Positive electrode mixture, method for manufacturing positive electrode mixture, and lithium ion battery

Abstract

This positive electrode mixture comprises a sulfur-based active material and a solid electrolyte, and in powder x-ray diffraction using CuKα radiation has a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 45.2 ± 1.0°, wherein the half width of the diffraction peak A is 0.25° or more.

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 manufacturing the positive electrode composite, and a lithium ion battery. Specifically, the present invention relates to a positive electrode composite that can reduce ionic resistance, a method for manufacturing the positive electrode composite, and a lithium ion battery.

[0002] In sulfur-based positive electrode composites used in lithium-ion batteries and the like, the reaction of insulating sulfur can be sufficiently induced by compounding sulfur with a conductive additive and a solid electrolyte (Patent Documents 1 to 3).

[0003] JP 2014-011033 A JP 2020-161288 A International Publication No. 2022 / 080435

[0004] However, it has been found that there is room for further improvement in the conventional techniques including those described in Patent Documents 1 to 3 in terms of reducing the ionic resistance of the positive electrode mixture.

[0005] An object of the present invention is to provide a positive electrode mixture capable of reducing ionic resistance, a method for manufacturing the positive electrode mixture, and a lithium ion battery.

[0006] As a result of extensive research, the inventors have found that a positive electrode composite satisfying certain conditions can reduce ionic resistance, and have thus completed the present invention. According to the present invention, the following positive electrode composites and the like can be provided. 1. A positive electrode composite comprising a sulfur-based active material and a solid electrolyte, which has, in powder X-ray diffraction using CuKα radiation, a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 45.2 ± 1.0°, and the half-width of the diffraction peak A is 0.25° or more. 2. A left-right asymmetry parameter ε' of the diffraction peak B is 1.50 × 10 ４The cathode mixture according to 1, wherein the cathode mixture is any one of the above. 3. The cathode mixture according to 1 or 2, further comprising a conductive additive. 4. The cathode mixture according to 3, wherein the conductive additive has pores with a pore diameter of less than 5 nm. 5. The cathode mixture according to 3 or 4, wherein the conductive additive comprises one or more selected from the group consisting of activated carbon and carbon black. 6. The cathode mixture according to any one of 1 to 5, obtained by heat-treating a cathode mixture precursor obtained by mechanically mixing a sulfur-based active material and a solid electrolyte having a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 45.2 ± 1.0° in powder X-ray diffraction using CuKα rays. 7. The cathode mixture according to 6, wherein the heat treatment is performed at a temperature of 160 to 280°C. 8. 9. A method for producing a positive electrode composite, comprising: mechanically mixing a sulfur-based active material with a solid electrolyte having a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 45.2 ± 1.0° in powder X-ray diffraction using CuKα radiation, to obtain a positive electrode composite precursor; and heat-treating the positive electrode composite precursor to obtain a positive electrode composite, wherein the heat treatment is performed at a temperature of 160 to 280° C. 9. A lithium-ion battery comprising the positive electrode composite according to any one of 1 to 7.

[0007] According to the present invention, it is possible to provide a positive electrode composite that can reduce ionic resistance, a method for manufacturing the positive electrode composite, and a lithium ion battery.

[0008] 1 is a diagram showing the results of powder X-ray diffraction (XRD), an enlarged view of the high-angle side of the XRD of FIG. 1, and a diagram showing the results of XRD of Example 3.

[0009] The cathode composite, the manufacturing method for the cathode composite, and the lithium-ion battery of the present invention will be described in detail below. In this specification, "x to y" represents a numerical range of "x or more and y or less." The upper and lower limits of the numerical ranges can be combined in any combination.

[0010] 1. Cathode Composite A cathode composite according to one embodiment of the present invention contains a sulfur-based active material and a solid electrolyte, and in powder X-ray diffraction using CuKα radiation, has a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 45.2 ± 1.0°, with the half-width of the diffraction peak A being 0.25° or greater. The cathode composite according to this embodiment has the effect of reducing ionic resistance.

