Positive electrode mix, production method for positive electrode mix, and lithium ion battery

Abstract

A positive electrode mix containing a sulfur-based active substance and a sulfide solid electrolyte, wherein the sulfide solid electrolyte contains phosphorous (P) and at least one halogen (X) including at least iodine (I) as constituent elements, the molar ratio (X / P) of the halogen (X) to the phosphorous (P) is 0.86 or greater, and the molar ratio (I / P) of the iodine (I) to the phosphorous (P) is 0.10 or greater.

Description

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

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

[0002] In sulfur-based positive electrode composites used in all-solid-state lithium-ion batteries, the insulating sulfur-based active material must be composited with a conductive additive and a solid electrolyte to fully react. Patent Document 1 discloses a method for producing a positive electrode composite by adding a solid electrolyte to a composite of a sulfur-based active material and a carbon material, mechanically mixing the composite with a strong energy source, and heating the mixture.

[0003] Patent No. 6243103

[0004] In the cathode mixture described in Patent Document 1, when a composite material of a sulfur-based active material and a carbon material is mechanically mixed with a solid electrolyte, the solid electrolyte is altered and its lithium ion conductivity is reduced. The reduction in the lithium ion conductivity of the solid electrolyte leads to a reduction in the rate characteristics of the cathode mixture and all-solid-state lithium ion battery containing the solid electrolyte.

[0005] Heat treatment is required to restore the lithium ion conductivity of the solid electrolyte, which has been reduced by mechanical mixing. However, this increases the number of steps and energy consumption, leading to higher manufacturing costs. It also involves the loss of sulfur-based active materials that have been composited with the solid electrolyte by mechanical mixing.

[0006] An object of the present invention is to provide a positive electrode mixture that does not require heat treatment to restore lithium ion conductivity and that can provide a battery with excellent rate characteristics.

[0007] The present invention provides the following cathode mixtures and the like. 1. A cathode mixture comprising a sulfur-based active material and a sulfide solid electrolyte, wherein the sulfide solid electrolyte comprises, as constituent elements, phosphorus (P) and a halogen (X) containing at least iodine (I), wherein the molar ratio (X / P) of the halogen (X) to the phosphorus (P) is 0.86 or more, and the molar ratio (I / P) of the iodine (I) to the phosphorus (P) is 0.10 or more. 2. The cathode mixture according to 1, wherein the sulfide solid electrolyte comprises, as a constituent element, lithium (Li), and wherein the molar ratio (Li / P) of the lithium (Li) to the phosphorus (P) is 2.00 or more. 3. The cathode mixture according to 1 or 2, wherein the sulfur-based active material comprises elemental sulfur or a discharge product thereof. 4. The cathode mixture according to any one of 1 to 3, further comprising a conductive additive. 5. The cathode mixture according to 4, wherein the conductive additive is activated carbon. 6. The cathode composite according to any one of 1 to 5, wherein a solid electrolyte alteration parameter Δ (Δ=α×β) calculated from the ionic conductivity α of the sulfide solid electrolyte and the ionic resistance β of the cathode composite is smaller than 750. 7. A method for producing a cathode composite, comprising a step of mechanically mixing a sulfur-based active material and a sulfide solid electrolyte to form a composite, wherein the sulfide solid electrolyte is synthesized from a mixed raw material containing lithium (Li), phosphorus (P), and a halogen (X) including at least iodine (I), and the mixed raw material is lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ ) and lithium halide (LiX), the following formulas (1) and (2) are satisfied: 45≦[Li ２ S]×100 / ([Li ２ S] + [P ２ S ５ ])≦90 (1) 30≦[LiX]×100 / ([Li ２ S] + [P ２ S ５ ]+[LiX]) (2) (wherein, [Li ２ S] is Li ２ S molar ratio, [P ２ S ５ ]is P ２ S ５and [LiX] is the molar ratio of LiX.) 8. The mixed raw material contains lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ 9. The method according to 7, wherein the compound represented by the formula (1) [Li ２ S]×100 / ([Li ２ S] + [P ２ S ５ ]) is 74 or more and 76 or less. 10. The manufacturing method according to any of 7 to 9, wherein the sulfur-based active material contains elemental sulfur or a discharge product thereof. 11. The manufacturing method according to any of 7 to 10, wherein a sulfur-based active material-conductive additive composite material is formed from the sulfur-based active material and the conductive additive, and then mechanically mixed with the sulfide solid electrolyte. 12. A cathode mixture obtained by the manufacturing method according to any of 7 to 11. 13. A cathode comprising the cathode mixture according to any of 1 to 6 and 12. 14. A lithium ion battery comprising the cathode according to 13.

