Positive electrode material, positive electrode and battery

Abstract

A positive electrode material (10) according to the present disclosure is provided with a coating active material (100) that contains a positive electrode active material (101) and a coating layer (102) that contains a first solid electrolyte and covers at least a part of the surface of the positive electrode active material (101), and a second solid electrolyte (105). The first solid electrolyte contains Li, Ti, M, and X, M is at least one selected from the group consisting of metal elements and semimetal elements other than Li and Ti, and X is at least one selected from the group consisting of F, Cl, Br, and I. The second solid electrolyte 105 contains Li and S. The ratio of the mass of the first solid electrolyte to the total mass of the positive electrode active material 101 and the first solid electrolyte is 1.00% or more and 4.10% or less.

Description

Technical Field

[0001] This disclosure relates to cathode materials, cathodes, and batteries. Background Art

[0002] Patent document 1 describes a method for manufacturing a composite active material by coating the positive electrode active material with an oxide solid electrolyte and then with a sulfide solid electrolyte.

[0003] Existing technical documents

[0004] Patent documents:

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-18735 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] In the prior art, it is desirable to suppress the increase in the internal resistance of the battery.

[0008] Methods for solving problems

[0009] This disclosure provides a positive electrode material comprising a coated active material and a second solid electrolyte. The coated active material includes a positive electrode active material and a coating layer. The coating layer includes a first solid electrolyte and coats at least a portion of the surface of the positive electrode active material. The first solid electrolyte includes Li, Ti, M, and X, where M is at least one selected from the group consisting of metallic elements and half-metallic elements other than Li and Ti, and X is at least one selected from the group consisting of F, Cl, Br, and I. The second solid electrolyte includes Li and S. The mass ratio of the first solid electrolyte to the total mass of the positive electrode active material and the first solid electrolyte is 1.00% or more and 4.10% or less.

[0010] The effects of the invention

[0011] According to the technology disclosed herein, it is possible to suppress the increase in the internal resistance of the battery. Attached Figure Description

[0012] [ Figure 1 ] Figure 1 This is a cross-sectional view showing the general structure of the positive electrode material in Embodiment 1.

[0013] [ Figure 2 ] Figure 2 This is a cross-sectional view showing the general configuration of the battery in Embodiment 2. Detailed Implementation

[0014] (The insights that form the basis of this disclosure)

[0015] If a battery using a solid electrolyte is repeatedly charged and discharged, oxygen may sometimes be generated from the positive electrode active material. This generated oxygen oxidizes the solid electrolyte, increasing the battery's internal resistance. This increased internal resistance leads to various problems such as decreased output voltage, battery overheating, and reduced discharge capacity. Therefore, a technology suitable for suppressing the increase in internal resistance of batteries using solid electrolytes is desired.

[0016] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments.

[0017] (Implementation Method 1)

[0018] Figure 1 This is a cross-sectional view showing the schematic structure of the positive electrode material according to Embodiment 1. The positive electrode material 10 has a coated active material 100 and a second solid electrolyte 105. The coated active material 100 is composed of a positive electrode active material 101 and a coating layer 102. The coating layer 102 contains the first solid electrolyte. The coating layer 102 coats at least a portion of the surface of the positive electrode active material 101. The coating layer 102 may coat only a portion of the surface of the positive electrode active material 101, or it may uniformly coat the surface of the positive electrode active material 101. The second solid electrolyte 105 contains Li and S.

[0019] In the coating layer 102, the first solid electrolyte comprises Li, Ti, M, and X. M is at least one selected from the group consisting of metallic elements and half-metallic elements other than Li and Ti. X is at least one selected from the group consisting of F, Cl, Br, and I. In the cathode material 10, the mass ratio of the first solid electrolyte to the total mass of the cathode active material 101 and the first solid electrolyte is 1.00% or more and 4.10% or less. Hereinafter, the mass ratio of the first solid electrolyte to the total mass of the cathode active material 101 and the first solid electrolyte is sometimes described as "ratio MA1 / MAt".

