Electrode material

Abstract

This electrode material includes: a sulfur-based active material and / or a discharge product of a sulfur-based active material; an electron-conductive material having pores; and fine particles of a transition metal oxide.

Description

electrode material

[0001] This invention relates to electrode materials used in lithium-ion secondary batteries and the like.

[0002] All-solid-state lithium-ion batteries, which use a solid electrolyte, are expected to be highly safe lithium-ion batteries because they have the advantage of being less prone to electrolyte leakage and ignition. Sulfur-based active materials, which are expected to be high-capacity active materials, have low electronic and ionic conductivity. Therefore, when manufacturing a positive electrode using sulfur-based active materials, it is common to use ionic conductive materials and electronically conductive materials together with the active material (see, for example, Patent Documents 1 and 2).

[0003] Sulfur-based active materials have a slow charge-discharge reaction, which presents the problem of large voltage differences (overvoltages) during charge-discharge. To address this problem, the use of PbS as an internal resistance reducing agent in the electrode active material layer has been disclosed (Patent Document 3). Furthermore, it has been reported that for positive electrodes using lithium cobalt oxide as the active material, the rate characteristics can be improved by interposing barium titanate at the interface between the positive electrode and the liquid or solid electrolyte (see, for example, Non-Patent Documents 1-3).

[0004] Furthermore, transition metal oxides, which are classified as strongly correlated electron system materials and include titanium (Ti), niobium (Nb), and vanadium (V), usually exhibit insulating properties, but when electrons occupy d orbitals, they acquire metallic properties and other characteristics. For example, Non-Patent Document 4 reports the contribution of titanium's d orbitals to electronic conductivity and the provision of lithium diffusion paths at the phase interface of two titanium oxides.

[0005] Furthermore, sulfide solid electrolytes have poor chemical stability and have been reported to decompose when in contact with polar substances such as water, ethanol, acetonitrile, N-methylpyrrolidone, and N,N-dimethylformamide (see, for example, Non-Patent Documents 5 and 6).

[0006] Japanese Patent Publication No. 2013-258079, Japanese Patent Publication No. 2013-258080, Japanese Patent Publication No. 2022-95484

[0007] Adv. Electron. Mater. 2018, 4, 1700413 Nano Lett. 2019, 19, 1688-1694 Nat Commun 11, 5889 (2020) Phys. Chem. Chem. Phys. , 2016, 18, 23383 Mater. Chem. Front. ,2023,7,5475-5499Energy Environ.Sci.,2022,15,991-1033

[0008] One of the objectives of the present invention is to provide an electrode material that can reduce the voltage difference during charging and discharging.

[0009] The inventors of this invention discovered that by adding fine particles of transition metal oxide as an auxiliary substance to a sulfur-based active material, the voltage difference during charging and discharging can be reduced compared to when the auxiliary substance is not included, and thus completed the present invention.

[0010] The present invention provides the following electrode materials, etc. 1. An electrode material comprising at least one of a sulfur-based active material and a discharge product of a sulfur-based active material, an electron-conductive material having pores, and fine particles of a transition metal oxide. 2. The electrode material according to 1, wherein the transition metal oxide comprises a Ti atom. 3. The electrode material according to 2, wherein the transition metal oxide further comprises at least one atom selected from Ba, Sr, and Ca. 4. The electrode material according to 1 or 2, wherein the transition metal oxide is one or more compounds selected from titanium oxide, barium titanate, strontium titanate, calcium titanate, magnesium titanate, lithium titanate, and lead zirconate titanate. 5. The electrode material according to any one of 1 to 4, further comprising a sulfide solid electrolyte. 6. The electrode material according to 5, wherein the sulfide solid electrolyte comprises Li, P, S, and halogen as constituent elements. 7. The electrode material according to any one of 1 to 6, wherein the electron-conductive material is a carbon material. 8. 1. An electrode material according to any one of 1 to 7, wherein the average particle size of the transition metal oxide fine particles is 100 nm or less. 9. An electrode material according to 1, wherein the transition metal oxide is a ferroelectric material. 10. An electrode material according to 1, wherein the transition metal oxide is a paraelectric material. 11. An electrode comprising the electrode material according to any one of 1 to 10. 12. An electrode according to 11, which is a positive electrode. 13. A lithium-ion battery comprising the electrode according to 11 or 12. 14. A method for manufacturing an electrode material, comprising the step of mixing a sulfur-based active material, an electron-conducting material having pores, and fine particles of a transition metal oxide. 15. The manufacturing method according to 14, wherein the sulfur-based active material, the electron-conducting material, and the fine particles of the transition metal oxide are subjected to mechanical milling.

