Composite, electrode material, positive electrode for lithium-ion battery, lithium-ion battery, activated carbon for all-solid-state lithium-sulfur battery, method for producing activated carbon for all-solid-state lithium-sulfur battery, method for producing composite, and method for producing electrode material

Abstract

This composite comprises: activated carbon in which a ratio of the volume of pores having a pore diameter of 4 nm or less to the volume of pores having a pore diameter of 100 nm or less is 25% to 90% inclusive; and at least one of elemental sulfur and a discharge product of elemental sulfur.

Description

Composite, electrode material, positive electrode for lithium ion battery, lithium ion battery, activated carbon for all-solid-state lithium-sulfur battery, method for producing activated carbon for all-solid-state lithium-sulfur battery, method for producing composite, and method for producing electrode material

[0001] The present invention relates to a composite, an electrode material, a positive electrode for a lithium ion battery, a lithium ion battery, activated carbon for an all-solid-state lithium-sulfur battery, a method for producing activated carbon for an all-solid-state lithium-sulfur battery, a method for producing a composite, and a method for producing an electrode material. Specifically, the present invention relates to a composite, an electrode material, a positive electrode for a lithium ion battery, a lithium ion battery, activated carbon for an all-solid-state lithium-sulfur battery, a method for producing activated carbon for an all-solid-state lithium-sulfur battery, a method for producing a composite, and a method for producing an electrode material that are excellent in initial capacity and can improve cycle characteristics, particularly when used in the positive electrode of an all-solid-state lithium ion battery.

[0002] It has been proposed to use a sulfur-activated carbon composite in the positive electrode of an all-solid-state lithium-ion battery, while it has also been proposed to reduce internal resistance by using a conductive material for the positive electrode in which the percentage of the pore volume of pores having a pore diameter in the range of 1 to 4 nm relative to the pore volume of pores having a pore diameter in the range of 1 to 100 nm is 20% or less (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2022-115375

[0004] However, it has been found that there is room for further improvement in the conventional techniques including Patent Document 1 in terms of improving the initial capacity and cycle characteristics (capacity retention rate when charging and discharging are repeated) of the battery.

[0005] An object of the present invention is to provide a composite, an electrode material, a positive electrode for a lithium ion battery, a lithium ion battery, activated carbon for an all-solid-state lithium-sulfur battery, a method for producing activated carbon for an all-solid-state lithium-sulfur battery, a method for producing a composite, and a method for producing an electrode material, which are excellent in initial capacity and can improve cycle characteristics, particularly when used in a positive electrode of an all-solid-state lithium ion battery.

[0006] As a result of extensive research, the present inventors have found that a specific sulfur-activated carbon composite has excellent initial capacity and can improve cycle characteristics, particularly when used in the positive electrode of an all-solid-state lithium-ion battery, and have thus completed the present invention. According to the present invention, the following composites and the like can be provided: 1. A composite comprising activated carbon in which the ratio of the volume of pores with a diameter of 4 nm or less to the volume of pores with a diameter of 100 nm or less is 25% to 90%, and at least one of elemental sulfur and a discharge product of elemental sulfur. 2. The composite according to 1, which contains 200 parts by mass or more of the elemental sulfur and the discharge product of elemental sulfur, calculated as sulfur, per 100 parts by mass of the activated carbon. 3. The composite according to 1 or 2, which shows a weight loss of 20% or less up to 175°C in thermogravimetric differential thermal analysis. 4. The composite according to any one of 1 to 3, in which no peak of elemental sulfur is observed in X-ray diffraction measurement. 5. The activated carbon has a specific surface area of ​​1900 m ２ / g or more. 6. An electrode material comprising the composite according to any one of 1 to 5. 7. The electrode material according to 6, further comprising a sulfide solid electrolyte. 8. The electrode material according to 7, wherein the sulfide solid electrolyte contains at least lithium atoms (Li), phosphorus atoms (P), sulfur atoms (S), and halogen atoms. 9. A positive electrode for a lithium ion battery, comprising the electrode material according to any one of 6 to 8. 10. A lithium ion battery, comprising the positive electrode for a lithium ion battery according to 9. 11. Activated carbon for an all-solid-state lithium-sulfur battery, in which the ratio of the volume of pores with a diameter of 4 nm or less to the volume of pores with a diameter of 100 nm or less is 25% or more and 90% or less. 12. A method for producing activated carbon for an all-solid-state lithium-sulfur battery, comprising: subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment in this order to obtain activated carbon. 13. 13. A method for producing a composite of sulfur and activated carbon, the method comprising, in this order: subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment, in this order, to obtain activated carbon, and compositeing the activated carbon with at least one of elemental sulfur and a discharge product of elemental sulfur to obtain a composite. 14. A method for producing an electrode material, the method comprising, in this order: subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment, in this order, to obtain activated carbon, compositeing the activated carbon with at least one of elemental sulfur and a discharge product of elemental sulfur to obtain a composite, and mixing the composite with a sulfide solid electrolyte to obtain an electrode material.