[0008] According to the present invention, it is possible to provide a positive electrode mixture that does not require heat treatment to restore lithium ion conductivity and that can provide a battery with excellent rate characteristics.

[0009] Hereinafter, embodiments of the present invention will be described. In this specification, the upper and lower limit values ​​of a range expressed as "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values.

[0010] 1. Cathode Composite A cathode composite according to one embodiment of the present invention includes a sulfur-based active material and a sulfide solid electrolyte. The sulfide solid electrolyte includes, as constituent elements, phosphorus (P) and a halogen (X) containing at least iodine (I), wherein the molar ratio (X / P) of the halogen (X) to the phosphorus (P) is 0.86 or more, and the molar ratio (I / P) of the iodine (I) to the phosphorus (P) is 0.10 or more.

[0011] In the cathode composite of this embodiment, the sulfide solid electrolyte exhibits sufficiently high lithium ion conductivity, and, compared to conventional cathode composites, deterioration of the sulfide solid electrolyte is suppressed even after mechanical mixing. This eliminates the need for heat treatment to restore lithium ion conductivity. Furthermore, a lithium ion battery having rate characteristics equal to or higher than those obtained when conventional cathode composites are used can be obtained. The components of this embodiment are described below.

[0012] (Sulfide Solid Electrolyte) The sulfide solid electrolyte used in the present application contains a predetermined amount of halogen (X) including at least iodine (I). The sulfide solid electrolyte is less susceptible to deterioration due to mechanical mixing. Therefore, heat treatment to restore lithium ion conductivity is not required.

[0013] In one embodiment, the molar ratio (X / P) is preferably 0.90 to 2.5, more preferably 1.00 to 2.00, and even more preferably 1.05 to 1.80. Examples of halogens other than iodine include fluorine, chlorine, and bromine. The halogen (X) may contain only iodine, or may consist of iodine and one other halogen. Preferably, the halogen (X) contains iodine and bromine.

[0014] The molar ratio (I / P) is preferably 0.50 to 2.00, more preferably 1.00 to 1.80.

[0015] In one embodiment, the sulfide solid electrolyte is preferably a solid electrolyte containing a glass (amorphous) component. The presence of the glass component can be confirmed by the presence of a broad peak (halo pattern) due to the amorphous component in X-ray diffraction (XRD) measurement. In the XRD measurement of the sulfide solid electrolyte, peaks due to the crystalline component and peaks due to the raw materials may be observed in part.

[0016] In one embodiment, the sulfide solid electrolyte preferably contains lithium (Li) as a constituent element. The molar ratio of lithium (Li) to phosphorus (P) (Li / P) is preferably 3.00 to 5.25, more preferably 3.50 to 5.20, and may be 4.00 to 5.00, or even 4.00 to 4.80.

[0017] In one embodiment, the molar ratio of sulfur (S) to phosphorus (P) (S / P) is preferably 3.0 to 4.4, more preferably 3.5 to 4.3, even more preferably 3.8 to 4.2, and even more preferably 3.9 to 4.1.

[0018] The types and molar ratios of the constituent elements of the sulfide solid electrolyte can be confirmed, for example, by an ICP atomic emission spectrometer. The molar ratio of the constituent elements of the sulfide solid electrolyte can be adjusted by controlling the raw material blending. The molar ratio of the constituent elements in the raw materials is approximately equal to the molar ratio of the constituent elements of the resulting sulfide solid electrolyte.

[0019] In one embodiment, the ionic conductivity of the sulfide solid electrolyte used is preferably 1.0 mS / cm or more, more preferably 1.5 mS / cm or more.

[0020] The sulfide solid electrolyte used in this embodiment can be produced, for example, by preparing starting materials for known lithium ion sulfide solid electrolytes so that the molar ratios of the constituent elements satisfy the above ranges, and mechanically mixing them.

[0021] As the starting material, a combination of two or more compounds or simple substances containing lithium, phosphorus, sulfur, and halogens including at least iodine as constituent elements can be used, and any compound or simple substance that exhibits ionic conductivity due to the metal atoms contained therein can be used without any particular limitation.

[0022] Examples of raw materials containing lithium (Li) include lithium sulfide (Li ２ S), lithium oxide (Li ２ O), lithium carbonate (Li ２ CO ３ Among these, lithium compounds are preferred, and lithium sulfide is more preferred.

[0023] The lithium sulfide can be used without any particular limitation, but high purity lithium sulfide is preferred. Lithium sulfide can be produced by the methods described in, for example, JP-A-7-330312, JP-A-9-283156, JP-A-2010-163356, and JP-A-2011-84438.

