Vanadium-containing lithium sulfide

Abstract

The present invention provides a vanadium-containing lithium sulfide which contains lithium, vanadium and sulfur, wherein: the content ratio of the lithium to the vanadium is 4.5 to 9.5 in terms of the molar ratio; the content ratio of the sulfur to the vanadium is 3.5 to 6.5 in terms of the molar ratio; and the full width at half maximum of a peak at 2θ = 27.0 ± 0.1° is 0.40° to 0.90° in an X-ray diffraction pattern using a CuKα ray. This vanadium-containing lithium sulfide serves as a positive electrode active material for lithium ion secondary batteries, the positive electrode active material having a high electron conductivity, while achieving a high capacity without using a large amount of a solid electrolyte or a large amount of a conductive material.

Description

[Technical Field]

[0001] The present invention relates to a vanadium-containing lithium sulfide. [Background technology]

[0002] Lithium-ion secondary batteries, which have high energy density, are currently widely used as power sources for small portable devices, electric vehicles, and other devices. Furthermore, ensuring even greater safety is also important in realizing secondary batteries with even higher energy densities to extend the driving range of electric vehicles. Among lithium-ion secondary batteries, all-solid-state lithium secondary batteries using solid electrolytes do not use flammable organic electrolytes like conventional lithium-ion secondary batteries. Therefore, they are ideal as secondary batteries for transportation media, which require high reliability and heat resistance, and are extremely safe energy storage devices. Furthermore, the solid electrolytes used in all-solid-state lithium-ion secondary batteries are less likely to cause side reactions, resulting in high durability.

[0003] On the other hand, sulfur has a high theoretical capacity and is one of the promising candidates for a high-capacity electrode active material in all-solid-state lithium-ion secondary batteries. However, since elemental sulfur does not contain lithium, lithium or a lithium-containing alloy must be used for the negative electrode, which limits the range of options for the negative electrode.

[0004] In contrast, lithium sulfide contains lithium, so alloys such as graphite and silicon can be used for the anode, dramatically expanding the range of anode options. However, although lithium sulfide has a high theoretical capacity of approximately 1170 mAh / g, its electronic conductivity is only 10 -8 Because the capacitance is significantly low, less than S / cm, excellent battery performance cannot be obtained.

[0005] For example, Patent Document 1 shows that the capacity can be improved by introducing vanadium and molybdenum into lithium sulfide, and Patent Document 2 shows that the capacity and cycle characteristics can be improved by introducing both cobalt, nickel, iron, chromium, manganese, zinc, etc. and titanium, molybdenum, vanadium, etc. into lithium sulfide. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-058295 [Patent Document 2] Japanese Patent Application Publication No. 2017-054633 Summary of the Invention [Problem to be solved by the invention]

[0007] However, Patent Documents 1 and 2 only describe examples in which the raw material was milled at a low rotation speed of 97 rpm. Patent Documents 1 and 2 state that this material can be charged and discharged, but the inventors' research has shown that when milling is performed at a low rotation speed, the raw material does not react sufficiently, and the electronic conductivity is 10 -8 Because the electrical conductivity was significantly low, less than S / cm, it was found that charging and discharging was not possible at all and that the material did not function as a positive electrode active material.

[0008] In particular, Patent Document 1 states that the content of the positive electrode active material in the positive electrode is preferably as low as 20 to 50 mass%. Patent Document 2 also states that the ratio of the conductive material content to the positive electrode active material content is preferably 0.20 to 2.0, and the ratio of the solid electrolyte content to the positive electrode active material content is preferably 0.50 to 5.0. In other words, the content of the positive electrode active material in the positive electrode is 12.5 to 58.8 mass%. This is because Patent Documents 1 and 2 use positive electrode active materials with low ionic and electronic conductivity, which suggests that it is necessary to supplement battery performance by adding large amounts of solid electrolyte or conductive material. However, as mentioned above, the need for large amounts of solid electrolyte or conductive material prevents high energy density from being achieved. Therefore, the positive electrode active material itself needs to be a material that improves electronic conductivity and exhibits excellent battery performance.

[0009] In view of the above, an object of the present invention is to provide a positive electrode active material for a lithium ion secondary battery that has high electronic conductivity and exhibits high capacity without using a large amount of a solid electrolyte or conductive material. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to achieve the above-mentioned object. As a result, they have found that a vanadium-containing lithium sulfide having a specific composition and an X-ray diffraction pattern in which the full width at half maximum of a peak at a specific position falls within a specific range has high electronic conductivity and exhibits high capacity without using a large amount of a solid electrolyte or conductive material. This vanadium-containing lithium sulfide can also improve charge / discharge cycle characteristics and rate characteristics. The present invention was completed based on this finding and further research. That is, the present invention includes the following features.

[0011] Item 1. Contains lithium, vanadium, and sulfur, the ratio of the lithium content to the vanadium content is 4.5 to 9.5 in terms of molar ratio; the molar ratio of the sulfur content to the vanadium content is 3.5 to 6.5; A vanadium-containing lithium sulfide having a full width at half maximum of a peak at 2θ=27.0±0.1° in an X-ray diffraction pattern using CuKα radiation of 0.40 to 0.90°.

[0012] Item 2. The vanadium-containing lithium sulfide according to Item 1, wherein the content of elements other than lithium, vanadium, and sulfur is 0 to 5 mol % relative to 100 mol % of the total amount of the vanadium-containing lithium sulfide.

[0013] Section 3. General formula (1): Li x VS y (1) [Wherein, 4.5≦x≦9.5 and 3.5≦y≦6.5 are indicated.] Item 1 or 2. The vanadium-containing lithium sulfide according to item 1 or 2, having a composition represented by the formula:

[0014] Item 4. The vanadium-containing lithium sulfide according to any one of Items 1 to 3, wherein in an X-ray diffraction pattern using CuKα rays, the full width at half maximum of the peak at 2θ=34.0±0.9° is 0.80 to 2.50°.

[0015] Item 5. The vanadium-containing lithium sulfide according to any one of Items 1 to 4, which is used as a positive electrode active material for a lithium ion secondary battery.

[0016] Item 6. A method for producing the vanadium-containing lithium sulfide according to any one of items 1 to 5, A process of subjecting a starting material containing lithium sulfide and vanadium sulfide to mechanical milling at a rotation speed of 120 rpm or more. A manufacturing method comprising:

[0017] Item 7. The manufacturing method according to Item 6, wherein the mechanical milling step is not followed by heat treatment at 200°C or higher.

[0018] Item 8. A positive electrode active material for a lithium ion secondary battery, comprising the vanadium-containing lithium sulfide according to any one of items 1 to 5.

[0019] Item 9. A positive electrode for a lithium ion secondary battery, comprising the positive electrode active material for a lithium ion secondary battery according to Item 8.

[0020] Item 10. The positive electrode for a lithium ion secondary battery according to Item 9, further comprising a solid electrolyte and a conductive material.

[0021] Item 11. The positive electrode for a lithium ion secondary battery according to Item 10, wherein the conductive material is a conductive carbon fiber.

[0022] Item 12. The positive electrode for a lithium ion secondary battery according to any one of Items 9 to 11, wherein the content of the positive electrode active material for a lithium ion secondary battery is 65 to 95 mass % relative to 100 mass % of the total amount of the positive electrode for a lithium ion secondary battery.

[0023] Item 13. The loading amount of the positive electrode mixture for the lithium ion secondary battery is 5.0 to 48.0 mg / cm 2 Item 13. The lithium ion secondary battery according to any one of items 9 to 12, wherein

[0024] Item 14. A lithium ion secondary battery comprising the positive electrode for lithium ion secondary batteries according to any one of items 9 to 12.

