Manufacturing method for sulfur-based active material-electron conductive material composite

Abstract

This manufacturing method for a sulfur-based active material-electron conductive material composite includes mixing, stirring and heating a sulfur-based active material and an electron conductive material having pores in a single process.

Description

Method for producing sulfur-based active material-electron conductive material composite

[0001] The present invention relates to a method for producing a composite of a sulfur-based active material and an electron conductive material, which is used for electrodes of lithium ion secondary batteries, etc.

[0002] In recent years, interest in next-generation automobiles such as electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) has been growing due to environmental issues and the depletion of fossil fuels. Currently, lithium-ion batteries use liquid electrolytes. Lithium-ion secondary batteries using organic electrolytes have the risk of leakage, fire, or explosion, and therefore, safer batteries are desired.

[0003] All-solid-state lithium-ion batteries, which use a safer solid electrolyte, are expected to solve the above problems. All-solid-state batteries using a solid electrolyte have the advantage of being less susceptible to electrolyte leakage and fire.

[0004] An example of an active material for lithium-ion secondary batteries is sulfur. Sulfur has a high capacity density, with a theoretical capacity of approximately 1670 mAh / g, and research and development of sulfur is being actively conducted. 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 a sulfur-based active material, an ion-conductive material and an electronic-conductive material are generally used together with the active material. In all-solid-state batteries, the active material, solid electrolyte (ion-conductive material), and electronic-conductive material are all particulate. Therefore, in order to increase the ionic and electronic conductivity within the electrode, it is necessary to increase the number of contact points between the active material and the solid electrolyte, and between the active material and the electronic-conductive material.

[0005] It is known that a composite in which a porous electron-conductive material is used and the pores are filled with an active material is effective for increasing the number of contact points. One example of a porous electron-conductive material is activated carbon, which has a large specific surface area. A method for producing a composite of sulfur, an active material, and a carbon material such as activated carbon is, for example, a vapor deposition method in which sulfur is vapor-deposited onto a carbon material. In the vapor deposition method, sulfur is vaporized in a vacuum and adsorbed onto the surface and pores of the carbon material (see, for example, Patent Document 1).

[0006] Another method is a liquefaction impregnation method, in which sulfur is heated to a temperature above its melting point to be liquefied and then impregnated into the pores of a carbon material (see, for example, Patent Document 2). Furthermore, a method using a vortex mixer and a twin-screw melt kneader has also been considered (see, for example, Patent Document 3).

[0007] Japanese Patent Application Laid-Open No. 2020-161288 Japanese Patent Application Laid-Open No. 2020-536360 Japanese Patent Application Laid-Open No. 2013-19106

[0008] The production of a composite of sulfur and a carbon material requires a combination of multiple steps and a long time. For example, in a vapor phase deposition method, a temperature increase to 200°C over 1 hour, a holding time at 200°C for 2 hours, and a subsequent cooling step are required. One object of the present invention is to provide a production method suitable for mass production of a composite of an electronic conductive material and a sulfur-based active material.

[0009] As a result of intensive research, the present inventors have found that a composite of an electronically conductive material and a sulfur-based active material can be produced in a short time by heating a sulfur-based active material and an electronically conductive material while mixing and stirring them, thereby liquefying the sulfur-based active material at a temperature above its melting point and impregnating the sulfur-based active material into the pores of the electronically conductive material. Furthermore, they have found that the ability to impregnate the molten sulfur-based active material deep into the pores of the electronically conductive material improves the retention of the sulfur-based active material in the resulting composite.

