (3) Fabrication of a lithium-ion battery A solid electrolyte layer (a layer of solid electrolyte F) was formed by placing 100 mg of solid electrolyte F 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.

[0059] (4) Charge and Discharge Tests Constant current charge and discharge tests were conducted on lithium-ion batteries using the positive electrode composite materials of each example and comparative example, and the capacity retention rate was calculated. 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 3 using the C rate determined based on the theoretical capacity of sulfur, 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. The capacity retention rate at 60 cycles relative to 10 cycles (60th / 10th:%) was calculated. The capacity retention rates are shown in Table 4.

[0060]

[0061]

[0062] As an anion, Cl－ and Br － In addition, I have different ionic radii － and OH － (or O ２－ In the example where a solid electrolyte containing ) was combined with a sulfur active material, the capacity retention rate (cycle characteristics) was improved. It is thought that a unique effect occurred in which the ion conduction pathway was maintained even after the charge-discharge cycle, by combining a sulfur-based active material that undergoes a large volume change with charge-discharge, with a solid electrolyte that contains anions with different ionic radii, which changes the lattice constant and causes distortion in the crystal lattice.

[0063] 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.

[0064] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will find it easy to make many modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and effects of the present invention. Accordingly, many of these modifications fall within the scope of the present invention. All references to the documents described in this specification and the contents of the application on which the priority claim under the Paris Convention of this application is based are incorporated herein by reference.

Claims

1. A positive electrode composite comprising a conductive additive which is a carbon material, a sulfur-based active material, and a solid electrolyte, wherein the solid electrolyte has diffraction peaks at 2θ = 25.7 ± 0.5° and 30.2 ± 0.5° in powder X-ray diffraction using CuKα rays, and contains anion A having an ionic radius of 1.75 Å or more and 2.00 Å or less, and at least one of anion B having an ionic radius of less than 1.75 Å and anion C having an ionic radius greater than 2.00 Å.

2. The anion A is Cl － and Br － The positive electrode composite material according to claim 1, wherein one or more are selected from the following.

3. The anion B is OH － and O ２－ A positive electrode composite material according to claim 1 or 2, wherein one or more are selected from the following.

4. The anion C is I － The positive electrode composite material according to any one of claims 1 to 3.

5. The anion A is Cl － and Br － The positive electrode composite material according to any one of claims 1 to 4.

6. The positive electrode composite material according to any one of claims 1 to 5, wherein the molar ratio of anion A to the total of anions A to C in the solid electrolyte (A / (A+B+C)) is 0.50 or more.

7. A lithium-ion battery comprising the positive electrode composite material described in any one of claims 1 to 6.

8. A method for producing a positive electrode composite, comprising the step of mechanically mixing a composite powder containing a conductive additive which is a carbon material, a sulfur-based active material, and a solid electrolyte, wherein the solid electrolyte has diffraction peaks at 2θ = 25.7 ± 0.5° and 30.2 ± 0.5° in powder X-ray diffraction using CuKα rays, and contains anion A having an ionic radius of 1.75 Å or more and 2.00 Å or less, and at least one of anion B having an ionic radius of less than 1.75 Å and anion C having an ionic radius greater than 2.00 Å.

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