[0020] "Semi-metallic elements" include B, Si, Ge, As, Sb, and Te.

[0021] "Metallic elements" include all elements in groups 1 to 12 of the periodic table except for hydrogen, and all elements in groups 13 to 16 of the periodic table except for B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metallic elements are the group of elements that can form cations when forming inorganic compounds with halogen elements.

[0022] The first solid electrolyte can be a halogen-containing solid electrolyte, also known as a halide solid electrolyte. Halide solid electrolytes have excellent oxidation resistance. Therefore, by coating the positive electrode active material 101 with the first solid electrolyte, the oxidation of the second solid electrolyte 105 can be suppressed. As a result, the increase in the internal resistance of the battery using the positive electrode material 10 can be suppressed, battery degradation can be suppressed, and the cycle characteristics of the battery using the positive electrode material 10 can be improved.

[0023] When the ratio MA1 / MAt meets the above-mentioned range, the positive electrode active material 101 is sufficiently coated by the first solid electrolyte, and the above-mentioned effects can be fully obtained. Furthermore, when the ratio MA1 / MAt meets the above-mentioned range, the positive electrode material 10 has sufficient electronic conductivity. The ratio MA1 / MAt can be 1.00% or more and 4.01% or less, 1.10% or more and 4.01% or less, 1.10% or more and 3.80% or less, 1.10% or more and 3.60% or less, 1.30% or more and 3.70% or less, or 1.60% or more and 3.60% or less. Depending on the situation, the ratio MA1 / MAt can be 1.10% or more and 4.10% or less, 1.30% or more and 4.10% or less, or 1.60% or more and 4.01% or less.

[0024] The total mass MAt of the positive electrode active material 101 and the first solid electrolyte is the sum of the mass MA2 of the positive electrode active material 101 and the mass MA1 of the first solid electrolyte. The mass MA1 of the first solid electrolyte is the total mass of the first solid electrolyte in the powder of the positive electrode material 10. The mass MA2 of the positive electrode active material 101 is the total mass of the positive electrode active material 101 in the powder of the positive electrode material 10. That is, the ratio MA1 / MAt is a value calculated from a certain amount of the powder of the positive electrode material 10.

[0025] The aforementioned ratio MA1 / MAt can also be calculated based on the amount of material used, or it can be calculated using the methods described below. By analyzing the positive electrode using the positive electrode material 10 using high-frequency inductively coupled plasma atomic emission spectrometry (ICP-AES), quantitative analysis is performed on elements contained in the positive electrode active material 101 but not in the first solid electrolyte, and elements contained in the first solid electrolyte but not in the positive electrode active material 101. This analysis of the mass ratio of the positive electrode active material 101 to the first solid electrolyte allows the ratio MA1 / MAt to be calculated. Alternatively, the ratio MA1 / MAt can be calculated from the composition ratio of the particle cross-section analyzed using energy-dispersive X-ray spectroscopy with a scanning electron microscope.

[0026] In the positive electrode material 10, the second solid electrolyte 105 and the coated active material 100 can be in contact with each other. At this time, the coating layer 102 is in contact with the second solid electrolyte 105. The positive electrode material 10 may contain a plurality of particles of the second solid electrolyte 105 and a plurality of particles of the coated active material 100.

[0027] <Positive Electrode Active Material>

[0028] The positive electrode active material 101 comprises a material with the property of intercalating and deintercalating metal ions (e.g., lithium ions). As the positive electrode active material 101, lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, transition metal oxynitrides, etc., can be used. In particular, using lithium-containing transition metal oxides as the positive electrode active material 101 can reduce the manufacturing cost of the battery and improve the average discharge voltage. Examples of lithium-containing transition metal oxides include Li(NiCoAl)O2, Li(NiCoMn)O2, and LiCoO2.

