Positive electrode mixture, method for manufacturing positive electrode mixture, and lithium-ion battery

Abstract

This positive electrode mixture contains a carbon-sulfur composite and a sulfide solid electrolyte, wherein a recovered specific surface area of a processed product obtained by removing the sulfur and the sulfide solid electrolyte from the positive electrode mixture is 1100 m2 / g or greater.

Description

Positive electrode mixture, method for producing the positive electrode mixture, and lithium ion battery

[0001] The present invention relates to a positive electrode composite, a method for producing the positive electrode composite, and a lithium ion battery.

[0002] Composite materials of sulfur-based active materials and carbon materials have been proposed as high-capacity positive electrode composites for use in all-solid-state lithium-ion batteries (Patent Documents 1 to 3, Non-Patent Documents 1 and 2). To further increase the energy density of lithium-ion batteries, for example, it is conceivable to increase the content of the active material that stores energy within the battery. Specifically, it is conceivable to increase the thickness of the electrode, which is a layer containing the active material.

[0003] JP 2015-72781 A JP 2014-529853 A JP 2014-11033 A International Publication No. 2022 / 260056

[0004] Small 2021, 2105678Adv. Mater. Interfaces 2022, 2200539

[0005] When a composite material of sulfur and a carbon material, which are active materials, is used in a positive electrode, if the electrode is formed thick, the influence of expansion and contraction of sulfur becomes large, resulting in a problem of deterioration in cycle characteristics. One of the objects of the present invention is to provide a positive electrode composite that enables a thicker positive electrode film and suppresses deterioration in cycle characteristics.

[0006] The present inventors investigated the relationship between the dispersion state of sulfur and the particle size of the carbon material in a cathode composite using a sulfur-carbon composite and a sulfide solid electrolyte. They estimated that a larger particle size of the carbon material forming the composite increases the amount of sulfur retained in the pores of the carbon material, resulting in greater expansion and contraction during charge and discharge. They concluded that the expansion and contraction during charge and discharge destroys the conductive path within the cathode, resulting in a deterioration in cycle performance. They also found that a cathode composite capable of suppressing the deterioration of cycle performance can be obtained by removing sulfur from the composite and increasing the calculated recovered specific surface area.

[0007] According to the present invention, the following cathode mixture and the like are provided: 1. A cathode mixture containing a carbon-sulfur composite and a sulfide solid electrolyte, wherein the recovered specific surface area of ​​a treated product obtained by removing the sulfur and the sulfide solid electrolyte from the cathode mixture is 1100 m ２ / g or more. 2. The cathode mixture according to 1, wherein the sulfide solid electrolyte contains lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms. 3. The cathode mixture according to 2, wherein the sulfide solid electrolyte contains two or more types of halogen atoms. 4. The cathode mixture according to 2, wherein the mass ratio of the phosphorus atoms (P) in the sulfide solid electrolyte (P / sulfide solid electrolyte) is less than 0.20. 5. The cathode mixture according to any one of 1 to 4, wherein the total mass (S) of the sulfur in the sulfur and the sulfur discharge product is 20 mass% or more. 6. A cathode mixture comprising: a step A of compounding a carbon material and sulfur to obtain a carbon-sulfur composite; and a step B of co-pulverizing the carbon-sulfur composite and the sulfide solid electrolyte to obtain a cathode mixture, wherein in step B, the recovered specific surface area of ​​the treated product obtained by removing the sulfur and the sulfide solid electrolyte from the cathode mixture is 1100 m ２ 7. The method for producing a positive electrode composite according to 6, wherein the carbon material has an average particle size of 50 μm or less. 8. The method for producing a positive electrode composite according to 6, wherein the carbon material has a specific surface area of ​​2300 m / g or more. ２ / g or more. 9. The manufacturing method according to any one of 6 to 8, wherein the mixing and grinding in step B is carried out using a planetary ball mill. 10. A cathode mixture obtained by the manufacturing method according to any one of 6 to 9. 11. A cathode comprising the cathode mixture according to any one of 1 to 5 and 10. 12. The cathode according to 11, wherein the thickness is 35 μm or more. 13. A treated product from which sulfur and sulfide solid electrolyte have been removed has a recovered specific surface area of ​​1,100 m ２ 14. A lithium ion battery comprising the positive electrode according to any one of 11 to 13.

