Positive electrode mixture

Abstract

A positive electrode mixture according to the present invention contains a sulfur-based active material, a carbon material that has pores, an ion conductor that contains elemental phosphorus and / or a modified product of the ion conductor, and a solid electrolyte, wherein in a P2p spectrum in surface element analysis by X-ray photoelectron spectroscopy, the following expression (1) is satisfied.　(1): IA / IB > 0.20 (In the formula, IA is the signal strength at a position A where the binding energy is around 135.4 eV, and IB is the signal strength at a position B where the binding energy is around 134.25 eV).

Description

Positive electrode mixture

[0001] The present invention relates to a positive electrode mixture.

[0002] Lithium-ion batteries require high battery capacity. To improve battery capacity, the use of sulfur in the cathode has been investigated due to its large theoretical capacity. However, sulfur has low lithium ion and electronic conductivity, so when sulfur is used in the cathode, it is necessary to ensure the lithium ion and electronic conductivity within the cathode.

[0003] To address the above-mentioned issues, a cathode composite has been investigated in which sulfur, a carbon material, diphosphorus pentasulfide, a solid electrolyte, etc. are mechanically mixed in a planetary ball mill to form a composite (see, for example, Patent Documents 1 and 2). Also, a cathode composite has been investigated in which sulfur, a carbon material having pores, and a solid electrolyte are combined, with the solid electrolyte being placed in the pores of the carbon material from a solution state (see, for example, Patent Documents 3 and 4).

[0004] Patent No. 7156157 Patent No. 6061139 Patent No. 7283657 International Publication No. 2023 / 187466

[0005] There is a demand for further improvement in charge-discharge characteristics compared to conventional techniques. Conventional mechanical mixing (mechanical milling) methods, such as those described in Patent Documents 1 and 2, result in insufficient interface formation between the sulfur and carbon material in the resulting composite and the solid electrolyte, diphosphorus pentasulfide, etc., limiting the formation of ion conduction paths between the sulfur and the carbon material. Techniques for precipitating a solid electrolyte from a solution, such as those described in Patent Documents 3 and 4, result in insufficient interface formation between the sulfur and carbon material in the resulting composite and the solid electrolyte, limiting the formation of ion conduction paths between the sulfur and the carbon material. One object of the present invention is to provide a positive electrode composite that can improve the charge-discharge characteristics of lithium-ion batteries.

[0006] According to the present invention, the following positive electrode composite and the like are provided. 1. A positive electrode composite comprising a sulfur-based active material, a carbon material having micropores, at least one of an ionic conductor containing elemental phosphorus and a modified form of the ionic conductor, and a solid electrolyte, wherein the P2p spectrum in surface elemental analysis by X-ray photoelectron spectroscopy satisfies the following formula (1):Ａ / I Ｂ >0.20 (1) (wherein, I Ａ is the signal intensity at position A where the binding energy is around 135.4 eV, I Ｂis the signal intensity at position B where the binding energy is around 134.25 eV.) 2. The cathode mixture according to 1, wherein the overlap rate of phosphorus and carbon elements is 28.0% or more in elemental mapping image analysis of a scanning electron microscope image by energy dispersive X-ray spectroscopy. 3. The cathode mixture according to 1, wherein the overlap rate of sulfur, phosphorus, and carbon elements is 4.0% or more in elemental mapping image analysis of a scanning electron microscope image by energy dispersive X-ray spectroscopy. 4. The cathode mixture according to any one of 1 to 3, wherein the melting point of the ionic conductor is 130°C to 450°C. 5. The cathode mixture according to any one of 1 to 4, wherein the ionic conductor comprises a lithium ion conductive material or a precursor thereof containing phosphorus and one or more elements selected from lithium, boron, sulfur, and oxygen. 6. The cathode mixture according to any one of 1 to 5, wherein the ionic conductor comprises phosphorus sulfide. 7. 8. The cathode mixture according to any one of 1 to 6, wherein the ionic conductor comprises diphosphorus pentasulfide. 9. The cathode mixture according to any one of 1 to 8, wherein the sulfur-based active material comprises elemental sulfur. 10. The cathode mixture according to any one of 1 to 8, wherein the mass ratio of the total of the sulfur-based active material, the ionic conductor containing elemental phosphorus, and a modified form of the ionic conductor to the carbon material is less than 5.00. 11. A method for producing a cathode mixture, comprising: mixing at least one of a composite and a mixture of a sulfur-based active material and a carbon material having pores with a molten ionic conductor to prepare a cathode mixture precursor; and co-pulverizing the cathode mixture precursor and a solid electrolyte to produce a cathode mixture, wherein the co-pulverizing comprises: a first mixing step of co-pulverizing the cathode mixture precursor to obtain a first mixture; and a second mixing step of adding the solid electrolyte to the first mixture and subjecting the mixture to a mixing treatment. 12. 12. The manufacturing method according to 10, wherein the composite of the sulfur-based active material and the carbon material having pores is mixed with the molten ionic conductor. 13. The manufacturing method according to any one of 10 to 12, wherein the solid electrolyte has crystallinity, and the mixing and pulverization in the second mixing step is carried out under conditions that do not cause the crystallinity of the solid electrolyte to be lost. 14. The manufacturing method according to any one of 10 to 12, wherein the melting point of the ionic conductor is 130°C to 450°C.14. The manufacturing method according to any one of 10 to 13, wherein the ion conductor comprises a lithium ion conductive material or a precursor thereof, which contains elemental phosphorus and one or more elements selected from lithium, boron, sulfur, and oxygen. 15. The manufacturing method according to any one of 10 to 14, wherein the ion conductor is diphosphorus pentasulfide. 16. The manufacturing method according to any one of 10 to 15, wherein the sulfur-based active material contains elemental sulfur. 17. The manufacturing method according to any one of 10 to 16, wherein the mass ratio of the sulfur-based active material, carbon material, and ion conductor satisfies the following relationship: (sulfur-based active material + carbon material): ion conductor = 50: 1 to 80. 18. The manufacturing method according to any one of 10 to 17, wherein the mass ratio of the total of the sulfur-based active material and ion conductor to the carbon material is less than 5.00. 19. A positive electrode comprising the positive electrode mixture according to any one of 1 to 9. 20. A lithium ion battery comprising the positive electrode mixture according to any one of 1 to 9 or the positive electrode of 19.