[0029] The positive electrode active material 101 may have a particle shape, for example. The shape of the particles of the positive electrode active material 101 is not particularly limited. The shape of the particles of the positive electrode active material 101 may be spherical, ellipsoidal, scaly, or fibrous.

[0030] The median particle size of the coated active material 100 can be 0.1 μm or more and 100 μm or less. When the median particle size of the coated active material 100 is 0.1 μm or more, the coated active material 100 and the second solid electrolyte 105 can form a good dispersion state in the cathode material 10. As a result, the charge and discharge characteristics of the battery are improved. When the median particle size of the coated active material 100 is 100 μm or less, the diffusion rate of lithium inside the coated active material 100 is sufficiently ensured. Therefore, the battery can operate with high output.

[0031] The median particle size of the coated active material 100 can be larger than the median particle size of the second solid electrolyte 105. As a result, the positive electrode active material 101 and the second solid electrolyte 105 can form a good dispersion state.

[0032] In this specification, "median particle size" refers to the particle size at which the cumulative volume of the particle size distribution in a volumetric reference is equal to 50%. The particle size distribution in a volumetric reference is determined, for example, by a laser diffraction measuring device or an image analysis device.

[0033] The specific surface area of ​​the coated active material 100 can be 0.60 m². 2 / g or more and 1.40m 2 Below / g, it can be 0.60m 2 / g or more and 1.30m 2 Below / g, it can be 0.60m 2 / g or more and 1.20m 2 Below / g, it can be 0.68m 2 / g or more and 1.16m 2 Below / g, it can be 0.68m 2 / g or more and 1.15m 2 / g or less. Depending on the situation, the specific surface area of ​​the coated active material 100 can be 0.80m². 2 / g or more and 1.40m 2 Below / g, it can be 0.80m 2 / g or more and 1.30m 2 Below / g, it can be 0.80m 2 / g or more and 1.20m 2 Below / g, it can be 0.80m 2 / g or more and 1.16m 2 Below / g, it can be 0.80m 2 / g or more and 1.20m 2 Below / g, it can be 0.81m 2 / g or more and 1.15m 2 / g or less. In this specification, specific surface area refers to the BET specific surface area that can be determined by the BET method.

[0034] <Covering>

[0035] The coating layer 102 contains a first solid electrolyte. The first solid electrolyte has ionic conductivity. Typically, lithium-ion conductivity is present. The coating layer 102 is formed on the surface of the positive electrode active material 101. The coating layer 102 may contain the first solid electrolyte as a main component, or it may contain only the first solid electrolyte. "Main component" refers to the component with the highest content by mass ratio. "Contains only the first solid electrolyte" means that no materials other than the first solid electrolyte are intentionally added, except for unavoidable impurities. For example, the raw materials of the first solid electrolyte, byproducts generated during the production of the first solid electrolyte, etc., are included in unavoidable impurities. The mass ratio of unavoidable impurities to the total mass of the coating layer 102 may be less than 5%, less than 3%, less than 1%, or less than 0.5%.

[0036] The first solid electrolyte is a material comprising Li, Ti, M, and X. M and X are as previously described. Such a material exhibits excellent ionic conductivity and oxidation resistance. Therefore, the cathode material 10 having a coating layer 102 comprising the first solid electrolyte improves the charge-discharge efficiency and thermal stability of the battery.

[0037] M may contain at least one selected from the group consisting of Ca, Mg, Al, Y, Ni, Fe, Cr, and Zr. M may contain at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. With such a composition, the halide solid electrolyte exhibits high ionic conductivity.

[0038] M may also contain Al (i.e., aluminum). That is, the halide solid electrolyte may contain Al as a metal element. When M contains Al, the halide solid electrolyte exhibits high ionic conductivity.

[0039] The halide solid electrolyte as the first solid electrolyte is represented, for example, by the following compositional formula (1). In compositional formula (1), α, β, γ, and δ are each independently a value greater than 0.

