Method for manufacturing positive electrode mixture

Abstract

This method for manufacturing a positive electrode mixture uses a device that is provided with: a rotor having a blade for applying an impact force to a mixture containing a sulfur-based active material, an electron conductive material, and a solid electrolyte; and a barrel storing the rotor, and that applies shear force to the mixture at a gap part between the blade or the rotor and the barrel.

Description

Positive electrode composite manufacturing method

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

[0002] With the recent development of mobile communications and information electronic devices, there has been an increasing demand for high-capacity, lightweight lithium-ion secondary batteries. Most electrolytes that exhibit high lithium-ion conductivity at room temperature are liquid, and many commercially available lithium-ion secondary batteries use organic electrolytes. However, lithium-ion secondary batteries using organic electrolytes pose a risk of leakage, fire, or explosion, so safer batteries are desired.

[0003] All-solid-state lithium-ion batteries, which use a safer solid electrolyte, are expected to solve the above problems and are the next generation of lithium-ion batteries. All-solid-state batteries using a solid electrolyte have the advantage of being less susceptible to electrolyte leakage and fire.

[0004] Many active materials for lithium-ion secondary batteries have low ionic and electronic conductivity, and therefore, when manufacturing electrodes, it is common to use not only the active material but also an ionic and electronic conductive material. In particular, in all-solid-state batteries, the active material, solid electrolyte (ionic conductive material), and electronic conductive material are all particulate, so in order to increase the ionic and electronic conductivity, it is necessary to increase the number of contact points between the active material and the solid electrolyte, and between the active material and the electronic conductive material. In particular, sulfur-based active materials, which are expected to be high-capacity active materials, have low electronic and ionic conductivity, and therefore, when combining them with a solid electrolyte or an electronic conductive material, it is extremely important to increase the contact points.

[0005] As a method for increasing the number of contact points, a method is known in which a mixture containing an active material, a solid electrolyte, and an electronically conductive material is mechanically milled using a planetary ball mill to form a composite (see, for example, Non-Patent Documents 1 and 2).

[0006] The planetary ball mill can freely combine various materials and is a user-friendly experimental device. However, it requires a large amount of power to impart kinetic energy to the balls, which act as the media, and the material adheres heavily to the balls, resulting in low yields, making it unsuitable for mass production.

[0007] Patent Document 1 also discloses a technique for producing a positive electrode composite by combining a sulfur-based active material, a solid electrolyte, and an electronically conductive material using a screw-equipped kneader. Screw kneaders have been industrially used in a variety of fields. However, in the examples of Patent Document 1, the composite operation in the kneader had to be repeated 100 times or more to produce the positive electrode composite. Repeating the composite operation several times was not enough to increase the number of contact points, and the high capacity characteristic of the sulfur-based positive electrode composite could not be achieved, particularly in battery evaluations at high rates.

[0008] JP 2016-213184 A

[0009] M. Tatsumisago et al., Journal of Power Sources, 274 (2015) 471Maohua Chen et al., Solid State Ionics, 262 (2014) 183

[0010] An object of the present invention is to provide a manufacturing method suitable for mass production of a positive electrode mixture.

[0011] As a result of extensive research, the present inventors have found that a specific apparatus is suitable for mass production of a positive electrode composite. Furthermore, they have found that by using an apparatus capable of applying impact force to a sulfur-based active material, a solid electrolyte, and an electronically conductive material without using a grinding medium such as balls or beads, a dense composite can be easily achieved, resulting in a positive electrode composite with a large electrical capacity.