[0007] The present invention can provide a composite, an electrode material, a positive electrode for a lithium ion battery, a lithium ion battery, an activated carbon for an all-solid-state lithium-sulfur battery, a method for producing the activated carbon for an all-solid-state lithium-sulfur battery, a method for producing the composite, and a method for producing an electrode material, which are excellent in initial capacity and can improve cycle characteristics, particularly when used in a positive electrode of an all-solid-state lithium ion battery.

[0008] The electrode material, lithium-ion battery positive electrode, lithium-ion battery, activated carbon for all-solid-state lithium-sulfur batteries, method for producing activated carbon for all-solid-state lithium-sulfur batteries, method for producing a composite, and method for producing an electrode material of the present invention are 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 of the numerical ranges can be arbitrarily combined. Furthermore, among the individual embodiments of the aspects of the present invention described below, two or more mutually exclusive embodiments can be combined, and an embodiment combining two or more embodiments is also an embodiment of the aspects of the present invention.

[0009] 1. Composite A composite according to one aspect of the present invention includes activated carbon having a ratio of the volume of pores with a diameter of 4 nm or less to the volume of pores with a diameter of 100 nm or less of 25% to 90%, and at least one of elemental sulfur and a discharge product of elemental sulfur.

[0010] The activated carbon of this embodiment, particularly when used in the positive electrode of an all-solid-state lithium-ion battery, can provide excellent initial capacity and improved cycle characteristics. It is believed that the reason for this effect is that the ratio of the volume of pores with a diameter of 4 nm or less to the volume of pores with a diameter of 100 nm or less in the activated carbon is controlled to a range of 25% to 90%. Specifically, it is believed that the sulfur in the pores with a diameter of 4 nm or less contributes to the excellent capacity (particularly the initial capacity), while the other pores with larger diameters provide sufficient space for the sulfur to expand and contract (suppressing electrode deterioration associated with expansion and contraction), thereby improving cycle characteristics. By using the composite of this embodiment, which has excellent initial capacity and excellent cycle characteristics, a battery with high energy density and high durability can be realized, and for example, an electric vehicle with longer driving distances and no battery deterioration even after long-term use can be realized.

[0011] (Activated Carbon) In one embodiment, the activated carbon has a ratio of the volume of pores with a pore diameter of 4 nm or less to the volume of pores with a pore diameter of 100 nm or less (also referred to as the "4 nm pore ratio") of 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, or 55% or more, and 90% or less, 85% or less, or 80% or less. The 4 nm pore ratio of the activated carbon is a value determined by the method described in the examples (BJH method).

[0012] In one embodiment, the specific surface area of ​​the activated carbon is 1900 m ２ / g or more, 2000m ２ / g or more, 2050m ２ / g or more, 2100m ２ / g or more, 2150m ２ / g or more, 2200m ２ / g or more, 2250m ２ / g or more or 2300m ２ / g or more. The upper limit is not particularly limited, and for example, ２ / g or less, 2800m ２ / g or less, 2600m ２ / g or less, 2500m ２ / g or less or 2400m ２ The specific surface area of ​​the activated carbon may be 2000 m / g or less. ２ / g or more, the larger the better. This allows the capacity (particularly the initial capacity) to be further improved. The specific surface area of ​​the activated carbon is a value measured by the method described in the examples (BET method).

[0013] (Elemental sulfur and discharge products of elemental sulfur) 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), amorphous sulfur, etc. These may be used alone or in combination of two or more. Elemental sulfur becomes a molten liquid when heated.

[0014] During the battery reaction, part or all of the elemental sulfur is converted into discharge products. Therefore, in one embodiment, a discharge product of elemental sulfur is present in the composite. When a discharge product is present, the amount of sulfur contained in the 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.

[0015] In one embodiment, in the composite, some or all of the elemental sulfur is attached (impregnated) within the pores of the activated carbon. Furthermore, the elemental sulfur that is not impregnated within the pores is present so as to coat part or all of the activated carbon. Whether sulfur is impregnated within the pores of the activated carbon can be confirmed by analyzing the cross section of the activated carbon particles using an analytical method capable of elemental mapping, such as SEM-EDS or TEM-EDX, and evaluating the overlap of elements derived from the activated carbon and the sulfur element. In one embodiment, due to the high content of elemental sulfur in the composite, elemental sulfur is also present outside the pores of the activated carbon. In this case, the composite may be in the form of a pellet-like mass, but can be powdered by mechanically pulverizing it.

[0016] In one embodiment, the composite contains 200 parts by weight or more, 210 parts by weight or more, 220 parts by weight or more, or 230 parts by weight or more of elemental sulfur and discharge products of elemental sulfur per 100 parts by weight of activated carbon. The upper limit is not particularly limited and may be, for example, 600 parts by weight or less, 500 parts by weight or less, 400 parts by weight or less, or 300 parts by weight or less. By having 200 parts by weight or more, a sufficient sulfur content can be ensured, further improving the energy density.