[0040] Li α Ti β M γ X δ Compositional formula (1)

[0041] The halide solid electrolyte represented by compositional formula (1) has higher ionic conductivity than a halide solid electrolyte such as LiI composed only of Li and a halogen element. Therefore, when the halide solid electrolyte represented by compositional formula (1) is used in a battery, the charge-discharge efficiency of the battery can be improved.

[0042] To further improve the ionic conductivity of the first solid electrolyte, in compositional formula (1), M may be Al.

[0043] The halide solid electrolyte as the first solid electrolyte may be represented by the following compositional formula (2). In compositional formula (2), M2 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the valence of M2, and 0.1 < x < 0.9, 0 ≤ y < 0.1, 0 ≤ z < 0.1, and 0.8 < b ≤ 1.2 are satisfied.

[0044] Li 6-(4-x-my)b (Ti 1-x-y Al x M2 y ) b F 6-2z O z Compositional formula (2)

[0045] In addition, in compositional formula (2), when M2 contains multiple elements, m is the total value of the product of the composition ratio of each element and the valence of that element. For example, when M2 contains element Me1 and element Me2, the composition ratio of element Me1 is a1, the valence is m1, the composition ratio of element Me2 is a2, and the valence of element Me2 is m2, m is represented by m1a1 + m2a2.

[0046] The halide solid electrolyte can be substantially formed of Li, Ti, Al, and X. Here, "the halide solid electrolyte is substantially formed of Li, Ti, Al, and X" means that the total molar amount of Li, Ti, Al, and X relative to the total molar amount of all elements constituting the halide solid electrolyte (i.e., the mole fraction) is 90% or more. As an example, this mole ratio (i.e., the mole fraction) can be 95% or more. The halide solid electrolyte can be formed only of Li, Ti, Al, and X.

[0047] In order to further improve the ionic conductivity of the first solid electrolyte, in the halide solid electrolyte, the ratio of the molar amount of Li to the total molar amount of Ti and Al can be 1.12 or more and 5.07 or less.

[0048] The halide solid electrolyte as the first solid electrolyte can be represented by the following compositional formula (3). In compositional formula (3), 0 < x < 1 and 0 < b ≤ 1.5 are satisfied.

[0049] Li 6-(4-x)b (Ti 1-x Al x ) b F6 Compositional formula (3)

[0050] The halide solid electrolyte having such a composition has a high ionic conductivity.

[0051] In order to improve the ionic conductivity of the first solid electrolyte, in compositional formula (3), 0.1 ≤ x ≤ 0.9 can be satisfied.

[0052] In compositional formula (3), 0.1 ≤ x ≤ 0.7 can be satisfied.

[0053] The upper and lower limit values of the range of x in compositional formula (3) can be defined by any combination selected from the values of 0.1, 0.3, 0.4, 0.5, 0.6, 0.67, 0.7, 0.8, and 0.9.

[0054] In order to improve the ionic conductivity of the first solid electrolyte, in compositional formula (3), 0.8 ≤ b ≤ 1.2 can be satisfied.

[0055] The upper and lower limit values of the range of b in compositional formula (3) can be defined by any combination selected from the values of 0.8, 0.9, 0.94, 1.0, 1.06, 1.1, and 1.2.

[0056] The halide solid electrolyte can be crystalline or can also be amorphous.

[0057] There are no restrictions on the shape of halide solid electrolytes. Examples of such shapes include needle-like, spherical, or ellipsoidal. Halide solid electrolytes can also be particles.

[0058] When the shape of the halide solid electrolyte is, for example, particulate (e.g., spherical), the solid electrolyte may have a median particle size of more than 0.01 μm and less than 100 μm.

[0059] Halide solid electrolytes can be sulfur-free solid electrolytes. In this case, the generation of sulfur-containing gases such as hydrogen sulfide can be avoided from the solid electrolyte. Sulfur-free solid electrolytes are solid electrolytes expressed in a compositional formula that does not contain sulfur. Therefore, solid electrolytes containing trace amounts of sulfur, such as solid electrolytes with a sulfur content of less than 0.1% by mass, are considered sulfur-free solid electrolytes. Halide solid electrolytes may further include oxygen as an anion other than halogen elements.