[0010] According to the present invention, the following methods for producing a sulfur-based active material-electron-conductive material composite are provided. 1. A method for producing a sulfur-based active material-electron-conductive material composite, comprising mixing, stirring, and heating a sulfur-based active material and an electron-conductive material having pores in a single step. 2. The method according to 1, wherein the mixing, stirring, and heating are carried out in a single container. 3. The method according to 1 or 2, wherein the mixing, stirring, and heating are carried out in a stirring, heating, and mixing machine. 4. The method according to 3, wherein the stirring, heating, and mixing machine has a vertical inverted conical container and a stirring blade that rotates around the vertical center of the container as its axis. 5. The method according to 4, wherein the stirring blade rotates at a speed of 20 to 130 rpm, the heating temperature is 120 to 150°C, and the heating time is 5 to 60 minutes. 6. The method according to any one of 1 to 5, wherein the sulfur-based active material contains elemental sulfur. 7. The method according to any one of 1 to 6, wherein the electron-conductive material is a carbon material. 8. A sulfur-based active material-electron-conductive material composite obtained by the production method according to any one of 1 to 7. 9. A sulfur-based active material-electron-conductive material composite, having a weight loss rate of 10% by weight or less at 200°C or higher and lower than 300°C, as measured by thermogravimetry. 10. The sulfur-based active material-electron-conductive material composite according to 9, having a weight loss rate of 60% by weight or more at 300°C or higher and lower than 490°C, as measured by thermogravimetry. 11. The sulfur-based active material-electron-conductive material composite according to 9 or 10, having a weight loss rate of 0.5% by weight or less at lower than 200°C, as measured by thermogravimetry. 12. A positive electrode composite comprising the sulfur-based active material-electron-conductive material composite according to any one of 8 to 11. 13. The positive electrode composite according to 12, further comprising a solid electrolyte. 14. A positive electrode comprising the positive electrode composite according to 12 or 13. 15. A lithium ion battery comprising the positive electrode composite according to 12 or 13 or the positive electrode according to 14.

[0011] According to the present invention, a manufacturing method suitable for mass production of a composite of an electron conductive material and a sulfur-based active material can be provided.

[0012] FIG. 1 is a schematic cross-sectional view illustrating a main part of an agitation, heating and mixing machine used in one embodiment of the present invention.

[0013] [Method for manufacturing a sulfur-based active material-electron-conductive material composite] In a method for manufacturing a sulfur-based active material-electron-conductive material composite (sometimes referred to as a composite) according to one embodiment of the present invention, a sulfur-based active material and an electron-conductive material having pores are mixed, stirred, and heated in one step. In this application, "mixing" refers to a powder (solid), and "stirring" refers to a mixture of a liquid and a solid. For example, mixing a powdered sulfur-based active material with a powdered electron-conductive material is mixing. On the other hand, mixing a melted and liquid sulfur-based active material with a powdered electron-conductive material is stirring.

[0014] In this embodiment, the powdered sulfur-based active material and the powdered electronic conductive material are mixed, and the sulfur-based active material that has been at least partially melted by heating and the powdered electronic conductive material are stirred (composite-formed) in one step, so that the time required for the composite-formation can be significantly reduced.

[0015] In one embodiment, the mixing, stirring, and heating are performed in one container. For example, the mixing, stirring, and heating are performed in a stirring / heating mixer. This reduces the area required for the manufacturing equipment. In addition, it is possible to prevent contamination with foreign matter from the introduction of raw materials to the collection of the final product.

[0016] It should be noted that extruders such as single-screw extruders and twin-screw extruders are not considered to be stirring, heating, and mixing devices of the present invention. Since extruders (kneaders) have no or poor mixing capabilities for solid materials such as pellets, when two or more solid raw materials are fed into an extruder, a raw material mixing process is usually provided as a pre-process. Hereinafter, examples of devices applicable to this embodiment will be described with reference to the drawings.

[0017] FIG. 1 is a schematic cross-sectional view illustrating the main components of a stirring, heating, and mixing machine used in one embodiment of the present invention. The stirring, heating, and mixing machine 1 primarily comprises a vertical inverted conical container 11 and a stirring blade 12 that rotates around the vertical center of the container. The inverted conical container 11 has flow paths for heat transfer medium and refrigerant for heating and cooling the container formed within its wall. The top of the container 11 also has an inlet 13 through which a sample can be introduced. The rotation speed of the stirring blade 12 can be freely set by a motor M. The stirring blade 12 has, for example, a structure in which paddle blades are arranged in multiple stages and auxiliary blades (vertical blades) are attached to the rotation shaft. The paddle blades are arranged along the inner wall of the container 11 from the bottom to the top, ensuring sufficient flow of the introduced sample within the container.

[0018] A gas flow path is provided inside the inverted conical vessel 11 so that the air can be replaced with, for example, nitrogen gas. The gas flow path is provided with a bag filter 14 to prevent leakage of the processed material, such as powder, inside the device. In addition to the main components described above, the device also includes, for example, a sealing member that seals the inside of the vessel and enables pressure reduction inside the vessel, a circulation system that supplies a heat medium and a refrigerant, a vessel temperature control unit, etc.

[0019] Next, a description will be given of a method for producing a sulfur-based active material-electronically conductive material composite using the stirring, heating, and mixing machine 1. The raw materials for the composite, a sulfur-based active material and an electronically conductive material, are supplied into the container 11 through the inlet 13. At this time, there is no need to mix the sulfur-based active material and the electronically conductive material in advance, and they can be separately charged into the container 11.

