Electrode material

Abstract

This electrode material contains a conductive additive, which is porous carbon, a sulfur-based active material, and iodine (I2).

Description

electrode material

[0001] This invention relates to electrode materials used in lithium-ion secondary batteries and the like.

[0002] Lithium-ion batteries are required to have high capacity. To improve battery capacity, methods using sulfur-based active materials such as sulfur in the positive electrode are being considered because of their large theoretical capacity. However, since sulfur has low lithium-ion conductivity and electronic conductivity, it is necessary to ensure lithium-ion conductivity and electronic conductivity within the positive electrode. To address the above problem, methods of compounding sulfur, a conductive additive, and a solid electrolyte are being investigated. In addition, a positive electrode consisting of a sulfur-iodine composite, vapor-processed carbon fiber (VGCF), and a solid electrolyte (LPS) is being investigated (Non-Patent Literature 1).

[0003] Nature 627, pages 301-305 (2024)

[0004] The battery using the positive electrode described in Non-Patent Document 1 had insufficient capacity and rate characteristics, and further improvements were needed. One of the objectives of the present invention is to provide an electrode material that can improve the capacity and rate characteristics of a battery.

[0005] The inventors of the present invention have discovered that the capacity and rate characteristics of a battery can be improved by using a composite material containing iodine or a molecular iodine compound, a sulfur-based active material, and porous carbon as electrodes, and have completed the present invention.

[0006] According to the present invention, the following electrode materials are provided: 1. A conductive additive which is porous carbon, a sulfur-based active material, and iodine (I ２ ) and an electrode material comprising. 2. The porous carbon having a BET specific surface area of ​​50 m². ２ 1. An electrode material according to 1, wherein the amount is 1 / g or more. 3. An electrode material according to 1 or 2, wherein the porous carbon is carbon black or activated carbon. 4. An electrode material according to any one of 1 to 3, wherein the sulfur-based active material is sulfur. 5. An electrode material according to any one of 1 to 4, comprising a sulfide solid electrolyte. 6. The sulfur-based active material, the conductive additive, the iodine (I ２ The number of moles (mol / g) of iodine element (I) per 1 g of the total mass of the sulfide solid electrolyte is 1.0 × 10⁻⁶. －４mol / g to 15×10 －４ mol / g. The electrode material according to 5. 7. The electrode material according to any one of 1 to 6, which is a positive electrode mixture. 8. A lithium ion battery comprising the electrode material according to any one of 1 to 7. 9. Porous carbon, a sulfur-based active material, and iodine (I ２ ) with each other. A method for producing an electrode material, comprising the step of mixing. 10. A step of heating a mixture of the porous carbon (C) and the sulfur-based active material (S) to form a C-S composite; and mixing the C-S composite and the iodine (I ２ ) with each other. The production method according to 9, comprising the step of mixing. 11. The production method according to claim 9 or 10, wherein the mixing comprises heating. 12. The production method according to any one of 9 to 11, wherein after the mixing step, the obtained mixture is heated. 13. The production method according to any one of 10 to 12, further comprising, after the mixing step, a step of mechanically mixing the obtained mixture and a sulfide solid electrolyte. 14. Iodine (I ２ ), wherein the mass ratio (S / I) of the sulfur-based active material (S) to iodine (I) is 1.0 to 10. The production method according to any one of 10 to 13. 15. The sulfur-based active material, the conductive aid, and iodine (I ２ ) and the sulfide solid electrolyte, wherein the total mass of the sulfur-based active material and the iodine (I ２ ) is blended so as to be 45 to 55 mass% based on the total amount. The production method according to 13 or 14.

[0007] According to the present invention, an electrode material capable of improving the capacity and rate characteristics of a battery can be provided.

[0008] The present invention will be described in detail below. In this specification, "x to y" represents a numerical range of "x or more, and y or less". The upper and lower limits described for the numerical range can be combined arbitrarily. Furthermore, it is possible to combine two or more non-conflicting embodiments of the embodiments of the present invention described below, and an embodiment that combines two or more embodiments is also an embodiment of the embodiments of the present invention. The "mass ratio" and "content" of each component in the electrode material refer to both the mass ratio and content of each component in the electrode material and the mass ratio and content of each component when compounded during the manufacture of the electrode material.

[0009] [Electrode Material] An electrode material according to one aspect of the present invention comprises a conductive additive which is porous carbon, a sulfur-based active material, and iodine (I ２ ) and molecular iodine compounds (iodine (I ２ The iodine raw materials include at least one of the following: ) and molecular iodine compounds. In this embodiment, the combination of porous carbon, sulfur, and iodine raw materials is thought to form a uniquely excellent interface and electron conduction path, thereby improving the capacity and rate characteristics of the battery. The constituent members of the electrode material will be described below.