[0017] In one embodiment, the composite exhibits a weight loss of 20% or less, 19% or less, 18% or less, 17% or less, or 16% or less up to 175°C in a thermogravimetric differential thermal analysis. A weight loss of 20% or less indicates that sulfur is adsorbed in the micropores, and an improvement in the initial capacity due to an improvement in sulfur utilization is achieved. The weight loss is a value measured by the method described in the examples (rate control mode). In this specification, "weight" can be interchangeably referred to as "mass."

[0018] In one embodiment, the composite does not exhibit a peak corresponding to elemental sulfur in X-ray diffraction measurement. This indicates that sulfur is dispersed in the pores of the activated carbon to form uniformly small particles, thereby rendering the composite amorphous. By imparting electronic conductivity to sulfur, the effect of enhancing electrochemical reactivity can be achieved. Note that "no peak corresponding to elemental sulfur is observed" means that in the X-ray diffraction measurement described in the examples, the differential value ΔA / Δ2θ of the peak intensity A with respect to the angle 2θ is calculated from 2θ = 10 to 60, and then the value obtained by dividing by the average value over the entire range of ΔA / Δ2θ (hereinafter also referred to as "value α") is 500 or less. In the portion where the peak corresponding to elemental sulfur is present, the value α is 500 or greater.

[0019] In one embodiment, 80% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, 99% by mass or more, 99.5% by mass or more, 99.8% by mass or more, 99.9% by mass or more, or substantially 100% by mass or more of the composite is activated carbon and at least one of elemental sulfur and discharge products of elemental sulfur. Note that "substantially 100% by mass or more" may contain inevitable impurities.

[0020] The method for producing the composite according to one aspect of the present invention described above is not particularly limited. In one embodiment, the composite according to one aspect of the present invention is produced by the "composite production method" described in detail below.

[0021] 2. Electrode Material An electrode material according to an embodiment of the present invention includes the composite according to an embodiment of the present invention. The electrode material according to this embodiment can exhibit excellent initial capacity and improved cycle characteristics, particularly when used in a positive electrode of an all-solid-state lithium-ion battery.

[0022] (Sulfide Solid Electrolyte) In one embodiment, the electrode material further includes a sulfide solid electrolyte. The sulfide solid electrolyte is a solid electrolyte that contains at least sulfur atoms and exhibits ionic conductivity due to the contained metal atoms. In addition to sulfur atoms, the sulfide solid electrolyte preferably contains lithium atoms and phosphorus atoms, and more preferably contains lithium atoms, phosphorus atoms, and halogen atoms, and has ionic conductivity due to lithium atoms. In one embodiment, the solid electrolyte contains at least lithium atoms (Li), phosphorus atoms (P), sulfur atoms (S), and halogen atoms. In one embodiment, the solid electrolyte contains lithium atoms, phosphorus atoms, sulfur atoms, bromine atoms, and iodine atoms. The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

[0023] (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., solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide; and solid electrolytes further 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 S５ 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.

[0024] 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 ５ In 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%.

[0025] 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. 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.

[0026] (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).

[0027] The crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms may have the following crystalline structure: ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ Examples include a crystal structure similar to that of thio-LISICON Region II type.

[0028] In X-ray diffraction measurement using CuKα radiation, Li ３ P.S. ４Diffraction 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°.

[0029] 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 Clｘ (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).

[0030] 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.

[0031] 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.

[0032] In one embodiment, the electrode material contains 30% by mass or more of elemental sulfur and discharge products of elemental sulfur, calculated as sulfur. Here, the elemental sulfur and discharge products of elemental sulfur are derived from the above-described complex. In one embodiment, the electrode material contains 30 to 90% by mass, 30 to 70% by mass, or 30 to 60% by mass of elemental sulfur and discharge products, calculated as sulfur. Here, the elemental sulfur and discharge products of elemental sulfur are derived from the above-described complex.

[0033] 3. Lithium-ion battery positive electrode and lithium-ion battery A lithium-ion battery positive electrode according to one embodiment of the present invention includes the electrode material according to one embodiment of the present invention. When used as a positive electrode for a lithium-ion battery, particularly an all-solid-state lithium-ion battery, the lithium-ion battery positive electrode according to this embodiment can achieve excellent initial capacity and improved cycle characteristics.

[0034] A lithium ion battery according to one aspect of the present invention includes the positive electrode for a lithium ion battery according to one aspect of the present invention. The lithium ion battery according to this aspect has excellent initial capacity and improved cycle characteristics.