[0060] The thickness of the coating layer 102 is, for example, 1 nm or more and 500 nm or less. By appropriately adjusting the thickness of the coating layer 102, the contact between the positive electrode active material 101 and the second solid electrolyte 105 can be sufficiently suppressed. The thickness of the coating layer 102 can be determined by thinning the coated active material using methods such as ion milling and observing the cross-section of the coated active material using a transmission electron microscope. The average thickness measured at any number of locations (e.g., 5 points) can be considered as the thickness of the coating layer 102.

[0061] <Methods for manufacturing halide solid electrolytes>

[0062] Halogenated solid electrolytes can be manufactured, for example, by the methods described below. Here, an example is given of a method for manufacturing a halide-based solid electrolyte with the composition formula (1).

[0063] The raw material powder is prepared and mixed in a manner that makes it the target composition. The raw material powder may be, for example, a halide.

[0064] As an example, in a target composition of Li 2.7 Ti 0.3 Al 0.7 In the case of F6, LiF, TiF4, and AlF3 are mixed in a molar ratio of approximately 2.7:0.3:0.7. To compensate for possible compositional changes during the synthesis process, the raw material powders can be mixed in a pre-adjusted molar ratio.

[0065] The raw material powders are mechanically and chemically reacted (i.e., using a mechanochemical grinding method) in a mixing device such as a planetary ball mill to obtain reactants. The reactants can then be calcined in a vacuum or an inert atmosphere. Alternatively, the mixture of raw material powders can also be calcined in a vacuum or an inert atmosphere to obtain reactants. Calcination is carried out, for example, at temperatures above 100°C and below 400°C for at least one hour. To suppress compositional changes during calcination, the raw material powders can be calcined in a sealed container such as a quartz tube.

[0066] These methods yield halide solid electrolytes.

[0067] <Second Solid Electrolyte>

[0068] The second solid electrolyte 105 contains Li and S. In other words, the second solid electrolyte 105 contains a sulfide solid electrolyte. Sulfide solid electrolytes have high ionic conductivity, which can improve the charge and discharge efficiency of the battery. On the other hand, sulfide solid electrolytes have poor oxidation resistance, but high efficiency can be obtained by applying the technology disclosed herein.

[0069] The second solid electrolyte 105 can contact the positive electrode active material 101 through the coating layer 102.

[0070] As sulfide solid electrolytes, for example, Li₂S-P₂S₅, Li₂S-SiS₂, Li₂S-B₂S₃, Li₂S-GeS₂, and Li₂S-P₂S₅ can be used. 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 Etc. LiX, Li₂O, and MO can also be added to them. q Li p MO q And so on. Here, X in "LiX" is at least one selected from the group consisting of F, Cl, Br, and I. "MO" q "and "Li p MO q The element M in "MO" is at least one selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q "and "Li p MO q In the formula, p and q are independent natural numbers.

[0071] In addition to the sulfide solid electrolyte, the second solid electrolyte 105 may also contain other solid electrolytes. For example, the second solid electrolyte 105 may contain at least one selected from the group consisting of sulfide solid electrolytes, polymeric solid electrolytes, and complexed hydride solid electrolytes.

[0072] Oxide solid electrolytes are solid electrolytes that contain oxygen. In addition to oxygen, oxide solid electrolytes may also contain anions other than sulfur and halogens.

[0073] As oxide solid electrolytes, examples include NASICON (sodium superionic conductor) type solid electrolytes represented by LiTi2(PO4)3 and its elemental substitutes, perovskite type solid electrolytes based on (LaLi)TiO3, and Li... 14 ZnGe4O 16 LISICON (lithium superion conductor) type solid electrolytes, represented by Li4SiO4, LiGeO4 and their elemental substitutes, and Li7La3Zr2O 12 Garnet-type solid electrolytes, represented by Li3PO4 and its N-substitutes, and glass or glass-ceramics containing Li2SO4, Li2CO3, and other materials added to the base material containing Li-BO compounds such as Li3PO4 and its N-substitutes, LiBO2, and Li3BO3.