[0012] According to the present invention, the following methods for producing a cathode mixture are provided. 1. A method for producing a cathode mixture, comprising: a rotor having a blade that applies an impact force to a mixture containing a sulfur-based active material, an electronically conductive material, and a solid electrolyte; and a barrel that houses the rotor, using an apparatus that applies a shear force to the mixture in a gap between the blade or rotor and the barrel. 2. The method for producing a cathode mixture as described in 1, in which the impact force is applied with a plate surface of the blade. 3. A method for producing a cathode mixture, comprising a step of applying an impact force to a mixture containing a sulfur-based active material, an electronically conductive material, and a solid electrolyte without using grinding media, but not using grinding media. 4. The method for producing a cathode mixture as described in 3, in which the step of applying an impact force without using grinding media applies an impact force and a shear force to the mixture. 5. The method for producing a cathode mixture as described in 3 or 4, in which the step of applying an impact force without using grinding media uses a rotor having a blade that rotates at high speed and applies an impact force to the mixture; and a barrel that houses the rotor, using an apparatus that applies a shear force to the mixture in a gap between the blade or rotor and the barrel. 6. The rotation speed of the rotor is set so that the maximum impact velocity is 10 m / s or more and the maximum shear velocity is 1000 s －１ 7. The manufacturing method according to 1 or 5, wherein the product of the maximum impact velocity (m / s) and the treatment time (h) is set to be 10 or more. 8. The manufacturing method according to 6, wherein the product of the maximum shear velocity (s －１) and the treatment time (h) are set so that the product of the number of times of impact and shear force is 2500 or more. 9. The manufacturing method according to any one of 1 to 8, wherein impact force and shear force are applied to the mixture by a high-velocity airflow impact method or an angmill grinding method. 10. The manufacturing method according to any one of 1 to 9, further comprising a step of mixing the solid electrolyte with a composite material of the sulfur-based active material and the electronically conductive material to prepare the mixture. 11. The manufacturing method according to 10, wherein the sulfur-based active material is composited with the electronically conductive material in a molten state. 12. The manufacturing method according to 10, wherein the sulfur-based active material and the electronically conductive material are composited using a twin-screw kneader or a precision shearing device. 13. The manufacturing method according to any one of 1 to 12, wherein the solid electrolyte is a sulfide solid electrolyte containing lithium atoms or sodium atoms, phosphorus atoms, and sulfur atoms as constituent elements.

[0013] According to the present invention, a manufacturing method suitable for mass production of a positive electrode mixture can be provided.

[0014] 1A and 1B are schematic diagrams illustrating the main parts of an example of a mixing and grinding apparatus used in the present invention, in which (A) is a front view and (B) is a side cross-sectional view. 2A and 2B are schematic diagrams illustrating the main parts of another example of a mixing and grinding apparatus used in the present invention, in which (A) is a front view and (B) is a side cross-sectional view.

[0015] The method for producing a positive electrode composite according to the first embodiment of the present invention uses an apparatus that includes a rotor having blades that apply an impact force to a mixture containing a sulfur-based active material, an electronically conductive material, and a solid electrolyte, and a barrel that houses the rotor, and that applies a shear force to the mixture in the gap between the blade or rotor and the barrel. Note that, in this embodiment, grinding media may or may not be used.

[0016] Furthermore, the method for producing a positive electrode composite according to the second embodiment of the present invention includes a step of applying an impact force to a mixture containing a sulfur-based active material, an electronically conductive material, and a solid electrolyte without using a grinding medium, and does not include a step of using a grinding medium in the entire process for producing the positive electrode composite. Preferably, the step of applying an impact force without using a grinding medium applies an impact force and a shear force to the mixture.

[0017] In order to realize the functionality of the positive electrode composite, the sulfur-based active material, solid electrolyte, and electronic conductive material, which are the main constituent raw materials of the positive electrode composite, must be densely combined. Specifically, it is important that (1) the contact area of ​​each raw material particle is increased by finely grinding it, and then (2) that the adhesion between the contacting raw material particles is sufficiently increased. The above (1) can be achieved mainly by applying an impact force to the raw material mixture. The above (2) can be achieved by applying a shear force to the raw material mixture. By applying a predetermined force or more to the raw material mixture, the performance of the positive electrode composite can be enhanced.

[0018] Conventionally, a mixing and grinding device using grinding media, such as a planetary ball mill, has been commonly used to apply high impact and shear forces to a raw material mixture. In the present invention, it has been discovered that it is possible to apply high impact and shear forces to a raw material mixture without using grinding media, as in the device used in the first embodiment. Note that the grinding media (media) is different from the grinding device itself and refers to objects (balls, beads, etc.) that are placed in the device for the purpose of applying a grinding force to the material to be ground. Furthermore, the manufacturing process of a positive electrode composite refers to a process for manufacturing a positive electrode composite from the main constituent raw materials of the positive electrode composite, and does not include, for example, a process for manufacturing the solid electrolyte itself, which is a constituent raw material.

[0019] Examples of techniques that can apply high impact and shear forces to a mixture include the high-velocity airflow impact method and the Angmill crushing method. Examples of equipment that applies the high-velocity airflow impact method include the Hybridization System (Nara Machinery Manufacturing Co., Ltd.). Examples of equipment that applies the Angmill crushing method include the Mechanofusion System, Nobilta, and Nobilta Belcom (Hosokawa Micron).

[0020] In one embodiment, the apparatus for the above method includes a rotor having blades that rotate at high speed and apply an impact force to the mixture, and a barrel that houses the rotor, and shear force is applied to the mixture in the gap between the blades or rotor and the barrel.

