Composite powder, positive electrode mix, and alkali metal ion battery

Abstract

This composite powder contains a porous carbon material and a first thermal impregnation material and a second thermal impregnation material that are present inside the pores. The first thermal impregnation material contains an alkali-metal-ion-conducting material containing one or more elements selected from lithium, boron, oxygen, phosphorus, halogens, and antimony, or a precursor of thereof. The second thermal impregnation material contains elemental sulfur.

Description

Composite powder, positive electrode mixture and alkali metal ion battery

[0001] The present invention relates to a composite powder, a positive electrode mixture, and an alkali metal ion battery containing the composite powder.

[0002] Alkali metal ion batteries, such as lithium ion batteries and sodium ion batteries, are desired to have excellent battery capacity under high current density. Regarding battery capacity, a method of using sulfur in the positive electrode has been investigated because of its large theoretical capacity (see, for example, Non-Patent Document 1). However, since sulfur has low electronic conductivity, when sulfur is used in the positive electrode, it is necessary to ensure electronic conductivity by some method.

[0003] To address the above-mentioned issues, composites of sulfur and porous carbon materials have been investigated (see, for example, Patent Document 1 and Non-Patent Document 2). However, sulfur-carbon composites have the problem of low discharge capacity (low rate characteristics) at high current densities due to the slow diffusion of alkali metal ions in sulfur. When using sulfur-carbon composites in the positive electrode of all-solid-state lithium batteries, it has been disclosed that composites of carbon materials, sulfur, and solid electrolytes can be prepared by mechanically mixing the sulfur-carbon composite with a solid electrolyte having high lithium ion conductivity or by using a solution containing the solid electrolyte (see, for example, Patent Documents 2 to 4). However, the lithium ion conductivity in the pores remains low, and the discharge capacity (rate characteristics) at high current densities is still insufficient.

[0004] Japanese Patent No. 5856979 Japanese Patent Application Laid-Open No. 2021-68663 Japanese Patent Application Laid-Open No. 2015-79622 Japanese Patent Application Laid-Open No. 2020-161288

[0005] An All-solid-state Sodium-Sulfur Battery Operating at Room Temperature Using a High-sulfur-content Positive Composite Electrode, Chem. Lett. 2014, 43, 1333-1334.A highly ordered nanostructured carbon-sulfur cathode for lithium-sulfur batteries, Nature Materials, 2009, 8, 500-506.

[0006] An object of the present invention is to provide a composite powder that can improve the discharge capacity (rate characteristics) of an alkali metal ion battery under high current density conditions.

[0007] According to the present invention, the following composite powders and the like are provided. 1. A composite powder comprising a carbon material having fine pores, and a first thermal impregnation material and a second thermal impregnation material present in the pores, wherein the first thermal impregnation material contains an alkali metal ion conductive material or a precursor thereof containing one or more elements selected from lithium, boron, oxygen, phosphorus, halogens, and antimony, and the second thermal impregnation material contains elemental sulfur. 2. The composite powder according to 1, wherein the melting point of the first thermal impregnation material is 130 to 950°C. 3. The composite powder according to 1 or 2, wherein the first thermal impregnation material and the second thermal impregnation material are impregnated into the pores by melting them. 4. The composite powder according to 1 or 2, wherein the first thermal impregnation material is selected from the group consisting of diphosphorus pentasulfide, red phosphorus, boron sulfide, lithium sulfide, and lithium polysulfide (Li ２ S ｎ 4. The composite powder according to any one of 1 to 3, wherein the carbon material is one or more compounds selected from the group consisting of lithium halide, lithium borohydride, lithium oxide, diphosphorus pentoxide, boron oxide, lithium triphosphate, and antimony sulfide, and wherein n satisfies 1<n≦8. 5. The composite powder according to any one of 1 to 3, wherein the carbon material has a BET specific surface area of ​​50 m ２ / g or more, 6000m ２ 6. The composite powder according to any one of 1 to 4, wherein the pore volume of the carbon material is 0.5 cm ３ / g or more, 6cm ３ / g or less. 7. A composite powder according to any one of 1 to 5, wherein the composite powder has a melting point of 130 to 950°C. 7. A cathode composite comprising the composite powder according to any one of 1 to 6 and a solid electrolyte. 8. An alkali metal ion battery comprising the composite powder according to any one of 1 to 6. 9. A method for producing a composite powder, comprising simultaneously or separately carrying out the following steps (1) and (2): Step (1): heating a carbon material having micropores and an alkali metal ion conductive material or a precursor thereof containing one or more elements selected from lithium, boron, oxygen, phosphorus, a halogen, and antimony at a temperature equal to or higher than the melting point of the alkali metal ion conductive material or a precursor thereof; and Step (2): heating the carbon material and elemental sulfur at a temperature equal to or higher than the melting point of elemental sulfur. 10. The production method according to 9, wherein the melting point of the alkali metal ion conductive material or a precursor thereof is 130 to 950°C. 11. The production method according to 9 or 10, wherein the step (2) is carried out after the step (1).

[0008] According to the present invention, it is possible to provide a composite powder that can improve the discharge capacity (rate characteristics) of an alkali metal ion battery under high current density conditions.