[0024] Specifically, lithium hydroxide and hydrogen sulfide are reacted in a hydrocarbon organic solvent at 70°C to 300°C to produce lithium hydrosulfide, and then this reaction solution is dehydrosulfided, thereby synthesizing lithium sulfide (JP 2010-163356 A).

[0025] Alternatively, lithium sulfide can be synthesized by reacting lithium hydroxide with hydrogen sulfide in an aqueous solvent at 10°C to 100°C to produce lithium hydrosulfide, and then dehydrosulfiding the reaction solution (JP 2011-84438 A).

[0026] Examples of raw materials containing phosphorus (P) include diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides, sodium phosphate (Na ３ P.O. ４ Among these, phosphorus sulfide is preferred, and diphosphorus pentasulfide (P ２ S ５ ) is more preferred. ２ S ５ The phosphorus compounds such as ammonium nitrate, ...

[0027] The raw material containing a halogen as a constituent element preferably contains, for example, a halogen compound represented by the following formula:

[0028] M ｌ -X ｍ In the formula, M represents sodium (Na), lithium (Li), boron (B), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), germanium (Ge), arsenic (As), selenium (Se), tin (Sn), antimony (Sb), tellurium (Te), lead (Pb), bismuth (Bi), or any of these elements bonded to an oxygen element or a sulfur element, and is preferably lithium (Li) or phosphorus (P), and more preferably lithium (Li).

[0029] X is a halogen element selected from fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0030] Furthermore, l is an integer of 1 or 2, and m is an integer of 1 to 10. When m is an integer of 2 to 10, that is, when there are multiple Xs, the Xs may be the same or different. For example, SiBrCl ３ In the formula, m is 4 and X is composed of two different elements, Br and Cl.

[0031] Specific examples of halogen compounds include sodium halides such as NaI, NaF, NaCl, and NaBr; lithium halides such as LiF, LiCl, LiBr, and LiI; and BCl. ３ , BBr ３ , B.I. ３ Boron halides such as AlF ３ , AlBr ３ , AlI ３ , AlCl ３ aluminum halides such as SiF ４ , SiCl ４ , SiCl ３ , Si ２ Cl ６ , SiBr ４ , SiBrCl ３ , SiBr ２ Cl ２ , SiI ４ Silicon halides such as PF ３ , P.F. ５ , PCl ３ , PCl ５ , POCl ３ , PBr ３ , POBr ３ , P.I. ３ , P ２ Cl ４ , P ２ I ４ Phosphorus halides such as SF ２ , SF ４ , SF ６ , S ２ F １０ , SC1 ２ , S ２ Cl ２ , S ２ Br２ sulfur halides such as GeF ４ , GeCl ４ , GeBr ４ , GeI ４ , GeF ２ , GeCl ２ , GeBr ２ , GeI ２ Germanium halides such as AsF ３ , AsCl ３ , AsBr ３ , AsI ３ , AsF ５ arsenic halides such as SeF ４ , SeF ６ , SeCl ２ , SeCl ４ , Se ２ Br ２ , SeBr ４ selenium halides such as SnF ４ , SnCl ４ , SnBr ４ , SnI ４ , SnF ２ , SnCl ２ , SnBr ２ , SnI ２ tin halides such as SbF ３ , SbCl ３ , SbBr ３ , SbI ３ , SbF ５ , SbCl ５ antimony halides such as TeF ４ , Te ２ F １０ , TeF ６ , TeCl ２ , TeCl ４ , TeBr ２ , TeBr ４ , TeI ４ Tellurium halides such as PbF ４ , PbCl ４ , PbF ２ , PbCl ２ , PbBr ２ , PbI ２ Lead halides such as BiF ３ , BiCl ３ , BiBr ３ , BiI３ and the like.

[0032] Among these, lithium halides such as lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), phosphorus pentachloride (PCl), ５ ), phosphorus trichloride (PCl ３ ), phosphorus pentabromide (PBr ５ ), phosphorus tribromide (PBr ３ ), and lithium halides such as LiCl, LiBr, and LiI, and PBr ３ is more preferred, lithium halides such as LiCl, LiBr and LiI are even more preferred, with LiI and LiBr being particularly preferred.

[0033] As the halogen compound, the iodine-containing compounds selected from the above compounds may be used alone or in combination of two or more.

[0034] In one embodiment, the mixed raw material is lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ When it is assumed that the mixture is a mixture of lithium fluoride (LiX) and lithium halide (LiX), the following formulas (1) and (2) are satisfied: 45≦[Li ２ S]×100 / ([Li ２ S] + [P ２ S ５ ])≦90 (1) 30≦[LiX]×100 / ([Li ２ S] + [P ２ S ５ ]+[LiX]) (2) (wherein, [Li ２ S] is Li ２ S molar ratio, [P ２ S ５ ]is P ２ S ５ and [LiX] is the molar ratio of LiX.