[0010] (Conductive additive) In this embodiment, porous carbon is used as a conductive additive. Porous carbon has a large surface area and a high ability to disperse and retain sulfur-based active materials, etc. Examples of porous carbon include carbon black such as Ketjenblack, acetylene black, and channel black, as well as graphite and activated carbon. These may be used alone or in combination of two or more.

[0011] In one embodiment, the BET specific surface area of ​​porous carbon is 50 m². ２ / g or more 6000m ２ The concentration is less than / g. This allows for the formation of a broad contact interface between porous carbon and 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, 1300m ２ / g or more is preferable. Also, 5500m ２ Preferably less than / g, and more preferably 5000m ２ Preferably, the amount is less than or equal to / g. In one embodiment, the BET specific surface area of ​​porous carbon is 70 m². ２ / g or more 5500m ２ / g or less, or 100m ２ / g or more 5000m ２ It is less than / g. The BET specific surface area of ​​porous carbon is 150 m². ２ / g to 3500m ２ / g, 200m ２ / g to 2000m ２ / g, or 500m ２ / g to 1500m ２ / g is preferred.

[0012] Furthermore, the pore volume of porous carbon is 0.5 cm³. ３ / g or more, 6cm ３ It is less than / g. This allows sulfur-based active materials to be impregnated into the pores of porous carbon, 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

[0013] 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.

[0014] (Sulfur-based active material) There are no particular limitations on sulfur-based active materials, but sulfur (elemental sulfur), lithium sulfide (Li２ S), Lithium polysulfide (Li ２ S ｎ : n satisfies 1 < n ≤ 8. ), Titanium sulfide (TiS ２ ), molybdenum sulfide (MoS ２ ), iron sulfide (FeS, FeS ２ ), copper sulfide (CuS), nickel sulfide (Ni ３ S ２ Examples include lithium sulfide and / or sulfur, with sulfur being particularly 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 especially preferably 97% by mass or higher. Examples of sulfur crystal systems include α-sulfur (orthorhombic), β-sulfur (monoclinic), γ-sulfur (monoclinic), amorphous sulfur, etc. These can be used individually or in combination of two or more.

[0015] In one embodiment, the mass ratio (C:I+S) of porous carbon C in the electrode material to the total of sulfur-based active material S, iodine, and molecular iodine compound I is 2:98 to 98:2, 5:95 to 60:40, or 10:90 to 40:60.

[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] (Iodine and molecular iodine compounds) In this embodiment, porous carbon, sulfur-based active material, and iodine (I ２The electrode material is used in combination with at least one of the following: iodine and a molecular iodine compound. A molecular iodine compound is a compound in which an iodine atom and other atoms are bonded together by covalent bonds. In other words, it is not an ionic compound such as lithium iodide. Examples of molecular iodine compounds include phosphorus iodide, iodine monobromide, iodine monochloride, and iodine trichloride. The electrode material of this form preferably contains iodine. Hereinafter, iodine and molecular iodine compounds may be collectively referred to as iodine raw material I.

[0018] In one embodiment, the mass ratio (S:I) of sulfur-based active material S to iodine raw material I in the electrode material is 2:98 to 98:2, 6:94 to 94:6, or 10:90 to 90:10. In one embodiment, the mass ratio (S / I) of sulfur-based active material S to iodine raw material I in the electrode material is preferably 0.5 to 20, more preferably 1.0 to 15, and particularly preferably 3.0 to 10. This results in a good electron conduction path, which further improves the rate characteristics.

[0019] In one embodiment, when the electrode material contains a sulfide solid electrolyte described later, the content of the solid electrolyte SE [SE / (S+C+I+SE)] relative to the total amount of sulfur-based active material S, conductive additive C, iodine raw material I, and sulfide solid electrolyte SE is 10% by mass or more and 60% by mass or less, 15% by mass or more and less than 40% by mass, or 25% by mass or more and 35% by mass or less.

[0020] In one embodiment, the total content of sulfur-based active material S and iodine raw material I [(S + I) / (S + C + I + SE)] relative to the total amount of sulfur-based active material S, conductive additive C, iodine raw material I, and sulfide solid electrolyte SE is 30% by mass or more and 80% by mass or less, greater than 40% by mass and 70% by mass or less, or 45% by mass or more and 55% by mass or less. Similarly, the total content of sulfur-based active material S and iodine raw material I relative to the entire electrode material is 30% by mass or more and 80% by mass or less, greater than 40% by mass and 70% by mass or less, or 45% by mass or more and 55% by mass or less.