[0011] According to the present invention, it is possible to provide an electrode material that can reduce the voltage difference during charging and discharging.

[0012] The present invention will be described in detail below. In this specification, "x to y" represents a numerical range of "x or more, and y or less". The upper and lower limits described for the numerical range can be combined in any way. Furthermore, it is possible to combine two or more non-conflicting embodiments of the embodiments of the present invention described below, and an embodiment that combines two or more embodiments is also an embodiment of the embodiments of the present invention.

[0013] [Electrode Material] An electrode material according to one embodiment of the present invention includes at least one of a sulfur-based active material and a discharge product of the sulfur-based active material (hereinafter, "at least one of the sulfur-based active material and a discharge product of the sulfur-based active material" may be collectively referred to as "sulfur-based active material"), an electron-conductive material having pores, and fine particles of a transition metal oxide. In this embodiment, it is presumed that by adding the fine particles to the sulfur-based active material, the oxidation and reduction of the sulfur-based active material is facilitated by the formation of lithium ion diffusion paths originating from empty d orbitals that are not normally occupied by electrons, and / or by the polarization electric field generated by the high dielectric constant, thereby promoting the movement of lithium ions at the interface between the electron-conductive material, the solid electrolyte, and the sulfur-based active material, and thus reducing the voltage difference during charging and discharging. The constituent members of the electrode material will be described below.

[0014] (Sulfur-based active material) There are no particular limitations on sulfur-based active materials, 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. may be mentioned. Among them, sulfur is preferred. Although there is no particular limitation on sulfur, those with high purity are 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. The crystal systems 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 kinds.

[0015] The sulfur-based active material partially or entirely changes into a discharge product during the battery reaction. Therefore, in the electrode material of one embodiment, a discharge product of the sulfur-based active material exists. For example, as the discharge product of sulfur, in the fully discharged state, Li ２ S and lithium polysulfide in its intermediate stage such as Li ２ S ２ , Li ２ S ４ , Li ２ S ６ , Li ２ S ８ etc. may be mentioned.

[0016] (Electron conductive material) The electron conductive material has pores and electron conductivity, and is not particularly limited as long as it is a material that can be complexed with the sulfur-based active material. Since it is lighter than other materials, the output density and capacity per unit mass of the battery can be increased, so the electron conductive material preferably contains a carbon material. Since the sulfur-based active material and transition metal oxide fine particles have high ability to disperse and retain, the electron conductive material preferably has pores. In order to exert the migration promotion medium effect of lithium ions by the transition metal oxide fine particles, it is important that the transition metal oxide fine particles are dispersed in the electrode material.

[0017] Examples of the carbon material having pores include carbon blacks such as ketjen black, acetylene black, Denka black, thermal black, channel black, graphite, activated carbon, etc. These may be used alone or in combination of two or more kinds.

[0018] In one embodiment, the BET specific surface area of the carbon material is 50 m ２ / g or more and 6000 m ２The concentration is less than / g. This allows for the formation of a broad contact interface between the carbon material and the sulfur-based active material, thereby improving the utilization rate of the sulfur-based active material. The BET specific surface area is 70 m². ２ Preferably, the amount is 100 m / g or more, and more preferably 100 m ２ / g or more, 1000m ２ / g or more, 1500m ２ / g or more is preferable. Also, 5500m ２ Preferably less than / g, and more preferably 5000m ２ Preferably less than / g

[0019] Furthermore, the pore volume of the carbon material is 0.5 cm³. ３ / g or more, 6cm ３ The concentration is less than / g. This allows sulfur-based active materials to be impregnated into the pores of the carbon material, further improving the battery capacity. The pore volume is 0.7 cm³. ３ Preferably, it is 1.0 cm or more. ３ A value of 5.5 cm or more is preferable. ３ Preferably less than / g, and moreover 5.0 cm ３ Preferably less than / g

[0020] In this invention, the BET specific surface area and pore volume can be determined using nitrogen adsorption isotherms obtained by adsorbing nitrogen gas onto a carbon material at liquid nitrogen temperature. Specifically, the BET specific surface area can be calculated using the Brunauer-Emmett-Teller (BET) multipoint method with respect to the nitrogen adsorption isotherms. The pore volume can be determined using the Barrett-Joyner-Halenda (BJH) method with respect to the nitrogen adsorption isotherms. As a measuring device, for example, the specific surface area and pore distribution analyzer (Autosorb-3) manufactured by Quantachrome can be used for measurement.