[0009] 1 shows an SEM image and EDX mapping (carbon element (C), phosphorus element (P), and sulfur element (S)) of the cross section of composite powder A. The second cycle (current density discharge: 0.187 mA cm) of the batteries prepared in Example 1 and Comparative Examples 1 and 2. －２ , Charging: 0.187mAcm －２ 8) of the batteries prepared in Example 1 and Comparative Examples 1 and 2 at the 8th cycle (current density discharge: 7.46 mA cm －２ , Charging: 0.373mAcm －２ 1 is a diagram showing the charge-discharge curves of the batteries fabricated in Example 1 and Comparative Examples 1 and 2. 2 is a diagram showing the cycle characteristics of the batteries fabricated in Example 1 and Comparative Examples 1 and 2. 3 is a diagram showing the charge-discharge curves of the batteries fabricated in Examples 2 to 4 at the second cycle (current density discharge: 0.187 mA cm －２ , Charging: 0.187mAcm －２ ) of the batteries prepared in Examples 2 to 4 at the 8th cycle (current density discharge: 7.46 mA cm －２ , Charging: 0.373mAcm －２) charge and discharge curves. A diagram showing the rate characteristics of the batteries produced in Examples 2 to 4. A diagram showing the cycle characteristics of the batteries produced in Examples 2 to 4. A SEM image and EDX mapping (carbon element (C) and iodine element (I)) of a cross section of composite powder G. A SEM image and EDX mapping (carbon element (C) and antimony element (Sb)) of a cross section of composite powder I. The second cycle (current density discharge: 0.187 mA cm) of the battery produced in Example 5. －２ , Charging: 0.187mAcm －２ 8) of the battery prepared in Example 5 at the 8th cycle (current density discharge: 7.46 mA cm －２ , Charging: 0.373mAcm －２ 1 is a charge / discharge curve of a battery prepared in Example 5; FIG. 2 is a graph showing the rate characteristics of a battery prepared in Example 5; FIG. 3 is a graph showing the cycle characteristics of a battery prepared in Example 5; FIG. 4 is an SEM image and EDX mapping (carbon element (C) and bromine element (Br)) of a cross section of composite powder K; FIG. 5 is an SEM image and EDX mapping (carbon element (C) and phosphorus element (P)) of a cross section of composite powder M;

[0010] A composite powder according to one embodiment of the present invention comprises a carbonaceous material having fine pores, and first and second thermal impregnation materials present in the pores. The first thermal impregnation material contains an alkali metal ion conductive material or a precursor thereof, containing one or more elements selected from lithium, boron, oxygen, phosphorus, a halogen, and antimony. The second thermal impregnation material contains elemental sulfur. In this embodiment, the first and second thermal impregnation materials are melted by heating and then infiltrated into the pores of the carbonaceous material, filling the pores. That is, the pores are impregnated by melting the thermal impregnation materials without using a solvent or diluting them. This allows the first and second thermal impregnation materials to be sufficiently incorporated into the pores, improving rate characteristics.

[0011] On the other hand, an impregnation method has been disclosed in the past, in which an alkali metal ion conductive material such as a solid electrolyte is dissolved in a solvent to form a solution, which is then filled into the pores of a carbon material, and the alkali metal ion conductive material is then precipitated (see, for example, Patent Document 4). This impregnation method, using a solvent, dilutes the impregnating material, making it impossible to impregnate a sufficient amount of alkali metal ion conductive material into the pores. This is thought to have prevented a significant improvement in rate performance. Furthermore, in a method in which a solid electrolyte is mechanically mixed with a sulfur-carbon composite, the solid electrolyte does not penetrate into the pores of the sulfur-impregnated carbon material, making it impossible to form a conduction path for alkali metal ions. Therefore, alkali metal ion conductivity in the pores is achieved solely by the diffusion of alkali metal ions in the sulfur. As a result, it is thought that the rate performance was not improved.

[0012] In this embodiment, the first thermal impregnation material contains a material having alkali metal ion conductivity containing one or more elements selected from lithium, boron, oxygen, phosphorus, a halogen, and antimony, or a precursor thereof. In this specification, an "alkali metal ion conductive material containing one or more elements selected from lithium, boron, oxygen, phosphorus, a halogen, and antimony" refers to a material that remains solid at 25°C under a nitrogen atmosphere and has ion conductivity due to alkali metal ions. Furthermore, a "precursor of an alkali metal ion conductive material containing one or more elements selected from lithium, boron, oxygen, phosphorus, a halogen, and antimony" refers to a material that, when used as an active material in an alkali metal ion battery, reacts with an alkali metal or an alkali metal ion to form a compound containing an alkali metal, thereby becoming the alkali metal ion conductive material.

[0013] In this specification, the above-mentioned “alkali metal ion conductive material” and “precursor of alkali metal ion conductive material” may be collectively referred to simply as “alkali metal ion conductive material or a precursor thereof.” In this specification, “halogen” includes elements such as fluorine, chlorine, bromine, and iodine.

[0014] The first thermal impregnation material is turned into a melt by heating, and therefore the melting point is preferably 130 to 950°C, and more preferably 220 to 950°C. The melting point of the first thermal impregnation material is preferably lower, such as 850°C or lower, 750°C or lower, 650°C or lower, 600°C or lower, or 550°C or lower. Lowering the temperature in the process reduces the energy required during production, leading to lower costs.