[0008] According to the present invention, it is possible to provide a positive electrode mixture that allows for a thicker positive electrode film and suppresses deterioration of cycle characteristics.

[0009] 1 is a graph showing the results of a constant current charge / discharge test of the all-solid-state lithium ion batteries produced in Examples 1 and 2 and Comparative Examples 1 and 2.

[0010] 1. Cathode Composite A cathode composite according to one embodiment of the present invention includes a carbon-sulfur composite and a sulfide solid electrolyte. The cathode composite has a recovered specific surface area of ​​1100 m2 after removal of sulfur and the sulfide solid electrolyte. ２ / g or more. ２ / g or more indicates that the particle size of the carbon material contained in the positive electrode mixture is sufficiently small, and the amount of elemental sulfur and discharge products of elemental sulfur held by the carbon material is appropriate.

[0011] When the particle size of the carbon material is large, the amount of sulfur held in the pores of the carbon material increases. If a single particle of carbon material holds a large amount of sulfur, expansion and contraction during charge and discharge increases, which destroys the conductive path in the positive electrode and reduces cycle characteristics. By using the positive electrode composite of this embodiment, expansion and contraction during charge and discharge can be suppressed, making it possible to thicken the positive electrode and obtain a battery with little deterioration in cycle characteristics.

[0012] The recovered specific surface area is the specific surface area of ​​a treated product (mainly a carbon material) obtained by removing the solid electrolyte and sulfur from the positive electrode composite through the following steps. Specific processes will be described in the Examples. (1) Solid Electrolyte Removal Step: The solid electrolyte is removed from the positive electrode composite by dispersing the positive electrode composite in an excess amount of solvent. Examples of the solvent include ethanol. (2) Sulfur Removal Step: The precipitate recovered in step (1) above is heated and dried to remove the solvent and sulfur from the precipitate. The specific surface area of ​​the treated product after steps (1) and (2) above is the recovered specific surface area.

[0013] If the particle size of the carbon material is large, the sulfur that has penetrated deep into the carbon material is not removed and remains in the carbon material, resulting in a small recovered specific surface area.On the other hand, if the particle size of the carbon material is small, most of the sulfur held in the carbon material is removed, resulting in a large recovered specific surface area.

[0014] In one embodiment, the recovered specific surface area is preferably 1200 m ２ / g or more, more preferably 1300m ２ The upper limit is not particularly limited, but is preferably 2000 m２ The recovered specific surface area of ​​the treated product is not larger than the specific surface area of ​​the carbon material that is the starting material.

[0015] In the present application, 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 to a sample at liquid nitrogen temperature. The measurement can be performed using, for example, a specific surface area and pore distribution measurement device (Autosorb-3) manufactured by Quantacrome.

[0016] The positive electrode mixture of this embodiment can be produced, for example, by the production method of the present invention described below.

[0017] 2. Method for Producing Cathode Composite A method for producing a cathode composite according to one embodiment of the present invention includes the following steps (A) and (B): Step (A): A step of compounding a carbon material with sulfur to obtain a carbon-sulfur composite; Step (B): A step of mixing and pulverizing the carbon-sulfur composite and a sulfide solid electrolyte to obtain a cathode composite.

[0018] [Step (A)] In step (A), a carbon material and sulfur are combined to obtain a carbon-sulfur composite. The carbon material is an electron-conductive carbon material having a specific surface area of ​​2300 m. ２ / g or more and can be composited with sulfur. A porous carbon material having a plurality of pores is preferable. Examples of porous carbon materials include carbon black, mesoporous carbon, carbon nanotubes, acetylene black, furnace black, carbon nanohorns, fullerenes, graphene, graphite, amorphous carbon, carbon fiber, natural graphite, artificial graphite, and activated carbon. These may be used alone or in combination of two or more. The specific surface area is 2500 m ２ / g or more is preferable, and 2700m ２ / g or more is particularly preferred. There is no particular upper limit to the specific surface area, but ２ / g or less is preferred. ２If the density is more than 1 / g, the bulk density may become extremely small, making handling difficult.