[0021] (Fine particles of transition metal oxide) The transition metal oxide used in the present invention preferably satisfies at least one of the following conditions (A) and (B).

[0022] (A) Transition metal oxides include elements that have empty d orbitals that are not occupied by electrons. Examples of elements that have empty d orbitals that are not occupied by electrons include titanium (Ti), niobium (Nb), and vanadium (V).

[0023] (B) Dielectric constants of transition metal oxides with a dielectric constant of 50 or more are the values ​​listed in Table 6.15 (page 1019) of the Ceramic Engineering Handbook (2nd edition) "1st edition, 1st printing April 10, 1989, 2nd edition, 1st printing March 31, 2002, Japan Ceramic Society, Publisher: Yoshitaka Nagai" (ε r ) Note that the value (ε r The values ​​shown are those measured using the resonator method; specific measurement methods can be found in the following literature: Jpn. J. Appl. Phys. 24 (1985) Supplement 24-2, 60-64.

[0024] For example, SrTiO ３ The dielectric constant of is 255, CaTiO ３ The dielectric constant of TiO is 170. ２ The dielectric constant of is 104.

[0025] In one embodiment, among transition metal oxides, oxides containing V, oxides containing Nb, or oxides containing Ti are preferred, and oxides containing Ti are more preferred. Examples of oxides containing V include vanadium oxide, lithium vanadate, cesium vanadate, and bismuth vanadate. Examples of oxides containing Nb include niobium oxide, lithium niobate, barium niobium oxide, magnesium niobium oxide, and potassium niobate. Examples of oxides containing Ti include titanium oxide, barium titanate, strontium titanate, calcium titanate, magnesium titanate, lithium titanate, and lead zirconate titanate.

[0026] In one embodiment, the Ti-containing oxide contains at least one atom selected from barium (Ba), strontium (Sr), and calcium (Ca). Such a compound has a high dielectric constant.

[0027] In one embodiment, the transition metal oxide may be a ferroelectric. A ferroelectric is a dielectric material that has dielectric polarization (spontaneous polarization) that forms spontaneously even without an externally applied electric field. Examples include barium titanate. In another embodiment, the transition metal oxide may be a paraelectric. A paraelectric is a dielectric material in which dielectric polarization appears only when an externally applied electric field is used. Examples include strontium titanate, calcium titanate, and titanium oxide.

[0028] In one embodiment, the average particle size of the fine particles is 100 nm or less. This makes them easily dispersed within the electrode. The average particle size may be 100 nm or less, 90 nm or less, or 80 nm or less. The average particle size is usually 1 nm or more. In this application, the average particle size of the fine particles is the average particle diameter (BET diameter) determined by the BET method.

[0029] (Optional components) In one embodiment, the electrode material preferably includes a sulfide solid electrolyte in addition to a sulfur-based active material, an electronically conductive material, and fine particles of a transition metal oxide. This facilitates the formation of lithium ion conduction paths within the electrode.

[0030] A sulfide solid electrolyte is a solid electrolyte that contains at least a sulfur atom and exhibits ionic conductivity due to the contained metal atoms, preferably containing lithium atoms and phosphorus atoms in addition to sulfur atoms, and more preferably containing lithium atoms, phosphorus atoms and halogen atoms, and having ionic conductivity due to the lithium atom. The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