[0035] An electrode material according to one embodiment of the present invention can be used, for example, as a positive electrode composite, and more specifically, can be suitably used, for example, as a positive electrode layer of a lithium-ion battery. In this case, other components of the lithium-ion battery known in the art can be used, and a negative electrode layer that does not contain lithium ions as the negative electrode active material can be selected. Note that the negative electrode active material contained in the negative electrode layer of a lithium-ion battery can be referred to as a "negative electrode active material containing lithium ions." Alternatively, the negative electrode active material contained in the negative electrode layer of a lithium-ion battery can be referred to as a "negative electrode active material that supplies lithium ions to the positive electrode."

[0036] The negative electrode of the lithium ion battery is not particularly limited as long as it is one that can be used in ordinary batteries. The negative electrode may be made of a negative electrode mixture in which a negative electrode active material and a solid electrolyte are mixed.

[0037] As the negative electrode active material, commercially available materials can be used. For example, carbon materials, Sn metal, In metal, Si metal, Li metal, alloys of these metals, etc. can be used. Specifically, natural graphite, various graphites, lithium titanate, metal powders of Si, Sn, Al, Sb, Zn, Bi, etc., SiAl, Sn ５ Cu ６ , Sn ２ Co, Sn ２ Examples include metal alloys such as Fe, amorphous alloys, and plated alloys. There are no particular restrictions on the particle size, but particles with an average particle size of several μm to 80 μm are preferably used.

[0038] The electrolyte layer is not particularly limited, and known electrolytes can be used. For example, oxide solid electrolytes, sulfide solid electrolytes, and polymer electrolytes are preferred, and sulfide solid electrolytes are more preferred from the viewpoint of ionic conductivity. The sulfide solid electrolyte is preferably the one used in the above-mentioned positive electrode composite.

[0039] The method for producing a lithium ion battery is not particularly limited, and examples thereof include a method in which a solid electrolyte layer is formed on a sheet in which a positive electrode layer made of an electrode material according to one embodiment of the present invention is formed on a positive electrode current collector, and the sheet in which the negative electrode layer is formed is laminated on a previously formed negative electrode current collector, followed by pressing.

[0040] 4. Activated Carbon for All-Solid-State Lithium-Sulfur Batteries In the activated carbon for all-solid-state lithium-sulfur batteries according to one embodiment of the present invention, the ratio of the volume of pores with a pore diameter of 4 nm or less to the volume of pores with a pore diameter of 100 nm or less is 25% or more and 90% or less. According to the activated carbon for all-solid-state lithium-sulfur batteries according to this embodiment, the activated carbon for all-solid-state lithium-sulfur batteries produced using the activated carbon for all-solid-state lithium-sulfur batteries has excellent initial capacity and improved cycle characteristics. In this specification, the term "all-solid-state lithium-sulfur battery" is also referred to as an all-solid-state LiS battery, and refers to an all-solid-state lithium-ion battery that uses at least one of elemental sulfur and a discharge product of elemental sulfur as the active material.

[0041] 5. Manufacturing Method of Activated Carbon for All-Solid-State Lithium-Sulfur Batteries One embodiment of the present invention relates to a method for manufacturing activated carbon for all-solid-state lithium-sulfur batteries, comprising: subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment, in that order, to obtain activated carbon. This embodiment effectively produces activated carbon (activated carbon having a 4 nm pore ratio of 25% to 90%) for use in a composite according to one embodiment of the present invention. While the reason for this effect is not entirely clear, it is believed that the chemical activation treatment of the activated carbon precursor forms mesopores and macropores (particularly pores with a pore diameter of more than 4 nm and not more than 100 nm), and the subsequent gas activation treatment further forms smaller pores (particularly pores with a pore diameter of 4 nm or less) within the macropores, thereby achieving a 4 nm pore ratio of 25% to 90% in the resulting activated carbon.

[0042] (Activated Carbon Precursor) A carbon material can be used as the activated carbon precursor. Examples of carbon materials include phenolic resin-derived activated carbon obtained by calcining and carbonizing spherical phenolic resin; plant-derived carbonized materials such as charcoal, bamboo charcoal, and coconut shell charcoal; petroleum pitch-derived carbon; coal pitch-derived carbon; rayon-derived carbon; and acrylonitrile-derived carbon. Phenolic resin-derived activated carbon has a high residual carbon rate and is an artificially synthesized resin raw material, making it highly desirable for its structural controllability. Furthermore, plant-derived carbonized materials are expected to exhibit a hierarchical structure derived from plant-derived structures, and are also desirable from the perspective of decarbonization, since plants occlude carbon dioxide in the air during growth. Furthermore, petroleum pitch- and coal pitch-derived carbons have the advantage of being available in large quantities at low cost.

[0043] Chemical activation treatment and gas activation treatment are explained below. The term "chemical activation treatment" refers to activation using a chemical (not a gas) such as phosphoric acid, zinc chloride, or alkali that can react with the carbon that constitutes the activated carbon precursor, while the term "gas activation treatment" refers to activation using a gas such as carbon dioxide, water vapor, or oxygen. The term "chemical activation treatment" refers to activation treatment using both a chemical and a gas.