[0007] The present invention provides a positive electrode composite that can improve the charge-discharge characteristics of lithium-ion batteries. Furthermore, the amount of solid electrolyte used, which is often produced through a complex manufacturing process, can be reduced, which is expected to result in cost savings.

[0008] 1 shows a P2p spectrum of Example 1. FIG. 2 shows a P2p spectrum of Example 2. FIG. 3 shows a P2p spectrum of Comparative Example 1. FIG. 4 shows a P2p spectrum of Reference Example 1. FIG. 5 shows a P2p spectrum of Reference Example 2. FIG. 6 shows a P2p spectrum of Reference Example 3. (a) is EDS mapping of carbon element (C) in Example 1, and (b) is an image obtained by image processing of (a). (a) is EDS mapping of phosphorus element (P) in Example 1, and (b) is an image obtained by image processing of (a). (a) is EDS mapping of sulfur element (S) in Example 1, and (b) is an image obtained by image processing of (a). (a) is EDS mapping of carbon element (C) in Comparative Example 1, and (b) is an image obtained by image processing of (a). (a) is EDS mapping of phosphorus element (P) in Comparative Example 1, and (b) is an image obtained by image processing of (a). 1A is EDS mapping of sulfur element (S) in Comparative Example 1, and FIG. 1B is an image obtained by image processing of FIG.

[0009] 1. First embodiment of positive electrode composite A positive electrode composite according to one embodiment of the present invention includes a sulfur-based active material, a carbon material having micropores, an ionic conductor containing phosphorus and / or a modified version of the ionic conductor, and a solid electrolyte. The P2p spectrum obtained by surface elemental analysis using X-ray photoelectron spectroscopy satisfies the following formula (1): Ａ / I Ｂ >0.20 (1) (wherein, I Ａ is the signal intensity at position A where the binding energy is around 135.4 eV, I Ｂ is the signal intensity at position B where the binding energy is near 134.25 eV.) Note that "near" means that the position of the binding energy may vary slightly depending on the measurement device, etc., but for example, position A means a peak that appears in the range of 135.0 eV or more and 136.5 eV or less, and position B means a peak that appears in the range of 133.5 eV or more and less than 135.0 eV. Furthermore, if no clear peak appears at each position, 135.4 eV is considered to be position A and 134.25 eV is considered to be position B.

[0010] Position B of the P2p spectrum is P ２ S ５ The signal intensity at position B is P ２ S ５ The signal intensity at position A is derived from the denatured form of the ionic conductor. Ａ / I Ｂ The fact that is large means that P ２ S ５ The positive electrode mixture of the present embodiment has a higher intensity ratio I than the conventional technique of mechanically mixing ion conductors in a solid state. Ａ / I Ｂ Specifically, the above formula (1) is satisfied. This is thought to indicate that the sulfur-based active material, the carbon material, the ion conductor, and the modified ion conductor form an interface in a form different from conventional forms. As a result, an ion conduction path is efficiently formed within the positive electrode composite, and a positive electrode composite that can improve the charge / discharge characteristics of a lithium ion battery is obtained. Details of the P2p spectrum analysis are as described in the Examples.

[0011] In a positive electrode composite according to one embodiment of the present invention, an overlap rate of phosphorus and carbon elements is 28.0% or more in an elemental mapping image analysis by energy dispersive X-ray spectroscopy (SEM-EDS analysis) of a scanning electron microscope image. Also, in a positive electrode composite according to one embodiment, an overlap rate of sulfur, phosphorus, and carbon elements is 4.0% or more in an elemental mapping image analysis by energy dispersive X-ray spectroscopy of a scanning electron microscope image.

[0012] SEM-EDS analysis allows for understanding the cross-section of the positive electrode composite, i.e., the state of elements present inside and on the surface of the pore-containing carbon material. A high overlap rate between each element and carbon means that the ionic conductor and sulfur-based active material penetrate and coat the interior and surface of the pores of the carbon material. In the positive electrode composite of this embodiment, the overlap rate between phosphorus and carbon is 28.0% or higher, which is higher than that of conventional positive electrode composites. Similarly, the overlap rate between sulfur, phosphorus, and carbon is 4.0% or higher. This indicates that the ionic conductor penetrates and coats the interior and surface of the carbon material. As a result, a strong interface and ionic conduction path are efficiently formed within the positive electrode composite, resulting in a positive electrode composite that can improve the charge / discharge characteristics of lithium-ion batteries. Details of the SEM-EDS analysis are as described in the Examples.

[0013] In one embodiment, the mass ratio of the sulfur-based active material (S), the ionic conductor containing elemental phosphorus, and the modified ionic conductor to the carbon material (C) is less than 5.00. For example, when the ionic conductor is diphosphorus pentasulfide, the mass ratio [(S + P ２ S ５ ) / C] is smaller than 5.00. When the mass ratio is less than 5.00, the charge / discharge characteristics are further improved. The mass ratio may be 4.80 or less, 4.50 or less, 4.30 or less, 4.00 or less, 3.70 or less, or 3.50 or less. The mass ratio can be adjusted by the amount of each constituent material.

[0014] 2. Manufacturing Method of Cathode Composite The cathode composite of this embodiment can be manufactured by, for example, a method of the present invention including the following steps. Step (A): A cathode composite precursor is prepared by mixing at least one of a composite and a mixture of a sulfur-based active material and a porous carbon material with a molten ion conductor. Step (B): The cathode composite precursor of step (A) is mixed and pulverized to obtain a first mixture (first mixing step). Subsequently, a solid electrolyte is added to the first mixture and mixed (second mixing step). In one embodiment, the cathode composite is obtained by the manufacturing method of the present invention. Hereinafter, methods for manufacturing the cathode composite precursor and the cathode composite will be described.

[0015] [Step (A)] In step (A), at least one of a composite and a mixture of a sulfur-based active material and a porous carbon material is mixed with a molten ion conductor to prepare a positive electrode composite precursor.

[0016] The sulfur-based active material is not particularly limited, but sulfur, lithium sulfide (Li ２ S), lithium polysulfide (Li ２ S ｎ : n satisfies 1<n≦8.), titanium sulfide (TiS ２ ), molybdenum sulfide (MoS ２ ), iron sulfide (FeS, FeS ２ ), copper sulfide (CuS), nickel sulfide (Ni ３ S ２ ), sulfur-containing polymer compounds, etc. Among these, sulfur is preferred. There are no particular limitations on the sulfur, but sulfur with a high purity is preferred. Specifically, the purity is preferably 95% by mass or more, more preferably 96% by mass or more, and particularly preferably 97% by mass or more. Examples of the crystal system of sulfur include α sulfur (orthorhombic system), β (monoclinic system), γ (monoclinic system), amorphous sulfur, etc. These can be used alone or in combination of two or more types.