[0021] FIG. 1 is a schematic diagram illustrating the main components of an example of a mixer / grinding apparatus used in the present invention, with (A) being a front view and (B) being a side cross-sectional view. The mixer / grinding apparatus 1 primarily comprises a barrel 11 having a cylindrical space, a rotor 12 that freely rotates around the center of the cylindrical space as its axis, and plate-shaped blades 13 attached to the outer periphery of the rotor 12 in the circumferential direction of the barrel. In the mixer / grinding apparatus 1, a raw material mixture is introduced into the cylindrical space within the barrel 11. As the rotor 12 rotates, the raw material mixture collides with the plate surfaces of the blades 13, thereby applying an impact force to the raw material mixture. Furthermore, centrifugal force causes the raw material mixture to densely deposit on the inner wall of the barrel 11, and shear force is applied by the ends of the blades 13. In addition to the above-described main components, the mixer / grinding apparatus may also include a circulation mechanism for the processed material, a sealing lid, etc.

[0022] FIG. 2 is a schematic diagram illustrating the main components of another example of a mixer / grinding apparatus used in the present invention, with (A) being a front view and (B) being a side cross-sectional view. The mixer / grinding apparatus 2 primarily comprises a barrel 21 having a cylindrical space, a cylindrical rotor 22 that freely rotates around the center of the cylindrical space, and a plate-like blade 23 attached to the inner wall of the cylindrical rotor 22 toward the center. In the mixer / grinding apparatus 2, the raw material mixture is introduced near the center of the cylindrical rotor 22. As the cylindrical rotor 22 rotates, the raw material mixture collides with the plate surface of the blade 23, thereby applying an impact force to the raw material mixture. Furthermore, centrifugal force moves the raw material mixture into the gap between the inner wall of the barrel 21 and the cylindrical rotor 22, where shear force is applied. In addition to the above-described main components, the mixer / grinding apparatus may also include a circulation mechanism for the processed material, a sealing lid, etc.

[0023] In the mixer-grinding devices 1 and 2, the faster the rotor rotates and the longer the blades, the greater the impact force applied to the raw material mixture. Also, the faster the rotor rotates and the smaller the gap d between the end of the blade or the outer periphery of the cylindrical rotor and the inner wall of the barrel 11, the greater the shear force applied to the raw material mixture.

[0024] The blade length, i.e., the size of the device and the gap d, vary depending on the device used. For example, the rotor rotation speed is set to a maximum impact velocity of 10 m / s or more and a maximum shear velocity of 1000 s －１ The maximum impact velocity and maximum shear velocity can be calculated from the rotation speed R (rpm) of the rotor, screw, etc. (rotating body), the distance r (mm) from the rotating shaft to the tip of the blade, and the gap d (mm) between the rotating body and the barrel, etc. (fixed body). Details will be explained in the Examples.

[0025] In one embodiment, the rotational speed of the rotor is set to a value such that the maximum impact velocity is 20 m / s or more and the maximum shear rate is 10,000 s －１ It is preferable to set the maximum impact velocity to 200 m / s or less, and the maximum shear velocity to 200,000 s －１ The maximum impact velocity is more preferably 30 m / s or more and 150 m / s or less, even more preferably 40 m / s or more and 100 m / s or less, and particularly preferably 80 m / s or more and 100 m / s or less. In addition, the maximum shear velocity is 10,000 s －１ More than 100000s －１ It is more preferable that it is 20,000 s or less. －１ Over 80,000s －１ More preferably, 25,000 s －１ Over 60,000s －１ The following are particularly preferred:

[0026] There are no particular restrictions on the amount of raw material mixture to be filled, but a sufficient amount is filled to apply shear force to the raw material mixture. Specifically, it is preferable to fill an amount equal to or greater than the volume fraction of the gap. For example, in the case of the Nobilta NOB-MINI (Hosokawa Micron), the filling amount is 4.4 to 99.0% of the device capacity, and in the case of the Hybridization System: Model NHS-0 (Nara Machinery Works), the filling amount is 10.9 to 99.0% of the device capacity.

[0027] The treatment time is adjusted appropriately depending on the equipment used. The adjustment can be performed by checking the performance and shape of the positive electrode composite after treatment. The higher the above-mentioned maximum impact velocity and maximum shear rate, the shorter the treatment time can be. In other words, the values ​​of the maximum impact velocity and maximum shear rate serve as a guide for determining the treatment time. For example, controlling the treatment time so that the product of the maximum impact velocity (m / s) and the treatment time (h) is 10 or more can further improve the performance of the resulting positive electrode composite. Preferably, the product value is 15 or more, more preferably 20 or more. Similarly, it is preferable to control the treatment time so that the product of the maximum shear rate (1 / s) and the treatment time (h) is 2500 or more. More preferably, it is 10,000 or more, and even more preferably 20,000 or more.