[0019] The elemental sulfur (sulfur) is not particularly limited, but preferably has a purity of 95% by mass or more, more preferably 96% by mass or more, and particularly preferably 97% by mass or more. Examples of the crystal system of elemental sulfur include α-sulfur (orthorhombic system), β-sulfur (monoclinic system), γ-sulfur (monoclinic system), and amorphous sulfur. These may be used alone or in combination of two or more. Elemental sulfur becomes a melt when heated.

[0020] The carbon material and sulfur are combined to form a carbon-sulfur composite. For example, the carbon material and elemental sulfur are mixed, sealed, and then the mixture is heated to melt the elemental sulfur, thereby impregnating the pores with the elemental sulfur, thereby producing a carbon-sulfur composite.

[0021] The blending amount of elemental sulfur relative to the total of the carbon material and elemental sulfur is preferably 30% by mass or more. To increase the battery capacity, the blending amount of elemental sulfur is better, but if it is too much, the electronic conductivity of the positive electrode decreases. The blending amount of elemental sulfur is more preferably 50% by mass or more, and even more preferably 70% by mass or more. Moreover, the blending amount of elemental sulfur is preferably 90% by mass or less.

[0022] In one embodiment, a mixture of a carbon material and elemental sulfur is heated in a sealed state at a temperature equal to or higher than the melting point of elemental sulfur (approximately 115°C). The heating temperature is adjusted depending on the carbon material and elemental sulfur, but is preferably 130°C or higher, and more preferably 150°C or higher. The upper limit of the heating temperature is a temperature equal to or lower than the boiling point of elemental sulfur (approximately 445°C). The heating time is preferably 0.1 to 24 hours. A carbon-sulfur composite is obtained by cooling after heating. If necessary, a pulverization step may be carried out after cooling.

[0023] The carbon-sulfur composite holds elemental sulfur and discharge products of elemental sulfur on the surface and / or pores of the carbon material. The carbon material keeps the particle size of these elements small, which not only allows for the smooth supply of electrons and ions, but also facilitates electron conduction throughout the positive electrode due to the high electronic conductivity of the carbon material.

[0024] In the positive electrode composite, part or all of the elemental sulfur is impregnated into the pores of the carbon material. The elemental sulfur that is not impregnated into the pores is present so as to coat part or all of the carbon material. Whether or not sulfur is impregnated into the pores of the carbon material can be confirmed by analyzing the particle cross-section of the carbon material using an analytical method capable of elemental mapping, such as SEM-EDS or TEM-EDX, and evaluating the overlap of elements derived from the carbon material and sulfur elements.

[0025] In one embodiment, the positive electrode composite contains a large amount of elemental sulfur, so that elemental sulfur is present outside the pores of the carbon material. In this case, the composite of elemental sulfur and the carbon material forms a pellet-like mass, but can be mechanically crushed into powder.

[0026] [Step (B)] In step (B), the carbon-sulfur composite and the sulfide solid electrolyte are mixed and pulverized to obtain a positive electrode composite. In step B, the carbon-sulfur composite and the sulfide solid electrolyte are removed from the positive electrode composite, and the treated product has a recovered specific surface area of ​​1100 m ２ / g or more.

[0027] In step (B), for example, the carbon-sulfur composite and the sulfide solid electrolyte are mixed and pulverized by applying mechanical stress. Here, "applying mechanical stress" means mechanically applying shear force, impact force, or the like. Examples of means for applying mechanical stress include pulverizers such as planetary ball mills, vibration mills, and tumbling mills, and kneaders. Part of the carbon-sulfur composite and the sulfide solid electrolyte may be pulverized by this step.