[0017] As the ion conductor, a lithium ion conductive material containing phosphorus or a precursor thereof can be used. Examples of the lithium ion conductive material include a lithium ion conductive material containing one or more elements selected from lithium, boron, oxygen, sulfur, phosphorus, halogens, and antimony, or a precursor thereof. A lithium ion conductive material containing phosphorus and one or more elements selected from lithium, boron, sulfur, and oxygen, or a precursor thereof, is preferred. A lithium ion conductive material that does not contain phosphorus can be used in combination with a lithium ion conductive material containing phosphorus.

[0018] In this specification, a "lithium ion conductive material containing one or more elements selected from lithium, boron, oxygen, sulfur, phosphorus, a halogen, and antimony" refers to a material that remains solid at 25°C under a nitrogen atmosphere and has ionic conductivity attributable to lithium ions. Also, a "precursor of a lithium 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 a lithium ion battery, reacts with lithium metal or lithium ions to form a lithium-containing compound, thereby becoming the lithium ion conductive material.

[0019] As used herein, the term "halogen" includes elements such as fluorine, chlorine, bromine, and iodine.

[0020] Since the ionic conductor is heated to form a melt, the melting point is preferably 130 to 450°C, and more preferably 220 to 450°C. Furthermore, the melting point of the ionic conductor is preferably lower, such as 440°C or lower, 430°C or lower, 420°C or lower, 410°C or lower, or 400°C or lower. Elemental sulfur, which is an example of a sulfur-based active material, has a boiling point of approximately 450°C. Mixing it with a melt of a substance having a melting point higher than this will volatilize the material, and it is believed that the desired positive electrode composite precursor cannot be obtained. Furthermore, lowering the temperature in the process reduces the energy required for production, leading to lower costs.

[0021] Lithium ion conductive material: lithium borohydride, LiBF ４, organic lithium salts, polymer electrolytes such as polyethylene oxide, etc. Precursors of lithium ion conductive materials include phosphorus sulfides such as diphosphorus pentasulfide, red phosphorus, boron sulfide, diphosphorus pentoxide, tin, etc. These compounds may be used alone or in combination of two or more.

[0022] 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 carboxylic acid salts such as trifluoromethanesulfonic acid, lithium acetate, lithium propionate, and lithium butyrate; lithium organic sulfonates such as lithium dodecylbenzenesulfonate and lithium p-styrenesulfonate; and lithium organic 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.

[0023] The ionic conductor is preferably one or more compounds selected from the group consisting of phosphorus sulfide, red phosphorus, boron sulfide, diphosphorus pentoxide, and polymer electrolytes such as polyethylene oxide, which are substantially free of lithium element. Ionic conductors that are substantially free of lithium element are considered to have high affinity with sulfur-based active materials and carbon materials.

[0024] More preferably, the ionic conductor is one or more compounds selected from the group consisting of phosphorus sulfide, red phosphorus, and diphosphorus pentoxide. ４ S ３ ), diphosphorus pentasulfide (P ２ S ５ ), phosphorus heptasulfide (P ４ S ７), tetraphosphorus pentasulfide (P ４ S ５ ) and the like. Furthermore, phosphorus sulfide may have a dimer or polysulfide structure, or may be a mixture. Particularly preferably, the ionic conductor is diphosphorus pentasulfide, which is expected to react with lithium to form a sulfide solid electrolyte exhibiting high ionic conductivity. The content of phosphorus sulfide or diphosphorus pentasulfide relative to the entire ionic conductor is 50% by mass or more, 80% by mass or more, 95% by mass or more, or 99% by mass or more, and is substantially 100% by mass. When it is substantially 100% by mass, it may contain unavoidable impurities.

[0025] Examples of carbon materials 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.

[0026] 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 the sulfur-based active material to be formed, improving the utilization rate of the sulfur-based active material. ２ / g or more, 100m ２ / g or more, 1000m ２ / g or more, 1500m ２ / g or more, 2000m ２ / g or more, 2500m ２ / g or more or 3000m ２ / g or more. ２ / g or less, and more preferably 5000m ２ / g or less is preferred.

[0027] In addition, the pore volume of the carbon material is 0.5 cm ３ / g or more, 6cm ３ This allows the sulfur-based active material to be impregnated into the pores of the carbon material, further improving the battery capacity. ３ / g or more, and more preferably 1.0 cm３ / g or more is preferable. ３ / g or less, and more preferably 5.0 cm ３ / g or less is preferred.

[0028] 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.

[0029] In the manufacturing method of this embodiment, at least one of the composite and mixture of the sulfur-based active material and the carbon material having pores is mixed with a molten ion conductor. In one embodiment, a composite of the sulfur-based active material and the carbon material having pores is prepared in advance, and then the composite is mixed with the molten ion conductor. As a result, the ion conductor is coated on the surface of the composite, i.e., on both the sulfur-based active material and the carbon material, and an ion conduction path between the three is efficiently formed. On the other hand, when a mixture of the sulfur-based active material and the carbon material having pores is mixed with a molten ion conductor, it is believed that the sulfur-based active material, which has a lower melting point than the ion conductor, melts first, thereby forming a composite of the sulfur-based active material and the carbon material having pores, and then the ion conductor melts, thereby forming a similar structure.

[0030] In one embodiment, the mass ratio of the sulfur-based active material (S) to the carbon material (C) is 1:9 to 9:1, preferably 5:5 to 9:1.

[0031] The method for compounding the sulfur-based active material and the carbon material having pores is not particularly limited. For example, the sulfur-based active material and the carbon material may be mixed and crushed using a mixer / crusher such as a planetary ball mill to compound them, or the sulfur-based active material and the carbon material may be heated in a sealed state to a temperature equal to or higher than the melting point of the sulfur-based active material to compound them.

[0032] At least one of the composite and mixture of the sulfur-based active material and the porous carbon material can be mixed with the molten ionic conductor by heating at a temperature equal to or higher than the melting point of the ionic conductor. The heating temperature is adjusted according to the ionic conductor used. Substances that are sublimable at normal pressure can be mixed in a molten state by applying pressure. The heating time is preferably 10 minutes to 24 hours. A positive electrode composite precursor is obtained by cooling after heating. If necessary, a pulverization step may be performed after cooling.