[0015] When the alkali metal is lithium, the alkali metal ion conductive material may be lithium sulfide or lithium polysulfide (Li ２ S ｎ (n satisfies 1<n≦8), lithium halides (LiCl, LiBr, LiI, etc.), lithium borohydride, lithium oxide, lithium triphosphate, lithium sulfate, lithium carbonate, LiBF ４ , lithium tetraborate, organic lithium salts, lithium hydroxide, etc. Precursors of lithium ion conductive materials include diphosphorus pentasulfide, red phosphorus, boron sulfide, diphosphorus pentoxide, boron oxide, antimony sulfide, antimony, tin sulfide, tin, germanium sulfide, bismuth sulfide, etc. These compounds may be used alone or in combination of two or more.

[0016] When the alkali metal is sodium, sodium polysulfide, sodium halide (NaCl, NaBr, NaI, etc.), sodium borohydride, sodium sulfate, sodium carbonate, NaBF ４ , sodium tetraborate, organic sodium salts, sodium hydroxide, etc. Precursors of the sodium ion conductive material include the same as those of the lithium ion conductive material described above. These compounds may be used alone or in combination of two or more.

[0017] Examples of organic lithium salts include bis(perfluoroalkylsulfonyl)imide lithium salts such as bis(trifluoromethanesulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, fluorosulfonyl-trifluoromethanesulfonylimide lithium, bis(pentafluoroethanesulfonyl)imide lithium, and bis(nonafluorobutanesulfonyl)imide lithium; lithium salts of perfluoroalkylsulfonimides such as 4,4,5,5-tetrafluoro-1,3,2-dithiazolidine-1,1,3,3-tetraoxide lithium salt; lithium salts of fluorosulfonylimides; lithium carboxylates such as trifluoromethanesulfonic acid, lithium acetate, lithium propionate, and lithium butyrate; lithium organic sulfonates such as lithium dodecylbenzenesulfonate and lithium p-styrenesulfonate; and organic lithium phosphates. These organic lithium salts are also preferably used together with ion-conductive polymers and ionic liquids, as they are expected to provide higher lithium conductivity. Examples of organic sodium salts include those in which the lithium ions of the above-mentioned organic lithium salts are replaced with sodium ions.

[0018] The first thermal impregnation material is preferably selected from the group consisting of diphosphorus pentasulfide, red phosphorus, boron sulfide, lithium sulfide, and lithium polysulfide (Li ２ S ｎ , n satisfies 1<n≦8), and one or more compounds selected from the group consisting of lithium halide, lithium borohydride, lithium oxide, diphosphorus pentoxide, boron oxide, trilithium phosphate, and antimony sulfide.

[0019] Particularly preferred are diphosphorus pentasulfide or boron sulfide, which are expected to react with lithium to form a sulfide solid electrolyte exhibiting high ionic conductivity, and lithium halides, which are reported to form solid solutions with lithium sulfide, a discharge product of sulfur, and to be able to improve the lithium ion conductivity of lithium sulfide.

[0020] In the present embodiment, examples of the carbon material having micropores include carbon black such as Ketjen black, acetylene black, Denka black, thermal black, channel black, and Knobel (registered trademark), graphite, activated carbon, etc. These may be used alone or in combination of two or more.

[0021] In one embodiment, the BET specific surface area of ​​the carbon material is 50 m ２ / g or more, 6000m ２ This allows a wide contact interface between the carbon material and elemental sulfur to be formed, improving the utilization rate of sulfur. The BET specific surface area is 70 m ２ / g or more is preferable, and 100m ２ / g or more, 1000m ２ / g or more, 1500m ２ / g or more is preferable. ２ / g or less, and more preferably 5000m ２ / g or less is preferred.

[0022] In addition, the pore volume of the carbon material is 0.5 cm ３ / g or more, 6cm ３ This allows a large amount of elemental sulfur to be impregnated into the pores of the carbon material together with the ion-conductive material or a precursor thereof, thereby further improving the capacity of the battery. ３ / g or more, and more preferably 1.0 cm ３ / g or more is preferable. ３ / g or less, and more preferably 5.0 cm ３ / g or less is preferred.

[0023] In the present invention, the BET specific surface area and pore volume can be determined using a nitrogen adsorption isotherm obtained by adsorbing nitrogen gas to a carbon material at liquid nitrogen temperature. Specifically, the BET specific surface area can be calculated by the Brenauer-Emmet-Telle (BET) multipoint method using the nitrogen adsorption isotherm. Furthermore, the pore volume can be determined by the Barret-Joyner-Halenda (BJH) method using the nitrogen adsorption isotherm. As a measuring device, for example, a specific surface area / pore distribution measuring device (Autosorb-3) manufactured by Quantacrome can be used for the measurement.