[0028] In this embodiment, a positive electrode composite is produced by applying an impact force, or an impact force and a shear force, to a mixture containing a sulfur-based active material, an electron conductive material, and a solid electrolyte using the above-mentioned device, etc. Hereinafter, raw materials for the positive electrode composite will be described.

[0029] [Sulfur-based active material] The sulfur-based active material is not particularly limited, but sulfur, lithium sulfide (Li ２ S), lithium polysulfide (Li ２ S ｎ : n satisfies 1<n≦8.), titanium sulfide (TiS ２ ), molybdenum sulfide (MoS ２ ), iron sulfide (FeS, FeS ２ ), copper sulfide (CuS), nickel sulfide (Ni ３ S ２ ), sulfur-containing polymer compounds, etc. Among these, sulfur is preferred. There are no particular limitations on the sulfur, but sulfur with a high purity is preferred. Specifically, the purity is preferably 95% by mass or more, more preferably 96% by mass or more, and particularly preferably 97% by mass or more. Examples of the crystal system of sulfur include α sulfur (orthorhombic system), β (monoclinic system), γ (monoclinic system), amorphous sulfur, etc. These can be used alone or in combination of two or more types.

[0030] [Electron-Conductive Material] The electron-conductive material is not particularly limited as long as it has electron conductivity and can be composited with a sulfur-based active material. The electron-conductive material preferably includes a carbon material, since it is lighter than other materials and can increase the output density and electrical capacity per unit mass of the battery. The carbon material is preferably a porous carbon material having multiple pores. Examples of carbon materials include carbon black, mesoporous carbon, carbon nanotubes, carbon nanohorns, fullerenes, amorphous carbon, carbon fiber, natural graphite, artificial graphite, and activated carbon. Of these, activated carbon is preferred. These materials may be used alone or in combination of two or more.

[0031] In one embodiment, the BET specific surface area of ​​the carbon material is 50 m ２ This allows a wide contact interface between the carbon material and elemental sulfur to be formed, improving the utilization rate of sulfur. The BET specific surface area is 70 m ２ / g or more is preferable, and 100m ２ The upper limit of the BET specific surface area is not particularly limited, but is preferably 5000 m ２ / g or less, and more preferably 4000m ２ / g or less is preferred.

[0032] In this embodiment, the specific surface area can be measured by the Brenauer-Emmet-Telle (BET) method or the BJH (Barrett-Joyner-Halenda) method. Specifically, the specific surface area can be determined using a nitrogen adsorption isotherm obtained by adsorbing nitrogen gas onto a carbon material at liquid nitrogen temperature. As a measuring device, for example, a specific surface area and pore distribution measuring device (Autosorb-3) manufactured by Quantacrome can be used for the measurement.

[0033] [Solid Electrolyte] Examples of solid electrolytes include sulfide solid electrolytes containing lithium atoms or sodium atoms, phosphorus atoms, and sulfur atoms as constituent elements. The sulfide solid electrolyte is a solid electrolyte that contains at least sulfur atoms and exhibits ionic conductivity due to the contained metal atoms, and in addition to sulfur atoms, preferably contains lithium atoms and phosphorus atoms, more preferably contains lithium atoms, phosphorus atoms, and halogen atoms, and has ionic conductivity due to lithium atoms. The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

[0034] (Amorphous sulfide solid electrolyte) The amorphous sulfide solid electrolyte can be used without any particular limitation as long as it contains at least sulfur atoms and exhibits ionic conductivity due to the contained metal atoms. Representative examples include Li ２ S-P ２ S ５ a solid electrolyte containing sulfur atoms, lithium atoms, and phosphorus atoms, which is composed of lithium sulfide and phosphorus sulfide such as Li; ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ -LiI-LiBr, etc., a solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide; ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ -P ２ S ５ In order to obtain higher ionic conductivity, a solid electrolyte such as Li ２ S-P ２ S ５ - LiI, Li２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as LiI-LiBr, is preferred. The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0035] The amorphous sulfide solid electrolyte contains at least Li ２ S-P ２ S ５ When Li ２ S and P ２ S ５ From the viewpoint of obtaining high chemical stability and higher ionic conductivity, the molar ratio of Li to Li is preferably 30 to 85:15 to 70, more preferably 40 to 80:20 to 60, and even more preferably 45 to 78:22 to 55. ２ S-P ２ S ５ In the case of -LiI-LiBr, the total content of lithium sulfide and diphosphorus pentasulfide is preferably 30 to 95 mol%, more preferably 35 to 90 mol%, and even more preferably 40 to 85 mol%. The ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, even more preferably 40 to 80 mol%, and particularly preferably 50 to 70 mol%.