[0033] In one embodiment, the mass ratio of the sulfur-based active material, the carbon material, and the ionic conductor in the positive electrode composite precursor satisfies the following relationship: (sulfur-based active material + carbon material): ionic conductor = 50:1 to 80, preferably (sulfur-based active material + carbon material): ionic conductor = 50:10 to 60.

[0034] In one embodiment, the mass ratio of the total of the sulfur-based active material (S) and the ionic conductor to the carbon material (C) is less than 5.00. For example, when the ionic conductor is diphosphorus pentasulfide, the mass ratio [(S + P ２ S ５ ) / C] is smaller than 5.00. When the mass ratio is less than 5.00, the charge / discharge characteristics are further improved. The mass ratio may be 4.80 or less, 4.50 or less, 4.30 or less, 4.00 or less, 3.70 or less, or 3.50 or less. The mass ratio may be 2.00 or more, 2.60 or more, or 3.20 or more. The mass ratio can be adjusted by the amount of each constituent material.

[0035] [Step (B)] In step (B), the cathode composite precursor from step (A) is mixed and pulverized to obtain a first mixture (first mixing step). Subsequently, a solid electrolyte is added to the first mixture and mixed (second mixing step). In this embodiment, in the first mixing step, the cathode composite precursor is mixed and pulverized under conditions of a relatively strong impact force to microparticleize the cathode composite precursor. This increases the number of contact points between the cathode composite particles, thereby improving the charge / discharge characteristics of the lithium-ion battery. The solid electrolyte may or may not be mixed in the first mixing step. For example, a device with a relatively strong impact force, such as a planetary ball mill, may be used in the first mixing step. Furthermore, conditions such as the rotation speed may be adjusted to mix and pulverize the precursor under a higher load than usual.

[0036] In the second mixing step, the solid electrolyte is blended and mixed, and therefore, if necessary, mixing and pulverization can be performed under conditions with a relatively low impact force. For example, a device with a relatively low impact force, such as a tumbling mill, may be used. Furthermore, conditions such as the rotation speed may be adjusted to mix and pulverize under a lower load than usual. In one embodiment, the solid electrolyte is a crystalline solid electrolyte, and in the second mixing step, the solid electrolyte is mixed and pulverized under conditions that do not cause the crystallinity of the solid electrolyte to be lost, to produce a positive electrode composite. Whether the crystallinity of the solid electrolyte is maintained can be confirmed, for example, by the presence of a crystalline peak and a change in the half-width by X-ray diffraction measurement.

[0037] The solid electrolyte is not particularly limited, and examples thereof include sulfide solid electrolytes used in lithium ion batteries, which will be described later. Examples of mixing devices used in the first and second mixing steps include planetary ball mills, tumbling mills, bead mills, Filmix, Nauta mixers, tornado mixers, twin-screw extruders, multi-screw rollers, and solid-phase shear kneaders.

[0038] 3. Lithium-ion Battery A lithium-ion battery according to one embodiment of the present invention includes the above-described cathode composite of the present invention. For example, an all-solid-state lithium-ion battery can be manufactured by using a solid electrolyte instead of a liquid electrolyte. By using the cathode composite of the present invention, an all-solid-state lithium-ion battery with good charge / discharge characteristics can be manufactured. The all-solid-state lithium-ion battery will now be described. An all-solid-state lithium-ion battery is primarily composed of a cathode layer, an anode layer, and an electrolyte layer, and the cathode composite of the present invention is suitable as a constituent material for the cathode layer. The anode layer and electrolyte layer can be manufactured by known methods. In addition to the cathode layer, anode layer, and electrolyte layer, a current collector is preferably used, and known current collectors can also be used.

[0039] 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 lithium ions contained therein. In addition to sulfur atoms, the solid electrolyte 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.

[0040] (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 lithium ions contained therein. 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 S５ -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.

[0041] 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 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 ５In 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%.

[0042] 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.

[0043] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 μm to 200 μm. ５０) is the particle size at which 50% of the total particle size is reached when the particle size distribution integral curve is drawn and the integral is calculated from the smallest particle size, and the volume distribution is an average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device.

[0044] (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).

[0045] The crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms may have a crystal structure such as Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure (Kanno et al., Journal of the Electrochemical Society, 148(7)A742-746(2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ Examples of the thio-lisicon region II crystal structure include those having a crystal structure similar to the thio-lisicon region II type (see Solid State Ionics, 177 (2006), 2721-2725). ４－ｘ Ge １－ｘ Pｘ S ４ Thio-LISICON Region II crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ This indicates that the thio-LISICON region II type has a similar crystal structure.

[0046] 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°.

[0047] The crystal structure of the crystalline sulfide solid electrolyte also includes an argyrodite-type crystal structure. ７ P.S. ６ Crystal structure; Li ７ P.S. ６ The structural skeleton of the composition formula Li ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ (x is −0.6 to 0.6, y is 0.1 to 0.6); Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ (0.8≦x≦1.7, 0<y≦−0.25x+0.5); Li ７－ｘ P.S. ６－ｘ Ha ｘ (Ha is Cl or Br, and x is preferably 0.2 to 1.8).

[0048] 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.

[0049] The shape of the crystalline sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) is the average particle size (D ５０ ) and the ranges of 0.01 μm to 500 μm and 0.1 μm to 200 μm can be exemplified.

[0050] 4. Other Forms of Cathode Composite A cathode composite according to one embodiment of the present invention includes a sulfur-based active material, a carbon material having micropores, at least one of an ion conductor and a modified form of the ion conductor, and a solid electrolyte, and has an overlap rate of phosphorus and carbon elements of 28.0% or more in element mapping image analysis of a scanning electron microscope image by energy dispersive X-ray spectroscopy.

[0051] A positive electrode composite according to one embodiment of the present invention includes a sulfur-based active material, a porous carbon material, at least one of an ion conductor and a modified form of the ion conductor, and a solid electrolyte, and has an overlap rate of 4.0% or more among the sulfur element, phosphorus element, and carbon element in an element mapping image analysis of a scanning electron microscope image by energy dispersive X-ray spectroscopy.