[0020] The amount of raw material charged is 10 to 90% of the total capacity of the container 11, preferably 20 to 90%, and more preferably 30 to 80%. Unlike an extruder, this embodiment does not compress the raw material, so the spacing between the raw material powder particles is sufficiently wide. Therefore, the powder flows freely within the container, facilitating mixing of the powder particles. Therefore, there is no need to premix the raw material before charging it into the container.

[0021] The temperature of the container 11 when the raw materials are charged may be near room temperature, or may be heated. In one embodiment, the container 11 is heated after the raw materials are charged. This provides the effect of melting the sulfur and impregnating it into the electronic conductive material. The temperature rise time is approximately 1 to 180 minutes, preferably 5 to 90 minutes. After the temperature rise, the heating time is preferably 5 to 60 minutes. The heating temperature can be adjusted appropriately depending on the sulfur-based active material. Specifically, the heating temperature is preferably equal to or higher than the melting point of the sulfur-based active material. For example, 130 to 150°C is preferred.

[0022] After the raw materials are charged, the stirring blade 12 is rotated. The rotation speed of the stirring blade is, for example, 20 to 200 rpm, preferably 20 to 130 rpm. By rotating the stirring blade 12 while heating the raw materials, the sulfur-based active material and the electronically conductive material are uniformly mixed. Thereafter, the sulfur-based active material dissolved by heating and the electronically conductive material are brought into contact with each other by stirring, and the sulfur-based active material is impregnated into the pores of the electronically conductive material.

[0023] After heating and stirring for a predetermined time, the heating is stopped and the mixture is cooled to produce a sulfur-based active material-electron conductive material composite. At this time, the set temperature of the container 11 may be lowered to promote cooling. The raw materials and the like used in the production method of this embodiment will now be described.

[0024] Sulfur-based active material There is no particular limitation on the sulfur-based active material, but sulfur, lithium sulfide (Li ２ S), lithium polysulfide (Li ２ S ｎ : n satisfies 1<n≦8.), titanium sulfide (TiS ２ ), molybdenum sulfide (MoS ２ ), iron sulfide (FeS, FeS ２ ), copper sulfide (CuS), nickel sulfide (Ni ３ S ２ ), sulfur-containing polymer compounds, etc.

[0025] In one embodiment, the sulfur-based active material preferably contains sulfur. Molten sulfur has low viscosity and surface tension, so it easily penetrates into the pores of the electronic conductive material. The sulfur is not particularly limited, but 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 sulfur crystal systems include α-sulfur (orthorhombic), β-sulfur (monoclinic), γ-sulfur (monoclinic), and amorphous sulfur. These may be used alone or in combination of two or more types.

[0026] -Electron-conductive material The electron-conductive material having pores is not particularly limited as long as it has electron conductivity and can be composited with a sulfur-based active material. It is preferable that the electron-conductive material contains a carbon material, since it is lighter than other materials and can increase the output density and electrical capacity per unit mass of the battery. Examples of carbon materials include carbon black, mesoporous carbon, carbon nanotubes, carbon nanohorns, fullerenes, amorphous carbon, carbon fiber, natural graphite, artificial graphite, and activated carbon. Of these, activated carbon is preferred. These may be used alone or in combination of two or more.

[0027] In one embodiment, the BET specific surface area of ​​the carbon material is 50 m 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 sulfur. The BET specific surface area is 70 m ２ / g or more is preferable, and 100m ２ The upper limit of the BET specific surface area is not particularly limited, but is preferably 5000 m ２ / g or less, and more preferably 4000m ２ / g or less is preferred.

[0028] In this embodiment, the specific surface area can be measured by the Brenauer-Emmet-Telle (BET) method or the BJH (Barrett-Joyner-Halenda) method. Specifically, the specific surface area can be determined using a nitrogen adsorption isotherm obtained by adsorbing nitrogen gas onto a carbon material at liquid nitrogen temperature. As a measuring device, for example, a specific surface area and pore distribution measuring device (Autosorb-3) manufactured by Quantacrome can be used for the measurement.

[0029] In one embodiment, the mass ratio (S:C) of the sulfur-based active material (S) to the electron conductive material (C) is 1:9 to 9:1, preferably 5:5 to 9:1.