[0074] As a polymeric solid electrolyte, a compound of polymer and lithium salt can be used, for example. The polymer can have an ethylene oxide structure. Polymers with an ethylene oxide structure can contain a large amount of lithium salt. Therefore, the ionic conductivity can be further improved. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. One lithium salt selected from these can be used alone, or a mixture of two or more lithium salts selected from these can be used.

[0075] As a complexed hydride solid electrolyte, LiBH4-LiI, LiBH4-P2S5, etc. can be used, for example.

[0076] The second solid electrolyte 105 may have a higher lithium-ion conductivity than the first solid electrolyte.

[0077] The second solid electrolyte 105 may contain unavoidable impurities such as starting materials, byproducts, and decomposition products used in the synthesis of the solid electrolyte. This also applies to the first solid electrolyte.

[0078] <Other Materials>

[0079] In the positive electrode material 10, a binder may be included to improve the adhesion between particles. The binder is used to improve the adhesion of the materials constituting the positive electrode. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aromatic polyamide resin, polyamide, polyimide, polyamide-imide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polycarbonate, polyethersulfone, polyetherketone, polyetheretherketone, polyphenylene sulfide, hexafluoropolypropylene, styrene-butadiene rubber, carboxymethyl cellulose, ethyl cellulose, etc. Alternatively, copolymers of two or more monomers selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, trifluorochloroethylene, ethylene, propylene, butadiene, styrene, pentafluoropropylene, fluoromethyl vinyl ether, acrylate, acrylic acid, and hexadiene may be used. You can use one of them individually, or you can use two or more in combination.

[0080] For the sake of excellent adhesion, the adhesive can be an elastomer. An elastomer is a polymer with rubber-like elasticity. The elastomer used as an adhesive can be a thermoplastic elastomer or a thermosetting elastomer. The adhesive can contain thermoplastic elastomers. Examples of thermoplastic elastomers include styrene-ethylene-butene-styrene (SEBS), styrene-ethylene-propylene-styrene (SEPS), styrene-ethylene-ethylene-propylene-styrene (SEEPS), butene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), styrene-butene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), hydrogenated isoprene rubber (HIR), hydrogenated butyl rubber (HIIR), hydrogenated nitrile butadiene rubber (HNBR), hydrogenated styrene-butene rubber (HSBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). One of these can be used alone, or two or more can be used in combination.

[0081] To improve electronic conductivity, the positive electrode material 10 may contain a conductive additive. Examples of conductive additives include graphite-based materials such as natural or artificial graphite, carbon blacks such as acetylene black and Ketjen black, conductive fibers such as carbon fibers or metal fibers, metal powders such as fluorinated carbon and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymers such as polyaniline, polypyrrole, and polythiophene. Using carbon-based conductive additives can reduce costs.

[0082] To improve electronic conductivity, the coating layer 102 may contain the aforementioned conductive additives.

[0083] <Method for manufacturing coated active substances>

[0084] The coated active material 100 can be manufactured by the following method.

[0085] A mixture is obtained by mixing the powder of the positive electrode active material 101 and the powder of the first solid electrolyte in an appropriate ratio. The mixture is then ground to impart mechanical energy. The grinding process can be performed using a mixing device such as a ball mill. To suppress oxidation of the material, the grinding process can be carried out in a dry and inactive atmosphere.

[0086] The coated active material 100 can be manufactured by a dry particle composite method. The process using the dry particle composite method involves imparting at least one mechanical energy selected from the group consisting of impact, compression, and shear to the positive electrode active material 101 and the first solid electrolyte. The positive electrode active material 101 and the first solid electrolyte are mixed in an appropriate ratio.