[0024] The composite powder of this embodiment can be produced by heating a porous carbon material, a first thermal infiltration material, and a second thermal infiltration material (hereinafter, the first and second thermal infiltration materials may be collectively referred to as the thermal infiltration materials) at a temperature equal to or higher than the melting point of each thermal infiltration material. Specifically, the carbon material, the first thermal infiltration material, and the second thermal infiltration material are mixed, and the mixture is heated to melt the first and second thermal infiltration materials, thereby impregnating the pores of the carbon material with the first and second thermal infiltration materials. In this embodiment, the first and second thermal infiltration materials can be simultaneously impregnated into the carbon material. In another embodiment, the first and second thermal infiltration materials can be separately impregnated into the carbon material. For example, the carbon material may be impregnated with the first thermal infiltration material, and then with the second thermal infiltration material.

[0025] The mixing ratio of the carbon material and the thermal impregnation material can be adjusted appropriately depending on the materials used. Typically, the mixing ratio of the carbon material [carbon material / (carbon material + first thermal impregnation material + second thermal impregnation material): mass ratio] is 0.073 to 0.990. Within this range, the thermal impregnation material is filled into the pores of the carbon material without shortage. The ratio is preferably 0.077 to 0.950, and more preferably 0.081 to 0.905.

[0026] The mixture of carbon material and thermal impregnation agent is heated to a temperature equal to or higher than the melting point of the thermal impregnation agent. The heating temperature is adjusted according to the thermal impregnation agent used. For substances that sublimate at normal pressure, they can be thermally impregnated under pressure. The heating time is preferably 10 minutes to 24 hours. Composite powder is obtained by cooling after heating. If necessary, a pulverization step may be carried out after cooling.

[0027] In this embodiment, the following steps (1) and (2) are preferably carried out simultaneously or separately: Step (1): A step of heating a porous carbon material and an alkali metal ion conductive material or a precursor thereof containing one or more elements selected from lithium, boron, oxygen, phosphorus, halogen, and antimony at a temperature equal to or higher than the melting point of the carbon material; and Step (2): A step of heating the carbon material and elemental sulfur at a temperature equal to or higher than the melting point of elemental sulfur.

[0028] In one embodiment, in step (1), it is preferable to heat an alkali metal ion conductive material or a precursor thereof having a melting point of 130 to 950° C. to a temperature equal to or higher than the melting point.

[0029] In one embodiment, step (2) is carried out after step (1). This allows the pores of the carbon material to be sufficiently impregnated with the alkali metal ion conductive material or its precursor without being affected by the melt of elemental sulfur. In step (2), the mixing ratio of the carbon material [carbon material / (carbon material + elemental sulfur): mass ratio] is preferably 0.075 to 0.990, more preferably 0.078 to 0.951, and even more preferably 0.082 to 0.906.

[0030] When an alkali metal ion conductive material containing one or more elements selected from lithium, boron, oxygen, phosphorus, halogens, and antimony, or a precursor thereof, and elemental sulfur are simultaneously impregnated into a carbon material, the mixing ratio of the carbon materials [carbon material / (carbon material + alkali metal ion conductive material containing one or more elements selected from lithium, boron, oxygen, phosphorus, halogens, and antimony, or a precursor thereof + elemental sulfur): mass ratio] is 0.073 to 0.990.

[0031] The heating temperature in step (2) is equal to or higher than the melting point of elemental sulfur (about 115°C). It is preferably equal to or higher than 130°C, and more preferably equal to or higher than 150°C. The heating in step (2) may be carried out in two or more stages. For example, the heating temperature in the first stage may be equal to or higher than the melting point of elemental sulfur and equal to or lower than the melting point of the alkali metal ion conductive material or its precursor, and the heating temperature in the second stage may be equal to or higher than the melting point of the alkali metal ion conductive material or its precursor. This makes it easier to impregnate the pores of the carbon material with a sufficient amount of elemental sulfur and the alkali metal ion conductive material or its precursor.

[0032] The composite powder of the present invention can be used as a constituent material for alkali metal ion batteries. While any type of alkali metal ion battery can be used, for example, a cathode can be formed from a cathode composite containing a solid electrolyte and the composite powder. An alkali metal ion battery according to one embodiment of the present invention includes the composite powder of the present invention described above. For example, an all-solid-state alkali metal ion battery can be manufactured by using a solid electrolyte instead of a liquid electrolyte. The composite powder of the present invention can be used to manufacture an all-solid-state alkali metal ion battery with excellent rate characteristics. Below, an all-solid-state lithium ion battery will be described as an example of an all-solid-state alkali metal ion battery. An all-solid-state lithium ion battery mainly consists of a positive electrode layer, a negative electrode layer, and an electrolyte layer, and the composite powder of the present invention is suitable as a constituent material for the positive electrode layer. The negative electrode layer and electrolyte layer can be manufactured by known methods. Furthermore, in addition to the positive electrode layer, the negative electrode layer, and the electrolyte layer, a current collector is preferably used, and known current collectors can also be used.