[0044] (Chemical Activation Treatment) Examples of chemical activation treatments that can be used include zinc chloride activation, phosphoric acid activation, and alkali activation. Oxidative activation (treatments that convert carbon into activated carbon: zinc chloride activation and phosphoric acid activation) are particularly preferred because they increase the pore volume of the resulting activated carbon. Compared to alkali activation, zinc chloride activation and phosphoric acid activation are also preferred because the chemicals used in chemical activation are easier to recycle, allowing for low-cost activation. Specific methods for zinc chloride activation include, for example, impregnating an activated carbon precursor with an aqueous zinc chloride solution, then holding the solution at a temperature of 500°C or higher and 1000°C or lower for 10 to 600 minutes in a nitrogen flow atmosphere, followed by washing to remove the zinc chloride. Specific methods for phosphoric acid activation include, for example, impregnating an activated carbon precursor with an aqueous phosphoric acid solution, then holding the solution at a temperature of 500°C or higher and 1000°C or lower for 10 to 600 minutes in a nitrogen flow atmosphere, followed by washing to remove the phosphoric acid. Specific examples of alkali activation methods include a method in which an activated carbon precursor and an alkali (such as potassium hydroxide) are kept at a temperature of 500° C. or higher and 1000° C. or lower for 10 to 600 minutes in a nitrogen flow atmosphere.

[0045] (Gas Activation Treatment) For gas activation treatment, activation can be performed using, for example, a mixed gas containing water vapor, carbon dioxide, oxygen, nitrogen, and an inert gas (such as argon). It is preferable to use a mixed gas of an inert gas and one or more gases selected from the group consisting of water vapor, carbon dioxide, oxygen, and nitrogen (preferably, one or more gases selected from the group consisting of water vapor and carbon dioxide) as the activation gas. In this case, since the activation reaction is an endothermic reaction, the reaction rate is easy to control. The concentration of carbon dioxide in the activation gas is, for example, 50 to 100% by volume. Oxygen can also be used as the activation gas, but since the activation reaction is an exothermic reaction, the reaction rate is fast and may be difficult to control.

[0046] In one embodiment, the time for the gas activation treatment is more than 0 minutes and not more than 99 hours, 1 minute or more and not more than 24 hours, or 5 minutes or more and not more than 8 hours. In one embodiment, the temperature for the gas activation treatment is preferably 600°C or more, more preferably 700°C or more. It is also preferably 1200°C or less, more preferably 1100°C or less. The gas activation treatment may be carried out under pressure. In one embodiment, the gas activation treatment is carried out under an absolute pressure of 2 atmospheres or more. In one embodiment, the gas activation treatment is carried out under an absolute pressure of 2 to 100 atmospheres, an absolute pressure of 3 to 10 atmospheres, or an absolute pressure of 5 to 9 atmospheres.

[0047] 6. Manufacturing Method of Composite A manufacturing method of a composite of sulfur and activated carbon according to one aspect of the present invention includes, in this order: subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment in this order to obtain activated carbon; and composite the activated carbon with at least one of elemental sulfur and a discharge product of elemental sulfur to obtain a composite. According to this aspect, the composite according to one aspect of the present invention can be successfully manufactured. Regarding "obtaining activated carbon by subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment in this order," the explanation given for "Method for manufacturing activated carbon for all-solid-state lithium-sulfur batteries" is incorporated herein by reference.

[0048] (Complexing Activated Carbon with Sulfur) "Complexing" activated carbon with sulfur means attaching at least one of elemental sulfur and discharge products of elemental sulfur to the surfaces (pore interior surfaces and pore exterior surfaces) of the activated carbon. This can mean coating the surface of the activated carbon with at least one of elemental sulfur and discharge products of elemental sulfur.

[0049] The method of compounding is not particularly limited, and examples include a method of mixing activated carbon with at least one of elemental sulfur and discharge products of elemental sulfur and heating. The heating temperature is not particularly limited, and is, for example, 130 to 445°C, 140 to 400°C, or 150 to 350°C. If the heating temperature is 130°C or higher, the melting point of elemental sulfur (115°C) is exceeded, and sulfur melts, and impregnation into the activated carbon can be expected. The upper limit of the heating temperature is preferably equal to or lower than the boiling point of elemental sulfur (445°C). In particular, lithium polysulfide and lithium sulfide, which are discharge products of elemental sulfur, have high melting points, so the temperature may be even higher than 445°C. The heating time is not particularly limited, and is, for example, 0.1 to 99 hours, 1 to 24 hours, or 2 to 8 hours.