[0052] A positive electrode composite according to one embodiment of the present invention includes a sulfur-based active material, a carbon material having micropores, an ion conductor and / or a modified product of the ion conductor, and a solid electrolyte, and has a specific surface area parameter x of 5.00 or less.

[0053] The positive electrode mixtures of the above-mentioned respective embodiments can all be obtained by, for example, the above-mentioned manufacturing method of the present invention.

[0054] [Solid Electrolyte] Production Example 1 (Preparation of Solid Electrolyte A) 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) at a rotation speed of 370 rpm for 40 hours to obtain a powder. The obtained powder was heated at 195 ° C. for 3 hours to obtain a solid electrolyte A.

[0055] Production Example 2 (Preparation of Solid Electrolyte B) Lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ ), lithium bromide (LiBr) and lithium chloride (LiCl) in a molar ratio of Li ２ S:P ２ S ５The raw materials were roughly mixed to obtain a ratio of 47.5:12.5:15.0:25.0 of LiBr:LiCl. The raw material mixture was dispersed in a mixed solvent of dehydrated toluene and 2% by mass of dehydrated isobutyronitrile relative to the raw material mixture to obtain a slurry of approximately 10% by mass. A bead mill was operated at a peripheral speed of 12 m / s and a flow rate of 500 mL / min, and the slurry was introduced into the mill and circulated for 1 hour to obtain a mixture. After removing the solvent from the obtained mixture, the mixture was heated at 400 to 430 °C for 2 hours in an electric furnace. The mixture was then slowly cooled to obtain a raw material sulfide solid electrolyte. The raw material sulfide solid electrolyte was dispersed in dehydrated toluene under a nitrogen atmosphere and placed in a zirconia pot of a planetary ball mill (manufactured by Fritsch: model number P-7) together with 0.3 mm diameter zirconia balls, and the pot was filled with an inert atmosphere. The planetary ball mill was rotated at 150 rpm for 2 hours to obtain a slurry containing a finely divided sulfide solid electrolyte. The slurry was transferred to a nitrogen-substituted Schlenk flask, dried at room temperature for 1 hour using a vacuum pump, and then heated to 80°C to 100°C to further remove the solvent contained in the finely divided sulfide solid electrolyte (drying under reduced pressure), to obtain a solid electrolyte B.

[0056] [Positive electrode composite] Example 1 (1) Preparation of activated carbon and sulfur composite (S-C composite) Activated carbon (MSC-30SSS, manufactured by Kansai Thermal Chemical Industry Co., Ltd.) and sulfur were placed in a glass bottle in a weight ratio of 3:7, and the bottle 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 powder of activated carbon and sulfur composite.

[0057] (2) Preparation of a cathode composite precursor The powder of the composite obtained in (1) above and diphosphorus pentasulfide (manufactured by Italmatch, melting point 286-290°C) were placed in a Tammann tube with an inner diameter of 12 mm in a weight ratio of 0.7143:0.2857, and the mixture was sealed in an SUS tube. The mixture was heated in an electric furnace at 350°C for 6 hours to obtain a cathode composite precursor. The mass ratio [(S + P ２ S ５ ) / C] is 3.67.

[0058] (3) Preparation of Positive Electrode Composite (a) First Mixing Step: 1.000 g of the positive electrode composite precursor prepared in (2) above was placed in a 45 mL zirconia pot together with 10 zirconia balls having a diameter of 10 mm, and the pot was sealed. The mixture was mixed and pulverized for 20 hours at room temperature and a rotation speed of 370 rpm using a planetary ball mill (manufactured by Fritsch GmbH, model number P-7).

[0059] (b) Second Mixing Step: 0.6300 g of the processed product (a) (first mixture) and 0.2700 g of solid electrolyte A were placed in a 45 mL zirconia pot together with 34 g of zirconia balls having a diameter of 2 mm, and the pot was sealed. The mixture was mixed at room temperature and a rotation speed of 600 rpm for 1 hour using a tumbling mill ("Small Ball Mill Stand," manufactured by Asahi Rika Seisakusho, Model AV-1) to obtain a powder of a positive electrode composite.

[0060] Example 2 A powder of a positive electrode mixture was obtained in the same manner as in Example 1, except that solid electrolyte B was used instead of solid electrolyte A in the second mixing step (b) of Example 1(3).

[0061] Comparative Example 1 (a) First Mixing Step The powder of the C-S composite obtained in the same manner as in Example 1(1) and diphosphorus pentasulfide were placed in a 45 mL zirconia pot together with ten zirconia balls having a diameter of 10 mm so as to have the same mass ratio as the treated product obtained in Example 1(3)(a), and the pot was sealed. The mixture was mixed and pulverized at room temperature and a rotation speed of 370 rpm for 20 hours using a planetary ball mill (manufactured by Fritsch GmbH, model number P-7).

[0062] (b) Second Mixing Step 0.6300 g of the processed product (a) (first mixture) and 0.2700 g of solid electrolyte A were mixed in the same manner as in Example 1(3)(b) to obtain a powder of a positive electrode mixture.

[0063] Reference Example 1 A positive electrode composite precursor was obtained in the same manner as in Example 1(2), except that the powder of the S—C composite obtained in Example 1(1) above and diphosphorus pentasulfide (manufactured by Italmatch, melting point 286 to 290° C.) were placed in a Tammann tube having an inner diameter of 12 mm in a weight ratio of 0.7143:0.2857.

[0064] Reference Example 2 A positive electrode composite precursor was obtained in the same manner as in Example 1(2), except that the powder of the S—C composite obtained in Example 1(1) above and diphosphorus pentasulfide (manufactured by Italmatch, melting point 286 to 290° C.) were placed in a Tammann tube having an inner diameter of 12 mm in a weight ratio of 0.8333:0.1667.

[0065] Reference Example 3 The powder of the S-C composite obtained in Example 1 (1) above and diphosphorus pentasulfide (manufactured by Italmatch, melting point 286 to 290°C) were charged into an agate mortar in a weight ratio of 0.7143:0.2857 and mixed for 5 minutes to obtain a positive electrode composite precursor.