[0033] The solid electrolyte is not particularly limited, but examples thereof include sulfide solid electrolytes. The sulfide solid electrolyte is a solid electrolyte that contains at least sulfur atoms and exhibits ionic conductivity due to the contained metal ions, and in addition to sulfur atoms, preferably contains lithium atoms and phosphorus atoms, more preferably contains lithium atoms, phosphorus atoms, and halogen atoms, and has ionic conductivity due to lithium atoms. The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

[0034] (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 ions. Representative examples include Li ２ S-P ２ S ５ a solid electrolyte containing sulfur atoms, lithium atoms, and phosphorus atoms, which is composed of lithium sulfide and phosphorus sulfide such as Li; ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ -LiI-LiBr, etc., a solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide; ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ -P ２ S ５ In order to obtain higher ionic conductivity, a solid electrolyte such as Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as LiI-LiBr, is preferred. The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0035] The amorphous sulfide solid electrolyte contains at least Li ２S-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 65 to 85:15 to 35, more preferably 70 to 80:20 to 30, and even more preferably 72 to 78:22 to 28. ２ S-P ２ S ５ In the case of -LiI-LiBr, the total content of lithium sulfide and diphosphorus pentasulfide is preferably 60 to 95 mol%, more preferably 65 to 90 mol%, and even more preferably 70 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%.

[0036] When the amorphous sulfide solid electrolyte contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, the compounding ratio (molar ratio) of these atoms is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.6, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.05 to 0.5, and even more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.08 to 0.4. Furthermore, when bromine and iodine are used in combination as halogen atoms, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine atoms, and iodine atoms is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.02 to 0.25: 0.02 to 0.25, more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.03 to 0.2: 0.03 to 0.2, and even more preferably 1.35 to 1.45: 1.4 to 1.7: 0.3 to 0.45: 0.04 to 0.18: 0.04 to 0.18. By setting the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, it becomes easier to obtain a solid electrolyte having a thiolisiconregion II type crystal structure described below and having higher ionic conductivity.

[0037] 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.

[0038] (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).

[0039] The crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms may have a crystal structure such as Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure (Kanno et al., Journal of the Electrochemical Society, 148(7)A742-746(2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ Examples of the thio-lisicon region II crystal structure include those having a crystal structure similar to the thio-lisicon region II type (see Solid State Ionics, 177 (2006), 2721-2725). ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４This indicates that the thio-LISICON region II type has a similar crystal structure.

[0040] In X-ray diffraction measurement using CuKα radiation, Li ３ P.S. ４ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.5°, 18.3°, 26.1°, 27.3°, and 30.0°. ４ P ２ S ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=16.9°, 27.1°, and 32.5°. ７ P.S. ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=15.3°, 25.2°, 29.6°, and 31.0°. ７ P ３ S １１ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, and Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II crystal structure appear, for example, at 2θ=20.1°, 23.9°, and 29.5°, and Li ４－ｘ Ge １－ｘ P ｘ S ４ Diffraction peaks of a crystal structure similar to that of thio-LISICON Region II type appear, for example, at 2θ=20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0041] The crystal structure of the crystalline sulfide solid electrolyte also includes an argyrodite-type crystal structure. ７ P.S. ６ Crystal structure; Li ７ P.S. ６ The structural skeleton of the composition formula Li ７－ｘ P １－ｙ Si ｙ S６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ (x is -0.6 to 0.6, y is 0.1 to 0.6); Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ (0.8≦x≦1.7, 0<y≦−0.25x+0.5); Li ７－ｘ P.S. ６－ｘ Ha ｘ (Ha is Cl or Br, and x is preferably 0.2 to 1.8).

[0042] 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.

[0043] 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.

[0044] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0045] Example 1 [Preparation of Composite Powder] (1) Preparation of Composite Powder A Activated carbon (MSC-30, manufactured by Kansai Thermal Chemicals) and diphosphorus pentasulfide (manufactured by Italmatch, melting point 286-290°C) were placed in a mass ratio of 68:32 in a Tammann tube with an inner diameter of 12 mm, and the tube was sealed in an SUS tube. The temperature was raised from room temperature to 350°C in an electric furnace over 1 hour, and then maintained at 350°C for 6 hours to obtain Composite Powder A. The average particle size D of the activated carbon (MSC-30) used was ５０ is 50 to 150 μm (catalog value), pore volume is 1.58 cm ３ / g, BET specific surface area is 2840 m ２ / g. The pore volume and BET specific surface area are values ​​for pores in the porous carbon having a pore diameter of 100 nm or less. A specific surface area / pore distribution measuring device (Autosorb-3) manufactured by Quantacrome was used to measure the pore volume and BET specific surface area.

[0046] Composite powder A was subjected to argon ion milling to expose the particle cross-section, and SEM-EDX analysis was performed to confirm the impregnation status of diphosphorus pentasulfide into the activated carbon. Figure 1 shows an SEM image and EDX mapping (carbon (C), phosphorus (P), and sulfur (S)) of the cross-section of composite powder A. Figure 1 shows the presence of elements P and S on the cross-section of the activated carbon confirmed by element C, confirming that diphosphorus pentasulfide has impregnated the pores of the activated carbon.

[0047] (2) Preparation of Composite Powder B The composite powder A and elemental sulfur (melting point 115°C) were placed in a Tammann tube with an inner diameter of 12 mm in a mass ratio of 39:61, and the tube was sealed in an SUS tube. 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 composite powder B of composite powder A and sulfur.