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

[0037] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 to 200 μm. ５０ ) is the particle size at which 50% of the total particle size is reached when the particle size distribution integral curve is drawn and the integral is calculated from the smallest particle size, and the volume distribution is an average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device.

[0038] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte may be, for example, a so-called glass ceramic obtained by heating the amorphous sulfide solid electrolyte to a temperature equal to or higher than the crystallization temperature, and a sulfide solid electrolyte having the following crystal structure may be used. Examples of crystal structures that the crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, and phosphorus atoms may have include Li ３ P.S. ４ Crystal structure, Li ４ P ２ S ６ Crystal structure, Li ７ P.S. ６ Crystal structure, Li ７ P ３ S １１ Examples of such structures include a crystal structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP 2013-16423 A).

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

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

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

[0042] Among the above crystal structures, the crystal structure of the crystalline sulfide solid electrolyte is Li ３ P.S. ４ The crystal structure, the thiolicon region II crystal structure, and the argyrodite crystal structure are preferred.

[0043] The shape of the crystalline sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) is the average particle size (D ５０ ) and the range of 0.01 μm to 500 μm, or 0.1 to 200 μm, for example, can be exemplified.

[0044] In one embodiment, the positive electrode mixture may or may not contain components other than the sulfur-based active material, the electron conductive material, and the solid electrolyte. The other components are not particularly limited, but examples thereof include an ion conductor, a binder, a solvent, and a dispersant.

[0045] The ion conductor may be a lithium ion conductive material containing one or more elements selected from lithium, boron, oxygen, phosphorus, halogen, and antimony, or a precursor thereof. Examples of the lithium ion conductive material include lithium borohydride, LiBF ４, organic lithium salts, polymer electrolytes such as polyethylene oxide, etc. Precursors of lithium ion conductive materials include phosphorus sulfides such as diphosphorus pentasulfide, red phosphorus, boron sulfide, diphosphorus pentoxide, tin, etc. These compounds may be used alone or in combination of two or more.

[0046] Examples of organic lithium salts include bis(perfluoroalkylsulfonyl)imide lithium salts such as bis(trifluoromethanesulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, fluorosulfonyl-trifluoromethanesulfonylimide lithium, bis(pentafluoroethanesulfonyl)imide lithium, and bis(nonafluorobutanesulfonyl)imide lithium; lithium salts of perfluoroalkylsulfonimides such as 4,4,5,5-tetrafluoro-1,3,2-dithiazolidine-1,1,3,3-tetraoxide lithium salt; lithium salts of fluorosulfonylimides; lithium carboxylic acid salts such as trifluoromethanesulfonic acid, lithium acetate, lithium propionate, and lithium butyrate; lithium organic sulfonates such as lithium dodecylbenzenesulfonate and lithium p-styrenesulfonate; and lithium organic phosphates. These organic lithium salts are also preferably used together with ion-conductive polymers and ionic liquids, as they are expected to provide higher lithium conductivity.

[0047] The ionic conductor is preferably one or more compounds selected from the group consisting of phosphorus sulfide, red phosphorus, boron sulfide, diphosphorus pentoxide, and polymer electrolytes such as polyethylene oxide, which are substantially free of lithium element. Ionic conductors that are substantially free of lithium element are considered to have high affinity with sulfur-based active materials and carbon materials.

[0048] More preferably, the ionic conductor is one or more compounds containing phosphorus selected from the group consisting of phosphorus sulfide, red phosphorus, and diphosphorus pentoxide. ４ S ３ ), diphosphorus pentasulfide (P ２ S ５ ), phosphorus heptasulfide (P ４ S７ ), tetraphosphorus pentasulfide (P ４ S ５ ) and the like. The phosphorus sulfide may have a dimer or polysulfide structure, or may be a mixture. Particularly preferred is diphosphorus pentasulfide, which is expected to react with lithium to form a sulfide solid electrolyte exhibiting high ionic conductivity.

[0049] In the positive electrode mixture, the contents of the sulfur-based active material, the electronically conductive material, and the solid electrolyte 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. In one embodiment, the content of the electronically conductive material is 10 to 300 parts by mass per 100 parts by mass of the solid electrolyte.