[0011] A cathode composite such as this embodiment could not be produced by conventional techniques. That is, when a method of adding a solid electrolyte to a sulfur-carbon composite and mechanically mixing it by applying strong energy was used, the crystallinity of the solid electrolyte was reduced by the mechanical mixing, and Li ＋ The conductivity decreases, resulting in an increase in ionic resistance. In contrast, by performing a heat treatment under specific temperature conditions (described in detail below) after mechanical mixing, the solid electrolyte can be endowed with characteristic crystallinity that contributes to a decrease in ionic resistance. Such crystallinity can be imparted as a result of the formation of a new crystalline phase with a slightly different lattice constant in addition to the original crystalline phase. The presence of these crystalline phases results in the half-width of the aforementioned diffraction peak A being 0.25° or more, and the left-right asymmetry parameter ε' of the diffraction peak B, described below, being preferably 1.50×10 ４ That's all.

[0012] Powder X-ray diffraction using CuKα radiation is performed by the method described in the Examples. The half-width of diffraction peak A is a value obtained by subtracting an instrument constant, and is specifically calculated by the method described in the Examples.

[0013] In one embodiment, the half width of the diffraction peak A is 0.25° or more, 0.26° or more, 0.27° or more, 0.28° or more, 0.29° or more, 0.30° or more, 0.31° or more, or 0.32° or more. The upper limit is not particularly limited, and is, for example, 2.0° or less.

[0014] In one embodiment, the left-right asymmetry parameter ε′ of the diffraction peak B is 1.50×10 ４ This is the end of the description. As a result, the effects of the present invention are more significantly exhibited. The left-right asymmetry parameter ε′ of the diffraction peak B is calculated by the method described in the Examples.

[0015] In one embodiment, the left-right asymmetry parameter ε′ of the diffraction peak B is 1.50×10 ４ That's it, 2.00 x 10 ４ That's it, 3.00 x 10 ４ That's it, 4.00 x 10 ４ or more or 5.00 x 10 ４ The upper limit is not particularly limited, and is, for example, 5.00 × 10 ５ The following is the result.

[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. 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.

[0017] The positive electrode composite may contain a solid electrolyte having a diffraction peak A at 2θ=25.6±0.5° and a diffraction peak B at 2θ=45.2±1.0° in powder X-ray diffraction using CuKα radiation. Examples of such a solid electrolyte include a solid electrolyte having an argyrodite-type crystal structure. Examples of the argyrodite-type crystal structure include Li 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 S６ (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). However, a solid electrolyte containing the above-mentioned argyrodite-type crystal structure alone as a crystal structure and a positive electrode composite obtained by mechanically mixing the solid electrolyte do not satisfy the condition that the half width of diffraction peak A is 0.25° or more, and the left-right asymmetry parameter ε' of diffraction peak B is 1.50 × 10 ４ As described above, these conditions are met by heat treatment under specific temperature conditions after mechanical mixing, which results in the generation of a new crystalline phase at a slightly shifted position in addition to the original crystalline phase.

[0018] (Conductive additive) In one embodiment, the positive electrode mixture further contains a conductive additive. In one embodiment, the conductive additive is a carbon material. The conductive additive, which is a carbon material, 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 unit weight of the battery can be increased. 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 ２The 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.

[0019] 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.

[0020] 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), carbon nanohorns, fullerenes, carbon fibers, natural graphite, artificial graphite, graphene, graphene oxide, and reduced graphene oxide. These may be used alone or in combination of two or more. Composites of these may also be used.

[0021] Mesoporous carbon is a carbon material having two-dimensional or three-dimensional pores, which can be obtained by the production method described in the following documents: S. J. Sang, S. H. Joo, R. Ryoo, et., J. Am. Chem. Soc., 122 (2000) 10712-10713, and T. Yokoi, Y. Sakamoto, O. Terasaki, et., J. Am. Chem. Soc., 128 (2006) 13664-13665.

[0022] In one embodiment, the conductive additive has pores with a pore diameter of less than 5 nm. In one embodiment, the conductive additive does not have pores with a pore diameter of 5 nm or more. The pore diameter is a value measured by nitrogen adsorption / desorption measurement. In one embodiment, the conductive additive includes one or more selected from the group consisting of activated carbon and carbon black. In one embodiment, the conductive additive does not include a "carbon replica having a three-dimensional honeycomb structure (closed cell structure) and having pores with a pore diameter of 5 nm or more and 20 nm or less."

[0023] In one embodiment, the positive electrode composite may or may not contain components other than the sulfur-based active material, the 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.