[0030] [Sulfur-based active material-electron-conductive material composite] The sulfur-based active material-electron-conductive material composite according to one embodiment of the present invention has a weight loss rate of 10% by weight or less at 200° C. or more and less than 300° C., as measured by thermogravimetry. In addition, the weight loss rate of 60% by weight or more at 300° C. or more and 490° C., as measured by thermogravimetry.

[0031] In this embodiment, the weight loss rate A at 200°C or higher but lower than 300°C measured by thermogravimetry refers to the amount of sulfur-based active material contained in the composite that is weakly bonded to the electronic conductive material and has weak retention. On the other hand, the weight loss rate B at 300°C or higher but lower than 490°C refers to the amount of sulfur-based active material contained in the composite that is composited with the electronic conductive material (impregnated into the pores of the electronic conductive material). Therefore, it is preferable that the weight loss rate A is low, and it is preferable that the weight loss rate B is high.

[0032] The sulfur-based active material-electron-conductive material composite of this embodiment has a high proportion of sulfur-based active material that is strongly bonded to the electron-conductive material, and the weight loss rate A can be 10 wt % or less or 5 wt % or less. Furthermore, the sulfur-based active material-electron-conductive material composite of this embodiment has a high proportion of sulfur-based active material that is strongly bonded to the electron-conductive material, and the weight loss rate B can be 60 wt % or more or 65 wt % or more. This value is higher than, for example, conventional composites in which a sulfur-based active material is evaporated and then composited with an electron-conductive material.

[0033] In one embodiment, the weight loss rate at temperatures below 200°C measured by thermogravimetry is 0.5% by weight or less. The weight loss rate at temperatures below 200°C mainly represents the amount of moisture contained in the sulfur-based active material-electron conductive material composite. In this embodiment, for example, heating can be performed while circulating nitrogen, and a mechanism is used to discharge moisture outside the system, thereby reducing the moisture content of the composite. Therefore, for example, when the composite is mixed with a sulfide solid electrolyte to form a positive electrode composite, deterioration of the solid electrolyte due to moisture can be suppressed.

[0034] The sulfur-based active material-electron conductive material composite of this embodiment can be obtained, for example, by the above-described production method of the present invention.

[0035] The composite of the present embodiment can be used for an electrode of a lithium ion secondary battery, etc. For example, a positive electrode mixture can be obtained by mixing or compounding the composite with a solid electrolyte.

[0036] Solid Electrolyte Examples of solid electrolytes include sulfide solid electrolytes containing lithium atoms, phosphorus atoms, and sulfur atoms as constituent elements. The sulfide solid electrolyte is a solid electrolyte that contains at least sulfur atoms and exhibits ionic conductivity due to the contained metal atoms, and in addition to sulfur atoms, preferably contains lithium atoms and phosphorus atoms, more preferably contains lithium atoms, phosphorus atoms, and halogen atoms, and has ionic conductivity due to lithium atoms. The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

[0037] (Amorphous sulfide solid electrolyte) The amorphous sulfide solid electrolyte can be used without any particular limitation as long as it contains at least sulfur atoms and exhibits ionic conductivity due to the contained metal atoms. Representative examples include Li ２ S-P ２ S ５ a solid electrolyte containing sulfur atoms, lithium atoms, and phosphorus atoms, which is composed of lithium sulfide and phosphorus sulfide such as Li; ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ -LiI-LiBr, etc., a solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide; ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ -P ２ S ５ In order to obtain a higher ionic conductivity, a solid electrolyte such as Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as LiI-LiBr, is preferred. The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0038] The amorphous sulfide solid electrolyte contains at least Li ２ S-P ２ S ５ When Li ２ S and P ２ S ５ From the viewpoint of obtaining high chemical stability and higher ionic conductivity, the molar ratio of Li to Li is preferably 30 to 85:15 to 70, more preferably 40 to 80:20 to 60, and even more preferably 45 to 78:22 to 55. ２ S-P ２ S ５In the case of -LiI-LiBr, the total content of lithium sulfide and diphosphorus pentasulfide is preferably 30 to 95 mol%, more preferably 35 to 90 mol%, and even more preferably 40 to 85 mol%. The ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, even more preferably 40 to 80 mol%, and particularly preferably 50 to 70 mol%.

[0039] When the amorphous sulfide solid electrolyte contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, the compounding ratio (molar ratio) of these atoms is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.6, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.05 to 0.5, and even more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.08 to 0.4. Furthermore, when bromine and iodine are used in combination as halogen atoms, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine atoms, and iodine atoms is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.02 to 0.25: 0.02 to 0.25, more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.03 to 0.2: 0.03 to 0.2, and even more preferably 1.35 to 1.45: 1.4 to 1.7: 0.3 to 0.45: 0.04 to 0.18: 0.04 to 0.18. By setting the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, it becomes easier to obtain a solid electrolyte having a thiolisiconregion II type crystal structure described below and having higher ionic conductivity.