[0031] (Amorphous sulfide solid electrolyte) As an amorphous sulfide solid electrolyte, any material that contains at least sulfur atoms and exhibits ionic conductivity due to the contained metal atoms can be used without particular restrictions. Typical examples include, for example, Li ２ S-P ２ S ５ A solid electrolyte containing sulfur atoms, lithium atoms, and phosphorus atoms, composed of lithium sulfide and phosphorus sulfide, etc. ２S-P ２ S ５ -LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ - A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as LiI-LiBr; further containing other elements such as oxygen and silicon, for example, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ -P ２ S ５ - Solid electrolytes such as LiI are preferred. From the viewpoint of obtaining higher ionic conductivity, 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 Solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as -LiI-LiBr, are preferred. The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0032] The amorphous sulfide solid electrolyte contains at least Li ２ S-P ２ S ５ If it has Li ２ S and P ２ S ５ The molar ratio of is preferably 30-85:15-70, more preferably 40-80:20-60, and even more preferably 45-78:22-55, from the viewpoint of obtaining high chemical stability and higher ionic conductivity. The amorphous sulfide solid electrolyte is, for example, Li ２ S-P２ S ５ In the case of -LiI-LiBr, the total content of lithium sulfide and phosphorus pentasulfide is preferably 30 to 95 mol%, more preferably 35 to 90 mol%, and even more preferably 40 to 85 mol%. Furthermore, 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%.

[0033] In amorphous sulfide solid electrolytes containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, the mixing 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 mixing 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 mixing 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 with higher ionic conductivity having the thiolysicon region II type crystal structure described later.

[0034] Furthermore, there are no particular restrictions on the shape of the amorphous sulfide solid electrolyte, but for example, particulate form can be given. The average particle size (D) of the particulate amorphous sulfide solid electrolyte. ５０ For example, the average particle size (D) can be exemplified by being in the range of 0.01 μm to 500 μm or 0.1 μm to 200 μm. In this specification, the average particle size (D) ５０)is the particle diameter at which, when the particle size distribution integrated curve is drawn, the cumulative total reaches 50% sequentially from the particles with the smallest particle diameter, and the volume distribution is, for example, the average particle diameter that can be measured using a laser diffraction / scattering type particle size distribution measuring device.

[0035] (Crystalline sulfide solid electrolyte) As the crystalline sulfide solid electrolyte, for example, a so-called glass-ceramics obtained by heating the above amorphous sulfide solid electrolyte to a temperature above the crystallization temperature may be used, and a sulfide solid electrolyte having the following crystal structure may be adopted. The crystal structure that a crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, and phosphorus atoms may have is Li ３ PS ４ crystal structure, Li ４ P ２ S ６ crystal structure, Li ７ PS ６ crystal structure, Li ７ P ３ S １１ crystal structure, a crystal structure having peaks in the vicinity of 2θ = 20.2° and 23.6° (for example, Japanese Patent Application Laid-Open No. 2013-16423) and the like can be mentioned.

[0036] Further, as the crystal structure that a crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms may have, Li ４－ｘ Ge １－ｘ P ｘ S ４ system thio-LISICON Region II (thio-LISICON Region II) type crystal structure (see Kanno et al., Journal of The Electrochemical Society, 148(7) A742-746 (2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ system thio-LISICON Region II (thio-LISICON Region II) type and similar crystal structures (see Solid State Ionics, 177(2006), 2721-2725)) and the like can be mentioned. Here, the "thio-LISICON Region II type crystal structure" is Li ４－ｘ Ge １－ｘ Pｘ S ４ Thio-Lisicon Region II type crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ This indicates that the crystal structure is similar to that of the thio-LISICON Region II system.

[0037] In X-ray diffraction measurements using CuKα rays, Li ３ PS ４ Diffraction peaks of the crystal structure appear, for example, around 2θ = 17.5°, 18.3°, 26.1°, 27.3°, and 30.0°, Li ４ P ２ S ６ Diffraction peaks of the crystal structure appear, for example, around 2θ = 16.9°, 27.1°, and 32.5°, Li ７ PS ６ The diffraction peaks of the crystal structure appear, for example, around 2θ = 15.3°, 25.2°, 29.6°, and 31.0°, and Li ７ P ３ S １１ Diffraction peaks of the crystal structure appear, for example, around 2θ = 17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II type crystal structure appear, for example, around 2θ = 20.1°, 23.9°, and 29.5°, Li ４－ｘ Ge １－ｘ P ｘ S ４ Diffraction peaks for crystal structures similar to the thio-LISICON Region II type appear, for example, around 2θ = 20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0038] Furthermore, argyrodite crystal structures can also be cited as crystalline sulfide solid electrolytes. For example, Li ７ PS ６ Crystal structure; Li ７ PS ６ Composition formula Li has a structural framework ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ Crystal structure represented by (x is -0.6 to 0.6, y is 0.1 to 0.6); Li ７－ｘ－２ｙ PS ６－ｘ－ｙ Cl ｘ Crystal structure shown by (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5); Li ７－ｘ PS ６－ｘ Ha ｘ Examples of crystal structures include those represented by (Ha is Cl or Br, and x is preferably 0.2 to 1.8).