[0035] The above formula (1) [Li ２ S]×100 / ([Li ２ S] + [P ２ S ５]) is preferably 70 or more and 80 or less, more preferably 72 or more and 78 or less, and particularly preferably 74 or more and 76 or less. ２ S] + [P ２ S ５ ]+[LiX]) is preferably 30 or more and 60 or less, and more preferably 35 or more and 55 or less.

[0036] In one embodiment, the mixed raw material of the sulfide solid electrolyte is lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ The lithium iodide (LiI) is a mixture of lithium iodide (LiI) and any lithium halide (LiX: X is F, Cl, or Br). The molar ratio of iodine (I) to phosphorus (P) (I / P) is preferably 0.10 or more.

[0037] In this embodiment, the raw materials are subjected to a mechanical stress to react with each other to produce a sulfide solid electrolyte. Here, "applying a mechanical stress" means mechanically applying a shear force, an impact force, or the like. Examples of means for applying the mechanical stress include a pulverizer such as a planetary ball mill, a vibration mill, or a tumbling mill, and a kneader. The raw material powder is pulverized and mixed by applying a strong mechanical stress until at least a portion of the raw material powder can no longer maintain its crystallinity.

[0038] As for the conditions for grinding and mixing, for example, when a planetary ball mill is used as the grinder, the rotation speed may be set to several tens to several hundreds of revolutions per minute, and processing may be performed for 0.5 to 100 hours. More specifically, in the case of the planetary ball mill (manufactured by Fritsch: Model No. P-7) used in the examples of the present application, the rotation speed of the planetary ball mill is preferably 100 rpm or more and 500 rpm or less, and more preferably 150 rpm or more and 400 rpm or less. The temperature during grinding may be room temperature, in which case external cooling may not be performed, and for example, a 5-minute operation suspension period may be provided every hour. Note that, as long as the conditions are such that crystallization does not occur during grinding, grinding may be performed while cooling without an operation suspension period. For example, when zirconia balls are used as grinding media, their diameter is preferably 0.2 to 20 mm.

[0039] (Sulfur-based active material)

[0040] 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. The sulfur is not particularly limited, but 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.

[0041] In addition, the elemental sulfur is partially or entirely converted into discharge products during the battery reaction. Therefore, in one embodiment, the discharge products of elemental sulfur are present in the positive electrode composite (positive electrode). The discharge products of elemental sulfur include Li in a fully discharged state. ２ S and its intermediate stage lithium polysulfide Li ２ S ２ , Li ２ S ４ , Li ２ S ６ , Li ２ S ８ etc.

[0042] (Conductive additive) In one embodiment of the present invention, the positive electrode composite preferably further contains a conductive additive. The conductive additive may be any material that is electronically conductive. The conductive additive preferably has a plurality of pores. A carbon material having pores is particularly preferred. Carbon materials have high conductivity and are lighter than other conductive materials, so the output density and capacity per weight of the battery can be increased.

[0043] The specific surface area of ​​the conductive additive is 0.1 m ２ / g or more 5000m ２ / g or less, and more preferably 1m ２ / g or more 4000m ２ / g or less, and more preferably 1m ２ / g or more 3000m ２ / g or less, and most preferably 10m ２ / g or more 3000m ２ / g or less.

[0044] The pore volume of the conductive additive is preferably 0.1 cc / g or more and 5.0 cc / g or less. The pores of the conductive additive preferably have an average diameter of 0.1 nm or more and 40 nm or less, more preferably 0.5 nm or more and 40 nm or less, even more preferably 0.5 nm or more and 20 nm or less, and most preferably 1 nm or more and 20 nm or less.

[0045] The specific surface area, pore volume, and pore diameter of the conductive additive can be determined using a nitrogen adsorption isotherm obtained by adsorbing nitrogen gas to the conductive additive at liquid nitrogen temperature. Specifically, the specific surface area can be calculated using the nitrogen adsorption isotherm by the Brenauer-Emmet-Telle (BET) multipoint method. Furthermore, the pore volume and pore diameter can be determined using the nitrogen adsorption isotherm by the Barret-Joyner-Halenda (BJH) method. As a measuring device, for example, a specific surface area and pore distribution measuring device (Autosorb-3) manufactured by Quantacrome can be used for measurement.

[0046] The carbon material is not particularly limited, but examples thereof include carbon black such as ketjen black, acetylene black, denka black, thermal black, and channel black, mesoporous carbon, activated carbon, amorphous carbon, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon nanohorns. Examples of conductive carbon materials include fullerene, carbon fiber, natural graphite, artificial graphite, graphene, graphene oxide, and reduced graphene oxide. Of these, activated carbon is preferred. These may be used alone or in combination of two or more. Composites of these may also be used.