[0048] [Preparation of Cathode Composite] (1) Preparation of Solid Electrolyte 0.4127 g of lithium sulfide, 0.6655 g of diphosphorus pentasulfide, 0.2137 g of lithium iodide, 0.2080 g of lithium bromide, and 10 zirconia balls with 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.

[0049] (2) Preparation of Positive Electrode Composite Material 0.51 g of composite powder B and 0.45 g of 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), the mixture was mixed at room temperature for 20 hours at a rotation speed of 370 rpm to obtain a positive electrode composite powder.

[0050] [Fabrication of Lithium-Ion Battery (All-Solid-State Battery)] 60 mg of the solid electrolyte prepared above was placed in a 10 mm diameter Macol cylinder and pressure-molded. 5.4 mg of the cathode composite powder prepared above was placed on the pressurized surface and pressure-molded again. Indium foil and lithium foil were placed on the pressurized surface opposite the cathode composite, and pressure was applied to fabricate an all-solid-state battery.

[0051] Comparative Example 1 (1) Preparation of Composite Powder Activated carbon (MSC-30) and elemental sulfur were placed in a glass tube in a mass ratio of 30:70, and the mixture was sealed in an SUS tubular 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 a composite powder. (2) Preparation of Cathode Composite and Lithium-Ion Battery A cathode composite was prepared under the same preparation conditions as in Example 1 using 0.45 g of the composite powder (1) above, 0.064 g of diphosphorus pentasulfide, and 0.45 g of the solid electrolyte prepared in Example 1 as raw material powders. An all-solid-state battery was also prepared under the same conditions as in Example 1.

[0052] Comparative Example 2 Using 0.32 g of elemental sulfur, 0.14 g of activated carbon (MSC-30), 0.064 g of diphosphorus pentasulfide, and 0.45 g of the solid electrolyte prepared in Example 1 as raw material powders, a positive electrode composite was prepared under the same preparation conditions as in Example 1. In addition, an all-solid-state battery was prepared under the same preparation conditions as in Example 1.

[0053] [Evaluation of Battery Characteristics] A constant current charge / discharge test was carried out on the all-solid-state batteries produced in Example 1 and Comparative Examples 1 and 2. The voltage range of the charge / discharge test was set to 0.8-2.2 V vs. Li—In, and the current density was set under the conditions shown in Table 1.

[0054]

[0055] FIG. 2A shows the second cycle (current density during discharge: 0.187 mA cm) of Example 1 and Comparative Examples 1 and 2. －２ 2B shows the charge-discharge curves of Example 1 and Comparative Examples 1 and 2 at the 8th cycle (current density during discharge: 7.46 mA cm －２) are charge / discharge curves. FIG. 3 is a diagram showing the discharge capacity (rate characteristics) at high current density, and FIG. 4 is a diagram showing the cycle characteristics. Comparing the battery characteristics of the Examples and Comparative Examples from FIGS. 2 to 4, it can be seen that the batteries of the Examples exhibit large discharge capacities at high current density (excellent rate characteristics) and also have good cycle characteristics.

[0056] Example 2 (1) Preparation of Composite Powder C Composite powder C was obtained under the same conditions as those for preparing composite powder A in Example 1, except that the mass ratio of activated carbon (MSC-30) to diphosphorus pentasulfide was changed to 81:19.

[0057] (2) Preparation of Composite Powder D Composite powder D was obtained under the same conditions as those for preparing composite powder B in Example 1, except that the mass ratio of composite powder C to elemental sulfur was changed to 35:65.

[0058] (3) Preparation of Positive Electrode Composite and Preparation of Lithium Ion Battery A positive electrode composite was prepared under the same preparation conditions as in Example 1 using 0.48 g of composite powder D and 0.45 g of the solid electrolyte prepared in Example 1 as raw material powders. An all-solid-state battery was prepared under the same conditions as in Example 1, except that 5.2 mg of positive electrode composite powder was used.

[0059] Example 3 (1) Preparation of Composite Powder E Composite powder E was obtained under the same conditions as those for preparing composite powder A in Example 1, except that the weight ratio of activated carbon (MSC-30) to diphosphorus pentasulfide was changed to 51:49.

[0060] (2) Preparation of Composite Powder F Composite powder F was obtained under the same conditions as those for preparing composite powder B in Example 1, except that the mass ratio of composite powder E to elemental sulfur was changed to 45:55.

[0061] (3) Preparation of cathode composite, preparation of lithium ion battery A cathode composite was prepared under the same preparation conditions as in Example 1 using 0.58 g of composite powder F and 0.45 g of the solid electrolyte prepared in Example 1 as raw material powders. An all-solid-state battery was prepared under the same conditions as in Example 1, except that 5.7 mg of cathode composite powder was used.

[0062] Example 4 (1) Preparation of Composite Powder G Activated carbon (MSC-30) and lithium iodide (melting point 459°C) were placed in a Tammann tube with an inner diameter of 12 mm in a mass ratio of 56:44, and the tube was sealed in an SUS tube. The tube was heated from room temperature to 520°C in an electric furnace over 1 hour, and then maintained at 520°C for 6 hours to obtain Composite Powder G.