[0021] In one embodiment, the number of moles (mol / g) of iodine element (I) per gram of total mass of sulfur-based active material, conductive additive, iodine raw material, and sulfide solid electrolyte is 1.0 × 10⁻⁶ －４ mol / g~15×10－４ mol / g, 5.0×10 －４ mol / g~10×10 －４ mol / g, or 7.2 × 10⁻⁶ －４ mol / g~8.2×10 －４ It is mol / g. Similarly, the number of moles of iodine (I) per gram of the entire electrode material (mol / g) is 1.0 × 10⁻⁶. －４ mol / g~15×10 －４ mol / g, 5.0×10 －４ mol / g~10×10 －４ mol / g, or 7.2 × 10⁻⁶ －４ mol / g~8.2×10 －４ The value is mol / g. In one embodiment, the number of moles of iodine (I) per gram of total mass of sulfur-based active material, conductive additive, and iodine raw material (mol / g) is 5.0 × 10⁻⁶. －５ mol / g~1.5×10 －２ mol / g, 1.0×10 －４ mol / g~5.0×10 －３ mol / g, or 5.0 × 10 －４ mol / g~2.0×10 －３ It is mol / g.

[0022] (Optional components) In one embodiment, the electrode material preferably includes a sulfide solid electrolyte in addition to porous carbon, a sulfur-based active material, and an iodine raw material. This facilitates the formation of lithium ion conduction paths within the electrode.

[0023] A sulfide solid electrolyte is a solid electrolyte that contains at least a sulfur atom and exhibits ionic conductivity due to the contained metal atoms, preferably containing lithium atoms and phosphorus atoms in addition to sulfur atoms, and more preferably containing lithium atoms, phosphorus atoms and halogen atoms, and having ionic conductivity due to the lithium atom. The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

[0024] (a) Amorphous sulfide solid electrolyte Any amorphous sulfide solid electrolyte can be employed without particular limitations as long as it contains at least sulfur atoms and exhibits ionic conductivity derived from the metal atoms contained therein. Representative examples thereof include Li ２ S-P ２ S ５ a solid electrolyte containing sulfur atoms, lithium atoms, and phosphorus atoms composed of lithium sulfide and phosphorus sulfide such as the above; 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 solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide such as -LiI-LiBr; furthermore, solid electrolytes containing other elements such as oxygen and silicon, for example, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ -P ２ S ５ solid electrolytes such as -LiI are preferably mentioned. From the viewpoint of obtaining higher ionic conductivity, 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 solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide such as -LiI-LiBr are preferred. The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed by, for example, an ICP emission spectroscopy analyzer.

[0025] The amorphous sulfide solid electrolyte contains at least Li ２S-P ２ S ５ If it has Li ２ S and P ２ S ５ The molar ratio of is preferably 30-85:15-70, more preferably 40-80:20-60, and even more preferably 45-78:22-55, from the viewpoint of obtaining high chemical stability and higher ionic conductivity. The amorphous sulfide solid electrolyte is, for example, Li ２ S-P ２ S ５ In the case of -LiI-LiBr, the total content of lithium sulfide and phosphorus pentasulfide is preferably 30 to 95 mol%, more preferably 35 to 90 mol%, and even more preferably 40 to 85 mol%. Furthermore, 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%.

[0026] In amorphous sulfide solid electrolytes containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, the 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. It is preferable to contain two or more halogen atoms, and particularly preferable to contain chlorine atoms and bromine atoms, or bromine atoms and iodine atoms. Furthermore, when bromine and iodine are used in combination as halogen atoms, the mixing 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 mixing 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 with higher ionic conductivity having the thiolysicon region II type crystal structure described later.

[0027] Furthermore, there are no particular restrictions on the shape of the amorphous sulfide solid electrolyte, but for example, particulate form can be given. The average particle size (D) of the particulate amorphous sulfide solid electrolyte. ５０ For example, the average particle size (D) can be exemplified by being in the range of 0.01 μm to 500 μm or 0.1 μm to 200 μm. In this specification, the average particle size (D) ５０ The volume distribution is the particle size at which the accumulation of particle diameters reaches 50% of the total when plotting a particle diameter distribution integral curve, starting from the smallest particle. The volume distribution is the average particle size, which can be measured, for example, using a laser diffraction / scattering particle diameter distribution analyzer.

[0028] In one embodiment, the molar ratio of lithium to phosphorus in the sulfide solid electrolyte (lithium / phosphorus) is preferably less than 3.5, more preferably 2 to 3.3, even more preferably 2.8 to 3.1, and particularly preferably 3. In one embodiment, the molar ratio of phosphorus to halogen atoms (X / P) in the sulfide solid electrolyte is preferably 0.33 or less. It is even more preferably 0.1 or less, and particularly preferably 0.05 or less. In one embodiment, the sulfide solid electrolyte does not contain halogen atoms. For example, the composition of the sulfide solid electrolyte is Li ３ PS ４ That is the case.