[0050] In one embodiment, the positive electrode composite comprises 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. Note that "substantially 100% by mass" may contain inevitable impurities.

[0051] In one embodiment, before the step of applying an impact force without using the grinding media, a step of mixing a composite material of a sulfur-based active material and an electronic conductive material with a solid electrolyte to prepare a raw material mixture may be performed. This can improve the mixing state of the composite material of a sulfur-based active material and an electronic conductive material with the solid electrolyte, resulting in a positive electrode composite having a larger electric capacity.

[0052] A composite material of a sulfur-based active material and an electronically conductive material can be obtained, for example, by mixing a molten sulfur-based active material with an electronically conductive material, or by mixing the sulfur-based active material and the electronically conductive material using a twin-screw kneader or a precision shearing device.

[0053] For example, in the case of a composite material of sulfur and a carbon material, a mixture of sulfur and a carbon material is heated in a sealed state at a temperature equal to or higher than the melting point of sulfur (approximately 115°C). The heating temperature is adjusted depending on the carbon material and sulfur, but is preferably 130°C or higher, more preferably 150°C or higher. The upper limit of the heating temperature is a temperature equal to or lower than the boiling point of sulfur (approximately 445°C). The heating time is preferably 0.1 to 24 hours. A sulfur-carbon composite material is obtained by cooling after heating. If necessary, a pulverization step may be carried out after cooling.

[0054] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0055] Production Example 1 (Sulfur-Carbon Composite Material) Sulfur and carbon (Ketjen Black) powders were lightly mixed in a mass ratio of 70:30 to obtain a 2 kg mixture. The mixture was compounded using a Miracle KCK (Asada Iron Works) under the following conditions to obtain a sulfur-carbon composite material. Rotating blade: fan-chrysanthemum-mortar Main shaft rotation speed: 40 rpm Temperature: 120°C Number of passes: 2

[0056] Production Example 2 (Lithium sulfide) (1) Lithium sulfide (Li ２ Lithium sulfide was produced according to the first embodiment (two-step method) of JP-A-7-330312. Specifically, 3,326.4 g (33.6 mol) of N-methyl-2-pyrrolidone (NMP) and 287.4 g (12 mol) of lithium hydroxide were charged into a 10 L autoclave equipped with a stirring blade, and the mixture was heated to 130°C at 300 rpm. After the temperature was raised, hydrogen sulfide was blown into the liquid at a feed rate of 3 liters / minute for 2 hours. Subsequently, the reaction liquid was heated under a nitrogen stream (200 cc / minute), and a portion of the reacted hydrogen sulfide was dehydrosulfided. As the temperature was raised, water produced as a by-product by the reaction of hydrogen sulfide with lithium hydroxide began to evaporate, and this water was condensed in a condenser and withdrawn from the system. The temperature of the reaction solution rose as water was distilled out of the system, but the temperature increase was stopped when the temperature reached 180° C., and the temperature was maintained constant. After the dehydrosulfurization reaction was completed (approximately 80 minutes), the reaction was terminated, and lithium sulfide was obtained.

[0057] (2) Purification of lithium sulfide After decanting the NMP from 500 mL of the slurry reaction solution (NMP-lithium sulfide slurry) obtained in (1) above, 100 mL of dehydrated NMP was added and stirred at 105°C for about 1 hour. The NMP was decanted while maintaining that temperature. Further, 100 mL of NMP was added, stirred at 105°C for about 1 hour, and the NMP was decanted while maintaining that temperature. The same operation was repeated four times in total. After decantation, the lithium sulfide was dried under normal pressure at 230°C (a temperature higher than the boiling point of NMP) in a nitrogen stream for 3 hours. The impurity content in the obtained lithium sulfide was measured. Note that lithium sulfite (Li ２ SO ３ ), lithium sulfate (Li ２ SO ４ ) and lithium thiosulfate (Li ２ S ２ O ３ The contents of sulfur oxides and lithium N-methylaminobutyrate (LMAB) were quantified by ion chromatography. The total sulfur oxide content was 0.13 mass %, and the LMAB content was 0.07 mass %.

[0058] Production Example 3 (Sulfide Solid Electrolyte 1) 32.54 g (0.708 mol) of lithium sulfide from Production Example 2 and 67.46 g (0.304 mol) of diphosphorus pentasulfide (manufactured by Aldrich Chemical Co.) were placed in a 500 mL alumina container containing 175 alumina balls with a diameter of 10 mm, and the container was sealed. The above weighing and sealing operations were all carried out in a glove box, and all of the equipment used had been previously dehydrated using a dryer.