[0050] 7. Manufacturing Method of Electrode Material A manufacturing method of an electrode material according to one aspect of the present invention includes, in this order: subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment, in this order, to obtain activated carbon; complexing the activated carbon with at least one of elemental sulfur and a discharge product of elemental sulfur to obtain a composite; and mixing the composite with a sulfide solid electrolyte to obtain an electrode material. According to this aspect, the electrode material according to one aspect of the present invention can be successfully manufactured. In this aspect, with regard to "obtaining activated carbon by subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment, in this order," the explanation given for "Method of manufacturing activated carbon for all-solid-state lithium-sulfur batteries" is incorporated herein. Furthermore, with regard to "complexing the activated carbon with at least one of elemental sulfur and a discharge product of elemental sulfur to obtain a composite," the explanation given for "Method of manufacturing a composite" is incorporated herein.

[0051] (Mixing of Composite and Sulfide Solid Electrolyte) A mixing device can be used to mix the composite and the sulfide solid electrolyte. Examples of mixing devices include a planetary ball mill, a tumbling mill, a bead mill, a Filmix, a Nauta mixer, a tornado mixer, a twin-screw extruder, a multi-screw roller, and a solid-phase shear mixer. The composite to be mixed can be in a solid state (including powder). The sulfide solid electrolyte to be mixed can be in a solid state (including powder). In Patent Document 1, a solution is prepared by dissolving the sulfide solid electrolyte in ethanol, and a conductive material is dispersed therein to impregnate the pores of the conductive material with the solid electrolyte. In this embodiment, it is not necessarily necessary to use such a method, and it is not necessarily necessary to use an organic solvent such as ethanol. In this embodiment, the sulfide solid electrolyte that has not yet been mixed with the composite can be mixed in a solid state (including powder) with the composite in a solid state (including powder). This eliminates the risk of deterioration of characteristics due to reaction between the solid electrolyte and the organic solvent or due to residual solvent, and because no solvent is used in the composite formation, the cost of the solvent and the energy required to remove it are unnecessary.

[0052] Examples of the present invention are described below, but the present invention is not limited to these examples. When handling samples that may be deteriorated by reaction with the atmosphere or moisture, such as sulfide solid electrolytes, or when evaluating batteries, care was taken to prevent deterioration reactions by using a glove box or a sealed container with an argon atmosphere.

[0053] (Production Example 1) 500 g of activated carbon ("Zinc chloride activated activated carbon S" manufactured by Futamura Chemical Co., Ltd.) that had been previously subjected to chemical activation treatment was placed in the furnace of a rotary kiln with an internal volume of 32 L, and the furnace was evacuated and replaced with nitrogen. Next, while flowing nitrogen through the furnace at 10 L / min, the temperature was raised to 950°C at 10°C / min, and further raised to 1000°C at 5°C / min, and then heat-treated at 1000°C for 1 hour. Next, the gas flowing through the furnace was switched to carbon dioxide, and while flowing carbon dioxide at 10 L / min, gas activation treatment was performed at 1000°C for 3 hours. The specific surface area of ​​the obtained activated carbon was 2321 m ２The specific surface area and the 4 nm pore ratio of the activated carbon were measured by the following methods.

[0054] <Method for Measuring the Specific Surface Area of ​​Activated Carbon> The specific surface area of ​​activated carbon can be measured by the Brenauer-Emmet-Telle (BET) 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 measuring device (Autosorb-3) manufactured by Quantacrome.

[0055] <Method for measuring 4 nm pore ratio> The pore volume of activated carbon with a pore diameter of 100 nm or less and the pore volume of pores with a pore diameter of 4 nm or less were determined according to the BJH method described in E. P. Barrett, L. G. Joyner and P. P. Halenda, J. Am. Chem. Soc., 73,373 (1951). The 4 nm pore ratio (the ratio of the pore volume with a pore diameter of 4 nm or less to the pore volume with a pore diameter of 100 nm or less) [%] was calculated as (pore volume with a pore diameter of 4 nm or less by the BJH method / pore volume with a pore diameter of 100 nm or less by the BJH method) × 100. In the BJH method, cylindrical pores are assumed and the pore diameter is calculated as the pore radius.

[0056] (Production Example 2) Activated carbon was obtained in the same manner as in Production Example 1, except that the activation treatment time under carbon dioxide flow was changed from 3 hours to 2 hours. The specific surface area of ​​the obtained activated carbon was 2047 m ２ / g, and the 4 nm pore ratio was 61%.

[0057] (Production Example 3) Activated carbon was obtained in the same manner as in Production Example 2, except that the heat treatment under nitrogen flow was changed from 1 hour to 0 hours. The specific surface area of ​​the obtained activated carbon was 1910 m ２ / g, and the 4 nm pore ratio was 58%.

[0058] Example 1 - Preparation of Composite Powder (Sulfur-Activated Carbon Composite) "Preparation of Composite Powder A" The activated carbon obtained in Production Example 1 and sulfur (S) were placed in a glass bottle in a weight ratio of 3:7, and this glass bottle was sealed in an SUS tubular container. The SUS tubular container was heated in an electric furnace at 150°C for 6 hours and at 300°C for 2.75 hours to obtain a composite powder of activated carbon and sulfur. The obtained composite powder was evaluated using a rate-controlled TG-DTA (thermogravimetric differential thermal analyzer), and the weight loss up to 175°C was 7%. Furthermore, no peaks of elemental sulfur were observed in XRD (X-ray diffraction measurement). Rate-controlled TG-DTA was performed using the following device, in the following measurement mode and under the following measurement conditions.