[0024] In the positive electrode composite, the contents of the sulfur-based active material, solid electrolyte, and conductive additive are not particularly limited. In one embodiment, the content of the sulfur-based active material is 40 to 350 parts by mass per 100 parts by mass of the solid electrolyte. When the positive electrode composite contains a conductive additive, the mass ratio of the sulfur-based active material to the conductive additive (sulfur-based active material:conductive additive) is 10:90 to 95:5, preferably 30 to 70:90 to 10. In one embodiment, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, 99.5% by mass or more, or substantially 100% by mass of the positive electrode composite is the sulfur-based active material and solid electrolyte, or the sulfur-based active material, solid electrolyte, and conductive additive. Note that "substantially 100% by mass" may include inevitable impurities.

[0025] In one embodiment, the positive electrode composite is obtained by heat-treating a positive electrode composite precursor obtained by mechanically mixing a sulfur-based active material and a solid electrolyte having a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 45.2 ± 1.0° in powder X-ray diffraction using CuKα radiation. In one embodiment, the heat treatment temperature is 160 to 280°C. The following description of the method for producing a positive electrode composite according to one aspect of the present invention is incorporated herein by reference for these embodiments.

[0026] 2. Manufacturing Method of Cathode Composite A manufacturing method of a cathode composite according to one embodiment of the present invention includes mechanically mixing a sulfur-based active material with a solid electrolyte having a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 45.2 ± 1.0° in powder X-ray diffraction using CuKα radiation to obtain a cathode composite precursor, and heat-treating the cathode composite precursor to obtain a cathode composite, wherein the heat-treatment temperature is 160 to 280°C. This manufacturing method of a cathode composite according to this embodiment can reduce the ionic resistance of the resulting cathode composite. That is, by performing heat treatment under specific temperature conditions of 160 to 280°C after mechanical mixing, the solid electrolyte can be imparted with characteristic crystallinity that contributes to reducing ionic resistance. Such crystallinity can be imparted as a result of the generation of a new crystal phase with a slightly different lattice constant in addition to the original crystal phase. In this manner, the cathode composite according to the above-described embodiment of the present invention can be manufactured. If the heat treatment temperature is less than 160° C., the generation of new crystalline phases is insufficient, and the ionic resistance is not reduced sufficiently. If the heat treatment temperature exceeds 280° C., the original crystalline phases decompose, and an impurity phase (2θ=29°) is generated, making the material unsuitable for use as a positive electrode composite.

[0027] Examples of mixing devices used in mechanical mixing include planetary ball mills, tumbling mills, bead mills, Filmics, Nauta mixers, tornado mixers, twin-screw extruders, multi-screw rollers, and solid-phase shear kneaders.

[0028] In one embodiment, the heat treatment temperature may be 160°C or higher, 165°C or higher, 170°C or higher, 175°C or higher, 180°C or higher, or 185°C or higher, and may be 280°C or lower, 270°C or lower, 260°C or lower, 250°C or lower, 240°C or lower, 230°C or lower, 220°C or lower, 215°C or lower, 210°C or lower, 205°C or lower, 200°C or lower, or 195°C or lower. From the viewpoint of more significantly reducing the ionic resistance of the positive electrode composite, the heat treatment temperature is preferably close to 190°C within the above-mentioned range. In the above description of the heat treatment temperature, "X°C or lower" means that heating is not performed at a temperature exceeding X°C.

[0029] The heat treatment time is not particularly limited, but it is preferable to heat for 30 minutes or more, 60 minutes or more, or 90 minutes or more in the above-mentioned temperature range. The upper limit is not particularly limited, and is, for example, 20 hours or less or 10 hours or less.

[0030] The sulfur-based active material may be the same as that described for the cathode composite according to one embodiment of the present invention. The solid electrolyte used has a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 45.2 ± 1.0° in powder X-ray diffraction using CuKα radiation. Examples of such a solid electrolyte include the solid electrolyte having an argyrodite-type crystal structure described for the cathode composite according to one embodiment of the present invention.