[0029] (b) Crystalline sulfide solid electrolyte As the crystalline sulfide solid electrolyte, for example, it may be a so-called glass ceramic obtained by heating the amorphous sulfide solid electrolyte above the crystallization temperature, and a sulfide solid electrolyte having the following crystal structure may be used. The crystal structure that a crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms and phosphorus atoms may have is Li ３ PS ４ Crystal structure, Li ４ P ２ S ６ Crystal structure, Li ７ PS ６ Crystal structure, Li ７ P ３ S １１ Examples include crystal structures, and crystal structures having peaks near 2θ = 20.2° and 23.6° (for example, Japanese Patent Publication No. 2013-16423).

[0030] Furthermore, the crystal structure that a crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms may have is Li ４－ｘ Ge １－ｘ P ｘ S ４ The thio-LISICON Region II type crystal structure (see Kanno et al., Journal of The Electrochemical Society, 148(7) A742-746 (2001)), Li ４－ｘ Ge １－ｘ Pｘ S ４ Examples include the thio-LISICON Region II type and similar crystal structures (see Solid State Ionics, 177 (2006), 2721-2725). Here, "thio-LISICON Region II type crystal structure" refers to Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-Lisicon Region II type crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ This indicates that the crystal structure is similar to that of the thio-LISICON Region II system.

[0031] In X-ray diffraction measurements using CuKα rays, Li ３ PS ４ Diffraction peaks of the crystal structure appear, for example, around 2θ = 17.5°, 18.3°, 26.1°, 27.3°, and 30.0°, Li ４ P ２ S ６ The diffraction peaks of the crystal structure appear, for example, around 2θ = 16.9°, 27.1°, and 32.5°, and Li ７ PS ６ The diffraction peaks of the crystal structure appear, for example, around 2θ = 15.3°, 25.2°, 29.6°, and 31.0°, and Li ７ P ３ S １１ Diffraction peaks of the crystal structure appear, for example, around 2θ = 17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II type crystal structure appear, for example, around 2θ = 20.1°, 23.9°, and 29.5°, Li ４－ｘ Ge １－ｘ P ｘ S ４Diffraction peaks for crystal structures similar to the thio-LISICON Region II type appear, for example, around 2θ = 20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0032] Furthermore, argyrodite crystal structures can also be cited as crystalline sulfide solid electrolytes. For example, Li ７ PS ６ Crystal structure; Li ７ PS ６ Composition formula Li has a structural framework ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ Crystal structure represented by (x is -0.6 to 0.6, y is 0.1 to 0.6); Li ７－ｘ－２ｙ PS ６－ｘ－ｙ Cl ｘ Crystal structure shown by (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5); Li ７－ｘ PS ６－ｘ Ha ｘ Examples of crystal structures include those represented by (Ha is Cl or Br, and x is preferably 0.2 to 1.8).

[0033] Among the crystal structures described above, Li is an example of a crystal structure found in crystalline sulfide solid electrolytes. ３ PS ４ A crystal structure, a thiolysicon region II type crystal structure, and an argyrodite type crystal structure are preferred.

[0034] There are no particular restrictions on the shape of the crystalline sulfide solid electrolyte, but for example, particulate form can be given. The average particle size (D) of the particulate crystalline sulfide solid electrolyte. ５０ ) is the average particle size (D) of the amorphous sulfide solid electrolyte described above. ５０ Similarly, examples include the ranges of 0.01 μm to 500 μm and 0.1 μm to 200 μm.

[0035] In one embodiment, the electrode material may or may not contain components other than the porous carbon, sulfur-based active material, iodine raw material, and sulfide solid electrolyte described above. The other components are not particularly limited, but examples include binders, solvents, and dispersants.

[0036] In electrode materials, the content of porous carbon, sulfur-based active material, iodine raw material, and sulfide solid electrolyte is not particularly limited. For example, when the electrode material contains a sulfide solid electrolyte, the content of sulfur-based active material is 40 to 300 parts by mass, preferably 60 to 250 parts by mass, and more preferably 100 to 150 parts by mass, per 100 parts by mass of sulfide solid electrolyte.

[0037] The porous carbon content is 10 to 150 parts by mass, preferably 30 to 100 parts by mass, and more preferably 60 to 90 parts by mass, per 100 parts by mass of sulfide solid electrolyte. The iodine raw material content is 1 to 90 parts by mass, preferably 10 to 50 parts by mass, and more preferably 25 to 40 parts by mass, per 100 parts by mass of sulfide solid electrolyte.

[0038] In one embodiment, 50% or more by mass of the electrode material, 60% or more by mass, 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, 99% or more by mass, 99.5% or more by mass, or substantially 100% by mass is porous carbon, sulfur-based active material, iodine raw material, and sulfide solid electrolyte. In the case of "substantially 100% by mass", unavoidable impurities may be included.