[0047] In one embodiment, the positive electrode composite may or may not contain components other than the sulfur-based active material, the sulfide solid electrolyte, and the conductive additive. The other components are not particularly limited, and examples thereof include a binder, a solvent, a dispersant, and the like.

[0048] In one embodiment, the solid electrolyte alteration parameter Δ (Δ = α × β) calculated from the ionic conductivity α of the sulfide solid electrolyte and the ionic resistance β of the positive electrode composite is less than 750. The larger the solid electrolyte alteration parameter Δ, the lower the retention rate of the ionic conductivity of the solid electrolyte. In other words, the greater the degree of alteration of the solid electrolyte occurring during the production of the positive electrode composite. In the present invention, when the solid electrolyte alteration parameter Δ of the positive electrode composite is 750 or more, the solid electrolyte is evaluated as having altered. The solid electrolyte alteration parameter Δ is preferably 600 or less, more preferably 500 or less, and even more preferably 250 or less.

[0049] The ionic conductivity α of the sulfide solid electrolyte can be measured by an AC impedance method. Details of the measurement method will be described later. The ionic resistance β of the positive electrode composite can be measured by preparing an ionic resistance measurement cell containing the positive electrode composite and a solid electrolyte and applying the AC impedance method to the ionic resistance measurement cell. Details of the measurement method will be described later. The positive electrode composite according to this embodiment can be produced, for example, by the method described below.

[0050] 2. Method for Producing Cathode Composite A method for producing a cathode composite according to one embodiment of the present invention includes a step of mechanically mixing the above-described sulfur-based active material and a sulfide solid electrolyte that satisfies the compositions represented by the above-described formulas (1) and (2) to form a composite.

[0051] In one embodiment, the sulfur-based active material-conductive additive composite material may be formed from the above-described sulfur-based active material and conductive additive, and then the sulfide solid electrolyte and the sulfur-based active material-conductive additive composite material may be mechanically mixed.

[0052] When the sulfur-based active material is elemental sulfur, in the step of forming the sulfur-conductive additive composite material, for example, the conductive additive and elemental sulfur are mixed and sealed, and then the mixture is heated to melt the elemental sulfur and impregnate the elemental sulfur into the pores, thereby forming the sulfur-conductive additive composite material.

[0053] The mixing ratio of elemental sulfur and conductive additive can be adjusted appropriately according to the materials used. For example, the mass ratio (S / C) of elemental sulfur (S) to conductive additive (C) in the sulfur-based active material-conductive additive composite material is 0.5 or more. The higher the ratio of elemental sulfur in the positive electrode composite, the higher the expected improvement in the energy density of the battery, assuming the same sulfur utilization rate. On the other hand, since it becomes difficult to provide sufficient electronic conductivity in the positive electrode, the mass ratio (S / C) is preferably 10 or less.

[0054] In one embodiment, the mixture of elemental sulfur and conductive additive is heated in a sealed state at a temperature equal to or higher than the melting point of elemental sulfur (approximately 115°C). The heating temperature is adjusted depending on the carbon material and elemental sulfur, but is preferably 130°C or higher, and more preferably 150°C or higher. The upper limit of the heating temperature is a temperature equal to or lower than the boiling point of elemental sulfur (approximately 445°C). The heating time is preferably 0.1 to 24 hours. A sulfur-conductive additive composite material is obtained by cooling after heating. If necessary, a pulverization step may be carried out after cooling.

[0055] In this embodiment, a sulfur-based active material or a sulfur-based active material-conductive additive composite material and a sulfide solid electrolyte are mechanically mixed to form a positive electrode composite. Here, "mechanical mixing" refers to the mechanical application of shear force, impact force, or the like. Examples of mechanical mixing methods include a pulverizer such as a planetary ball mill, a vibration mill, or a tumbling mill, and a kneader. This process may pulverize the sulfur-based active material, the sulfur-based active material-conductive additive composite material, and the sulfide solid electrolyte.

[0056] For example, in the case of a planetary ball mill (manufactured by Fritsch: Model No. P-7), the rotation speed of the planetary ball mill is preferably 100 rpm or more and 500 rpm or less, and more preferably 150 rpm or more and 400 rpm or less. When zirconia balls are used as the grinding media, their diameter is preferably 0.2 to 20 mm.

[0057] The content of the sulfide solid electrolyte is preferably 5 to 200 parts by mass, and more preferably 10 to 120 parts by mass, based on 100 parts by mass of the sulfur-based active material or sulfur-based active material-conductive additive composite material. If the content of the solid electrolyte is 5 parts by mass or less, it becomes difficult to obtain sufficient ion conduction, and if it is 200 parts by mass or more, the content of the active material decreases, making it difficult to improve the energy density.