[0025] Item 15. The lithium ion secondary battery according to Item 14, which is an all-solid-state lithium ion secondary battery. [Effects of the Invention]

[0026] The vanadium-containing lithium sulfide of the present invention is a material that has high electronic conductivity and exhibits high capacity without using a large amount of a solid electrolyte or conductive material. [Brief explanation of the drawings]

[0027] [Figure 1] 1 shows X-ray diffraction patterns (Test Example 1) of the powders obtained in Examples 1 to 5. [Figure 2] The X-ray diffraction patterns (Test Example 1) of the powders obtained in Examples 1, 6, and 7 and Comparative Examples 1 and 2 are shown. [Figure 3] 1 shows charge / discharge curves (Test Example 4) using the all-solid-state lithium ion secondary batteries obtained in Examples 11 to 15. [Figure 4] The results of rate characteristics using the all-solid-state lithium ion secondary batteries obtained in Examples 11 and 12 (Test Example 5) are shown. [Figure 5] 1 shows the results of the initial charge capacity using the all-solid-state lithium ion secondary batteries obtained in Examples 16 to 23. [Figure 6] The results of the initial charge capacity when the all-solid-state lithium ion secondary battery obtained in Example 26 was operated at 25°C or 45°C are shown. [Figure 7] The results of cycle characteristics when the all-solid-state lithium ion secondary batteries obtained in Examples 16 to 21 and 23 to 26 were operated at 25°C or 45°C are shown. DETAILED DESCRIPTION OF THE INVENTION

[0028] In this specification, the term "containing" is a concept that encompasses all of "comprise," "consist essentially of," and "consist only of."

[0029] In addition, in this specification, the expression "A to B" means "A or more and B or less."

[0030] Furthermore, in this specification, the term "lithium ion secondary battery" is a concept that also encompasses "metal lithium secondary batteries" that use metallic lithium as the negative electrode material. Furthermore, in the present invention, the term "lithium ion secondary battery" refers to both "nonaqueous lithium ion secondary batteries" that use a nonaqueous electrolyte and "all-solid-state lithium ion secondary batteries" that use a solid electrolyte.

[0031] 1. Vanadium-containing lithium sulfide The vanadium-containing lithium sulfide of the present invention contains lithium, vanadium, and sulfur, and has a molar ratio of the lithium content to the vanadium content of 4.5 to 9.5, a molar ratio of the sulfur content to the vanadium content of 3.5 to 6.5, and a full width at half maximum of a peak at 2θ=27.0±0.1° in an X-ray diffraction diagram using CuKα rays of 0.40 to 0.90°.

[0032] Thus, by including a certain amount of vanadium in the vanadium-containing lithium sulfide of the present invention, it is possible to improve electronic conductivity, charge / discharge cycle characteristics, rate characteristics, etc. Furthermore, the vanadium-containing lithium sulfide of the present invention has an X-ray diffraction pattern using CuKα rays in which the full width at half maximum of the peak at 2θ=27.0±0.1° is not too small, thereby improving electronic conductivity and capacity.

[0033] As described above, in the present invention, by adjusting the vanadium content within an appropriate range, it is possible to particularly improve the electronic conductivity, charge / discharge cycle characteristics, and rate characteristics. Therefore, the molar ratio of the lithium content to the vanadium content is preferably 4.5 to 9.5. In particular, from the viewpoint of easily improving the electronic conductivity, charge / discharge cycle characteristics, rate characteristics, etc., the molar ratio of the lithium content to the vanadium content is preferably 4.6 to 8.5, more preferably 4.7 to 7.5, and even more preferably 4.8 to 6.5. Furthermore, as will be described later, from the viewpoint of easily improving the capacity by increasing the operating temperature and easily bringing the measured capacity closer to the theoretical capacity, the molar ratio of the lithium content to the vanadium content is preferably 5.5 to 9.4, more preferably 6.5 to 9.3, and even more preferably 7.5 to 9.2.

[0034] As described above, in the present invention, by adjusting the vanadium content within an appropriate range, it is possible to particularly improve the electronic conductivity, charge / discharge cycle characteristics, and rate characteristics. Therefore, the molar ratio of the sulfur content to vanadium is preferably 3.5 to 6.5. In particular, from the viewpoint of easily improving the electronic conductivity, charge / discharge cycle characteristics, rate characteristics, etc., the molar ratio of the sulfur content to vanadium is preferably 3.6 to 6.3, more preferably 3.7 to 5.8, and even more preferably 3.8 to 5.3. Furthermore, as will be described later, from the viewpoint of easily improving the capacity by increasing the operating temperature and easily bringing the measured capacity closer to the theoretical capacity, the molar ratio of the sulfur content to vanadium is preferably 4.3 to 6.4, more preferably 4.8 to 6.3, and even more preferably 5.3 to 6.2.

[0035] The vanadium-containing lithium sulfide of the present invention contains lithium, vanadium, and sulfur, and may contain small amounts of other elements derived from the raw materials, etc. Therefore, the abundance ratio of elements other than lithium, vanadium, and sulfur is preferably 0 to 5 mol%, more preferably 0 to 3 mol%, and even more preferably 0 to 2 mol%, based on 100 mol% of the total amount of the vanadium-containing lithium sulfide of the present invention. Most preferably, the vanadium-containing lithium sulfide of the present invention does not contain impurity elements other than lithium, vanadium, and sulfur.

[0036] From the above, the vanadium-containing lithium sulfide of the present invention has the general formula (1): Li x VS y (1) [Wherein, 4.5≦x≦9.5 and 3.5≦y≦6.5 are indicated.] It is preferable that the composition be represented by the following formula:

[0037] In general formula (1), similarly to the above, from the viewpoint of easily improving electronic conductivity, charge / discharge cycle characteristics, rate characteristics, etc., x is preferably 4.6 to 8.5 in molar ratio, more preferably 4.7 to 7.5, and even more preferably 4.8 to 6.5. Furthermore, as will be described later, from the viewpoint of easily improving capacity by increasing the operating temperature and easily bringing the measured capacity closer to the theoretical capacity, x is preferably 5.5 to 9.4 in molar ratio, more preferably 6.5 to 9.3, and even more preferably 7.5 to 9.2.

[0038] In general formula (1), from the viewpoint of easily improving electronic conductivity, charge / discharge cycle characteristics, rate characteristics, etc., similarly to the above, y is preferably 3.6 to 6.3 in molar ratio, more preferably 3.7 to 5.8, and even more preferably 3.8 to 5.3. Furthermore, from the viewpoint of easily improving capacity by increasing the operating temperature and easily bringing the measured capacity closer to the theoretical capacity, as will be described later, y is preferably 4.3 to 6.4 in molar ratio, more preferably 4.8 to 6.3, and even more preferably 5.3 to 6.2.

[0039] In general formula (1), the relationship between the x value and the y value is not particularly limited, but from the viewpoints of electronic conductivity, capacity, charge / discharge cycle characteristics, rate characteristics, etc., it is preferable that y = 0.5x + 1.5.

[0040] The vanadium-containing lithium sulfide of the present invention preferably has a peak at a position where lithium sulfide and lithium-containing vanadium sulfide (such as LiVS2 when Li2S and V2S3 are used as raw materials) have peaks in an X-ray diffraction pattern using CuKα radiation. However, both peaks tend to be broader than those of lithium sulfide and lithium-containing vanadium sulfide, respectively.

[0041] Specifically, the vanadium-containing lithium sulfide of the present invention has a peak with a maximum value at 2θ=27.0±0.1° in an X-ray diffraction pattern using CuKα radiation, and the full width at half maximum of the peak at 2θ=27.0±0.1° is 0.40 to 0.90°, preferably 0.50 to 0.88°, and more preferably 0.60 to 0.86°. If the full width at half maximum of the peak at 2θ=27.0±0.1° is less than 0.40°, the electronic conductivity is low, the capacity is significantly reduced, and charge / discharge is impossible. On the other hand, if the full width at half maximum of the peak at 2θ=27.0±0.1° exceeds 0.90°, the vanadium-containing lithium sulfide of the present invention cannot be produced.