[0031] The method for producing a solid electrolyte having an argyrodite-type crystal structure is not particularly limited, and any known method can be used. The raw material mixture is more preferably a combination of lithium sulfide, phosphorus sulfide, and lithium halide, and Li ２ S and P ２ S ５ It is more preferable to use a combination of LiCl and / or LiBr. For example, as a raw material for the argyrodite-type solid electrolyte, ２ S, P ２ S ５ When LiCl and LiBr are used, the molar ratio of the input raw materials is ２ S:P ２ S ５ : The total of LiCl and LiBr = 30 to 60: 10 to 25: 15 to 50.

[0032] A solid electrolyte containing an argyrodite-type crystal structure can be produced by thoroughly mixing the raw material mixture using, for example, a mortar, a ball mill, a vibration mill, a tumbling mill, or a kneader, followed by heat treatment. Mixing is preferably performed using a kneader because it allows continuous processing in a short time. The kneader is not particularly limited, but a multi-shaft kneader equipped with two or more shafts is preferred. During this mixing, the raw material mixture may be reacted to form a glass.

[0033] The heat treatment temperature is preferably 350 to 480°C, more preferably 360 to 460°C, and particularly preferably 380 to 450°C. The heat treatment time varies depending on the composition and temperature, but may be adjusted, for example, within a range of 10 minutes to 48 hours. The heat treatment atmosphere is not particularly limited, but is preferably an inert gas atmosphere such as nitrogen or argon, rather than a hydrogen sulfide stream.

[0034] The shape of the solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) is the average particle size (D ５０ ) and the range of 0.01 μm to 500 μm, or 0.1 to 200 μm, for example, can be exemplified.

[0035] In one embodiment, the sulfur-based active material to be mechanically mixed is pre-composited with a conductive additive. The conductive additive may be any of those described for the positive electrode composite according to one aspect of the present invention. For example, prior to mechanical mixing, the sulfur-based active material can be composited with the conductive additive by heating the sulfur-based active material together with the conductive additive. The heating temperature is not particularly limited, and is, for example, 120 to 350°C. The mass ratio of the sulfur-based active material to the conductive additive (sulfur-based active material:conductive additive) is 10:90 to 95:5, preferably 30:70 to 90:10.

[0036] In one embodiment, the positive electrode composite produced by the method for producing a positive electrode composite according to this aspect is the positive electrode composite according to the aspect of the present invention described above.

[0037] 3. Lithium-ion battery A lithium-ion battery according to one aspect of the present invention includes the positive electrode composite according to the above-described one aspect of the present invention. The lithium-ion battery according to this aspect can reduce the ionic resistance of the positive electrode composite, thereby achieving the effect of being able to operate at low resistance.

[0038] The positive electrode composite can be used as the positive electrode layer of a lithium-ion battery. In this case, other components of the lithium-ion battery known in the art can be used, and the negative electrode layer can be selected so that the negative electrode active material does not contain lithium ions. The negative electrode active material contained in the negative electrode layer of the lithium-ion battery can be a "negative electrode active material containing lithium ions." Alternatively, the negative electrode active material contained in the negative electrode layer of the lithium-ion battery can be a "negative electrode active material that supplies lithium ions to the positive electrode."

[0039] The negative electrode of the lithium ion battery is not particularly limited as long as it is one that can be used in ordinary batteries. The negative electrode may be made of a negative electrode mixture in which a negative electrode active material and a solid electrolyte are mixed.

[0040] As the negative electrode active material, commercially available materials can be used. For example, carbon materials, Sn metal, In metal, Si metal, alloys of these metals, etc. can be used. Specifically, natural graphite, various graphites, metal powders of Si, Sn, Al, Sb, Zn, Bi, etc., SiAl, Sn ５ Cu ６ , Sn ２ Co, Sn ２ Examples include metal alloys such as Fe, amorphous alloys, and plated alloys. There are no particular restrictions on the particle size, but particles with an average particle size of several μm to 80 μm are preferably used.

[0041] The electrolyte layer is not particularly limited, and known electrolytes can be used. For example, oxide-based solid electrolytes, sulfide-based solid electrolytes, and polymer-based electrolytes are preferred, and sulfide-based solid electrolytes are more preferred from the viewpoint of ionic conductivity. The sulfide-based solid electrolyte is preferably the one used in the above-mentioned positive electrode composite.

[0042] The method for producing a lithium ion battery is not particularly limited, and examples thereof include a method in which a sheet is formed by forming a positive electrode layer made of the positive electrode composite according to one embodiment of the present invention on a positive electrode current collector, forming a solid electrolyte layer on the sheet, and laminating the sheet on which the negative electrode layer is formed on a previously formed negative electrode current collector, followed by pressing.