[0028] The content of the sulfide solid electrolyte is preferably 5 to 200 parts by mass, and more preferably 10 to 120 parts by mass, based on 100 parts by mass of the carbon-sulfur composite. If the content of the solid electrolyte is 5 parts by mass or less, it becomes difficult to obtain sufficient ionic conduction, and if it is 200 parts by mass or more, the content of the active material decreases, making it difficult to improve the energy density.

[0029] In one embodiment, the content of elemental sulfur relative to the total of the carbon-sulfur composite and the sulfide solid electrolyte is 20% by mass or more. The content of elemental sulfur is preferably 30% by mass or more, and more preferably 40% by mass or more. A high content of elemental sulfur increases the battery capacity but decreases the electronic conductivity in the positive electrode. The upper limit of the content of elemental sulfur is 80% by mass or less.

[0030] Recovery specific surface area is 1100m ２ To achieve a specific surface area of ​​the carbon material, the average particle size, and the processing conditions of the grinder (for example, the type of grinding media, the processing time, and the rotation speed) can be adjusted. ５０ ) is preferably 50 μm or less. The average particle size of the carbon material may be 40 μm or less, or may be 10 μm or less. The lower limit of the average particle size is not particularly limited, but is usually 0.1 μm. In this specification, the average particle size (D ５０ ) is the particle size at which the particle size distribution cumulative curve is drawn, and the cumulative total is calculated from the smallest particle size to reach 50% of the total. The volume distribution can be measured, for example, using a laser diffraction / scattering particle size distribution measuring device. The smaller the average particle size of the carbon material and the larger the specific surface area, the less likely coarse carbon-sulfur composite particles will remain, and the larger the recovered specific surface area, the less likely it is to have a particle size distribution of 1,100 m. ２ / g or more.

[0031] For example, when a planetary ball mill is used for mixing and grinding, the type of grinding media, processing time, and rotation speed are controlled taking into account the average particle size of the raw carbon material. When using a carbon material with a large average particle size as the raw material, the particle size of the carbon-sulfur composite in the final cathode composite can be uniformly reduced by performing the grinding process for as long as possible and with as much energy as possible under conditions that do not cause deterioration of the material. This enables removal of the solid electrolyte and sulfur from the interior of the composite particles, thereby increasing the recovered specific surface area. It is also effective to use a carbon material with a small average particle size or a fibrous carbon material with a high aspect ratio that is easily broken, or a carbon material that does not have coarse particles even without grinding, or that can be finely ground in a short time.

[0032] More specifically, in the case of the planetary ball mill (manufactured by Fritsch: Model No. P-7) used in the examples of the present application, the rotation speed of the planetary ball mill is preferably 100 rpm or more and 600 rpm or less, and more preferably 150 rpm or more and 400 rpm or less. When zirconia balls are used as the grinding media, for example, the diameter of the balls is preferably 0.2 to 20 mm.

[0033] In one embodiment, the cathode mixture is heated after the step of mixing the carbon-sulfur composite and the sulfide solid electrolyte. The solid electrolyte, whose crystallinity has decreased in the mixing step, is recrystallized or heated to form an interface, thereby improving ionic conductivity and battery characteristics.

[0034] The sulfide solid electrolyte used in this embodiment 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.

[0035] (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 S ５ -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 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.

[0036] 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%.

[0037] 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 thiolicon region II type crystal structure described below and having higher ionic conductivity.

[0038] 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 to 200 μm.

[0039] (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).

[0040] 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 P ｘ S ４ Thio-LISICON Region II crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４This indicates that the thio-LISICON region II type has a similar crystal structure.

[0041] 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°.

[0042] 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 S６ 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).

[0043] 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.

[0044] 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 range of 0.01 μm to 500 μm, or 0.1 to 200 μm, for example, can be exemplified.