[0039] Among the crystal structures described above, Li is an example of a crystal structure found in crystalline sulfide solid electrolytes. ３ PS ４ A crystal structure, a thiolysicon region II type crystal structure, and an argyrodite type crystal structure are preferred.

[0040] There are no particular restrictions on the shape of the crystalline sulfide solid electrolyte, but for example, particulate form can be given. The average particle size (D) of the particulate crystalline sulfide solid electrolyte. ５０ ) is the average particle size (D) of the amorphous sulfide solid electrolyte described above. ５０ Similarly, examples include the ranges of 0.01 μm to 500 μm and 0.1 μm to 200 μm.

[0041] In one embodiment, the electrode material may or may not contain components other than the sulfur-based active material, electronically conductive material, fine particles of transition metal oxide, and sulfide solid electrolyte described above. The other components are not particularly limited, but examples include binders, solvents, and dispersants.

[0042] In electrode materials, the content of sulfur-based active material, transition metal oxide fine particles, electronically conductive material, and sulfide solid electrolyte is not particularly limited. For example, the mass ratio (A:B) of electronically conductive material A to sulfur-based active material B in the electrode material is 10:90 to 90:10, 50:50 to 90:10, or 70:30 to 90:10. The mass ratio (A+B:C) of the total of electronically conductive material A and sulfur-based active material B (A+B) to the transition metal oxide fine particles C in the electrode material is 99:1 to 1:99, 98:2 to 90:10, 85:15 to 80:20, or 75:25 to 70:30.

[0043] For example, when the electrode material contains a sulfide solid electrolyte, the content of sulfur-based active material is 10 to 200 parts by mass per 100 parts by mass of sulfide solid electrolyte. The content of electronically conductive material is 10 to 150 parts by mass per 100 parts by mass of sulfide solid electrolyte. The content of transition metal oxide fine particles is 0.5 to 20 parts by mass per 100 parts by mass of sulfide solid electrolyte.

[0044] In one embodiment, 50% or more by mass of the electrode material is 60% or more by mass, 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, 99% or more by mass, 99.5% or more by mass, or substantially 100% by mass, of a sulfur-based active material, an electronically conductive material, fine particles of transition metal oxides, and a sulfide solid electrolyte. In the case of "substantially 100% by mass," unavoidable impurities may be included.

[0045] [Method for Manufacturing Electrode Material] The electrode material of the present invention can be manufactured by mixing the above-mentioned sulfur-based active material, an electronically conductive material, fine particles of transition metal oxide, and optionally a sulfide solid electrolyte. The mixing method is not particularly limited and can be carried out by known methods and apparatus. Examples of mixing apparatus used in the mixing process include planetary ball mills, rolling mills, bead mills, film mixers, Nauta mixers, tornado mixers, twin-screw extruders, multi-screw rollers, solid-phase shear kneaders, and the like.

[0046] In one embodiment, a sulfur-based active material is heated and melted to impregnate the pores of an electronically conductive material. By melting the sulfur-based active material, impregnation into the pores can be promoted. Furthermore, the sulfur-based active material can be highly dispersed in the electronically conductive material.

[0047] The heating temperature can be appropriately set according to the sulfur-based active material used. For example, if the sulfur-based active material is sulfur, the temperature should be above the melting point of sulfur (approximately 115°C). Preferably, it should be 130°C or higher, and more preferably 150°C or higher. Heating may be carried out in two or more stages.

[0048] In one embodiment, a sulfur-based active material, an electronically conductive material, and fine particles of a transition metal oxide are subjected to mechanical milling. Various mills, such as planetary ball mills, can be used for mechanical milling. Mechanical milling allows for the compounding of the sulfur-based active material, the electronically conductive material, and the fine particles of the transition metal oxide.

[0049] In one embodiment, fine particles of a transition metal oxide and an electronically conductive material may be compounded, and then the compound may be mixed and compounded with a sulfur-based active material. Alternatively, the fine particles of the transition metal oxide, the sulfur-based active material, and the electronically conductive material may be mixed and compounded simultaneously.