[0058] 3. Positive Electrode and Lithium-Ion Battery A positive electrode or lithium-ion battery according to one embodiment of the present invention includes the above-described positive electrode 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 positive electrode composite of the present invention, an all-solid-state lithium-ion battery with good rate characteristics can be manufactured.

[0059] An all-solid-state lithium-ion battery mainly comprises a positive electrode layer, a negative electrode layer, and an electrolyte layer, and the positive electrode composite of the present invention is suitable as a constituent material of the positive electrode layer. The negative electrode layer and the electrolyte layer can be manufactured by known methods. In addition to the positive electrode layer, the negative electrode layer, and the electrolyte layer, a current collector is preferably used, and a known current collector is also used. The solid electrolyte is not particularly limited, and a known solid electrolyte can be used.

[0060] The present invention will be specifically described below based on examples, but the embodiments of the present invention are not limited to the examples.

[0061] Example 1 (1) Preparation of sulfur-based active material-conductive additive composite material Activated carbon (MSC-30 manufactured by Kansai Coke Chemical Industries, Ltd.) and sulfur were placed in a glass bottle in a mass ratio of 3:7, and the bottle was sealed in an SUS tubular container. The bottle was heated in an electric furnace at 150°C for 6 hours and then at 300°C for 2.75 hours to obtain a sulfur-based active material-conductive additive composite material containing activated carbon and sulfur.

[0062] (2) Preparation of sulfide solid electrolyte 0.2309 g of lithium sulfide, 0.3719 g of diphosphorus pentasulfide, and 0.5972 g of lithium iodide were used as raw materials. The mixed raw materials and ten zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. A planetary ball mill (manufactured by Fritsch, model number P-7) was used to mix the materials at a rotation speed of 370 rpm for 40 hours to obtain a sulfide solid electrolyte.

[0063] (3) Preparation of Positive Electrode Composite 0.45 g of the sulfur-based active material-conductive additive composite and 0.45 g of the above solid electrolyte were placed in a 45 mL zirconia pot together with ten zirconia balls with a diameter of 10 mm and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), mixing was carried out at a rotation speed of 370 rpm and room temperature for 20 hours to obtain a positive electrode composite.

[0064] Example 2 A positive electrode composite was obtained in the same manner as in Example 1 (2) except that in the production of the sulfide solid electrolyte of Example 1 (2), the raw materials were changed to 0.2553 g of lithium sulfide, 0.4112 g of diphosphorus pentasulfide, and 0.5334 g of lithium iodide.

[0065] Example 3 A positive electrode composite was obtained in the same manner as in Example 1, except that in the production of the sulfide solid electrolyte of Example 1 (2), the raw materials were changed to 0.2360 g of lithium sulfide, 0.3802 g of diphosphorus pentasulfide, 0.5342 g of lithium iodide, and 0.0495 g of lithium bromide.

[0066] Comparative Example 1 A positive electrode composite was obtained in the same manner as in Example 1, except that a sulfide solid electrolyte prepared by the following manufacturing method was used. 0.4127 g of lithium sulfide, 0.6655 g of diphosphorus pentasulfide, 0.2137 g of lithium iodide, and 0.2080 g of lithium bromide were used as raw materials. The mixed raw materials and ten 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 at a rotation speed of 370 rpm for 40 hours to obtain a glassy treated product. The treated product was heated at 195°C for 3 hours to produce a sulfide solid electrolyte.

[0067] Comparative Example 2 A positive electrode composite was obtained in the same manner as in Example 1, except that a sulfide solid electrolyte prepared by the following manufacturing method was used. 0.3830 g of lithium sulfide and 0.6170 g of diphosphorus pentasulfide were used as raw materials. The mixed raw materials 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 at a rotation speed of 370 rpm for 40 hours. 0.8053 g of the resulting processed material, 0.1947 g of lithium borohydride, and 100 g of zirconia balls with a diameter of 4 mm were placed in a 45 mL zirconia pot and sealed. The mixture was mixed for 15 hours at a rotation speed of 510 rpm using a planetary ball mill to obtain a sulfide solid electrolyte.

[0068] Comparative Example 3 A positive electrode composite was obtained in the same manner as in Example 1, except that a sulfide solid electrolyte prepared by the following manufacturing method was used. 0.4129 g of lithium sulfide, 0.5875 g of diphosphorus pentasulfide, 0.2241 g of lithium chloride, and 0.2755 g of lithium bromide were used as raw materials. The mixed raw materials and ten 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 for 40 hours at a rotation speed of 370 rpm. The treated material was heated at 430°C for 8 hours to obtain a sulfide solid electrolyte.