[0045] In one embodiment, the sulfide solid electrolyte preferably contains a halogen atom, and the sulfide solid electrolyte preferably contains two or more types of halogen atoms. It also preferably has a thiolicon region II crystal structure. The mass ratio of phosphorus atoms in the sulfide solid electrolyte (P / sulfide solid electrolyte) is preferably less than 0.20. It is particularly preferably less than 0.15, and even more preferably less than 0.13. This reduces the decrease in ionic conductivity even when mixed and pulverized with a carbon-sulfur composite. Furthermore, since the phosphorus ratio is small, the sulfide solid electrolyte itself reacts during discharge, reducing the effects of alteration and expansion. This maintains the conduction paths of electrons and lithium within the positive electrode composite, and high cycle characteristics can be expected.

[0046] In one embodiment, the above-described cathode composite of the present invention and the cathode composite obtained by the manufacturing method of the present invention may or may not contain components other than the carbon material, sulfur, sulfur discharge products, and sulfide solid electrolyte. The other components are not particularly limited, and examples thereof include a binder, a solvent, and a dispersant.

[0047] Here, the elemental sulfur is partially or entirely converted into discharge products during the battery reaction. Therefore, in one embodiment, a discharge product of elemental sulfur is present in the positive electrode composite (positive electrode). When a discharge product is present, the amount of sulfur contained in the positive electrode composite is the total amount of sulfur contained in the elemental sulfur and the discharge product. The discharge product of elemental sulfur is Li in a fully discharged state. ２ S and its intermediate stage lithium polysulfide Li ２ S ２ , Li ２ S ４ , Li ２ S ６ , Li ２ S ８ etc.

[0048] In one embodiment, the total mass (S) of elemental sulfur and sulfur in the discharge product of elemental sulfur is 20% by mass or more. The total mass (S) is preferably 30% by mass or more, more preferably 40% by mass or more. A large total mass (S) increases the battery capacity, but decreases the electronic conductivity at the positive electrode. The upper limit of the total mass (S) is 80% by mass or less.

[0049] 3. Positive electrode and lithium ion battery A positive electrode according to one embodiment of the present invention includes the above-described positive electrode mixture of the present invention. In addition, a positive electrode according to another embodiment of the present invention is a positive electrode having a recovered specific surface area of ​​1100 m2 or less after treatment with sulfur and sulfide solid electrolyte removed from the positive electrode. ２ / g or more. The positive electrode of this embodiment can be made thicker, and a battery with little deterioration in cycle characteristics can be obtained. The recovered specific surface area is the same as that of the positive electrode composite of the present invention described above. The thickness of the positive electrode can be 35 μm or more, and can also be 40 μm or more. It is usually 500 μm or less.

[0050] A lithium ion battery according to one embodiment of the present invention includes the above-described cathode composite or cathode of the present invention. For example, an all-solid-state lithium ion battery can be manufactured by using a solid electrolyte instead of a liquid electrolyte. By using the cathode composite of the present invention, an all-solid-state lithium ion battery with good rate characteristics can be manufactured.

[0051] An all-solid-state lithium-ion battery mainly comprises a positive electrode layer, a negative electrode layer, and an electrolyte layer, and the positive electrode composite of the present invention is suitable as a constituent material of the positive electrode layer. The negative electrode layer and the electrolyte layer can be manufactured by known methods. In addition to the positive electrode layer, the negative electrode layer, and the electrolyte layer, a current collector is preferably used, and a known current collector is also used. The solid electrolyte is not particularly limited, but examples thereof include the sulfide solid electrolyte described above.

[0052] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0053] (Example 1) (1) Preparation of carbon-sulfur composite Activated carbon (MSF-A30M, manufactured by Kansai Coke Chemical Industry Co., Ltd., average particle size (D ５０ ) 36μm, specific surface area 3100m ２ The activated carbon-element sulfur composite powder was obtained by heating in an electric furnace at 150°C for 6 hours and then at 300°C for 2.75 hours.