[0050] In one embodiment, a sulfur-based active material and an electronically conductive material are composited, and then the composite, along with fine particles of a transition metal oxide and a sulfide solid electrolyte, is mechanically milled. This allows for a combination of composite formation by heating and composite formation by mechanical milling.

[0051] The electrode material of the present invention can be suitably used, for example, as a component material of a secondary battery. For example, it can be used as the positive electrode of a lithium-ion battery. A lithium-ion battery according to one embodiment of the present invention includes the electrode material of the present invention described above. For example, by using a solid electrolyte, an all-solid-state lithium-ion battery can be manufactured. By using the electrode material of the present invention, an all-solid-state lithium-ion battery with reduced voltage difference during charging and discharging can be manufactured. A lithium-ion battery mainly consists of a positive electrode layer, a negative electrode layer, and an electrolyte layer. The negative electrode layer and the electrolyte layer can be manufactured by known methods. For example, the sulfide solid electrolyte described above can be used for the electrolyte layer. In addition to the positive electrode layer, negative electrode layer, and electrolyte layer, it is preferable that a current collector is used, and known current collectors can also be used.

[0052] The present invention will be described in detail below based on examples. The present invention is not limited to these examples.

[0053] [Preparation of Solid Electrolyte] Production Example 1 0.4127 g of lithium sulfide, 0.6655 g of phosphorus pentasulfide, 0.2137 g of lithium iodide, 0.2080 g of lithium bromide, and 10 zirconia balls with a diameter of 10 mm were placed in a 45 mL zirconia pot and sealed. Using a planetary ball mill (Fritsch, model P-7), the mixture was mixed (mechanical milling) at a rotation speed of 370 rpm for 40 hours to obtain a powder. The obtained powder was heated at 195°C for 3 hours to obtain a solid electrolyte.

[0054] [Preparation of Electrode Material] Example 1 0.600 g of sulfur and 1.40 g of activated carbon (MSC-30, manufactured by Kansai Thermal Chemical Co., Ltd.) were placed in a glass bottle and sealed in a SUS tube container. The mixture was heated in an electric furnace at 150°C for 6 hours and then at 300°C for 2.75 hours to obtain a composite powder of sulfur and activated carbon. 500 mg of the above composite powder, 50 mg of barium titanate (manufactured by Sigma-Aldrich, average particle size less than 100 nm (BET measurement), dielectric constant 150), and 450 mg of the solid electrolyte from Production Example 1 were placed in a 45 mL zirconia pot along with 10 zirconia balls with a diameter of 10 mm and sealed. Using a planetary ball mill (manufactured by Fritsch, model P-7), the mixture was ground at a rotation speed of 370 rpm for 20 hours at room temperature to obtain a positive electrode composite material (electrode material) powder.

[0055] Example 2 A cathode composite powder was obtained in the same manner as in Example 1, except that the amount of barium titanate was changed to 20 mg and the amount of solid electrolyte to 480 mg.

[0056] Example 3 A positive electrode composite powder was obtained in the same manner as in Example 1, except that the amount of barium titanate was changed to 10 mg and the amount of solid electrolyte to 490 mg.

[0057] Example 4 A cathode composite powder was obtained in the same manner as in Example 1, except that barium titanate was replaced with strontium titanate (manufactured by Sigma-Aldrich, average particle size less than 100 nm, dielectric constant 300).

[0058] Example 5 A positive electrode composite powder was obtained in the same manner as in Example 2, except that barium titanate was replaced with strontium titanate.

[0059] Example 6 A cathode composite powder was obtained in the same manner as in Example 3, except that barium titanate was replaced with calcium titanate (manufactured by Sigma-Aldrich, average particle size less than 100 nm).

[0060] Example 7 A cathode composite powder was obtained in the same manner as in Example 1, except that barium titanate was replaced with titanium oxide (rutile type, manufactured by Sigma-Aldrich, average particle size less than 100 nm).

[0061] Example 8 A cathode composite powder was obtained in the same manner as in Example 1, except that barium titanate was replaced with 100 mg of lithium titanate (Ishihara Sangyo Co., Ltd., LT-112) and the solid electrolyte was changed to 400 mg.