[0063] SEM-EDX analysis was performed on composite powder G in the same manner as in Example 1 to confirm the state of impregnation of lithium iodide into the activated carbon. Figure 8 shows an SEM image and EDX mapping (carbon element (C) and iodine element (I)) of a cross section of composite powder G. From Figure 8, it can be confirmed that element I is present on the cross section of the activated carbon confirmed by element C, and therefore lithium iodide is impregnated inside the pores of the activated carbon.

[0064] (2) Preparation of Composite Powder H Composite powder H was obtained under the same conditions as those for preparing composite powder B in Example 1, except that the mass ratio of composite powder G to elemental sulfur was changed to 43:57.

[0065] (3) Preparation of Positive Electrode Composite and Preparation of Lithium Ion Battery A positive electrode composite was prepared under the same preparation conditions as in Example 1 using 0.56 g of composite powder H and 0.45 g of the solid electrolyte prepared in Example 1 as raw material powders. An all-solid-state battery was prepared under the same conditions as in Example 1, except that 5.6 mg of positive electrode composite powder was used.

[0066] The all-solid-state batteries fabricated in Examples 2 to 4 were evaluated in the same manner as in Example 1. Figure 5A shows the second cycle (current density during discharge: 0.187 mA cm) of Examples 2 to 4. －２ ) and FIG. 5B shows the charge-discharge curves of Examples 2 to 4 at the 8th cycle (current density during discharge: 7.46 mA cm －２ ) are charge / discharge curves. Fig. 6 shows the discharge capacity (rate characteristics) at high current density, and Fig. 7 shows the cycle characteristics. Figs. 5 to 7 confirm that the battery exhibits a large discharge capacity (excellent rate characteristics) at high current density and also has good cycle characteristics.

[0067] Example 5 (1) Preparation of Composite Powder I Composite powder I was obtained under the same conditions as those for preparing composite powder A in Example 1, except that diphosphorus pentasulfide was changed to antimony sulfide (melting point 550°C), the mass ratio of activated carbon (MSC-30) to antimony sulfide was 49:51, and the heating temperature was changed to 580°C.

[0068] SEM-EDX analysis was performed on composite powder I in the same manner as in Example 1 to confirm the state of impregnation of antimony sulfide into the activated carbon. Figure 9 shows an SEM image and EDX mapping (carbon element (C) and antimony element (Sb)) of a cross section of composite powder I. From Figure 9, it can be seen that element Sb is present on the cross section of the activated carbon confirmed by element C, and therefore it can be confirmed that antimony sulfide has impregnated into the pores of the activated carbon.

[0069] (2) Preparation of Composite Powder J Composite powder J was obtained under the same conditions as those for preparing composite powder B in Example 1, except that composite powder I was used and the mass ratio of composite powder I to elemental sulfur was changed to 47:53.

[0070] (3) Preparation of Positive Electrode Composite and Preparation of Lithium Ion Battery A positive electrode composite and an all-solid-state battery were prepared under the same preparation conditions as in Example 1, except that Composite Powder J was used as the raw material powder.

[0071] The all-solid-state battery fabricated in Example 5 was evaluated in the same manner as in Example 1. Figure 10A shows the second cycle of Example 5 (current density during discharge: 0.187 mA cm －２ ) and FIG. 10B shows the charge-discharge curve of Example 5 at the 8th cycle (current density during discharge: 7.46 mA cm －２ 10 to 12 show the charge-discharge curves of the battery. Fig. 11 shows the discharge capacity (rate characteristics) at high current density, and Fig. 12 shows the cycle characteristics. Figs. 10 to 12 confirm that the battery exhibits a large discharge capacity (excellent rate characteristics) at high current density and has good cycle characteristics.

[0072] Example 6 (1) Preparation of Composite Powder K Composite powder K was obtained under the same conditions as those for preparing composite powder A in Example 1, except that diphosphorus pentasulfide was changed to lithium bromide (melting point 547°C), the mass ratio of activated carbon (MSC-30) to lithium bromide was 56:44, and the heating temperature was changed to 552°C.

[0073] SEM-EDX analysis was performed on composite powder K in the same manner as in Example 1 to confirm the state of impregnation of lithium bromide into the activated carbon. Figure 13 shows an SEM image and EDX mapping (carbon element (C) and bromine element (Br)) of a cross section of composite powder K. From Figure 13, it can be seen that element Br is present on the cross section of the activated carbon confirmed by element C, and therefore it can be confirmed that lithium bromide has impregnated inside the pores of the activated carbon.

[0074] (2) Preparation of Composite Powder L Composite powder L was obtained under the same conditions as those for preparing composite powder B in Example 1, except that composite powder K was used and the mass ratio of composite powder K to elemental sulfur was changed to 43:57. SEM-EDX analysis of composite powder L was performed in the same manner as in Example 1, and it was confirmed that lithium bromide had been impregnated into the activated carbon.

[0075] Example 7 (1) Preparation of Composite Powder M Composite powder M was obtained under the same conditions as those for preparing composite powder A in Example 1, except that diphosphorus pentasulfide was changed to red phosphorus (melting point: 589.5°C, sublimation temperature: 416°C), the mass ratio of activated carbon (MSC-30) to red phosphorus was set to 67:33, and the heating temperature was changed to 450°C.