[0042] The vanadium-containing lithium sulfide of the present invention has a peak with a maximum value at 2θ=34.0±0.9° in an X-ray diffraction diagram using CuKα radiation, and the full width at half maximum of the peak at 2θ=34.0±0.9° is preferably 0.80 to 2.50°, more preferably 0.90 to 2.00°, and even more preferably 1.00 to 1.80° from the viewpoint of easily improving electronic conductivity, charge / discharge cycle characteristics, rate characteristics, etc. Furthermore, the full width at half maximum of the peak at 2θ=34.0±0.9° is preferably 0.80 to 2.50°, more preferably 1.00 to 2.40°, and even more preferably 1.40 to 2.30° from the viewpoint of easily improving capacity by increasing the operating temperature and easily bringing the measured capacity closer to the theoretical capacity.

[0043] Furthermore, in an X-ray diffraction diagram using CuKα rays, the vanadium-containing lithium sulfide of the present invention preferably has peaks with maximum values at at least one position (preferably all positions) such as 31.3°, 45.0°, 53.0°, 65.4°, etc., in addition to 27.0° and 34.0°, within an allowable range of ±1.0° (preferably an allowable range of ±0.5°) within the range of diffraction angle 2θ=23 to 70°.

[0044] In the present invention, the X-ray diffraction pattern is determined by powder X-ray diffraction measurement, for example, under the following measurement conditions: Measurement equipment: Empyrean (Malvern PANalytical) X-ray source: CuKα 45kV / 40mA Measurement conditions: 2θ = 24 to 70°, 0.1° step, scanning speed 0.02° / sec It can be measured by

[0045] The vanadium-containing lithium sulfide of the present invention has a peak with a maximum at 2θ = 27.0 ± 0.1°, which is also possessed by lithium sulfides with high theoretical capacities (such as Li2S), and by further containing vanadium, the low electronic conductivity of lithium sulfides (such as Li2S) can be significantly improved, making it possible to obtain a material with high capacity and excellent cycle and rate characteristics. Furthermore, the vanadium-containing lithium sulfide of the present invention can be sufficiently mixed with vanadium sulfide because the full width at half maximum of the peak with a maximum at 2θ = 27.0 ± 0.1° in an X-ray diffraction diagram using CuKα radiation is not too small, allowing it to be sufficiently mixed with vanadium sulfide, thereby enabling high electronic conductivity to be obtained.

[0046] Furthermore, in the vanadium-containing lithium sulfide of the present invention, the lithium sulfide phase and the lithium-containing vanadium sulfide phase are mixed at the nano level. From the viewpoints of electronic conductivity, capacity, charge / discharge cycle characteristics, rate characteristics, etc., the average size of the lithium sulfide phase and the lithium-containing vanadium sulfide phase is preferably 1.0 to 100.0 nm, more preferably 1.00 to 50.0 nm, and even more preferably 1.0 to 20.0 nm. The average size of the lithium sulfide phase and the lithium-containing vanadium sulfide phase means (major axis + minor axis) / 2 of each of the lithium sulfide phase and the lithium-containing vanadium sulfide phase observed by transmission electron microscope (TEM). The fact that the lithium sulfide phase and the lithium-containing vanadium sulfide phase are mixed at the nano level means that peaks characteristic of the lithium sulfide phase and the lithium-containing vanadium sulfide phase are observed in an X-ray diffraction diagram, and the full width at half maximum of the peaks characteristic of the lithium sulfide phase and the lithium-containing vanadium sulfide phase are large. Specifically, in an X-ray diffraction pattern using CuKα radiation, it is preferable that the full width at half maximum of the peak having a maximum value at 2θ=27.0±0.1° and the peak having a maximum value at 2θ=34.0±0.9° are within the above-mentioned ranges.

[0047] In the present invention, other impurities may be contained in addition to the vanadium-containing lithium sulfide of the present invention, as long as the impurities do not impair the performance of the vanadium-containing lithium sulfide of the present invention. Examples of such impurities include raw material lithium sulfides (e.g., Li2S), vanadium sulfides (e.g., VS3, VS4), etc., lithium, vanadium, etc. that may be mixed into the raw materials, as well as oxygen, etc. that may be mixed into the raw materials or during production.

[0048] The amount of these impurities is preferably within a range that does not impair the performance of the vanadium-containing lithium sulfide of the present invention described above, and is usually preferably 0 to 2.0 mass%, more preferably 0 to 1.5 mass%, based on 100 mass% of the total amount of the vanadium-containing lithium sulfide of the present invention.

[0049] As described above, the vanadium-containing lithium sulfide of the present invention has high electronic conductivity and can improve capacity, charge / discharge cycle characteristics, and rate characteristics, and is therefore useful as a positive electrode active material for lithium ion secondary batteries (particularly, a positive electrode active material for all-solid-state lithium ion secondary batteries).

[0050] 2.Method for producing vanadium-containing lithium sulfide The method for producing the vanadium-containing lithium sulfide of the present invention is not particularly limited, but may be, for example, A process of subjecting a starting material containing lithium sulfide and vanadium sulfide to mechanical milling at a rotation speed of 120 rpm or more. The manufacturing method can be obtained by the following steps.

[0051] Mechanical milling is a method of grinding and mixing raw materials while applying mechanical energy. According to this method, by grinding and mixing the raw materials by applying mechanical impact and friction, lithium sulfide and vanadium sulfide come into vigorous contact with each other, becoming finer, and causing a reaction of the raw materials. In other words, mixing, grinding, and reaction occur simultaneously. This makes it possible to more reliably react the raw materials without heating them to high temperatures. Mechanical milling can sometimes produce a metastable crystal structure that cannot be obtained by ordinary heat treatment.

[0052] Specifically, the mechanical milling treatment can be carried out by mixing and grinding using a mechanical grinding device such as a ball mill, a bead mill, a rod mill, a vibration mill, a disk mill, a hammer mill, a jet mill, etc. Among these, Pulverrisette7 Premium Line (Fritsch) is preferred from the viewpoint of easily mixing the lithium sulfide phase and the lithium-containing vanadium sulfide phase at the nano level.

[0053] These raw materials can be all mixed together and subjected to mechanical milling treatment, or some of the materials or intermediates can be subjected to mechanical milling treatment first, and then the remaining materials can be added and subjected to mechanical milling treatment.

[0054] Specific examples of the raw material include lithium sulfide, such as lithium sulfide (LiS). The lithium sulfide is not particularly limited, and any commercially available lithium sulfide can be used. In particular, it is preferable to use a high-purity lithium sulfide. Furthermore, since the lithium sulfide is mixed and pulverized by mechanical milling, there is no limitation on the particle size of the lithium sulfide used, and commercially available powdered lithium sulfide can usually be used.

[0055] Furthermore, it is preferable to use crystalline vanadium(III) sulfide (VS), crystalline vanadium(VIII) sulfide (VS), or the like as the vanadium sulfide. There are no particular limitations on the vanadium sulfide, and any commercially available vanadium sulfide can be used. In particular, it is preferable to use a vanadium sulfide of high purity. Furthermore, since the vanadium sulfide is mixed and pulverized by mechanical milling, there are no limitations on the particle size of the vanadium sulfide used, and commercially available powdered vanadium sulfide can usually be used.

[0056] The mixing ratio of the raw materials can be determined according to the element ratio of lithium and vanadium in the target vanadium-containing lithium sulfide, since the charging ratio of the raw materials almost directly determines the ratio of each element in the product.

[0057] When performing mechanical milling, it is preferable to add grinding media as needed, such as zirconia beads, zirconia balls, and alumina balls.

[0058] When these grinding media are used, the average diameter of the grinding media is not particularly limited, but is preferably 5 to 20 mm, more preferably 7 to 15 mm, from the viewpoints of facilitating the reaction between the raw materials, facilitating mixing of the lithium sulfide phase and the lithium-containing vanadium sulfide phase at the nano level, and facilitating improvements in electronic conductivity, capacity, charge / discharge cycle characteristics, rate characteristics, etc.