[0040] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 μm to 200 μm. ５０) is the particle size at which 50% of the total particle size is reached when the particle size distribution integral curve is drawn and the integral is calculated from the smallest particle size, and the volume distribution is an average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device.

[0041] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte may be, for example, a so-called glass ceramic obtained by heating the amorphous sulfide solid electrolyte to a temperature equal to or higher than the crystallization temperature, and a sulfide solid electrolyte having the following crystal structure may be used. Examples of crystal structures that the crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, and phosphorus atoms may have include Li ３ P.S. ４ Crystal structure, Li ４ P ２ S ６ Crystal structure, Li ７ P.S. ６ Crystal structure, Li ７ P ３ S １１ Examples of such structures include a crystal structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP 2013-16423 A).

[0042] The crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms may have a crystal structure such as Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure (Kanno et al., Journal of the Electrochemical Society, 148(7)A742-746(2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ Examples of the thio-lisicon region II crystal structure include those having a crystal structure similar to the thio-lisicon region II type (see Solid State Ionics, 177 (2006), 2721-2725). ４－ｘ Ge １－ｘ Pｘ S ４ Thio-LISICON Region II crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ This indicates that the thio-LISICON region II type has a similar crystal structure.

[0043] In X-ray diffraction measurement using CuKα radiation, Li ３ P.S. ４ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.5°, 18.3°, 26.1°, 27.3°, and 30.0°. ４ P ２ S ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=16.9°, 27.1°, and 32.5°. ７ P.S. ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=15.3°, 25.2°, 29.6°, and 31.0°. ７ P ３ S １１ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, and Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II crystal structure appear, for example, at 2θ=20.1°, 23.9°, and 29.5°, and Li ４－ｘ Ge １－ｘ P ｘ S ４ Diffraction peaks of a crystal structure similar to that of thio-LISICON Region II type appear, for example, at 2θ=20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0044] The crystal structure of the crystalline sulfide solid electrolyte also includes an argyrodite-type crystal structure. 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).

[0045] Among the above crystal structures, the crystal structure of the crystalline sulfide solid electrolyte is Li ３ P.S. ４ The crystal structure, the thiolicon region II crystal structure, and the argyrodite crystal structure are preferred.

[0046] The shape of the crystalline sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) is the average particle size (D ５０ ) and the ranges of 0.01 μm to 500 μm and 0.1 μm to 200 μm can be exemplified.

[0047] In one embodiment, the positive electrode mixture may or may not contain components other than the composite and the solid electrolyte. The other components are not particularly limited, but examples thereof include a binder, a solvent, and a dispersant.

[0048] In the positive electrode mixture, the contents of the composite (sulfur-based active material and electronically conductive material) and the solid electrolyte are not particularly limited. In one embodiment, the content of the sulfur-based active material is 40 to 350 parts by mass per 100 parts by mass of the solid electrolyte. In one embodiment, the content of the electronically conductive material is 10 to 300 parts by mass per 100 parts by mass of the solid electrolyte.

[0049] In one embodiment, the positive electrode composite 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 composite and the solid electrolyte. Note that "substantially 100% by mass" may contain inevitable impurities.

[0050] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0051] Example 1 The stirring, heating and mixing machine shown in Figure 1 was used. The stirring blades were multi-stage inclined paddle blades. Sulfur S and activated carbon C (MSC-30, manufactured by Kansai Thermal Chemical Industry Co., Ltd.) were charged into the stirring, heating and mixing machine so that the weight ratio (S:C) was 70:30 and the total amount was 950 g. Nitrogen gas was circulated through the mixer to obtain N ２ The mixture was heated to 145°C in a 100°C atmosphere and the rotation speed of the stirring blade was set to 130 rpm. The mixture was heated to 145°C over 40 minutes and then maintained at that temperature for 5 minutes. The heating was stopped, and the coolant temperature was set to 25°C and the mixture was cooled for 30 minutes to produce a sulfur-carbon composite.

[0052] Example 2 A sulfur-carbon composite was produced in the same manner as in Example 1, except that the holding time was changed to 60 minutes.

[0053] Example 3 A sulfur-carbon composite was produced in the same manner as in Example 1, except that the rotation speed of the stirring blade was set to 20 rpm and the temperature-raising time was set to 70 minutes.