[0043] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0044] 1. Production of Positive Electrode Composite Material (Example 1) (1) Preparation of Composite Powder A Activated carbon (MSC-30 manufactured by Kansai Thermal Chemicals 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 bottle was heated in an electric furnace at 150°C for 6 hours and then at 300°C for 2.75 hours to obtain composite powder A of activated carbon and sulfur.

[0045] (2) Preparation of solid electrolyte 0.4129 g of lithium sulfide, 0.5875 g of diphosphorus pentasulfide, 0.2241 g of lithium chloride, 0.2755 g of lithium bromide, 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 (mechanical milling) at a rotation speed of 370 rpm for 60 hours to obtain a powder. The obtained powder was heated at 430 ° C for 8 hours to obtain solid electrolyte A.

[0046] (3) Preparation of Positive Electrode Composite Powder 0.45 g of composite powder A and 0.45 g of solid electrolyte A were placed in a 45 ml zirconia pot along with 10 zirconia balls with a diameter of 10 mm and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), mixing was performed at a rotation speed of 370 rpm, for 20 hours, and at room temperature to obtain composite powder B (cathode composite precursor). The obtained composite powder B was heated at 190 ° C for 2 hours to obtain a positive electrode composite.

[0047] Example 2 A positive electrode composite was obtained in the same manner as in Example 1, except that the heating temperature of composite powder B was set to 160°C.

[0048] Example 3 A positive electrode composite was obtained in the same manner as in Example 1, except that the heating temperature of composite powder B was set to 200°C.

[0049] Example 4 A positive electrode composite was obtained in the same manner as in Example 1, except that the heating temperature of composite powder B was set to 220°C.

[0050] Comparative Example 1 A positive electrode mixture was obtained in the same manner as in Example 1, except that the heating of composite powder B was omitted.

[0051] Comparative Example 2 A positive electrode composite was obtained in the same manner as in Example 1, except that the heating conditions for composite powder B were changed to 150° C. for 6 hours and then 300° C. for 2 hours and 45 minutes.

[0052] 2. Measurement Method and Evaluation Method (1) Powder X-ray Diffraction of Positive Electrode Composite Powder The obtained positive electrode composite powder was measured by XRD measurement. The positive electrode composite powder of each example was filled into a groove with a diameter of 20 mm and a depth of 0.2 mm and leveled with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured without contact with air. As a reference ("Ref." in Figures 1 and 2), powders mixed with composite powder A in a mortar at 0.45 g each were also measured so as not to impair the crystallinity of solid electrolyte A. As a result, peaks derived from the argyrodite-type crystal structure were observed in the XRD pattern at 2θ = 25.6°, 30.2°, 45.2°, etc. Measurements were performed using a powder X-ray diffraction measurement device D2 PHASER from BRUKER Co., Ltd. under the following conditions. Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα radiation (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° Step width, scan speed: 0.05°, 0.05° / sec

[0053] The X-ray diffraction pattern was examined to determine whether or not a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 45.2 ± 1.0° were present, and the half-value width of the diffraction peak A was determined by the following method.

[0054] Method for determining whether or not diffraction peak A and diffraction peak B are present Diffraction peak A Whether or not diffraction peak A is present in the range of 2θ = 25.6 ± 0.5° is determined by multiplying the average of the X-ray intensities (counts) at 2θ = (25.6 - 0.5) ± 0.2°, i.e., 2θ = 25.1 ± 0.2°, and 2θ = (25.6 + 0.5) ± 0.2°, i.e., 2θ = 26.1 ± 0.2°, in the X-ray diffraction pattern, by the background (BG) intensity I ｂｇ The maximum value of the X-ray intensity (counts) at 2θ=25.1±0.5° is defined as the peak intensity I ｐｅａｋ When the ratio (I ｐｅａｋ / I ｂｇ If the ratio (I) of the diffraction peak A is 1.200 or more, it is determined that the diffraction peak A exists. ｐｅａｋ / I ｂｇ ) is preferably 1.250 or more, more preferably 1.300 or more.