[0059] The rotation speed during mechanical milling is 120 rpm or higher, preferably 250 to 500 rpm, and more preferably 300 to 400 rpm. If the rotation speed during mechanical milling is less than 120 rpm, the resulting material will have an extremely small full width at half maximum of the peak at 2θ=27.0±0.1° in the X-ray diffraction pattern using CuKα rays, resulting in low electronic conductivity and extremely low capacity, making it almost impossible to charge and discharge.

[0060] The temperature for carrying out the mechanical milling treatment is not particularly limited, but is preferably 20 to 35°C, more preferably 22 to 33°C, and even more preferably 25 to 30°C, from the viewpoints that the full width at half maximum of the peak at 2θ=27.0±0.1° in an X-ray diffraction pattern using CuKα rays can be appropriately adjusted, and that it is easy to improve the electronic conductivity as well as the capacity, charge / discharge cycle characteristics, and rate characteristics.

[0061] The time for the mechanical milling treatment is not particularly limited, and is preferably 40 to 200 hours, more preferably 80 to 180 hours, and even more preferably 150 to 170 hours, from the viewpoints that the full width at half maximum of the peak at 2θ=27.0±0.1° in an X-ray diffraction pattern using CuKα rays can be appropriately adjusted, and that it is easy to improve the electronic conductivity as well as the capacity, charge / discharge cycle characteristics, and rate characteristics.

[0062] The mechanical milling process can be carried out in multiple steps with breaks in between, if necessary. When the mechanical milling process is repeated multiple times, the above conditions can be applied to each step of the mechanical milling process.

[0063] The mechanical milling process described above allows the target vanadium-containing lithium sulfide to be obtained as a fine powder. The particle size range is not particularly limited, but the average particle size can be, for example, 1 to 200 μm, preferably 1 to 50 μm, and more preferably 1 to 25 μm. The particle size of the vanadium-containing lithium sulfide is measured by observation with an electron microscope.

[0064] After the mechanical milling step, the obtained vanadium-containing lithium sulfide can be subjected to heat treatment. However, from the viewpoint of being able to appropriately adjust the full width at half maximum of the peak at 2θ=27.0±0.1° in the X-ray diffraction diagram using CuKα radiation, and being able to easily improve the electronic conductivity, capacity, charge / discharge cycle characteristics, and rate characteristics, it is preferable not to perform heat treatment at 200°C or higher, for example, 200 to 1000°C, and more preferably not to perform heat treatment at 150°C or higher, for example, 150 to 1000°C.

[0065] 3. Uses of vanadium-containing lithium sulfide As described above, the vanadium-containing lithium sulfide of the present invention has high electronic conductivity and can improve capacity, cycle characteristics, and rate characteristics, and is therefore particularly useful as a positive electrode active material for lithium ion secondary batteries. Lithium ion secondary batteries in which the vanadium-containing lithium sulfide of the present invention can be effectively used as a positive electrode active material can be nonaqueous electrolyte lithium ion secondary batteries that use a nonaqueous electrolyte as the electrolyte, or all-solid-state lithium ion secondary batteries that use a lithium ion-conductive solid electrolyte. The vanadium-containing lithium sulfide of the present invention has high electronic conductivity and can improve capacity, cycle characteristics, and rate characteristics, and is therefore particularly useful when used in all-solid-state lithium ion secondary batteries.

[0066] The nonaqueous electrolyte lithium ion secondary battery and all-solid-state lithium ion secondary battery of the present invention use the vanadium-containing lithium sulfide of the present invention as a positive electrode active material.

[0067] For the positive electrode, for example, the vanadium-containing lithium sulfide of the present invention is used as a positive electrode active material, and a positive electrode mixture containing the vanadium-containing lithium sulfide of the present invention and, if necessary, a solid electrolyte and a conductive material can be supported on a positive electrode current collector such as Al, Ni, stainless steel, or carbon cloth.

[0068] From the viewpoint of energy density, it is preferable to increase the content of the positive electrode active material in the positive electrode as much as possible, while a lower content of the positive electrode active material facilitates improvements in capacity, charge / discharge cycle characteristics, rate characteristics, etc. However, even when the content of the positive electrode active material is high, the capacity, charge / discharge cycle characteristics, rate characteristics, etc. can be easily improved by adding a small amount of conductive carbon fiber as a conductive material. For this reason, it is preferable to increase the content of the positive electrode active material in the positive electrode, and, assuming the total amount of the positive electrode as 100% by mass, it is preferably 65 to 95% by mass, more preferably 70 to 90% by mass, and even more preferably 75 to 87% by mass, and may be 75 to 83% by mass.

[0069] The solid electrolyte may be any solid electrolyte that can be used in lithium ion secondary batteries, such as a polymer solid electrolyte including a polyethylene oxide polymer compound and a polymer compound containing at least one of a polyorganosiloxane chain and a polyoxyalkylene chain, as well as a sulfide solid electrolyte and an oxide solid electrolyte.

[0070] Examples of sulfide-based solid electrolytes include sulfide-based solid electrolytes obtained using a raw material composition containing Li2S and LiI, LiCl, SiS2, P2S5, etc. The content of each component in the raw material composition is, for example, preferably 60 to 80 mol% of Li2S, and more preferably 40 to 20 mol% of LiI, LiCl, SiS2, P2S5, etc., based on 100 mol% of the total amount of the solid electrolyte.

[0071] Examples of such sulfide-based solid electrolytes include Li2S-SiS2, Li2S-P2S5, LiI-Li2S-SiS2, and LiI-Li2S-P2S 5、 Examples include LiCl-Li2S-SiS2 and LiCl-Li2S-P2S5.

[0072] Examples of oxide-based solid electrolytes include (Li,La)TiO3 and the like as oxides having a perovskite structure containing lithium, and Li 1+x+y Mx E 2-x Si y P 3-y O 12 (0 ≤ x ≤ 0.4, 0 < y ≤ 0.6; M represents Al and / or Ga, and E represents at least one selected from the group consisting of Ti, Ge, and Zr.) etc. are mentioned, and oxides having a garnet structure such as Li7La3Zr2O 12 etc. are mentioned.

[0073] These solid electrolytes can be used alone or in combination of two or more.

[0074] From the perspective of energy density, it is preferable to minimize the content of the solid electrolyte in the positive electrode. On the other hand, a higher content of the solid electrolyte is more likely to improve the capacity, charge-discharge cycle characteristics, rate characteristics, etc. However, even when the content of the solid electrolyte is low, it is easy to improve the capacity, charge-discharge cycle characteristics, rate characteristics, etc. by adding a small amount of conductive carbon fiber as a conductive material. Therefore, the content of the solid electrolyte in the positive electrode is preferably reduced. Assuming the total amount of the positive electrode is 100% by mass, 3 - 33% by mass is preferable, 8 - 28% by mass is more preferable, 13 - 23% by mass is even more preferable, and it can also be 16 - 23% by mass.

[0075] As the conductive material, for example, graphite; coke; carbon blacks such as acetylene black and ketjen black; conductive carbon fibers such as vapor-grown carbon fibers, and carbon materials such as needle-like carbon like carbon nanotubes can be used, and conductive carbon fibers such as vapor-grown carbon fibers can also be used. Among them, from the perspective of being more likely to improve the capacity, charge-discharge cycle characteristics, rate characteristics, etc., needle-like carbon is preferable, conductive carbon fibers are more preferable, and vapor-grown carbon fibers are even more preferable.

[0076] In particular, when conductive carbon fiber is used as the conductive material, even a small amount of conductive carbon fiber can easily improve capacity, charge / discharge cycle characteristics, rate characteristics, etc., making it easy to increase the amount of positive electrode active material or the amount of positive electrode mixture. Therefore, the content of the conductive material in the positive electrode is preferably 0 to 5.0 mass%, more preferably 0 to 4.0 mass%, and even more preferably 0 to 3.0 mass%, based on 100 mass% of the total amount of the positive electrode. When a conductive material is used, the lower limit of its content can be preferably 0.1 mass%, more preferably 0.2 mass%, and even more preferably 0.3 mass%. Furthermore, from the viewpoint of improving energy density, it is also effective to use no conductive material (0 mass%).