[0039] [Method for Manufacturing Electrode Material] The electrode material of the present invention can be manufactured by mixing the above-mentioned porous carbon, sulfur-based active material, and iodine raw material with an optional sulfide solid electrolyte, etc. The mixing method is not particularly limited and can be carried out by known methods and apparatus. Examples of mixing apparatus used in the mixing process include planetary ball mills, rolling mills, bead mills, film mixers, Nauta mixers, tornado mixers, twin-screw extruders, multi-screw rollers, solid-phase shear kneaders, etc.

[0040] In one embodiment, a C-S composite may be prepared by mechanically mixing a processed product obtained by heating and mixing porous carbon (C) and sulfur-based active material (S). In another embodiment, an electrode material can be prepared by mechanically mixing and / or heating an iodine raw material with a processed product obtained by heating and mixing porous carbon and sulfur-based active material. In this case, among porous carbon, sulfur-based active material, and iodine raw material, at least one of heating and mixing can be applied to the porous carbon and sulfur-based active material as a pretreatment for the mixing process. Here, examples of means for mechanical mixing include a planetary ball mill.

[0041] The pretreatment heating can be carried out, for example, by melting the sulfur-based active material while porous carbon and sulfur-based active material are present together. The heating temperature can be set to a temperature above the melting point of the sulfur-based active material. When elemental sulfur is used as the sulfur-based active material, it is preferable to set the heating temperature to 110°C or higher. The pretreatment mixing can be carried out by grinding the porous carbon and / or sulfur-based active material while porous carbon and sulfur-based active material are present together. This mixing is preferably done by mechanical mixing.

[0042] In pretreatment, when both heating and mixing are performed, heating and mixing may be performed simultaneously, heating followed by mixing, or mixing followed by heating. During the transition from heating to mixing, or from mixing to heating, a period of simultaneous heating and mixing may or may not be provided. As an example of pretreatment, if the sulfur-based active material is elemental sulfur, the elemental sulfur may be heated and melted to impregnate the pores of the porous carbon. By melting the sulfur-based active material, impregnation into the pores can be promoted. In addition, the sulfur-based active material can be highly dispersed in the porous carbon. It is preferable that the porous carbon is porous carbon, and the sulfur-based active material contains sulfur, with at least a portion of the sulfur impregnated into the pores of the porous carbon. For example, the treated material can be obtained by melting the sulfur-based active material in a system in which porous carbon and sulfur-based active material coexist.

[0043] Pretreatment allows for the compounding of porous carbon and sulfur-based active material, thereby forming a C-S composite. In the C-S composite, it is preferable that one or more states selected from the group consisting of the following are formed: the porous carbon and sulfur-based active material are attached to each other; the sulfur-based active material covers at least one part of the surface of the porous carbon; the sulfur-based active material is impregnated into the pores of the porous carbon; and the sulfur-based active material and porous carbon are chemically bonded, particularly covalently bonded. When the sulfur-based active material and porous carbon are chemically bonded, the chemical bond may be formed at the interface between the sulfur-based active material and the porous carbon.

[0044] In one embodiment, the C-S composite described above is mixed with an iodine raw material. In the following description, the description of the "processed product" described above will be appropriately applied to the "C-S composite." Here, the C-S composite can be obtained by heating and / or mixing a sulfur-based active material and porous carbon. In this case, the heating of the sulfur-based active material and porous carbon can be such that the sulfur-based active material and the conductive additive are heated to a temperature above the melting point of the sulfur-based active material.

[0045] In one embodiment, a C-S composite may be formed from the porous carbon and sulfur-based active material described above, and then the C-S composite may be mechanically mixed with an iodine raw material. In one embodiment, the C-S composite is formed by performing at least one treatment selected from mixing, grinding, and heating on the mixture containing the porous carbon and sulfur-based active material described above, preferably by heating and melting. Alternatively, if the sulfur-based active material is elemental sulfur, for example, the porous carbon and elemental sulfur described above may be mixed and sealed, and then the mixture may be heated to melt the elemental sulfur, impregnating the pores of the porous carbon with the elemental sulfur to form the C-S composite. Alternatively, for example, at least one treatment selected from mixing, grinding, and heating may be performed on the mixture of porous carbon and elemental sulfur described above to compound the elemental sulfur and porous carbon without melting them, thereby forming the C-S composite.

[0046] The mixing ratio of elemental sulfur to porous carbon can be appropriately adjusted according to the material used. For example, the mass ratio of elemental sulfur (S) to porous carbon (C) in a C-S composite (S / C) is 0.5 or higher. When the utilization rate of sulfur is the same, increasing the sulfur content in the electrode material can be expected to improve the energy density of the battery. Furthermore, the mass ratio (S / C) is preferably 0.5 to 6.0, more preferably 1.0 to 4.0, and even more preferably 2.0 to 2.5.