[0069] Comparative Example 4 A positive electrode composite was obtained in the same manner as in Example 1, except that a sulfide solid electrolyte prepared by the following manufacturing method was used. 0.3830 g of lithium sulfide and 0.6170 g of diphosphorus pentasulfide were used as raw materials. The mixed raw materials 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), mixing was performed for 40 hours at a rotation speed of 370 rpm. 0.8936 g of the resulting processed material, 0.1064 g of lithium borohydride, and 100 g of zirconia balls with a diameter of 4 mm were placed in a 45 mL zirconia pot and sealed, and mixed for 15 hours at a rotation speed of 370 rpm using a planetary ball mill to obtain a sulfide solid electrolyte.

[0070] The sulfide solid electrolytes prepared in each example were evaluated as follows: (1) Ion conductivity of solid electrolyte A 10 mm diameter (cross-sectional area S: 0.785 cm) sample was taken from the solid electrolyte. ２ ), and a height (L) of 0.1 to 0.5 cm were molded into a circular pellet to prepare a sample. Electrode terminals were attached to the top and bottom of the sample, and measurements were made at 25°C using an AC impedance method (frequency range: 1 MHz to 1 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high-frequency region was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following formula: R = ρ (L / S) σ = 1 / ρ

[0071] (2) Ion resistance of positive electrode composite - Preparation of solid electrolyte A 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) 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.

[0072] Preparation of an ionic resistance measurement cell 100 mg of the solid electrolyte A prepared by the above procedure was pressure-molded in a Macol cylinder with a diameter of 10 mm. 20 mg of positive electrode composite powder was added to the pressure-pressed surface, and the mixture was again pressure-molded. 20 mg of positive electrode composite powder was added to the pressure-pressed surface opposite the positive electrode composite, and pressure was applied to prepare an ionic resistance measurement cell.

[0073] Measurement of Ion Resistance Using the ion resistance measurement cell prepared by the above procedure, AC impedance was measured under the following conditions: Frequency range: 1 MHz-1 mHz Amplitude: 10 mV

[0074] (3) Method for Calculating Solid Electrolyte Alteration Parameter The solid electrolyte alteration parameter Δ was calculated as follows: (Solid electrolyte alteration parameter Δ) = [Solid electrolyte ionic conductivity α] × [Positive electrode composite ionic resistance β] When the solid electrolyte alteration parameter Δ was 750 or more, it was determined that the solid electrolyte had altered.

[0075] (4) Evaluation of Battery Characteristics 100 mg of the solid electrolyte A prepared in (2) above was pressure-molded in a Macol cylinder with a diameter of 10 mm. The cathode composite powder prepared in the Examples and Comparative Examples was added to the pressurized surface so that the sulfur content was 1.75 mg, and the mixture was again pressure-molded. Three sheets of indium foil and two sheets of lithium foil were alternately stacked and placed on the pressurized surface opposite the cathode composite, and then pressed to prepare an all-solid-state lithium-ion battery. A constant current charge / discharge test was performed on the resulting battery. The voltage range for the constant current charge / discharge test was set to 0.8-2.2 V, and the current value was set under the conditions in Table 1 below. The discharge capacity at 0.5 C (per sulfur mass) at the seventh cycle under the following conditions was measured.

[0076]

[0077] (5) Properties of the Solid Electrolyte The solid electrolyte was analyzed by powder X-ray diffraction (XRD) measurement. If the spectrum obtained by the XRD measurement below had no peaks or only peaks derived from the raw materials, the solid electrolyte was determined to be amorphous. On the other hand, if there was a peak derived from the lithium ion conductive crystal structure, the solid electrolyte was determined to be crystalline. In the sulfide solid electrolyte of Comparative Example 1, a thiolicon region II crystal structure was observed, and in the sulfide solid electrolytes of Comparative Examples 2 and 3, an argyrodite crystal structure was observed.

[0078] XRD Measurement: The powder to be measured was filled into a groove 20 mm in diameter and 0.2 mm deep, and leveled with glass to prepare a sample. The sample was sealed with Kapton film for XRD to prevent it from coming into contact with air, and measurements were performed using a powder X-ray diffraction measurement device D2 PHASER manufactured by BRUKER Co., Ltd. under the following measurement conditions.