[0077] The positive electrode mixture can be obtained by mixing the vanadium-containing lithium sulfide of the present invention with a solid electrolyte and a conductive material as required.

[0078] The mixing method is not particularly limited, and may be manual mixing or mechanical milling.

[0079] Mechanical milling is a method of grinding and mixing a sample while applying mechanical energy, and by applying mechanical impact and friction to the sample, the positive electrode active material, solid electrolyte, and conductive material come into vigorous contact with each other and are pulverized. In other words, mixing and grinding occur simultaneously.

[0080] Specifically, the mechanical milling treatment can be carried out by mixing and pulverizing using a mechanical mill such as a ball mill, a bead mill, a rod mill, a vibration mill, a disk mill, a hammer mill, a jet mill, etc. Among these, Pulverrisette7 Premium Line (Fritsch) is preferred from the viewpoint of easily and uniformly mixing the positive electrode active material, the solid electrolyte, and the conductive material.

[0081] When performing mechanical milling, it is preferable to add grinding media as needed, such as zirconia beads, zirconia balls, and alumina balls.

[0082] The rotation speed during mechanical milling is preferably 10 to 200 rpm, more preferably 50 to 180 rpm, and even more preferably 100 to 180 rpm, from the viewpoints of capacity, charge / discharge cycle characteristics, rate characteristics, and the like.

[0083] The temperature at which the mechanical milling treatment is carried out is not particularly limited, but is preferably 20 to 35°C, more preferably 22 to 33°C, from the viewpoints of capacity, charge / discharge cycle characteristics, rate characteristics, and the like.

[0084] The time for the mechanical milling treatment is not particularly limited, but is preferably 0.5 to 1.5 hours, more preferably 0.8 to 1.2 hours, from the viewpoints of capacity, charge / discharge cycle characteristics, rate characteristics, and the like.

[0085] The mechanical milling process can be carried out in multiple steps with breaks in between, if necessary. When the mechanical milling process is repeated multiple times, the above conditions can be applied to each step of the mechanical milling process.

[0086] By the mechanical milling treatment described above, the target positive electrode mixture can be obtained as a fine powder, and by supporting it on the positive electrode current collector in a conventional manner, a positive electrode can be obtained.

[0087] In this case, it is preferable not to use too much of the mixture from the viewpoint of capacity, charge / discharge cycle characteristics, rate characteristics, etc. However, when conductive carbon fiber is used as the conductive material, even a small amount of the mixture can easily improve the capacity, charge / discharge cycle characteristics, rate characteristics, etc., so it is also possible to use a large amount of the positive electrode mixture. For this reason, the loading amount of the positive electrode mixture is set to 5.0 to 48.0 mg / cm. 2 is preferred, and 12.0 to 48.0 mg / cm 2 In this case, the loading amount of the positive electrode mixture is preferably in the range of 5.0 to 26.0 mg / cm. 2 ) or thick films (26.0 to 48.0 mg / cm 2) is also possible.

[0088] For the negative electrode, for example, a negative electrode mixture containing a negative electrode active material and, if necessary, a solid electrolyte and a conductive material can be supported on a negative electrode current collector such as Al, Ni, stainless steel, or carbon cloth.

[0089] As the negative electrode active material, known negative electrode active materials such as metallic lithium, lithium alloys (Li-In alloys, etc.), indium metal, carbon-based materials (activated carbon, graphite, etc.), silicon, silicon oxide, Si-SiO-based materials, and lithium titanium oxide can be used.

[0090] As the solid electrolyte and the conductive material, those mentioned above can be used.

[0091] As the electrolyte layer for the all-solid-state lithium ion secondary battery, for example, one made of the same components as the above-mentioned solid electrolyte can be used.

[0092] As the solvent for the non-aqueous electrolyte for the non-aqueous electrolyte lithium ion secondary battery, solvents known as solvents for non-aqueous lithium ion secondary batteries, such as carbonates, ethers, nitriles, and sulfur-containing compounds, can be used.

[0093] The separator may be made of a material such as a polyolefin resin, such as polyethylene or polypropylene, a fluororesin, nylon, aromatic aramid, or inorganic glass, and may be in the form of a porous film, nonwoven fabric, or woven fabric.

[0094] There are no particular limitations on the shape of the non-aqueous electrolyte lithium ion secondary battery and the all-solid-state lithium ion secondary battery, and any shape such as a cylindrical shape or a prismatic shape can be used. [Example]

[0095] The present invention will be described in more detail below with reference to examples, but it goes without saying that the present invention is not limited to the following examples.

[0096] [Example 1: Synthesis of Li5VS4 powder (300 rpm, no heat treatment)] Commercially available lithium sulfide (LiS; manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: LII06PB) and commercially available crystalline vanadium(III) sulfide (VS; manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: VVI07PB) were weighed at 25°C in a glove box (dew point: -80°C) under an argon gas atmosphere so that the molar ratio was 5:1. The mixture was then mechanically milled for 160 hours in a ball mill (Fritsch PL-7) (ball diameter: 10 mm, rotation speed: 300 rpm) to synthesize vanadium-containing lithium sulfide LiVS. For the synthesized Li5VS4, the theoretical capacity was defined as the capacity when 5 mol of Li react with 1 mol of Li5VS4. When the theoretical capacity was calculated as 26801 [mAh / mol] × N ÷ M (where N is the number of electrons available for reaction per 1 mol of electrode active material [mol / mol], and M is the molar mass of the electrode active material [g / mol]), assuming N = 5 and M = 214, the theoretical capacity was 626 mAh / g.

[0097] Example 2: Li6VS 4.5 Powder synthesis] Commercially available lithium sulfide (LiS; manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: LII06PB) and commercially available crystalline vanadium(III) sulfide (VS; manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: VVI07PB) were weighed in an argon gas atmosphere glove box (dew point: -80°C) at 25°C so that the molar ratio was 6:1. The mixture was mechanically milled for 160 hours in a ball mill (Fritsch PL-7) (ball diameter: 10 mm, rotation speed: 400 rpm) to obtain vanadium-containing lithium sulfide LiVS. 4.5 The synthesized Li6VS 4.5 The theoretical capacity of Li6VS per 1 mol 4.5 When the theoretical capacity is defined as the capacity when 6 mol of Li reacts with 1 mol of electrode active material, the calculation is 26801 [mAh / mol] × N ÷ M (N is the number of electrons available for reaction per mol of electrode active material [mol / mol], and M is the molar mass of the electrode active material [g / mol]), where N = 6 and M = 237, and the theoretical capacity is 679 mAh / g.

[0098] [Example 3: Synthesis of Li7VS5 powder] Vanadium-containing lithium sulfide Li7VS5 was synthesized in the same manner as in Example 2, except that the molar ratio of lithium sulfide to vanadium(III) sulfide was adjusted to 7:1. For the synthesized Li7VS5, the theoretical capacity was defined as the capacity when 7 moles of Li react with 1 mole of Li7VS5. When N = 7 and M = 260, the theoretical capacity was calculated to be 722 mAh / g, where N is the number of reactive electrons per mole of electrode active material [mol / mol] and M is the molar mass of the electrode active material [g / mol].

[0099] Example 4: Li8VS 5.5 Powder synthesis] Vanadium-containing lithium sulfide Li8VS was prepared in the same manner as in Example 2, except that the molar ratio of lithium sulfide to vanadium (III) sulfide was adjusted to 8:1. 5.5 The synthesized Li8VS 5.5 The theoretical capacity of Li8VS per 1 mol 5.5 When the theoretical capacity is defined as the capacity when 8 mol of Li reacts with 1 mol of electrode active material, the calculation was made as 26801 [mAh / mol] × N ÷ M (where N is the number of electrons available for reaction per mol of electrode active material [mol / mol], and M is the molar mass of the electrode active material [g / mol]), with N = 8 and M = 283, and the theoretical capacity was 758 mAh / g.