[0059] <Apparatus> "STA7200RV" manufactured by Hitachi High-Tech Science Corporation <Measurement Mode> - Automatic step temperature control (commonly known as controlled rate thermal analysis (CRTA)) - Loss rate threshold (rate at which heating is stopped): For sample amounts of 5 to 10 mg, the loss rate threshold was set so that 2% of the sample mass would be lost per minute, controlling the heating rate. For sample amounts of 5 mg, the loss rate threshold was set to 10 μg / min, and for sample amounts of 10 mg, the loss rate threshold was set to 20 μg / min, so that the ratio of the loss rate threshold to the sample mass was constant. <Measurement Conditions> - The temperature was increased from 35°C to 650°C at a rate of 10°C / min. - Measurements were performed in an environment where nitrogen was circulating at a flow rate of 200 ml / min.

[0060] - Preparation of positive electrode composite (electrode material) "Preparation of solid electrolyte" 0.4398 g of lithium sulfide, 0.7084 g of diphosphorus pentasulfide, 0.2133 g of lithium iodide, 0.1384 g of lithium bromide, and 10 zirconia balls having a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), the mixture was mixed (mechanical milling) for 40 hours at a rotation speed of 370 rpm to obtain a powder. The obtained powder was heated at 195 ° C. for 3 hours to obtain a solid electrolyte.

[0061] "Preparation of Positive Electrode Composite Powder" 0.7 g of the composite powder and 0.3 g of the solid electrolyte were placed in a 45 ml zirconia pot together with ten 10 mm diameter zirconia balls 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 positive electrode composite powder.

[0062] - Preparation of Lithium Ion Battery (All-Solid State) 100 mg of the solid electrolyte prepared above was placed in an electrically insulating ceramic cylinder with a diameter of 10 mm and pressure molded. The cathode composite powder prepared above was placed on the pressurized surface so that the sulfur content was 3.5 mg, and pressure molding was performed again. 166 mg of the anode composite was placed on the pressurized surface opposite the cathode composite and pressed, and then lithium foil was placed and pressed to prepare an all-solid state battery. The anode composite was composed of lithium titanate ("LT-112" manufactured by Ishihara Sangyo Kaisha), a conductive additive ("Li-100" manufactured by Denka Co., Ltd., powdered acetylene black), and Li. ２ S-P ２ S ５ -LiCl-LiBr type solid electrolyte B was mixed in a mortar for 5 minutes in a mass ratio of 60:5:35 (also referred to as "LTO (lithium titanate) negative electrode mixture").

[0063] (Example 2) "Preparation of Positive Electrode Composite Powder" A composite powder was obtained in the same manner as in Example 1, except that the activated carbon obtained in Production Example 2 was used instead of the activated carbon obtained in Production Example 1. The obtained composite powder was evaluated using rate-controlled TG-DTA, and the weight loss up to 175°C was 11%. Furthermore, no peak of elemental sulfur was observed in XRD. A positive electrode composite powder was obtained in the same manner as in Example 1, except that this composite powder was used.

[0064] - Fabrication of Lithium Ion Battery (All-Solid State) An all-solid state battery was fabricated in the same manner as in Example 1, except that the positive electrode composite powder obtained above was used.

[0065] (Example 3) "Preparation of Positive Electrode Composite Powder" A composite powder was obtained in the same manner as in Example 1, except that the activated carbon obtained in Production Example 3 was used instead of the activated carbon obtained in Production Example 1. The obtained composite powder was evaluated using rate-controlled TG-DTA, and the weight loss up to 175°C was 16%. Furthermore, no peak of elemental sulfur was observed in XRD. A positive electrode composite powder was obtained in the same manner as in Example 1, except that this composite powder was used.

[0066] - Fabrication of Lithium Ion Battery (All-Solid State) An all-solid state battery was fabricated in the same manner as in Example 1, except that the positive electrode composite powder obtained above was used.

[0067] Comparative Example 1 Preparation of Positive Electrode Composite Powder In Example 1, activated carbon (Ajinomoto Fine-Techno Co., Inc. "Y-G1700", specific surface area: 2110 m) was used instead of the activated carbon obtained in Production Example 1. ２ A composite powder was obtained in the same manner as in Example 1, except that a composite powder having a pore size of 1000 nm / g and a 4 nm pore ratio of 94%) was used. The obtained composite powder was evaluated using rate-controlled TG-DTA, and the weight loss up to 175°C was 20%. In addition, a peak of elemental sulfur was observed in XRD. A positive electrode composite powder was obtained in the same manner as in Example 1, except that this composite powder was used.