[0055] Diffraction Peak B Whether or not diffraction peak B exists in the range of 2θ = 45.2 ± 1.0° can be determined by multiplying the average of the X-ray intensities (counts) at 2θ = (45.2 - 1.0) ± 0.2°, i.e., 2θ = 44.2 ± 0.2°, and 2θ = (45.2 + 1.0) ± 0.2°, i.e., 2θ = 46.2 ± 0.2°, in the X-ray diffraction pattern, by the background (BG) intensity I ｂｇ The maximum value of the X-ray intensity (counts) at 2θ=45.2±1.0° is defined as the peak intensity I ｐｅａｋ When the ratio (I ｐｅａｋ / I ｂｇ If the ratio (I) of the diffraction peak B is 1.250 or more, it is determined that the diffraction peak B exists. ｐｅａｋ / I ｂｇ ) is preferably 1.300 or more, more preferably 1.350 or more.

[0056] As a result of the above, in the positive electrode composites of Examples 1 to 4 and Comparative Example 1, the diffraction peak A was ｐｅａｋ / I ｂｇ ) are 2.578, 2.629, 2.704, 2.838, and 2.311, respectively, and therefore it is determined to be "present." The diffraction peak B is ｐｅａｋ / I ｂｇ On the other hand, in the positive electrode composite of Comparative Example 2, the diffraction peak A was determined to be "present" because the ratios (I ｐｅａｋ / I ｂｇ ) is 1.108, so it is determined to be "absent," and the diffraction peak B is ｐｅａｋ / I ｂｇ ) was 1.198, so it was determined to be "not present."

[0057] Calculation of half-width The half-width β obtained by subtracting the instrument constant was calculated from β = w - B. w: half-width of the peak (diffraction peak A) at 25.6 ± 0.5° obtained by measurement B: instrument constant (a standard material (silicon) was measured in the same way, and B = 0.1269° was obtained from the peak at 2θ = 28.4°.) w (half-width obtained by measurement) was calculated as follows. A linear baseline was set for the peak shape obtained by XRD measurement, and the difference between the intensity at each point and the baseline was calculated to obtain an XRD curve. The XRD curve was fitted with the equation (f(x) = (1 - α) × L(x) + α × G(x)) consisting of a Lorentzian function L(x) and a Gaussian function G(x), and the parameters A (corrected peak intensity), w, and x were calculated by curve fitting. ０ (2θ of the peak top) and α (the ratio of the Lorentzian function) were determined.

[0058] In curve fitting, a range of approximately ±1.0° from the peak top is appropriately set as the fitting range. Fitting was performed by taking the error between the intensity of the fitting curve calculated by f(x) at each θ and the intensity of the XRD curve, and minimizing the sum of the errors over the entire fitting range. Here, the solver function (GRG nonlinear) of spreadsheet software (Excel, Microsoft) was used.

[0059] Asymmetry parameter ε' The same process as in "(3) Calculation of half-width of powder X-ray diffraction" above was performed on the peak at 2θ = 45.2 ± 1.0° (diffraction peak B), to obtain a baseline-corrected XRD curve and fitting curve f(x) (44.38° ≦ θ ≦ 46.05°). Note that f(x) is a symmetric curve fitted to minimize the error ε with the XRD curve, i.e., the sum of the squares of the intensity differences at each θ. In this case, if the error rate ε' is defined as follows, the larger the ε', the larger the error when fitting with a symmetric curve, i.e., the higher the peak's asymmetry. ε' = sum of errors / number of elements (number of plots at 44.38° ≦ θ ≦ 46.05°)

[0060] (2) Evaluation of ionic resistance Preparation of solid electrolyte 0.4127 g of lithium sulfide, 0.6655 g of diphosphorus pentasulfide, 0.2137 g of lithium iodide, 0.2080 g of lithium bromide, and 10 zirconia balls with a diameter of 10 mm were placed in a 45 ml zirconia pot and sealed. Using a planetary ball mill (manufactured by Fritsch, model number P-7), the mixture was mixed (mechanical milling) at a rotation speed of 370 rpm for 40 hours to obtain a powder. The obtained powder was heated at 195 ° C. for 3 hours to obtain solid electrolyte B.

[0061] Preparation of ionic resistance measurement cell 100 mg of the solid electrolyte B 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 surface, and the cylinder was again pressure-molded. 20 mg of positive electrode composite powder was added to the pressure surface opposite the positive electrode composite, and pressure was applied to prepare an ionic resistance measurement cell.