[0054] (2) Preparation of sulfide solid electrolyte 0.4127 g of lithium sulfide, 0.6655 g of diphosphorus pentasulfide, 0.2137 g of lithium iodide, 0.2080 g of lithium bromide, and ten zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. A planetary ball mill (manufactured by Fritsch, model number P-7) was used to mix (mechanical mill) the mixture 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 a sulfide solid electrolyte. The P content in the sulfide solid electrolyte was 0.12.

[0055] (3) Preparation of Cathode Composite Material 0.7 g of the activated carbon-element sulfur composite powder obtained in (1) above and 0.3 g of the sulfide solid electrolyte obtained in (2) above 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 (manufactured by Fritsch, model number P-7), grinding was carried out at a rotation speed of 370 rpm for 20 hours at room temperature to obtain a powder of the cathode composite material.

[0056] (4) Preparation of all-solid-state lithium-ion battery 100 mg of the sulfide solid electrolyte prepared in (2) above was placed in a Macol (registered trademark) cylinder with a diameter of 10 mm and pressure-molded. The cathode composite powder prepared in (3) above was placed on the pressurized surface so that the elemental sulfur content was 3.5 mg, and pressure-molded again. Indium foil and lithium foil were placed on the pressurized surface opposite the cathode composite, and pressure was applied to prepare an all-solid-state battery.

[0057] (Example 2) The activated carbon (MSF-A30M) in Example 1 was replaced with MSC30-SSS (manufactured by Kansai Thermal Chemical Industry Co., Ltd., average particle size (D ５０ ) 3.2μm, specific surface area 3016m ２ A positive electrode composite powder was obtained in the same manner as in Example 1, except that the positive electrode composite powder was changed to ( / g). An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained positive electrode composite powder was used.

[0058] (Comparative Example 1) The activated carbon (MSF-A30M) in Example 1 was replaced with MSC30 (manufactured by Kansai Ceramic Chemicals, average particle size (D ５０ )56μm, specific surface area 3200m ２ A positive electrode composite powder was obtained in the same manner as in Example 1, except that the amount of the positive electrode composite powder was changed to ( / g). An all-solid-state battery was fabricated in the same manner as in Example 1, except that the obtained positive electrode composite powder was used.

[0059] (Comparative Example 2) MSC30-SS (Kansai Ceramic Chemicals, average particle size (D ５０ )5.3μm, specific surface area 3087m ２ZnO / g), sulfur, and diphosphorus pentasulfide as a solid electrolyte were mixed in a mass ratio of 10:60:30, and 0.2 g of the mixed powder was placed in a 45 mL zirconia pot together with 40 g of zirconia balls with a diameter of 5 mm and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), the mixture was milled at a rotation speed of 370 rpm for 4 hours at room temperature to obtain a powder of a positive electrode composite. Because diphosphorus pentasulfide was used as the solid electrolyte, the P content in the solid electrolyte was 0.28.

[0060] [Evaluation] (Measurement of recovered specific surface area) The specific surface area of ​​the cathode composites prepared in the examples and comparative examples was measured after the solid electrolyte removal step and sulfur removal step described below. (1) Solid electrolyte removal step 0.8 g of the cathode composite was dispersed in an excess of 5 mL of ethanol and irradiated with ultrasonic waves for 1 minute using an ultrasonic cleaner. The dispersion was centrifuged at 12,000 rpm for 1 minute using a tabletop centrifuge (FB-4000) to dissolve and remove the solid electrolyte. This procedure was repeated four times until the supernatant was no longer colored.

[0061] (2) Sulfur Removal Step The precipitate after the centrifugation was vacuum dried at 200°C for 6 hours. Then, it was further heated at 600°C for 4 hours in a glove box. This removed ethanol and sulfur from the precipitate. For each example and comparative example, the specific surface area (recovered specific surface area) of the treated product was measured.

[0062] (3) Measurement of the recovered specific surface area of ​​the treated product. Measurement was performed using a specific surface area and pore distribution measuring device (Autosorb-3) manufactured by Quantacrome. The precipitate obtained by the above procedure was heated at liquid nitrogen temperature to adsorb nitrogen gas, and the specific surface area was calculated by the Brenauer-Emmet-Telle (BET) multipoint method using the resulting nitrogen adsorption isotherm. The results are shown in Table 1.