[0100] [Example 5: Synthesis of Li9VS6 powder] Vanadium-containing lithium sulfide Li9VS6 was synthesized in the same manner as in Example 2, except that the molar ratio of lithium sulfide to vanadium (III) sulfide was adjusted to 9:1. For the synthesized Li9VS6, the theoretical capacity was defined as the capacity when 9 mol of Li reacts with 1 mol of Li9VS6. When N = 9 and M = 306 were used to calculate the theoretical capacity, the theoretical capacity was 789 mAh / g. The theoretical capacity was 26801 [mAh / mol] × N ÷ M (N is the number of reactive electrons per mol of electrode active material [mol / mol], and M is the molar mass of the electrode active material [g / mol]).

[0101] Example 6: Synthesis of Li5VS4 powder (300 rpm, 300°C, 4 hours) Commercially available lithium sulfide (LiS; manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: LII06PB) and commercially available crystalline vanadium(III) sulfide (VS; manufactured by Kojundo Chemical Laboratory Co., Ltd., model number: VVI07PB) were weighed at 25°C in an argon gas atmosphere glove box (dew point: -80°C) so that the molar ratio was 5:1. The mixture was then mechanically milled for 160 hours in a ball mill (Fritsch PL-7) (ball diameter: 10 mm, rotation speed: 300 rpm). The resulting material was then heat-treated at 300°C for 4 hours to synthesize the vanadium-containing lithium sulfide LiVS.

[0102] Example 7: Synthesis of Li5VS4 powder (300 rpm, 400°C, 4 hours) Vanadium-containing lithium sulfide Li5VS4 was synthesized in the same manner as in Example 6, except that the heat treatment temperature after the mechanical milling treatment was set to 400°C.

[0103] [Comparative Example 1: Synthesis of Li5VS4 powder (100 rpm, no heat treatment)] Vanadium-containing lithium sulfide Li5VS4 was synthesized in the same manner as in Example 1, except that the mechanical milling conditions were a rotation speed of 100 rpm and a time of 120 hours.

[0104] Comparative Example 2: Synthesis of Li5VS4 powder (100 rpm, no heat treatment) Vanadium-containing lithium sulfide Li5VS4 was synthesized in the same manner as in Example 1, except that the mechanical milling conditions were a rotation speed of 100 rpm and a time of 160 hours.

[0105] [Test Example 1: X-ray diffraction] Regarding the powders obtained in Examples 1 to 7 and Comparative Examples 1 and 2, Measurement equipment: Empyrean (Malvern PANalytical) X-ray source: CuKα 45kV / 40mA 0.1°step Scanning speed: 0.02° / sec X-ray diffraction (XRD) was measured in the range of 2θ = 24 to 70° using a fluorine-containing fluoride (HF) ...

[0106] In the X-ray diffraction patterns shown in FIG. 1, all of the samples of Examples 1 to 5 had a peak characteristic of Li2S with a maximum at 2θ = 27.0° and a peak characteristic of LiVS2 with a maximum at 2θ = 34.0°. The full width at half maximum of the peak with a maximum at 2θ = 27.0° was 0.86° in Example 1, 0.64° in Example 2, 0.79° in Example 3, 0.74° in Example 4, and 0.60° in Example 5. The full width at half maximum of the peak with a maximum at 2θ = 34.0° was 1.12° in Example 1, 1.79° in Example 2, 1.29° in Example 3, 2.30° in Example 4, and 1.95° in Example 5. The results are shown in Table 1.

[0107] In the X-ray diffraction diagrams shown in FIG. 2, samples 1, 6, and 7 all had a peak characteristic of Li2S with a maximum at 2θ = 27.0° and a peak characteristic of LiVS2 with a maximum at 2θ = 34.0°. On the other hand, samples 1 and 2 all had a peak characteristic of Li2S with a maximum at 2θ = 27.0° and a peak characteristic of V2S3 with a maximum at 2θ = 35.0°. The full width at half maximum of the peak with a maximum at 2θ = 27.0° was 0.86° in Example 1, 0.75° in Example 6, 0.55° in Example 7, 0.38° in Comparative Example 1, and 0.38° in Comparative Example 2. The full width at half maximum of the peak with a maximum at 2θ = 34.0° was 1.12° in Example 1, 1.14° in Example 6, and 0.82° in Example 7. The full width at half maximum of the peak having a maximum value at 2θ=35.0° was 0.32° in Comparative Example 1 and 0.32° in Comparative Example 2. The results are shown in Table 1. Therefore, when heat treatment was performed at 200°C or higher, the intensity of the peak having a maximum value at 2θ=27.0° increased, and when the mechanical milling treatment was performed at a low rotation speed (120 rpm or less), the intensity of the peak having a maximum value at 2θ=27.0° increased significantly.

[0108] [Test Example 2: Electronic Conductivity] 80 mg of the sulfide powder obtained in Examples 1 to 7 was pressure-molded using a uniaxial hydraulic press in a tablet press with a diameter of 10 mm at room temperature (25°C) at 360 MPa for 5 minutes to obtain a pressed compact for measuring electronic conductivity. The obtained pressed compact was subjected to DC polarization measurement using stainless steel as a blocking electrode to measure the electronic conductivity at 25°C. As a result, the Li5VS4 of Example 1 had a conductivity of 1.3 x 10 -1 S / cm, Li6VS of Example 2 4.5 is 1.8 x 10 -1 S / cm, and Li7VS5 in Example 3 was 1.1 × 10 -1 S / cm, Li8VS of Example 4 5.5 is 5.9 x 10 -2 S / cm, and Li9VS6 in Example 5 is 3.5 × 10 -2 S / cm, and Li5VS4 in Example 6 is 5.4 × 10 -2S / cm, and Li5VS4 in Example 7 is 9.4 × 10 -2 Both have an electronic conductivity of 10 S / cm. -8 S / cm), the electronic conductivity was significantly improved. -8 S / cm or less, and Comparative Example 2 is 2.4 × 10 -9 It has an electronic conductivity of 10 S / cm and is -8 The results are shown in Table 1.

[0109] [Table 1]

[0110] [Example 8: Production of lithium ion secondary battery (Example 1; hand mixing)] Using the Li5VS4 powder obtained in Example 1 as a positive electrode active material, a test electrochemical cell (all-solid lithium ion secondary battery) was produced by the following method.

[0111] First, the working electrode (positive electrode) was prepared by adding 50 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte and 10 parts by mass of acetylene black as a conductive material to 40 parts by mass of the Li5VS4 powder obtained in Example 1 to adjust the total weight to 10 mg, and then manually mixing the mixture in a mortar for 5 minutes. A lithium-indium alloy (lithium foil manufactured by Honjo Metals Co., Ltd., indium foil manufactured by Furuuchi Chemical Co., Ltd.) was used as the counter electrode (negative electrode). 80 mg of an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte layer. The above-mentioned electrolyte layer was pressure-molded together with the above-mentioned positive and negative electrodes to prepare a test electrochemical cell (all-solid-state lithium-ion secondary battery).

[0112] [Example 9: Production of lithium ion secondary battery (Example 6; hand mixing)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 8, except that the Li5VS4 powder obtained in Example 6 was used as the sulfide powder for the positive electrode active material.

[0113] [Example 10: Production of lithium ion secondary battery (Example 7; hand mixing)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 8, except that the Li5VS4 powder obtained in Example 7 was used as the sulfide powder for the positive electrode active material.

[0114] [Example 11: Production of lithium ion secondary battery (Example 1; milling)] Using the Li5VS4 powder obtained in Example 1 as a positive electrode active material, a test electrochemical cell (all-solid lithium ion secondary battery) was produced by the following method.