[0062] Measurement of Ion Resistance Using the ion resistance measurement cell prepared by the above procedure, AC impedance measurement was carried out under the following conditions: Frequency range: 1 MHz-1 mHz Amplitude: 10 mV

[0063] Table 1 shows the half-width of diffraction peak A, the left-right asymmetry parameter ε' of diffraction peak B, and the ionic resistance for each composite. Figure 1 shows the XRD spectrum, and Figure 2 shows an enlarged view of the high-angle side of the XRD spectrum.

[0064]

[0065] 3. Evaluation Table 1 shows that the positive electrode composites of Examples 1 to 4 have larger half-widths of diffraction peak A and larger asymmetry parameters ε' of diffraction peak B, and lower ionic resistance, compared to Comparative Example 1. FIG. 1 also shows that mechanical mixing reduces the crystallinity of the solid electrolyte (for example, by comparing Ref., which was not mechanically mixed, with Comparative Example 1, which was mechanically mixed). In contrast, Examples 1 to 4, which underwent heat treatment at 160 to 220°C after mechanical mixing, exhibit peaks at positions similar to those of Ref., confirming crystallinity. Meanwhile, Comparative Example 2, which was heated to 300°C, exhibited smaller peaks at positions similar to those of Ref., suggesting decomposition of the solid electrolyte (instead, the formation of an impurity phase (2θ = 29°) was confirmed). In Examples 1 to 4, the half-width of diffraction peak A was large, and as shown in FIG. 2, diffraction peak B was asymmetric (the asymmetry parameter ε' was large). This suggests that in addition to the original crystalline phase, a new crystalline phase with a slightly different lattice constant was generated in the solid electrolyte (such slight differences in lattice constant and peak position in the XRD spectrum are significant at the high-angle side shown in FIG. 2). These characteristics are thought to contribute to the reduction in ionic resistance. The results of XRD measurement of the cathode composite obtained in Example 3 under the same conditions as in Patent Document 3 are shown in FIG. 3. From FIG. 3, it can be seen that the behavior (way of splitting) of the crystalline peak of the cathode composite obtained in Example 3 is clearly different from that of the cathode composite described in Patent Document 3 (XRD spectrum in FIG. 1 described in Patent Document 3), indicating a difference in the crystalline phase (this is also thought to be the case for other Examples).

[0066] 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.

[0067] 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. Contains a sulfur-based active material and a solid electrolyte, In powder X-ray diffraction using CuKα radiation, it has a diffraction peak A at 2θ=25.6±0.5° and a diffraction peak B at 2θ=45.2±1.0°, The positive electrode composite, wherein the half width of the diffraction peak A is 0.25° or more.

2. The left-right asymmetry parameter ε′ of the diffraction peak B is 1.50×10 ４ The positive electrode mixture according to claim 1 .

3. The positive electrode mixture according to claim 1 or 2, further comprising a conductive additive.

4. The positive electrode mixture according to claim 3 , wherein the conductive additive has pores with a pore diameter of less than 5 nm.

5. The positive electrode mixture according to claim 3 , wherein the conductive additive comprises at least one selected from the group consisting of activated carbon and carbon black.

6. 3. The cathode composite according to claim 1, obtained by heat-treating a cathode composite precursor obtained by mechanically mixing a sulfur-based active material with a solid electrolyte having a diffraction peak A at 2θ = 25.6 ± 0.5° and a diffraction peak B at 2θ = 45.2 ± 1.0° in powder X-ray diffraction using CuKα rays.

7. The positive electrode mixture according to claim 6, wherein the heat treatment temperature is 160 to 280°C.

8. Obtaining a positive electrode composite precursor by mechanically mixing a sulfur-based active material with a solid electrolyte having a diffraction peak A at 2θ = 25.6 ± 0.5 ° and a diffraction peak B at 2θ = 45.2 ± 1.0 ° in powder X-ray diffraction using CuKα rays; and obtaining a positive electrode mixture by heat-treating the positive electrode mixture precursor; Including, The method for producing a positive electrode mixture, wherein the heat treatment temperature is 160 to 280°C.

9. A lithium ion battery comprising the positive electrode mixture according to claim 1 or 2.