[0054] Example 4 A sulfur-carbon composite was produced in the same manner as in Example 1, except that the rotation speed of the stirring blade was set to 20 rpm and the holding temperature was set to 130°C.

[0055] Example 5 A sulfur-carbon composite was produced in the same manner as in Example 1, except that the temperature-raising time was 30 minutes and the holding temperature was 120°C.

[0056] Comparative Example 1: 1.5 g of sulfur and activated carbon (weight ratio 70:30) were mixed in a mortar, then the mixture was placed in an airtight stainless steel container and heated in an electric furnace to produce a sulfur-carbon composite. The heating conditions were as follows: temperature increase from room temperature to 150°C at 10°C / min, holding at 150°C for 6 hours, temperature increase from 150°C to 300°C at 10°C / min, holding at 300°C for 2.75 hours, and then natural cooling.

[0057] [Evaluation of sulfur-carbon composite] (1) Thermogravimetry The sulfur retention capacity of the composite was evaluated by thermogravimetry (TG). The thermogravimetry was performed under the conditions of placing 10 mg of a sample on an aluminum pan and heating with N ２ The flow rate was 200 mL / min, and the temperature rise rate was 20°C / min. The measurement temperature was from room temperature (25°C) to 600°C. After reaching 600°C, N ２ The gas flow rate was switched to air (200 mL / min). The weight loss rate A (wt%) at 200°C or higher and lower than 300°C, and the weight loss rate B (wt%) at 300°C or higher and 490°C or lower were measured. The weight loss rate A was the amount of unimpregnated sulfur contained in the composite, and the weight loss rate B was the amount of impregnated sulfur contained in the composite. The results are shown in Table 1.

[0058] (2) Water Content The weight loss rate was measured under the conditions of (1) above, and the weight loss rate (wt%) from room temperature (25° C.) to less than 200° C. was taken as the water content in the composite. The results are shown in Table 1.

[0059]

[0060] From Table 1, it can be seen that the time required for composite formation in the manufacturing methods of the examples is 35 to 100 minutes, which is significantly shorter than that in the comparative examples. It can also be confirmed that the sulfur retention capacity of the composite is improved.

[0061] The sulfur-based active material-electron-conductive material composite produced by the present invention is suitable as a structural material for lithium-ion batteries. Furthermore, lithium-ion batteries containing the cathode composite produced by the present invention are suitable for use in, for example, information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and 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 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 method for producing a sulfur-based active material-electron-conductive material composite, in which a sulfur-based active material and an electron-conductive material having micropores are mixed, stirred, and heated in a single step.

2. The method of claim 1, wherein the mixing, stirring, and heating are carried out in one vessel.

3. The method according to claim 1 or 2, wherein the mixing, stirring and heating are carried out in a stirring / heating mixer.

4. The manufacturing method according to claim 3, wherein the stirring, heating and mixing machine has a vertical inverted cone-shaped container and a stirring blade that rotates around the vertical center of the container as an axis.

5. The method according to claim 4, wherein the rotation speed of the stirring blade is 20 to 130 rpm, the heating temperature is 120 to 150°C, and the heating time is 5 to 60 minutes.

6. The method according to any one of claims 1 to 5, wherein the sulfur-based active material contains elemental sulfur.

7. The manufacturing method according to any one of claims 1 to 6, wherein the electron-conductive material is a carbon material.

8. A sulfur-based active material-electron conductive material composite obtained by the manufacturing method according to any one of claims 1 to 7.

9. A sulfur-based active material-electron conductive material composite having a weight loss rate of 10% by weight or less at 200°C or higher and lower than 300°C as measured by thermogravimetry.

10. The sulfur-based active material-electron conductive material composite according to claim 9, wherein the weight loss rate at 300° C. or higher and 490° C. or lower by thermogravimetry is 60% by weight or higher.

11. The sulfur-based active material-electron conductive material composite according to claim 9 or 10, wherein the weight loss rate at temperatures below 200° C. as measured by thermogravimetry is 0.5% by weight or less.

12. A positive electrode mixture comprising the sulfur-based active material-electron conductive material composite according to any one of claims 8 to 11.

13. The cathode mixture of claim 12, further comprising a solid electrolyte.

14. A positive electrode comprising the positive electrode mixture according to claim 12 or 13.

15. A lithium ion battery comprising the positive electrode mixture according to claim 12 or 13 or the positive electrode according to claim 14.

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