[0115] First, the working electrode (positive electrode) was prepared by adding 50 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte and 10 parts by mass of acetylene black as a conductive material to 40 parts by mass of the Li5VS4 powder obtained in Example 1 to adjust the total weight to 10 mg, and mechanically milling the mixture for 1 hour using a ball mill (PL-7 manufactured by Fritsch) (ball diameter: 4 mm, rotation speed: 160 rpm). A lithium-indium alloy (lithium foil manufactured by Honjo Metals Co., Ltd., indium foil manufactured by Furuuchi Chemical Co., Ltd.) was used as the counter electrode (negative electrode). 80 mg of an argyrodite-type sulfide-based solid electrolyte was used as the electrolyte layer. The electrolyte layer was then pressure-molded together with the positive and negative electrodes to prepare a test electrochemical cell (all-solid-state lithium-ion secondary battery).

[0116] [Example 12: Production of lithium ion secondary battery (Example 2; milling)] As the sulfide powder, Li6VS obtained in Example 2 was used. 4.5 A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the powder was used as the positive electrode active material.

[0117] [Example 13: Production of lithium ion secondary battery (Example 3; milling)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the Li7VS5 powder obtained in Example 3 was used as the sulfide powder for the positive electrode active material.

[0118] [Example 14: Production of lithium ion secondary battery (Example 4; milling)] As the sulfide powder, Li8VS obtained in Example 4 was used. 5.5 A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the powder was used as the positive electrode active material.

[0119] [Example 15: Production of lithium ion secondary battery (Example 5; milling)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the Li9VS6 powder obtained in Example 5 was used as the sulfide powder for the positive electrode active material.

[0120] [Example 16: Production of lithium ion secondary battery (Example 1; milling)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the positive electrode mixture was adjusted to a total of 5 mg by adding 30 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte to 70 parts by mass of the Li5VS4 powder obtained in Example 1.

[0121] [Example 17: Production of lithium ion secondary battery (Example 1; milling)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the positive electrode mixture was adjusted to a total of 10 mg by adding 30 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte to 70 parts by mass of the Li5VS4 powder obtained in Example 1.

[0122] [Example 18: Production of lithium ion secondary battery (Example 1; milling)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the positive electrode mixture was adjusted to a total of 5 mg by adding 20 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte to 80 parts by mass of the Li5VS4 powder obtained in Example 1.

[0123] [Example 19: Production of lithium ion secondary battery (Example 1; milling)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the positive electrode mixture was adjusted to a total of 10 mg by adding 20 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte to 80 parts by mass of the Li5VS4 powder obtained in Example 1.

[0124] [Example 20: Production of lithium ion secondary battery (Example 1; milling)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the positive electrode mixture was adjusted to a total of 4 mg by adding 20 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte and 1 part by mass of vapor-grown carbon fiber VGCF (manufactured by Showa Denko K.K.) to 80 parts by mass of the Li5VS4 powder obtained in Example 1.

[0125] [Example 21: Production of lithium ion secondary battery (Example 1; milling)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the positive electrode mixture was adjusted to a total of 10 mg by adding 20 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte and 1 part by mass of vapor-grown carbon fiber VGCF (Showa Denko K.K.) to 80 parts by mass of the Li5VS4 powder obtained in Example 1.

[0126] [Example 22: Production of lithium ion secondary battery (Example 1; milling)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the positive electrode mixture was adjusted to a total of 20 mg by adding 20 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte and 1 part by mass of vapor-grown carbon fiber VGCF (Showa Denko K.K.) to 80 parts by mass of the Li5VS4 powder obtained in Example 1.

[0127] [Example 23: Production of lithium ion secondary battery (Example 1; milling)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that the positive electrode mixture was adjusted to a total of 10 mg by adding 20 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte and 2 parts by mass of vapor-grown carbon fiber VGCF (Showa Denko K.K.) to 80 parts by mass of the Li5VS4 powder obtained in Example 1.

[0128] [Example 24: Production of lithium ion secondary battery (Example 2; milling)] The positive electrode mixture was Li6VS obtained in Example 2. 4.5 A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that 20 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte was added to 80 parts by mass of the argyrodite-type sulfide-based solid electrolyte to adjust the total weight to 5 mg.

[0129] [Example 25: Production of lithium ion secondary battery (Example 4; milling)] The positive electrode mixture was Li8VS obtained in Example 4. 5.5 A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that 25 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte and 1 part by mass of vapor grown carbon fiber VGCF (Showa Denko K.K.) were added to 75 parts by mass of the sintered body to adjust the total weight to 5 mg.

[0130] [Example 26: Production of lithium ion secondary battery (Example 4; milling)] The positive electrode mixture was Li8VS obtained in Example 4. 5.5A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 11, except that 20 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte and 1 part by mass of vapor grown carbon fiber VGCF (Showa Denko K.K.) were added to 80 parts by mass of the sintered body to adjust the total weight to 5 mg.

[0131] [Example 27: Production of lithium ion secondary battery (Example 4; hand mixing)] Li8VS obtained in Example 4 5.5 Using the powder as a positive electrode active material, a test electrochemical cell (all-solid lithium ion secondary battery) was produced by the following method.

[0132] First, the working electrode (positive electrode) was Li8VS obtained in Example 4. 5.5 To 80 parts by mass of the powder, 20 parts by mass of an argyrodite-type sulfide-based solid electrolyte was added to adjust the total weight to 33 mg, and the mixture was hand-mixed in a mortar for 15 minutes. A lithium-indium alloy (lithium foil manufactured by Honjo Metals Co., Ltd., indium foil manufactured by Furuuchi Chemical Co., Ltd.) was used as the counter electrode (negative electrode). 80 mg of the argyrodite-type sulfide-based solid electrolyte was used as the electrolyte layer. The above-mentioned electrolyte layer was pressure-molded together with the above-mentioned positive and negative electrodes to prepare a test electrochemical cell (all-solid-state lithium-ion secondary battery).

[0133] [Example 28: Production of lithium ion secondary battery (Example 4; hand mixing)] The positive electrode mixture was Li8VS obtained in Example 4. 5.5 A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 27, except that 15 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte was added to 85 parts by mass of the powder so as to adjust the total weight to 10 mg.

[0134] [Example 29: Production of lithium ion secondary battery (Example 4; hand mixing)] The positive electrode mixture was Li8VS obtained in Example 4. 5.5A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 27, except that 30 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte was added to 70 parts by mass of the sintered body to adjust the total weight to 37 mg.

[0135] [Example 30: Production of lithium ion secondary battery (Example 4; hand mixing)] The positive electrode mixture was Li8VS obtained in Example 4. 5.5 A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 27, except that 20 parts by mass of an argyrodite-type sulfide-based solid electrolyte as a solid electrolyte was added to 80 parts by mass of the argyrodite-type sulfide-based solid electrolyte to adjust the total weight to 46 mg.

[0136] [Comparative Example 3: Production of Lithium-ion Secondary Battery (Comparative Example 1; Hand Mixing)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 8, except that the Li5VS4 powder obtained in Comparative Example 1 was used as the sulfide powder for the positive electrode active material.

[0137] [Comparative Example 4: Production of Lithium-ion Secondary Battery (Comparative Example 2; Hand Mixing)] A test electrochemical cell (all-solid-state lithium ion secondary battery) was produced in the same manner as in Example 8, except that the Li5VS4 powder obtained in Comparative Example 2 was used as the sulfide powder for the positive electrode active material.

[0138] [Test Example 3: Charge / Discharge Test (Part 1)] Using the test electrochemical cells (all-solid-state lithium ion secondary batteries) obtained in Examples 8 to 10 and Comparative Examples 3 and 4, a current density of 0.13 mA / cm was measured at 25°C. 2 Constant current charge / discharge measurements were carried out within a voltage range of 1.1 to 3.0 V. The initial charge was up to 3.0 V, and the discharge was cut off at 1.1 V.

[0139] As a result, the initial discharge capacity was 514 mAh / g in Example 8, 333 mAh / g in Example 9, 271 mAh / g in Example 10, 8 mAh / g in Comparative Example 3, and 15 mAh / g in Comparative Example 4. The results are shown in Table 2.