[0068] - Fabrication of Lithium Ion Battery (All-Solid State) An all-solid state battery was fabricated in the same manner as in Example 1, except that the positive electrode composite powder obtained above was used.

[0069] Comparative Example 2 Preparation of Positive Electrode Composite Powder In Example 1, the activated carbon obtained in Production Example 1 was replaced with carbon black ("EC-600JD" manufactured by Lion Specialty Chemical Co., Ltd., specific surface area: 1357 m ２ A composite powder was obtained in the same manner as in Example 1, except that a composite powder having a pore size of 1000 nm / g and a 4 nm pore ratio of 21%) was used. The obtained composite powder was evaluated using rate-controlled TG-DTA, and the weight loss up to 175°C was found to be 29%. In addition, a peak of elemental sulfur was observed in XRD. A positive electrode composite powder was obtained in the same manner as in Example 1, except that this composite powder was used.

[0070] - Fabrication of Lithium Ion Battery (All-Solid State) An all-solid state battery was fabricated in the same manner as in Example 1, except that the positive electrode composite powder obtained above was used.

[0071] Comparative Example 3 "Preparation of Positive Electrode Composite Powder" A composite powder was obtained in the same manner as in Example 1, except that carbon black ("BLACK PEARLS (registered trademark) 2000" manufactured by Cabot Corporation) was used instead of the activated carbon obtained in Production Example 1. The obtained composite powder was evaluated using a rate-controlled TG-DTA, and the weight loss up to 175°C was 25%. Furthermore, no peak of elemental sulfur was observed in XRD. A positive electrode composite powder was obtained in the same manner as in Example 1, except that this composite powder was used.

[0072] - Fabrication of Lithium Ion Battery (All-Solid State) An all-solid state battery was fabricated in the same manner as in Example 1, except that the positive electrode composite powder obtained above was used.

[0073] <Evaluation of Battery Characteristics> A constant current charge / discharge test was carried out on the all-solid-state batteries obtained in Examples and Comparative Examples. The cutoff potential of the constant current test was set to −0.4 to +1.3 V vs. Li-LTO, and the current density was set under the conditions shown in Table 1 below.

[0074]

[0075] Table 2 shows the results of the constant current charge / discharge test, including the initial capacity (discharge capacity at the fourth cycle) and the capacity retention rate (the percentage of the discharge capacity at the 30th cycle relative to the discharge capacity at the 10th cycle).

[0076]

[0077] <Evaluation> From Table 2, it can be seen that the Examples exhibit excellent initial capacity and good capacity retention rate (rate characteristics).

[0078] 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 composite comprising activated carbon in which the ratio of the volume of pores with a diameter of 4 nm or less to the volume of pores with a diameter of 100 nm or less is 25% or more and 90% or less, and at least one of elemental sulfur and a discharge product of elemental sulfur.

2. The composite according to claim 1, containing 200 parts by mass or more of the elemental sulfur and discharge products of elemental sulfur in terms of sulfur per 100 parts by mass of the activated carbon.

3. The composite according to claim 1 or 2, which exhibits a weight loss of 20% or less at 175°C in a thermogravimetric differential thermal analysis.

4. The complex according to any one of claims 1 to 3, in which no peak of elemental sulfur is observed in X-ray diffraction measurement.

5. The specific surface area of ​​the activated carbon is 1900 m ２ The composite according to any one of claims 1 to 4, wherein the molecular weight is 1 / g or more.

6. An electrode material comprising the composite according to any one of claims 1 to 5.

7. The electrode material according to claim 6, further comprising a sulfide solid electrolyte.

8. The electrode material according to claim 7, wherein the sulfide solid electrolyte contains at least lithium atoms (Li), phosphorus atoms (P), sulfur atoms (S), and halogen atoms.

9. A positive electrode for a lithium ion battery, comprising the electrode material according to any one of claims 6 to 8.

10. A lithium ion battery comprising the positive electrode for a lithium ion battery according to claim 9.

11. Activated carbon for all-solid-state lithium-sulfur batteries, in which the ratio of the volume of pores with a diameter of 4 nm or less to the volume of pores with a diameter of 100 nm or less is 25% or more and 90% or less.

12. A method for producing activated carbon for an all-solid-state lithium-sulfur battery, the method comprising: subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment in this order to obtain activated carbon.

13. A method for producing a composite of sulfur and activated carbon, the method comprising, in this order, subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment to obtain activated carbon, and compounding the activated carbon with at least one of elemental sulfur and a discharge product of elemental sulfur to obtain the composite.

14. A method for producing an electrode material, comprising, in this order: subjecting an activated carbon precursor to a chemical activation treatment and a gas activation treatment in this order to obtain activated carbon; compounding the activated carbon with at least one of elemental sulfur and a discharge product of elemental sulfur to obtain a composite; and mixing the composite with a sulfide solid electrolyte to obtain an electrode material.

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