[0047] In one embodiment, a mixture of elemental sulfur and porous carbon is heated in a sealed state at a temperature above the melting point of elemental sulfur (approximately 115°C). The heating temperature is adjusted according to the elements of elemental sulfur and porous carbon, but is preferably 130°C or higher, and more preferably 150°C or higher. The upper limit of the heating temperature is below the boiling point of elemental sulfur (approximately 445°C). The heating time is preferably 0.1 to 24 hours. After heating, the mixture is cooled to obtain a C-S composite. A grinding step may be performed after cooling if necessary.

[0048] In one embodiment, the process involves first bringing the porous carbon and the sulfur-based active material into contact (first contact) to produce a first mixture (which may be a treated product or a sulfur-based active material-conductive additive composite material), and then bringing this first mixture into contact with an iodine raw material (second contact) to produce a second mixture. Here, it is preferable to heat the porous carbon and the sulfur-based active material before the second contact. The first contact may be bringing the porous carbon into contact with the heated sulfur-based active material.

[0049] In one embodiment, at least one of the sulfur-based active material and the iodine raw material is heated and melted to impregnate the pores of porous carbon. By melting the sulfur-based active material and the iodine raw material, impregnation into the pores can be promoted. In addition, the sulfur-based active material and the iodine raw material can be highly dispersed in the porous carbon. For example, the manufacturing method of one embodiment includes the steps of heating a mixture of porous carbon (C) and sulfur-based active material (S) to form a C-S composite, and mixing the C-S composite with the iodine raw material.

[0050] The heating temperature can be appropriately set according to the sulfur-based active material and iodine raw material used. Heating may be carried out in two or more stages. For example, the heating temperature for the first stage may be set to be above the melting point of sulfur, and the heating temperature for the second stage may be set to be above the melting point of the iodine raw material.

[0051] In one embodiment, at least one of a sulfur-based active material and an iodine raw material is subjected to mechanical milling with porous carbon. Various mills, such as planetary ball mills, can be used for mechanical milling. Mechanical milling allows for the compounding of the sulfur-based active material, the iodine raw material, and the porous carbon.

[0052] In one embodiment, a sulfur-based active material and porous carbon may be compounded, and then the compound may be mixed and compounded with an iodine raw material. Alternatively, the iodine raw material, sulfur-based active material, and porous carbon may be mixed and compounded simultaneously. Furthermore, the resulting mixture (compound) may be heated after mixing and compounding.

[0053] In one embodiment, a sulfur-based active material, an iodine raw material, and porous carbon are combined into a composite, and then the composite and a sulfide solid electrolyte are mechanically milled. This allows for a combination of composite formation by heating and composite formation by mechanical milling.

[0054] In a composite of a sulfur-based active material and / or iodine raw material and porous carbon, it is preferable that one or more states selected from the group consisting of: the conductive additive and the sulfur-based active material and / or iodine raw material are attached to each other; the sulfur-based active material and / or iodine raw material covers at least one portion of the surface of the conductive additive; the sulfur-based active material and / or iodine raw material is impregnated into the pores of the conductive additive; and the sulfur-based active material and / or iodine raw material and the conductive additive are chemically bonded, particularly covalently bonded. When the sulfur-based active material and / or iodine raw material and the conductive additive are chemically bonded, the chemical bond may be formed at the interface between the sulfur-based active material and / or iodine raw material and the conductive additive.

[0055] The electrode material of the present invention can be suitably used, for example, as a component 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 electrode material of the present invention described above. For example, an all-solid-state lithium-ion battery can be manufactured by using a solid electrolyte. 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.

[0056] The present invention will be specifically described below based on examples. The present invention is not limited to these examples. When handling samples that may degrade by reacting with air or moisture, such as solid electrolytes, and when evaluating batteries, care was taken to prevent degradation reactions by using argon atmosphere glove boxes or sealed containers. The BET specific surface area of ​​the carbon material was calculated using the Brunauer-Emmett-Teller (BET) multipoint method with nitrogen adsorption isotherms. It was measured using a specific surface area and pore distribution analyzer (Autosorb-3) manufactured by Quantachrome.

[0057] Manufacturing Example 1 [Preparation of Solid Electrolyte A] 0.4127 g of lithium sulfide, 0.6655 g of phosphorus pentasulfide, 0.2137 g of lithium iodide, 0.2080 g of lithium bromide, and 10 zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was mixed (mechanical milling) at a rotation speed of 370 rpm for 40 hours to obtain a powder. The obtained powder was heated at 195°C for 3 hours to obtain solid electrolyte A.