[0140] [Table 2]

[0141] [Test Example 4: Charge / Discharge Test (Part 2)] Using the test electrochemical cells (all-solid-state lithium ion secondary batteries) obtained in Examples 11 to 15, a current density of 0.13 mA / cm was measured at 25°C. 2 Constant current charge / discharge measurements were performed within a voltage range of 0 to 3.4 V. The initial charge was up to 3.0 V, and the discharge was cut off at the initial charge capacity.

[0142] The initial charge / discharge curves for the test electrochemical cells (all-solid-state lithium-ion secondary batteries) obtained in Examples 11 to 15 are shown in Figure 3. As a result, the initial charge capacity was 629 mAh / g in Example 11 (initial charge capacity / theoretical capacity ratio: 100%), the initial charge capacity was 588 mAh / g in Example 12 (initial charge capacity / theoretical capacity ratio: 87%), the initial charge capacity was 599 mAh / g in Example 13 (initial charge capacity / theoretical capacity ratio: 83%), the initial discharge capacity was 649 mAh / g in Example 14 (initial charge capacity / theoretical capacity ratio: 86%), and the initial discharge capacity was 639 mAh / g in Example 15 (initial charge capacity / theoretical capacity ratio: 81%). Thus, the smaller the amount of Li2S, the closer the actual capacity was to the theoretical capacity.

[0143] [Test Example 5: Rate Characteristics (Part 1)] The test electrochemical cells (all-solid-state lithium-ion secondary batteries) obtained in Examples 11 to 15 were used to evaluate the rate characteristics under high current density. At 25°C, the current density was 0.13 mA / cm up to the 10th cycle. 2 , 11 to 20 cycles: current density 0.25 mA / cm 2, and the current density for cycles 21 to 30 was 0.64 mA / cm 2 , 31 to 40 cycles: current density 1.3 mA / cm 2 , and the current density for cycles 41 to 50 was 0.13 mA / cm 2 Constant current charge / discharge measurements were performed within the voltage range of 0 to 3.4 V and the initial charge capacity. A 10-minute break was allowed between each cycle, and the initial charge was charged to 3.0 V, and the discharge was cut off at the initial charge capacity.

[0144] The results of the rate characteristics using the test electrochemical cells (all-solid-state lithium ion secondary batteries) obtained in Examples 11 and 12 are shown in Figure 4. As a result, it can be seen that Examples 11 and 12 have excellent rate characteristics even under high current density.

[0145] [Test Example 6: Charge / Discharge Test (Part 3)] Using the test electrochemical cells (all-solid-state lithium ion secondary batteries) obtained in Examples 16 to 26, a current density of 0.13 mA / cm was measured at 25°C or 45°C. 2 A 10-cycle constant current charge / discharge measurement was performed within the voltage range of 0 to 3.4 V and the initial charge capacity. The initial charge was up to 3.0 V, and the discharge was cut off at the initial charge capacity.

[0146] The results of the initial charge capacity using the test electrochemical cells (all-solid-state lithium ion secondary batteries) obtained in Examples 16 to 23 are shown in Table 3 and Fig. 5. As a result, it can be seen that when the Li5VS4 powder obtained in Example 1 was used, Examples 21 and 23, which contained vapor grown carbon fiber VGCF in the positive electrode mixture, had a higher capacity when the amount of the positive electrode mixture was 10 mg, compared to Example 19, which did not contain vapor grown carbon fiber VGCF in the positive electrode mixture.

[0147] [Table 3]

[0148] Next, the test electrochemical cells (all-solid-state lithium-ion secondary batteries) obtained in Examples 20, 22, and 24 to 26 were used, and the results of the initial charge capacity when operated at 25°C or 45°C are shown in Table 4 and Fig. 6. As a result, it can be seen that in Example 26, the capacity is improved when operated at 45°C.

[0149] [Table 4]

[0150] Next, Fig. 7 shows the results of the discharge capacity of the test electrochemical cells (all-solid-state lithium ion secondary batteries) obtained in Examples 16 to 21 and 23 to 26 after 10 cycles when operated at 25°C or 45°C. As a result, it can be seen that Examples 16 to 21 and 23 to 26 also have excellent cycle characteristics.

[0151] [Test Example 7: Charge / Discharge Test (Part 4)] Using the test electrochemical cells (all-solid-state lithium ion secondary batteries) obtained in Examples 27 to 30, a current density of 0.16 mA / cm was measured at 25°C or 60°C. 2 (Example 27), current density 0.18 mA / cm 2 (Example 28) or current density 0.28 mA / cm 2 In Examples 29 and 30, 10 cycles of constant current charge / discharge measurements were carried out at voltages of 0.6 to 3.0 V. During initial charging, charging was performed up to 3.0 V, and during discharging, the capacity was cut off at the initial charge capacity.

[0152] The results of the initial charge capacity using the test electrochemical cells (all-solid-state lithium ion secondary batteries) obtained in Examples 27 to 30 are shown in Table 5. As a result, the Li8VS obtained in Example 4 5.5 It can be seen that when powder is used, the capacity is sufficiently high even without using a conductive material. Also, in Examples 29 and 30, when operated at 60°C, the capacity is high even when the positive electrode mixture amount is 37 mg and 46 mg, resulting in a thick film.

[0153] [Table 5]

Claims

1. Contains lithium, vanadium and sulfur, The ratio of the lithium content to the vanadium content is 4.5 to 9.5 in terms of molar ratio, and the ratio of the sulfur content to the vanadium content is 3.5 to 6.5 in terms of molar ratio, A vanadium-containing lithium sulfide having a full width at half maximum of a peak at 2θ=27.0±0.1° in an X-ray diffraction pattern using CuKα radiation of 0.40 to 0.90°.

2. The vanadium-containing lithium sulfide according to claim 1, wherein the abundance ratio of elements other than lithium, vanadium, and sulfur is 0 to 5 mol% with the total amount of the vanadium-containing lithium sulfide being 100 mol%.

3. General formula (1): LixVSy (1) [Wherein, 4.5≦x≦9.5; and 3.5≦y≦6.5.] The vanadium-containing lithium sulfide according to claim 1, having a composition represented by the formula:

4. The vanadium-containing lithium sulfide according to claim 1, wherein the full width at half maximum of the peak at 2θ = 34.0 ± 0.9 ° in an X-ray diffraction diagram using CuKα rays is 0.80 to 2.50 °.

5. The vanadium-containing lithium sulfide according to claim 1, which is used as a positive electrode active material for a lithium ion secondary battery.

6. The method for producing the vanadium-containing lithium sulfide according to any one of claims 1 to 5, A step of subjecting a starting material containing lithium sulfide and vanadium sulfide to mechanical milling at a rotation speed of 120 rpm or more. A manufacturing method comprising:

7. The method according to claim 6 , wherein the mechanical milling step is not followed by a heat treatment at 200° C. or higher.

8. A positive electrode active material for a lithium ion secondary battery, comprising the vanadium-containing lithium sulfide according to any one of claims 1 to 5.

9. A positive electrode for a lithium ion secondary battery, comprising the positive electrode active material for a lithium ion secondary battery according to claim 8.

10. The positive electrode for a lithium ion secondary battery according to claim 9 , further comprising a solid electrolyte and a conductive material.

11. 11. The positive electrode for a lithium ion secondary battery according to claim 10, wherein the conductive material is a conductive carbon fiber.

12. The positive electrode for a lithium ion secondary battery according to claim 10, wherein the content of the positive electrode active material for a lithium ion secondary battery is 65 to 95 mass%, where the total amount of the positive electrode for a lithium ion secondary battery is 100 mass%.

13. In the positive electrode for the lithium ion secondary battery, the loading amount of the positive electrode mixture containing the vanadium-containing lithium sulfide is 5.0 to 48.0 mg / cm ２ The positive electrode for a lithium ion secondary battery according to claim 9 ,

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

15. The lithium ion secondary battery according to claim 14, which is an all-solid-state lithium ion secondary battery.

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