[0079] [Measurement conditions] Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: focusing method Slit configuration: Soller slit 4° (on both the incident and receiving sides), divergence slit 1 mm, Kβ filter (Ni plate 0.5%), air scatter screen 3 mm) Detector: semiconductor detector Measurement range: 2θ = 10-60 deg Step width, scan speed: 0.05 deg, 0.05 deg / sec

[0080] For each of the above Examples and Comparative Examples, the raw material compositions of the sulfide solid electrolytes are shown in Table 2. The raw material compositions of the sulfide solid electrolytes are expressed by formulas (1) and (2) in Table 3. The molar ratios of the raw material constituent elements to phosphorus (P) are shown in Table 4. The evaluation results of the sulfide solid electrolytes, positive electrode composites, and batteries are shown in Table 5.

[0081]

[0082]

[0083]

[0084]

[0085] Tables 2 to 5 show that the cathode composites produced in Examples 1 to 3, which were obtained by mechanically mixing the sulfide solid electrolyte and the sulfur-based active material-conductive additive composite, exhibited reduced degradation of the solid electrolyte. It can be seen that all-solid-state lithium-ion batteries containing this solid electrolyte as a cathode composite exhibited excellent rate characteristics (discharge capacity). On the other hand, the cathode composites containing the sulfide solid electrolyte of Comparative Examples 1 to 4 exhibited higher ionic conductivity of the solid electrolyte than those of Examples 1 to 3, but also exhibited higher ionic resistance of the cathode composite than those of Examples 1 to 3, resulting in a higher solid electrolyte degradation parameter Δ. Furthermore, when the cathode composites of Comparative Examples 1 to 4 were used in lithium-ion batteries, the discharge capacity (rate characteristics) was lower than that of Examples 1 to 3. Therefore, it is presumed that the solid electrolyte in the cathode composites of Comparative Examples 1 to 4 was altered by mechanical mixing.

[0086] The positive electrode composite of the present invention is suitable for use as a positive electrode for a lithium ion battery. The lithium ion battery of the present invention is also suitable for use in, for example, information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and vehicles such as electric vehicles.

[0087] 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. It contains a sulfur-based active material and a sulfide solid electrolyte, The sulfide solid electrolyte comprises phosphorus (P) and a halogen (X) containing at least iodine (I) as constituent elements. The molar ratio (X / P) of the halogen (X) to the phosphorus (P) is 0.86 or greater. A positive electrode composite material in which the molar ratio (I / P) of iodine (I) to phosphorus (P) is 0.10 or greater.

2. The sulfide solid electrolyte contains lithium (Li) as a constituent element. The positive electrode composite material according to claim 1, wherein the molar ratio (Li / P) of lithium (Li) to phosphorus (P) is 2.00 or more.

3. The positive electrode mixture according to claim 1, wherein the sulfur-based active material includes elemental sulfur or its discharge product.

4. The positive electrode composite material according to claim 1, further comprising a conductive additive.

5. The positive electrode composite material according to claim 4, wherein the conductive additive is activated carbon.

6. The positive electrode mixture according to claim 1, wherein the solid electrolyte alteration parameter Δ (Δ = α × β), calculated from the ionic conductivity α of the sulfide solid electrolyte and the ionic resistance β of the positive electrode mixture, is less than 750.

7. A method for producing a positive electrode composite, comprising the step of mechanically mixing and compounding a sulfur-based active material and a sulfide solid electrolyte, The sulfide solid electrolyte is synthesized from a mixed raw material containing lithium (Li), phosphorus (P), and a halogen (X) containing at least iodine (I). The aforementioned mixed raw materials are lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ A manufacturing method that satisfies the following formulas (1) and (2), assuming that the product is a mixture of ) and lithium halide (LiX). 45≦[L] ２ S]×100 / ([L+ ２ S]+[P ２ S ５ ])≦90 (1) 30≦[LiX]×100 / ([Li ２ S]+[P ２ S ５ ]+[LiX]) (2) (In the formula, [Li ２ S] is Li ２ The molar ratio of S is [P ２ S ５ ] is P ２ S ５ This is the molar ratio, and [LiX] is the molar ratio of LiX.

8. The aforementioned mixed raw materials include lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ The manufacturing method according to claim 7, wherein the mixture is of ) and lithium halide (LiX).

9. The above formula (1) [Li ２ S]×100 / ([Li ２ S] + P ２ S ５ The manufacturing method according to claim 7, wherein ) is 74 or more and 76 or less.

10. The manufacturing method according to claim 7, wherein the sulfur-based active material includes elemental sulfur or its discharge product.

11. The manufacturing method according to claim 7, comprising forming a sulfur-based active material-conductive additive composite material from the sulfur-based active material and a conductive additive, and then mechanically mixing it with the sulfide solid electrolyte.

12. A positive electrode composite obtained by the manufacturing method described in claim 7.

13. A positive electrode comprising the positive electrode composite material according to any one of claims 1 to 6 and 12.

14. A lithium-ion battery comprising the positive electrode described in claim 13.