[0058] Example 1 (1) Preparation of electrode material A-1 Ketjenblack (C: Lion Specialty Chemicals Co., Ltd. EC600JD, specific surface area 1357 m²) was placed in a glass bottle. ２Weighed out C, sulfur (S), and iodine (I) in a mass ratio (C:S:I) of 30:56:14, lightly mixed them, and sealed them in a stainless steel tube container. The mixture was heated in an electric furnace at 100°C for 2 hours to obtain powdered electrode material A-1.

[0059] (2) Preparation of Cathode Composition Material A-1 700 mg of electrode material A-1, 300 mg of solid electrolyte A, and 10 zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was heated at a rotation speed of 370 rpm for 20 hours at room temperature to obtain powdered cathode composition material A-1.

[0060] Example 2 (1) Preparation of C-S composite 1400 mg of sulfur and activated carbon (MSC-30 manufactured by Kansai Thermal Chemical Co., Ltd., specific surface area 2809 m²) were placed in a glass bottle. ２ 600 mg ( / g) was placed in a stainless steel tube container and sealed. It was heated in an electric furnace at 150°C for 6 hours and then at 300°C for 2.75 hours to obtain a powdered C-S composite.

[0061] (2) Preparation of cathode composite A-2 700 mg of C-S composite, 50 mg of iodine, 250 mg of solid electrolyte A, and 10 zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was heated at a rotation speed of 370 rpm for 20 hours at room temperature to obtain a powdered cathode composite A-2.

[0062] Comparative Example 1 (1) Preparation of Electrode Material A-3 1400 mg of sulfur and 600 mg of activated carbon (MSC-30, manufactured by Kansai Thermal Chemical Co., Ltd.) were placed in a glass bottle and sealed inside a SUS tube container. The mixture was heated in an electric furnace at 150°C for 6 hours and then at 300°C for 2.75 hours to obtain powdered electrode material A-3.

[0063] (2) Preparation of Cathode Composition Material A-3 700 mg of electrode material A-3 and 300 mg 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 heated at a rotation speed of 370 rpm for 20 hours at room temperature to obtain Cathode Composition Material A-3.

[0064] Comparative Example 2 (1) Preparation of electrode material A-4 A glass bottle was filled with 651 mg of sulfur, 49 mg of iodine, and VGCF (Resonac, specific surface area 22 m²). ２ 300 mg ( / g) was placed in a stainless steel tube container and sealed. It was heated in an electric furnace at 100°C for 2 hours to obtain powdered electrode material A-4.

[0065] (2) Preparation of Cathode Composition Material A-4 700 mg of electrode material A-4, 300 mg of solid electrolyte A, and 10 zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was mixed at a rotation speed of 370 rpm for 20 hours at room temperature to obtain Cathode Composition Material A-4.

[0066] Example 3 (1) Solid Electrolyte C In a glove box, 3.83 g of lithium sulfide, 6.17 g of phosphorus pentasulfide, and 600 g of zirconia balls with a diameter of 10 mm were weighed and placed in a 500 mL zirconia pot, and the lid was screwed on to seal it. Using a planetary ball mill (Fritsch, model P-5), the process was repeated for 40 cycles of 1 hour of operation at 220 rpm followed by a 10 minute rest (the direction of rotation was reversed after each cycle). The powder obtained in the glove box was collected and sieved through a 53 μm sieve to obtain the solid electrolyte C (Li ３ PS ４ ) was obtained.

[0067] (2) Preparation of electrode material A-5 Ketjenblack (C: Lion Specialty Chemicals Co., Ltd. EC600JD, specific surface area 1357 m²) is placed in a glass bottle. ２ Weighed out C, sulfur (S), and iodine (I) in a mass ratio (C:S:I) of 30:60:10, lightly mixed them, and sealed them in a stainless steel tube container. The mixture was heated in an electric furnace at 150°C for 2 hours to obtain powdered electrode material A-5.

[0068] (3) Preparation of Cathode Composition Material A-5 700 mg of electrode material A-5, 300 mg of solid electrolyte C, and 10 zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was heated at a rotation speed of 370 rpm for 20 hours at room temperature to obtain powdered cathode composition material A-5.

[0069] [Evaluation of battery characteristics] (1) Preparation of negative electrode composite material (a) Preparation of solid electrolyte B Under a nitrogen atmosphere, lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ ), lithium bromide (LiBr) and lithium chloride (LiCl), in molar ratio (Li ２ S:P ２ S ５ The raw materials were weighed and roughly mixed so that the ratio of :LiBr:LiCl was 47.5:12.5:15.0:25.0.