[0059] The sealed alumina container was subjected to mechanical milling in a planetary ball mill (PM400 manufactured by Retsch) at room temperature for 36 hours to obtain whitish yellow solid electrolyte glass particles. The recovery rate was 78%. X-ray diffraction measurement (CuKα: λ=1.5418 Å) of the obtained solid electrolyte glass particles revealed that the raw material Li ２ No S peak was observed, and a halo pattern was observed due to the solid electrolyte glass.

[0060] The solid electrolyte glass particles were sealed in an SUS tube under an Ar atmosphere in a glove box and subjected to heat treatment at 300°C for 2 hours to obtain sulfide solid electrolyte 1, which is glass ceramic particles (average particle size 14.52 µm). X-ray diffraction measurement of sulfide solid electrolyte 1 showed peaks at 2θ = 17.8, 18.2, 19.8, 21.8, 23.8, 25.9, 29.5, and 30.0°. From this, it was found that sulfide solid electrolyte 1 contains Li ７ P ３ S １１ It can be seen that crystals are formed. The ionic conductivity of sulfide solid electrolyte 1 is 1.3 × 10 －３ The viscosity was S / cm.

[0061] Production Example 4 (Sulfide Solid Electrolyte 2) Sulfide solid electrolyte 2, which was a sulfide glass, was produced in the same manner as Production Example 3, except that the amounts of lithium sulfide and diphosphorus pentasulfide in Production Example 2 were changed to 38.3 g (0.833 mol) and 61.8 g (0.278 mol), respectively, and the heat treatment at 300°C for 2 hours was not performed. Vitrification (sulfide glass) was confirmed by X-ray diffraction measurement. ３１ The P-NMR measurement showed a main peak at 83.0 ppm. The ionic conductivity of sulfide solid electrolyte 2 was 1.3 × 10 －４ The viscosity was S / cm.

[0062] Example 1 (1) Preparation of Cathode Composite Material The sulfur-carbon composite material of Production Example 1 and the sulfide solid electrolyte 1 of Production Example 3 were lightly mixed in a mass ratio of 50:50, and 14 g of the mixture was charged into a Nobilta NOB-MINI (Hosokawa Micron) for composite processing to prepare a cathode composite material. The operating conditions were as follows: (Nobilta operating conditions) Clearance d: 1.0 mm Rotor radius r: 44 mm Rotation speed R: 9000 rpm Time: 30 minutes

[0063] (2) Preparation of an all-solid-state lithium-ion battery 60 mg of the sulfide solid electrolyte 1 prepared in Preparation Example 3 was placed in a plastic cylinder with a diameter of 10 mm and pressure-molded to form a solid electrolyte layer. Then, 6.9 mg of the above-mentioned positive electrode composite was placed in the cylinder and pressure-molded again to form a laminate of a solid electrolyte layer and a positive electrode. Next, indium foil (manufactured by Furuuchi Chemical Co., Ltd., thickness 0.3 mm, diameter 10 mm) and lithium foil (manufactured by Furuuchi Chemical Co., Ltd., thickness 0.25 mm, diameter 8 mm) were placed on the surface opposite the positive electrode composite layer and pressure-molded to prepare a battery.

[0064] Example 2 A positive electrode composite and an all-solid-state lithium ion battery were produced in the same manner as in Example 1, except that the treatment time was 60 minutes.

[0065] Example 3 15 g of a light mixture of the sulfur-carbon composite material of Production Example 1 and the sulfide solid electrolyte 1 of Production Example 3 in a mass ratio of 50:50 was placed in a hybridization system, Model NHS-0 (Nara Machinery Works, Ltd.), and subjected to a composite treatment to prepare a positive electrode composite. The operating conditions were as follows: (Hybridization operating conditions) Clearance d: 3.5 mm Rotor radius r: 59 mm Rotation speed R: 15,000 rpm Time: 5 hours An all-solid-state lithium-ion battery was fabricated in the same manner as in Example 1, except for using the resulting positive electrode composite.

[0066] Example 4 A positive electrode composite and an all-solid-state lithium ion battery were fabricated in the same manner as in Example 3, except that sulfide solid electrolyte 2 was used instead of sulfide solid electrolyte 1.

[0067] Comparative Example 1 250 g of sulfide solid electrolyte 1 and 250 g of sulfur-carbon composite material were lightly mixed and then placed in a Miracle KCK-L (Asada Iron Works) for processing. This device has a rotating disk and a fixed disk, and is designed to apply shear between the surfaces of the two disks. The operating conditions were as follows: (Miracle KCK) Rotating disk configuration: fan-shaped - chrysanthemum-shaped - chrysanthemum-shaped clearance between disks d: 1 mm Rotating disk radius r: 30 mm Rotation speed R: 40 rpm Number of passes: 2 An all-solid-state lithium-ion battery was fabricated in the same manner as in Example 1, except that the obtained positive electrode composite was used.