[0063]

[0064] (Evaluation of Battery Characteristics) A constant current charge / discharge test was carried out on the all-solid-state batteries prepared in each example. The cutoff potential of the constant current test was set to 0.8-2.2 V vs. Li—In, and the current density was set under the conditions shown in Table 2. The results are shown in FIG.

[0065]

[0066] From FIG. 1, the recovered specific surface area of ​​the carbon material forming the composite material in the example is set to 1100 m ２ / g or more, the cycle characteristics of the all-solid-state lithium-ion battery are confirmed to be excellent. It can also be confirmed that when the particle size of the carbon material forming the composite material is large and the recovery specific surface area is small, as in Comparative Example 1, the cycle characteristics are degraded. Furthermore, when the phosphorus content of the solid electrolyte is high, as in Comparative Example 2, the capacity change during initial charge and discharge is large, and the subsequent charge and discharge capacity remains constant but decreases. This is thought to be because the solid electrolyte changes in quality during initial charge and discharge, and the expansion and contraction of the solid electrolyte cuts off the electron conduction path and ion conduction path, resulting in a decrease in the amount of sulfur that contributes to charge and discharge.

[0067] The positive electrode composite of the present invention is suitable for use in the positive electrode of a lithium ion battery. The lithium ion battery of the present invention is also 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.

[0068] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will readily be able to make numerous modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and advantages of the present invention. Accordingly, these numerous modifications are within the scope of the present invention. The contents of all documents cited in this specification and of the applications from which this application claims priority under the Paris Convention are incorporated by reference in their entirety.

Claims

1. A positive electrode composite comprising a carbon-sulfur composite and a sulfide solid electrolyte, The recovered specific surface area of ​​the treated material obtained by removing the sulfur and the sulfide solid electrolyte from the aforementioned positive electrode mixture is 1100 m². ２ A positive electrode composite material with a value of 1 / g or more.

2. The positive electrode mixture according to claim 1, wherein the sulfide solid electrolyte comprises lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms.

3. The positive electrode composite material according to claim 2, wherein the sulfide solid electrolyte contains two or more halogen atoms.

4. The positive electrode composite material according to claim 2, wherein the mass ratio of phosphorus atoms (P) in the sulfide solid electrolyte (P / sulfide solid electrolyte) is less than 0.

20.

5. The positive electrode mixture according to claim 1, wherein the total mass (S) of the sulfur and the sulfur in the sulfur discharge product is 20% by mass or more.

6. Step A involves compounding a carbon material with sulfur to obtain a carbon-sulfur composite, The process includes step B, which involves mixing and grinding the carbon-sulfur composite and sulfide solid electrolyte to obtain a positive electrode composite material. In step B, the recovered specific surface area of ​​the treated material obtained by removing the sulfur and the sulfide solid electrolyte from the positive electrode mixture is 1100 m². ２ A method for producing a positive electrode composite material, which is prepared to have a concentration of 1g or more.

7. The manufacturing method according to claim 6, wherein the average particle size of the carbon material is 50 μm or less.

8. The specific surface area of ​​the carbon material is 2300 m². ２ The manufacturing method according to claim 6, wherein the amount is 1 / g or more.

9. The manufacturing method according to claim 6, wherein the mixing and grinding in step B is carried out using a planetary ball mill.

10. A positive electrode composite obtained by the manufacturing method described in claim 6.

11. A positive electrode comprising the positive electrode composite material according to any one of claims 1 to 5 and claim 10.

12. The positive electrode according to claim 11, wherein the thickness is 35 μm or more.

13. The recovered specific surface area of ​​the treated material after removing sulfur and sulfide solid electrolytes is 1100 m². ２ The positive electrode is greater than or equal to / g.

14. A lithium-ion battery comprising the positive electrode described in claim 11.