[0070] The raw material mixture was dispersed in a mixed solvent consisting of dehydrated toluene and 2% by mass of dehydrated isobutyronitrile relative to the raw material mixture to obtain a slurry of approximately 10% by mass. A bead mill was operated at a peripheral speed of 12 m / s and a flow rate of 500 mL / min, and the slurry was introduced into the mill and circulated for 1 hour to obtain the mixture. After removing the solvent from the obtained mixture, it was heated in an electric furnace at 400-430°C for 2 hours. Subsequently, the raw material sulfide solid electrolyte was obtained by slow cooling.

[0071] Under a nitrogen atmosphere, the raw material sulfide solid electrolyte was dispersed in dehydrated toluene and placed together with 0.3 mm diameter zirconia balls in a zirconia pot of a planetary ball mill (Fritsch: model P-7), creating an inert atmosphere inside the pot. The planetary ball mill was operated at 150 rpm for 2 hours to obtain a slurry containing the finely particulated sulfide solid electrolyte. The slurry was transferred to a nitrogen-purged Schlenk bottle, dried at room temperature for 1 hour using a vacuum pump, and then heated to 80°C to 100°C to further remove the solvent contained in the finely particulate sulfide solid electrolyte (vacuum drying) to obtain solid electrolyte B.

[0072] (b) Preparation of negative electrode composite: Lithium titanate (LT-112, manufactured by Ishihara Sangyo Co., Ltd.), a conductive additive (Li-100, manufactured by Denka Co., Ltd., powdered acetylene black), and solid electrolyte B were mixed in a mortar and pestle in a mass ratio of 60:5:35 for 5 minutes to obtain a negative electrode composite (also called "LTO (lithium titanate) negative electrode composite").

[0073] (2) Manufacturing of a lithium-ion battery A solid electrolyte layer (a layer of solid electrolyte A) was formed by placing 100 mg of solid electrolyte A into a 10 mm diameter Macol cylinder and pressurizing it. Next, a positive electrode mixture prepared so that the amount of sulfur contained in the positive electrode mixture was 3.5 mg was placed on one pressurized surface of the solid electrolyte layer and pressurized again. Subsequently, 166 mg of LTO negative electrode mixture 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 manufactured by placing a 9 mm diameter, 0.1 mm thick Li foil on top of that and pressurizing it again.

[0074] (3) Charge and Discharge Tests Constant current charge and discharge tests were performed on lithium-ion batteries using the positive electrode composite materials of each example and comparative example. The voltage range for the constant current charge and discharge tests was set to -0.4 to 1.3V, and the current values ​​were set as shown in Table 1 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 evaluation results are shown in Table 2. From Table 2, it can be seen that the example has a larger capacity than the comparative example at all rates.

[0075]

[0076]

[0077] The electrode material of the present invention can be suitably used as a component material of lithium-ion batteries, for example, as a positive electrode. 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.

[0078] 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 conductive additive which is porous carbon, a sulfur-based active material, and iodine (I ２ ) and electrode material including 2. The BET specific surface area of ​​the porous carbon is 50 m². ２ The electrode material according to claim 1, wherein the amount is 1g or more.

3. The electrode material according to claim 1 or 2, wherein the porous carbon is carbon black or activated carbon.

4. The electrode material according to any one of claims 1 to 3, wherein the sulfur-based active material is sulfur.

5. An electrode material according to any one of claims 1 to 4, comprising a sulfide solid electrolyte.

6. The sulfur-based active material, the conductive additive, and the iodine (I ２ The number of moles (mol / g) of iodine element (I) per 1 g of the total mass of the sulfide solid electrolyte is 1.0 × 10⁻⁶. －４ mol / g~15×10 －４ The electrode material according to claim 5, wherein the concentration is mol / g.

7. An electrode material according to any one of claims 1 to 6, which is a positive electrode composite material.

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

9. Porous carbon, sulfur-based active material, and iodine (I ２ A method for manufacturing an electrode material, comprising the step of mixing ) and .

10. A step of heating a mixture of the porous carbon (C) and the sulfur-based active material (S) to form a C-S composite, and a step of heating the C-S composite and the iodine (I ２ The manufacturing method according to claim 9, comprising the step of mixing ) and ).

11. The method according to claim 9 or 10, wherein the mixing is heated.

12. The manufacturing method according to any one of claims 9 to 11, wherein the mixture obtained is heated after the mixing step.

13. The manufacturing method according to any one of claims 10 to 12, further comprising the step of mechanically mixing the obtained mixture with a sulfide solid electrolyte after the mixing step.

14. The iodine (I ２ The manufacturing method according to any one of claims 10 to 13, wherein the mass ratio (S / I) of the sulfur-based active material (S) to ) is 1.0 to 10.

15. The iodine (I ２ ), the sulfur-based active material, the conductive aid, based on the total amount of said sulfur-based active material, said conductive aid, said iodine (I ２ ), the total mass of ) is 45 to 55 mass%, according to claim 13 or 14, the production method according to.

Images