[0087] The apparatus used in manufacturing the coated active material 100 is not particularly limited and can be any apparatus capable of imparting impact, compression, and shear mechanical energy to the mixture of the positive electrode active material 101 and the first solid electrolyte. Examples of apparatus capable of imparting mechanical energy include ball mills, "Mechano fusion" (manufactured by Hosokawa Micron), and "NOBILTA" (manufactured by Hosokawa Micron), which are compression and shear processing devices (particle composite devices).

[0088] "Mechano fusion" is a particle fusion device that uses dry mechanical fusion technology based on applying strong mechanical energy to multiple different raw material powders. In mechano fusion, the raw material powders fed between a rotating container and a pressure head are subjected to mechanical energy of compression, shearing, and friction. This causes particle fusion.

[0089] NOBILTA is a particle composite device that utilizes dry mechanical composite technology, developed to create composites from nanoparticles. NOBILTA manufactures composite particles by applying mechanical energy of impact, compression, and shear to various raw material powders.

[0090] In "NOBILTA," a rotor, positioned with a predetermined gap between itself and the inner wall of a horizontal cylindrical mixing container, rotates at high speed, repeatedly forcing the raw material powder through the gap. This allows impact, compression, and shear forces to be applied to the mixture, creating composite particles of the positive electrode active material 101 and the first solid electrolyte. By adjusting conditions such as rotor speed, processing time, and feed rate, the thickness of the coating layer 102 and the coating ratio of the first solid electrolyte to the positive electrode active material 101 can be controlled.

[0091] However, the above-mentioned processing is not necessary. The coated active material 100 can also be manufactured by mixing the positive electrode active material 101 with the first solid electrolyte using a mortar, mixer, or the like. The first solid electrolyte can also be deposited on the surface of the positive electrode active material 101 by various methods such as spraying, spray drying, electrolysis, impregnation, or mechanical mixing using a disperser.

[0092] <Manufacturing Methods of Cathode Materials>

[0093] The positive electrode material 10 is obtained by mixing the coated active material 100 with the second solid electrolyte 105. There is no particular limitation on the method of mixing the coated active material 100 with the second solid electrolyte 105. The coated active material 100 and the second solid electrolyte 105 can be mixed using a mortar and pestle, or a mixing device such as a ball mill.

[0094] (Implementation Method 2)

[0095] Figure 2 This is a cross-sectional view showing the schematic configuration of the battery according to Embodiment 2. The battery 200 includes a positive electrode 201, a separator layer 202, and a negative electrode 203. The separator layer 202 is disposed between the positive electrode 201 and the negative electrode 203. The positive electrode 201 includes the positive electrode material 10 described in Embodiment 1. With this configuration, the increase in the internal resistance of the battery 200 can be suppressed.

[0096] The thickness of the positive electrode 201 and the negative electrode 203 can be greater than 10 μm and less than 500 μm. When the thickness of the positive electrode 201 and the negative electrode 203 is greater than 10 μm, sufficient energy density of the battery can be ensured. When the thickness of the positive electrode 201 and the negative electrode 203 is less than 500 μm, high output operation of the battery 200 can be achieved.

[0097] The membrane layer 202 is a layer containing an electrolyte material. The membrane layer 202 may contain at least one solid electrolyte selected from the group consisting of sulfide solid electrolytes, oxide solid electrolytes, halide solid electrolytes, polymeric solid electrolytes, and complexed hydride solid electrolytes. Details of each solid electrolyte are as described in Embodiment 1.

[0098] The thickness of the separator layer 202 can be greater than 1 μm and less than 300 μm. When the thickness of the separator layer 202 is greater than 1 μm, the positive electrode 201 and the negative electrode 203 can be separated more reliably. When the thickness of the separator layer 202 is less than 300 μm, the battery 200 can operate at high output.

[0099] The negative electrode 203 contains a material with the properties of intercalating and deintercalating metal ions (e.g., lithium ions) as the negative electrode active material.