[0066] [Evaluation] The following evaluations were performed on the positive electrode composites prepared in the examples and comparative examples. (1) X-ray photoelectron spectroscopy (XPS) measurement (a) XPS measurement In a glove box controlled to an Ar atmosphere with a dew point of -60°C or less, double-sided carbon tape was attached to a metal substrate, and a powder sample was pressed onto the tape with a spatula. The surface of the spatula used was cleaned with an organic solvent such as acetone. A metal perforated mask (hole diameter 5 mm) was placed on the tape with the powder sample fixed and fixed with screws to prepare a measurement sample. To prevent the sample from being exposed to the atmosphere, a transfer vessel was used to introduce the sample into the XPS apparatus, and measurements were performed. Detailed measurement conditions for XPS are shown below.

[0067] XPS equipment: VersaProbe II (ULVAC-PHI, Inc.) X-ray source: Monochromated AlKα rays (1486.6 eV) measured at a high power of 100 W X-ray diameter: 100 μm (measured by sweeping within a range of 200 μm x 1200 μm) Pass energy: 23.5 eV (C1s, S2p, P2p) 46.95 eV (O1s, Li1s, Br3d, I3d5 / 2, Cl2p) Step energy: 0.1 eV (C1s, S2p, P2p) 0.2 eV (O1s, Li1s, Br3d, I3d5 / 2, Cl2p) Photoelectron detection angle: 45° XPS measurement was performed on the surface (outermost surface) of the sample. The sample was placed in an ultra-high vacuum (1.0 × 10 －７ The measurements were taken immediately after the sample was introduced into a vacuum (less than 1000 Pa).

[0068] (b) Relative intensity of the sample surface in the P2p spectrum. The analysis software used was MultiPak manufactured by ULVAC-PHI. ８ The peak position of the P2p orbital was set to 164.1 eV for charge correction. The background of the spectrum derived from the P2p orbital was subtracted by the Shirley method, and the cps values ​​(signal intensity: I) were extracted for three peaks: a peak with a binding energy of approximately 135.4 eV (Peak A), a peak with a binding energy of approximately 134.25 eV (Peak B), and a peak with a binding energy of approximately 133.0 eV (Peak C). The signal intensity ratio (I Ａ / I Ｂ and I Ｃ / I Ｂ ) was calculated. Note that "near" means that the binding energy position may vary slightly depending on the measurement device, etc. For example, position A refers to a peak appearing in the range of 135.0 eV to 136.5 eV, position B refers to a peak appearing in the range of 133.5 eV to less than 135.0 eV, and position C refers to a peak appearing in the range of 132.0 eV to less than 133.5 eV. Furthermore, if no clear peak appears at each position, 135.4 eV is designated as position A, 134.25 eV as position B, and 133.0 eV as position C. The P2p relative intensity on the sample surface is the value at one point near the center of the measurement area (diameter 5 mm). It was confirmed that the spectra of each element were nearly identical at a total of three points in the measurement area: near the center and two points approximately 500 μm away from the center. The results are shown in Table 1.

[0069] The P2p spectra of Examples 1 and 2 and Comparative Example 1 are shown in Figures 1 to 3. The P2p spectra of Reference Examples 1 to 3 are shown in Figures 4 to 6. In the figures, A indicates position A where the binding energy is around 135.4 eV, B indicates position B where the binding energy is around 134.25 eV, and C indicates position C where the binding energy is around 133.0 eV.

[0070] * "P ２ S ５ The "state of" is the S-C complex and P ２ S ５* Regarding the parentheses for solid electrolytes, (A) indicates solid electrolyte A, and (B) indicates solid electrolyte B.

[0071] As shown in Table 1, in the example, the signal intensity ratio I Ａ / I Ｂ In order to consider the results of this analysis, the P2p spectra of the positive electrode composite precursors of Reference Examples 1 to 3 are shown in FIGS. ２ S ５ The peak due to P appears at position B. In Reference Example 3, peak B appears clearly, and ２ S ５ It was suggested that P exists in its original chemical state. ２ S ５ In Reference Examples 1 and 2, in which P was mixed in a molten state with the SC composite, it was confirmed that peaks A and C appeared instead of peak B. Peaks A and C are P ２ S ５ This indicates the presence of modified P. ２ S ５ It is believed that P exists in the positive electrode composite precursor in a chemical state different from the original state. ２ S ５ It is presumed that the peak contains elements such as O and C derived from activated carbon in addition to P and S in the activated carbon. Carbon materials such as activated carbon generally contain C and O. Peak A is the peak of molten P. ２ S ５ It is thought that this represents a component generated by a reaction between P and a part of the activated carbon inside or on the surface of the activated carbon. ２ S ５ Since the difference in bond energy between ２ S ５ It is not, but does not contain O or C, etc. ２ It is presumed that the components are Sx (5<x). ２ S ５It is thought that the peak C is due to the influence of the component of peak A produced during melting of activated carbon, and the component produced inside or on the surface of activated carbon by reacting with sulfur in the molten state. ２ S ５ When comparing the results of Reference Examples 1 and 2, which have different blending amounts of P, Peak A has the same signal intensity, while Peak C has P ２ S ５ It was confirmed that the signal intensity was high in Reference Example 1, which contained a large amount of molten P. ２ S ５ It is thought that the change in the S-C complex is due to the reaction inside or on the surface of the activated carbon, which produces the component indicated by peak A first, and the remaining part changes to the component indicated by peak C, also inside or near the surface of the activated carbon, and both components coat the S-C complex. ２ S ５ This is thought to indicate that the S—C composite was coated with the SiO2 and a strong interface was formed.

[0072] From Table 1 and Figures 1 to 3, P in the molten state ２ S ５ By mixing a solid electrolyte into the cathode composite precursor obtained by mixing the S-C composite, the peak shape changes, and the relationship between the three binding energies (A to C), i.e., the signal intensity ratio I Ａ / I Ｂ and signal intensity ratio I Ｃ / I Ｂ When a solid electrolyte is added to the cathode composite precursor of the above-mentioned Reference Example, the P content of many sulfide solid electrolytes is increased. ２ Sx (5<x), that is, the influence of the peak C component is considered to be apparent. From this perspective, it can be seen that the influence of peak C is relatively increased in both the Examples and Comparative Examples, but the final peak shapes are different. It can be seen that in the Examples using a precursor that has undergone melting, the relative intensity of peak A is higher than in the Comparative Examples that do not include melting treatment. As explained in the Reference Example, this is the result of the increase in the intensity of peak C due to the effect of adding a solid electrolyte to the Examples in which the relative intensity of peak A is high at the precursor stage. From this, it can be seen that, as in the Examples, P ２ S５ In a molten state, the solid electrolyte is mixed with the cathode composite precursor mixed with the SC composite. ２ S ５ covers the S-C composite, forming a strong interface, and the signal intensity ratio I Ａ / I Ｂ It is considered that the value of the saturation voltage Vs is equal to or greater than a certain value (for example, 0.2).