[0068] [Evaluation] (1) Maximum impact velocity and maximum shear velocity The rotational speed of the rotor, screw, etc. (rotating body) is R (rpm), and the distance from the rotation axis to the tip of the blade is r (mm) (Fig. 1). The angular velocity ω is calculated from the rotational speed R using the following formula (1): ω = 2πR / 60 (1)

[0069] The maximum impact velocity V is expressed by the following formula (2): V = rω = 2πRr / 60 (m / s) (2)

[0070] If the gap between the rotor and the barrel (stationary body) is d (mm), the maximum shear rate D is expressed by the following formula (3): D = V / d = 2πRr / 60d(s －１ ) (3)

[0071] In addition, when the rotor does not have a blade that impacts the sample, as in the comparative example, the maximum shear rate D occurring between the parallel disks is calculated from the velocity Vp (m / s) of the outermost part of the rotor instead of the maximum impact velocity V.

[0072] (2) Discharge Capacity A constant current charge / discharge test was performed on the prepared battery at a charge / discharge potential range of 0.7 to 2.2 V and a charge / discharge temperature of 25°C. The charge current density was 0.5 mA / cm. ２ , discharge current density is 0.5 mA / cm ２ or 5.0 mA / cm ２ The results are shown in Table 1. In Table 1, SE1 represents sulfide solid electrolyte 1, and SE2 represents sulfide solid electrolyte 2.

[0073]

[0074] From Table 1, it can be seen that the all-solid-state lithium ion battery produced using the positive electrode mixture obtained by the production method of the present invention has a larger discharge capacity, particularly at high current density, than Comparative Example 1.

[0075] The cathode composite produced by the present invention is suitable as a structural material for lithium ion batteries. Furthermore, lithium ion batteries containing the cathode composite produced by the present invention are suitable for use in, for example, information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and vehicles such as electric vehicles.

[0076] 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. A method for producing a positive electrode composite using an apparatus having a rotor with a blade that applies an impact force to a mixture containing a sulfur-based active material, an electronically conductive material, and a solid electrolyte, and a barrel that stores the rotor, and applies a shear force to the mixture in the gap between the blade or rotor and the barrel.

2. The method for producing a positive electrode mixture according to claim 1, wherein the impact force is applied with the plate surface of the blade.

3. A method for producing a positive electrode composite, comprising a step of applying an impact force to a mixture containing a sulfur-based active material, an electronic conductive material, and a solid electrolyte without using a grinding media, and not including a step of using a grinding media.

4. The method of claim 3, wherein the step of applying an impact force without using grinding media applies an impact force and a shear force to the mixture.

5. The manufacturing method according to claim 3 or 4, wherein in the step of applying an impact force without using grinding media, a device is used which comprises a rotor having a blade which rotates at high speed and applies an impact force to the mixture, and a barrel which houses the rotor, and which applies a shear force to the mixture in the gap between the blade or rotor and the barrel.

6. The rotation speed of the rotor is set to a maximum impact speed of 10 m / s or more and a maximum shear speed of 1000 s －１ The method according to claim 1 or 5, wherein the temperature is set to be equal to or higher than the above.

7. The manufacturing method according to claim 6, wherein the product of the maximum impact velocity (m / s) and the treatment time (h) is set to be 10 or more.

8. The maximum shear rate (s －１ 8. The method according to claim 6, wherein the product of the number of cycles (h) and the treatment time (h) is set to be 2500 or more.

9. The method according to any one of claims 1 to 8, wherein the mixture is subjected to impact and shear forces by a high-velocity air current impact method or an angstrom mill grinding method.

10. The method according to any one of claims 1 to 9, further comprising a step of mixing the composite material of the sulfur-based active material and the electronic conductive material with the solid electrolyte to prepare the mixture.

11. The method according to claim 10, wherein the sulfur-based active material is combined with the electronic conductive material in a molten state.

12. The method according to claim 10, wherein the sulfur-based active material and the electronic conductive material are compounded using a twin-screw kneader or a precision shearing device.

13. The method according to any one of claims 1 to 12, wherein the solid electrolyte is a sulfide solid electrolyte containing lithium atoms or sodium atoms, phosphorus atoms, and sulfur atoms as constituent elements.

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