[0076] SEM-EDX analysis was performed on composite powder M in the same manner as in Example 1 to confirm the impregnation state of phosphorus into the activated carbon. Figure 14 shows an SEM image and EDX mapping (carbon element (C) and phosphorus element (P)) of a cross section of composite powder M. From Figure 14, it can be confirmed that phosphorus is impregnated inside the pores of the activated carbon, as element P is present on the cross section of the activated carbon confirmed by element C.

[0077] (2) Preparation of Composite Powder N Composite powder N was obtained under the same conditions as those for preparing composite powder B in Example 1, except that composite powder M was used and the mass ratio of composite powder M to elemental sulfur was changed to 39:61. SEM-EDX analysis was performed on composite powder N in the same manner as in Example 1, and the impregnation of red phosphorus into activated carbon was confirmed.

[0078] The composite powder of the present invention is suitable as a structural material, particularly a positive electrode composite, for alkali metal ion batteries. The alkali metal ion batteries of the present invention are also suitable for use in, for example, information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and in vehicles such as electric vehicles.

[0079] 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. The material comprises a carbon material having pores, and a first heat-impregnating material and a second heat-impregnating material present within the pores. The first heat-impregnating material comprises an alkali metal ion conductive material or a precursor thereof containing one or more elements selected from lithium, boron, oxygen, phosphorus, halogen, and antimony. The aforementioned second heat-impregnating material is a composite powder containing elemental sulfur.

2. The composite powder according to claim 1, wherein the melting point of the first heat-impregnating material is 130 to 950°C.

3. The composite powder according to claim 1, wherein the first heat-impregnating material and the second heat-impregnating material are impregnated into the pores by melting them.

4. The first heat-impregnating material is phosphorus pentasulfide, red phosphorus, boron sulfide, lithium sulfide, lithium polysulfide (Li ２ S ｎ The composite powder according to claim 1, wherein n satisfies 1 < n ≤ 8, and is one or more compounds selected from the group consisting of lithium halides, lithium borohydride, lithium oxide, phosphorus pentoxide, boron oxide, trilithium phosphate, and antimony sulfide.

5. The BET specific surface area of ​​the carbon material is 50 m². ２ / g or more, 6000m ２ The composite powder according to claim 1, wherein the amount is less than or equal to / g.

6. The pore volume of the carbon material is 0.5 cm³. ３ / g or more, 6cm ３ The composite powder according to claim 1, wherein the amount is less than or equal to / g.

7. The first heat-impregnating material is one or more compounds selected from the group consisting of phosphorus pentasulfide, red phosphorus, boron sulfide, lithium sulfide, lithium polysulfide (Li₂S₄, where n satisfies 1 < n ≤ 8), lithium halide, lithium borohydride, lithium oxide, phosphorus pentoxide, boron oxide, trilithium phosphate, and antimony sulfide. The composite powder according to claim 1, wherein the BET specific surface area of ​​the carbon material is 50 m² / g or more and 6000 m² / g or less.

8. The composite powder according to claim 1, wherein the mass ratio of the carbon material to the sum of the carbon material and elemental sulfur [carbon material / (carbon material + elemental sulfur)] is 0.075 to 0.

990.

9. The composite powder according to claim 1, wherein the mass ratio of the carbon material to the total of the carbon material, the alkali metal ion conductive material or its precursor, and the elemental sulfur [carbon material / (carbon material + alkali metal ion conductive material or its precursor + elemental sulfur)] is 0.073 to 0.

990.

10. The composite powder according to claim 1, wherein the first heat-impregnating material is phosphorus sulfide.

11. The composite powder according to claim 10, wherein the molar ratio (P / S) of phosphorus (P) to sulfur (S) is 0.01 to 0.

3.

12. The composite powder according to claim 10, wherein the molar ratio (P / S) of phosphorus (P) to sulfur (S) is 0.03 to 0.

09.

13. A positive electrode composite material comprising the composite powder according to any one of claims 1 to 12 and a solid electrolyte.

14. An alkali metal ion battery comprising the composite powder described in any one of claims 1 to 12.

15. A method for producing a composite powder, comprising performing the following steps (1) and (2) simultaneously or separately. Step (1): A step of heating a carbon material having pores and an alkali metal ion conductive material or its precursor containing one or more elements selected from lithium, boron, oxygen, phosphorus, halogen, and antimony at a temperature above the melting point. Step (2): A step of heating the carbon material and elemental sulfur at a temperature above the melting point of elemental sulfur.

16. The manufacturing method according to claim 15, wherein the melting point of the alkali metal ion conductive material or its precursor is 130 to 950°C.

17. The manufacturing method according to claim 15 or 16, wherein step (2) is performed after step (1).

18. The manufacturing method according to claim 15 or 16, wherein in step (2), the mass ratio of the carbon material to the sum of the carbon material and elemental sulfur [carbon material / (carbon material + elemental sulfur)] is 0.075 to 0.

990.

19. The manufacturing method according to claim 15 or 16, wherein the mixing ratio of the carbon material to the total of the carbon material, the alkali metal ion conductive material or its precursor, and the elemental sulfur [carbon material / (carbon material + alkali metal ion conductive material or its precursor + elemental sulfur): mass ratio] is 0.073 to 0.990.