[0073] (2) Energy dispersive X-ray spectroscopy (SEM-EDS analysis) of scanning electron microscope images and calculation of the overlap rate of carbon and phosphorus, and the overlap rate of carbon, phosphorus, and sulfur (a) Preparation of positive electrode composite pellets 100 mg of solid electrolyte A was placed in a Macol cylinder with a diameter of 10 mm and pressure molded. The obtained positive electrode composite powder was placed on the pressure surface so that it became 20 mg, and pressure molded again. Subsequently, 20 mg of positive electrode composite powder was placed on the pressure surface on the opposite side, pressure molded again, and the molded body was extracted from the cylinder to obtain a positive electrode composite pellet.

[0074] (b) SEM-EDS analysis The positive electrode composite pellet was split vertically, and the exposed surface was subjected to ion milling (Hitachi High-Tech Corporation, IM4000) to expose the cross section of the positive electrode composite pellet. SEM-EDS elemental mapping measurement was performed on the obtained cross section using an SEM (Hitachi High-Tech Corporation, SU8220) and an EDS (Bruker, QUANTAX FlatQUAD), and secondary electron images and EDS images of carbon, phosphorus, and sulfur were obtained from 10 fields of view. The observation magnification was 5000x, the acceleration voltage was 10 kV, and the scan area was 1024 x 768. For EDS mapping, a smoothing process was performed using the software of the EDS device, and the obtained image was used. In addition, during the SEM-EDS elemental mapping measurement, the area cross-sectionally processed by ion milling was divided into two equal parts, top and bottom, and each of the two equal parts was divided into five equal parts on the left and right. The central portion of each of the 10 divided regions was subjected to SEM-EDS elemental mapping at a magnification of 5000 times.

[0075] (c) Calculation of the overlap rate of carbon and phosphorus, and the overlap rate of carbon, phosphorus, and sulfur. The images obtained using the above procedure were processed using Python (3) OpenCV (4.5.1). All 10 fields of view of the carbon, phosphorus, and sulfur EDS images were subjected to smoothing twice using a bilateral filter with d = 15, sigmaColor = 64, and sigmaSpace = 64. The resulting images were compressed to 1 / 3 of their original size using MaxPooling2D (pool_size = 3, strides = 3) in the neural network open library Keras (2.4.3), and smoothed using a median filter with ksize = 3. The smoothed image was converted to grayscale, and binarized using the standard binarization format THRESH_BINARY, with carbon at a minimum brightness of 30 and a maximum brightness of 255, phosphorus at a minimum brightness of 47 and a maximum brightness of 255, and sulfur at a minimum brightness of 73 and a maximum brightness of 255. These processes converted the image data into a numerical matrix with 0 if the element was not present and 255 if the element was present. The overlap rate for one field of view was calculated by dividing the total number of pixels where 255 overlapped at the same coordinate in the numerical matrices for carbon, phosphorus, and sulfur by the total number of pixels. The overlap rate was calculated as the average of the overlap rates for all 10 fields of view. The results are shown in Table 2.

[0076] FIG. 7(a) is EDS mapping of carbon element (C) in Example 1, and FIG. 7(b) is an image obtained by image processing of (a). FIG. 8(a) is EDS mapping of phosphorus element (P) in Example 1, and FIG. 8(b) is an image obtained by image processing of (a). FIG. 9(a) is EDS mapping of sulfur element (S) in Example 1, and FIG. 9(b) is an image obtained by image processing of (a). FIG. 10(a) is EDS mapping of carbon element (C) in Comparative Example 1, and FIG. 10(b) is an image obtained by image processing of (a). FIG. 11(a) is EDS mapping of phosphorus element (P) in Comparative Example 1, and FIG. 11(b) is an image obtained by image processing of (a). FIG. 12(a) is EDS mapping of sulfur element (S) in Comparative Example 1, and FIG. 12(b) is an image obtained by image processing of (a).

[0077]

[0078] The overlapping ratio of carbon element (C) and phosphorus element (P), and the overlapping ratio of C, P and sulfur element (S) are higher in Example 1 than in Example 2, where the S-C composite and P are formed by fusion coating. ２ S ５ It is thought that the increase is due to the fact that the two are now in close proximity to each other.

[0079] (3) Specific Surface Area Parameter The BET specific surface areas of the positive electrode composite and the solid electrolyte were measured using a specific surface area and pore distribution analyzer (Autosorb-3) manufactured by Quantacrome. The specific surface area parameter was calculated using the following formula: Specific surface area parameter = (specific surface area of ​​positive electrode composite) / (specific surface area of ​​solid electrolyte). ａ (In the formula, a is the mass ratio of the solid electrolyte to the entire positive electrode composite (mass of solid electrolyte / mass of the entire positive electrode composite). The specific surface area parameter corrects for the effect of the specific surface area of ​​the solid electrolyte and allows the difference between the presence and absence of melt treatment of the ionic conductor to be evaluated. The results are shown in Table 3.

[0080]

[0081] From Table 3, P ２ S ５ By mixing the molten P with the S-C composite, the specific surface area parameter of the resulting positive electrode composite material became smaller. ２ S ５ This is thought to be because the S-C composite and its modified form coated the S-C composite, forming a strong interface. The specific surface area parameter can correct the effect of the specific surface area of ​​the solid electrolyte and evaluate the difference due to the presence or absence of melting treatment. From this result, it can be seen that in the positive electrode composite, as in the precursor, the S-C composite melted P ２ S ５ This suggests that the nanoparticles are coated with the modified nanoparticles.

[0082] [All-solid-state lithium-ion battery] All-solid-state lithium-ion batteries were fabricated using the positive electrode composites fabricated in the examples and comparative examples as described below, and the battery characteristics (charge and discharge characteristics) were evaluated. - Fabrication of negative electrode composite Lithium titanate ("LT-112" manufactured by Ishihara Sangyo Kaisha), a conductive additive ("Li-100" manufactured by Denka Co., Ltd., powdered acetylene black), and solid electrolyte B were mixed in a mortar in a mass ratio of 60:5:35 for 5 minutes to obtain a negative electrode composite (also referred to as "LTO (lithium titanate) negative electrode composite").