[0062] Comparative Example 1 A cathode composite powder was obtained in the same manner as in Example 1, except that barium titanate was not included and the composite powder was changed to 500 mg and the solid electrolyte to 500 mg.

[0063] [Evaluation] All-solid-state lithium-ion batteries were fabricated using the positive electrode mixture powder prepared in the examples and comparative examples, and their charge-discharge characteristics were evaluated. (1) Fabrication of all-solid-state lithium-ion batteries 100 mg of the solid electrolyte from Production Example 1 was placed in a 10 mm diameter Macol cylinder and pressurized. The positive electrode mixture prepared in the examples and comparative examples was placed on the pressurized surface so that the sulfur content was 3.5 mg, and the pressurized surface was pressed again. 166 mg of negative electrode mixture (LTO (lithium titanate) negative electrode mixture) was placed on the pressurized surface opposite the positive electrode mixture and pressurized, and then lithium foil was placed on top and pressurized to fabricate an all-solid-state lithium-ion battery. The LTO negative electrode mixture consists of lithium titanate (Ishihara Sangyo Co., Ltd. "LT-112"), conductive additive (Denka Co., Ltd. "Li-100", powdered acetylene black), and Li ２ S-P ２ S ５ A solid electrolyte of the -LiCl-LiBr type was prepared by adding it to a mortar in a mass ratio of 60:5:35 and mixing it in the mortar for 5 minutes.

[0064] (2) Constant Current Charge / Discharge Test For the all-solid-state lithium-ion batteries prepared in (1) above, the cutoff potential for the constant current test was set to -0.4V to +1.3V vs. Li-LTO. The current density during the charge / discharge cycle is shown in Table 1. The overvoltage during charge / discharge was defined as the difference between the charge potential and the discharge potential when the amount of electricity [mAh / g] was half of the maximum electrical capacity. The results are shown in Table 2.

[0065]

[0066]

[0067] Table 2 shows that the overvoltage in the example is smaller than in Comparative Example 1. This indicates that the internal resistance of the all-solid-state lithium-ion battery can be reduced in the example.

[0068] The electrode material of the present invention can be suitably used as a component material of lithium-ion batteries, for example, as a positive electrode. Furthermore, the lithium-ion battery of the present invention can be suitably used in information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, as well as batteries used in vehicles such as electric vehicles and air mobility.

[0069] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will find it easy to make many modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and effects of the present invention. Accordingly, many of these modifications fall within the scope of the present invention. All references to the documents described in this specification and the contents of the application on which the priority claim under the Paris Convention of this application is based are incorporated herein by reference.

Claims

1. An electrode material comprising at least one of a sulfur-based active material and a discharge product of a sulfur-based active material, an electron-conductive material having pores, and fine particles of a transition metal oxide.

2. The electrode material according to claim 1, wherein the transition metal oxide contains Ti atoms.

3. The electrode material according to claim 2, wherein the transition metal oxide further comprises at least one atom selected from Ba, Sr, and Ca.

4. The electrode material according to claim 1 or 2, wherein the transition metal oxide is one or more compounds selected from titanium oxide, barium titanate, strontium titanate, calcium titanate, magnesium titanate, lithium titanate, and lead zirconate titanate.

5. The electrode material according to any one of claims 1 to 4, further comprising a sulfide solid electrolyte.

6. The electrode material according to claim 5, wherein the sulfide solid electrolyte contains Li, P, S, and halogen as constituent elements.

7. The electrode material according to any one of claims 1 to 6, wherein the electronically conductive material is a carbon material.

8. The electrode material according to any one of claims 1 to 7, wherein the average particle size of the transition metal oxide fine particles is 100 nm or less.

9. The electrode material according to claim 1, wherein the transition metal oxide is a ferroelectric.

10. The electrode material according to claim 1, wherein the transition metal oxide is a paraelectric material.

11. An electrode comprising the electrode material according to any one of claims 1 to 10.

12. The electrode according to claim 11, which is the positive electrode.

13. A lithium-ion battery comprising the electrode described in claim 11 or 12.

14. A method for producing an electrode material, comprising the step of mixing a sulfur-based active material, an electron-conductive material having pores, and fine particles of a transition metal oxide.

15. The manufacturing method according to claim 14, wherein the sulfur-based active material, the electronically conductive material, and the fine particles of the transition metal oxide are subjected to mechanical milling.

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