[0083] - Preparation of Lithium-ion Battery 100 mg of solid electrolyte A was placed in a 10 mm diameter Macol cylinder and pressure molded to form a solid electrolyte layer (layer of solid electrolyte A). Next, 10 mg of positive electrode composite powder was placed on one pressure surface of the solid electrolyte layer and pressure molded again. Next, 166 mg of LTO negative electrode composite was placed on the other pressure surface of the solid electrolyte layer (the pressure surface opposite the positive electrode) and pressure was applied. A Li foil with a diameter of 9 mm and a thickness of 0.1 mm was placed on top of it and pressure was applied again to prepare a lithium-ion battery.

[0084] Charge / Discharge Test A constant current charge / discharge test was performed on the lithium ion batteries using the positive electrode composites of each Example and Comparative Example. The voltage range for the constant current charge / discharge test was set to -0.4 to 1.3 V, and the current value was set as shown in Table 4 at a C rate determined based on the theoretical capacity of sulfur of 1672 mAh / g. The test was performed. For charging, CC-CV charging was performed, in which constant voltage charging was performed with a termination condition of 0.02 C after constant current charging, and for discharging, constant current discharge (CC discharge) was performed. The results are shown in Table 5.

[0085]

[0086]

[0087] It was confirmed that the Examples had higher discharge capacities at both low and high rates than the Comparative Examples. ２ S ５The improvement in charge-discharge characteristics was confirmed in the examples in which a cathode composite precursor was prepared by melting an ion conductor (a cathode composite precursor). It is believed that the excellent charge-discharge characteristics were obtained in the examples by using a cathode composite precursor having a strong interface and a good ion conduction path.

[0088] The positive electrode composite of the present invention is suitable as a structural material for lithium ion batteries. Furthermore, lithium ion batteries containing the positive electrode composite of the present invention are suitable for use in, for example, information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and vehicles such as electric vehicles.

[0089] 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 references cited in this specification and the applications from which this application claims priority under the Paris Convention are incorporated by reference in their entirety. In this specification, "x to y" represents a numerical range of "greater than or equal to x and less than or equal to y." The upper and lower limits of numerical ranges can be arbitrarily combined. Furthermore, two or more of the individual embodiments of the present invention that are not mutually exclusive can be combined, and an embodiment combining two or more embodiments is also an embodiment of the present invention.

Claims

1. A positive electrode composite material comprising a sulfur-based active material, a carbon material having pores, at least one of an ion conductor containing a phosphorus element and a modified body of the ion conductor, and a solid electrolyte, which satisfies the following formula (1) in a P2p spectrum in surface element analysis by X-ray photoelectron spectroscopy. I Ａ / I Ｂ >0.20 (1) (In the formula, I Ａ is the signal intensity at position A where the binding energy is around 135.4 eV, and I Ｂ is the signal intensity at position B where the binding energy is around 134.25 eV.) 2. The positive electrode composite material according to claim 1, wherein in the elemental mapping image analysis by energy dispersive X-ray spectroscopy of a scanning electron microscope image, the overlap rate of phosphorus element and carbon element is 28.0% or more.

3. The positive electrode composite material according to claim 1, wherein in the elemental mapping image analysis by energy dispersive X-ray spectroscopy of a scanning electron microscope image, the overlap rate of sulfur element, phosphorus element and carbon element is 4.0% or more.

4. The positive electrode composite material according to any one of claims 1 to 3, wherein the melting point of the ion conductor is 130°C to 450°C.

5. The positive electrode composite material according to any one of claims 1 to 4, wherein the ion conductor includes a lithium ion conductive material containing phosphorus element and one or more elements selected from lithium, boron, sulfur and oxygen, or a precursor thereof.

6. The positive electrode composite material according to any one of claims 1 to 5, wherein the ion conductor contains phosphorus sulfide.

7. The positive electrode composite material according to any one of claims 1 to 6, wherein the ion conductor contains diphosphorus pentasulfide.

8. The positive electrode composite material according to any one of claims 1 to 7, wherein the sulfur-based active material contains elemental sulfur.

9. The positive electrode composite material according to any one of claims 1 to 8, wherein the total mass ratio of the sulfur-based active material, the ion conductor containing phosphorus element and the modified body of the ion conductor to the carbon material is less than 5.

00.

10. A method for manufacturing a positive electrode composite material, comprising mixing at least one of a composite and a mixture of a sulfur-based active material and a carbon material having pores with a molten ion conductor to prepare a positive electrode composite material precursor, and mixing and pulverizing the positive electrode composite material precursor and a solid electrolyte to manufacture a positive electrode composite material, wherein the mixing and pulverizing includes a first mixing step of mixing and pulverizing the positive electrode composite material precursor to obtain a first mixture, and a second mixing step of adding the solid electrolyte to the first mixture and performing a mixing treatment.

11. The manufacturing method according to claim 10, wherein the composite of the sulfur-based active material and the carbon material having pores is mixed with the molten ion conductor.

12. The manufacturing method according to claim 10 or 11, wherein the solid electrolyte has crystallinity, and the mixing and pulverizing in the second mixing step is performed under conditions where the crystallinity of the solid electrolyte does not disappear.

13. The manufacturing method according to any one of claims 10 to 12, wherein the melting point of the ion conductor is 130°C to 450°C.

14. The manufacturing method according to any one of claims 10 to 13, wherein the ion conductor comprises a lithium ion conductive material containing phosphorus element and one or more elements selected from lithium, boron, sulfur and oxygen, or a precursor thereof.

15. The manufacturing method according to any one of claims 10 to 14, wherein the ion conductor is phosphorus pentasulfide.

16. The manufacturing method according to any one of claims 10 to 15, wherein the sulfur-based active material contains elemental sulfur.

17. The manufacturing method according to any one of claims 10 to 16, wherein the mass ratio of the sulfur-based active material, the carbon material and the ion conductor satisfies the following relationship: (sulfur-based active material + carbon material): ion conductor = 50:1 to 80.

18. The manufacturing method according to any one of claims 10 to 17, wherein the total mass ratio of the sulfur-based active material and the ion conductor to the carbon material is less than 5.

00.

19. A positive electrode comprising the positive electrode composite material according to any one of claims 1 to 9.

20. A lithium ion battery comprising the positive electrode composite material according to any one of claims 1 to 9 or the positive electrode according to claim 19.

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