[0100] As negative electrode active materials, metallic materials, carbon materials, oxides, nitrides, tin compounds, silicon compounds, etc., can be used. Metallic materials can also be elemental metals, or alloys. Examples of metallic materials include lithium metal and lithium alloys. Examples of carbon materials include natural graphite, coke, graphitized carbon, carbon fibers, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, and tin compounds are preferred.

[0101] The median particle size of the negative electrode active material can be above 0.1 μm and below 100 μm.

[0102] The negative electrode 203 may also contain other materials such as a solid electrolyte. As a solid electrolyte, the materials described in Embodiment 1 can be used.

[0103] (Other implementation methods)

[0104] (Supplementary Explanation)

[0105] The following technology has been disclosed through the above description of the embodiments.

[0106] (Technology 1)

[0107] A positive electrode material comprises a coated active material and a second solid electrolyte, the coated active material comprising a positive electrode active material and a coating layer, the coating layer comprising a first solid electrolyte, and coating at least a portion of the surface of the positive electrode active material.

[0108] The first solid electrolyte contains Li, Ti, M, and X.

[0109] M is selected from at least one of the group consisting of metallic elements and half-metallic elements other than Li and Ti.

[0110] X is at least one selected from the group consisting of F, Cl, Br and I.

[0111] The second solid electrolyte contains Li and S.

[0112] The ratio of the mass of the first solid electrolyte to the total mass of the positive electrode active material and the first solid electrolyte is more than 1.00% and less than 4.10%.

[0113] This design helps to suppress the increase in the battery's internal resistance.

[0114] (Technology 2)

[0115] According to the positive electrode material of Technology 1, the ratio is 1.6% or more and 3.6% or less. With this configuration, the increase in the internal resistance of the battery can be further suppressed.

[0116] (Technology 3)

[0117] According to the cathode material described in technique 1 or 2, the specific surface area is 0.6 m². 2 / g or more and 1.4m 2 / g or less. This configuration helps to suppress the increase in the battery's internal resistance.

[0118] (Technology 4)

[0119] According to any one of techniques 1 to 3, the positive electrode material, wherein M comprises at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. With this configuration, the first solid electrolyte exhibits high ionic conductivity.

[0120] (Technology 5)

[0121] According to any one of techniques 1 to 4, the positive electrode material, wherein M comprises Al. With this configuration, the first solid electrolyte exhibits high ionic conductivity.

[0122] (Technology 6)

[0123] According to any one of techniques 1 to 5, the positive electrode material wherein the first solid electrolyte is represented by the following compositional formula (1).

[0124] Li α Ti β M γ X δ Composition formula (1)

[0125] Here, in the above compositional formula (1), α, β, γ, and δ are each independently a value greater than 0. When the first solid electrolyte represented by the compositional formula (1) is used in a battery, the output characteristics of the battery can be improved.

[0126] (Technology 7)

[0127] According to the positive electrode material described in any one of Technologies 1 to 6, wherein the first solid electrolyte is represented by the following compositional formula (2),

[0128] Li 6-(4-x-my)b (Ti 1-x-y Al x M2 y ) b F 6-2z O z Compositional formula (2)

[0129] Here, in the above compositional formula (2), M2 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the valence of the above M2, and 0.1 < x < 0.9, 0 ≤ y < 0.1, 0 ≤ z < 0.1, and 0.8 < b ≤ 1.2 are satisfied. According to such a configuration, the output characteristics of the battery can be improved.

[0130] (Technology 8)

[0131] A positive electrode having the positive electrode material described in any one of Technologies 1 to 7. By such a configuration, an increase in the internal resistance of the battery can be suppressed.

[0132] (Technology 9)

[0133] A battery having the positive electrode described in Technology 8. By such a configuration, an increase in the internal resistance of the battery can be suppressed.

[0134] Examples

[0135] Hereinafter, the details of the present disclosure will be described using examples and comparative examples. Furthermore, the electrodes and batteries of the present disclosure are not limited to the following examples.

[0136] <Example 1>

[0137] [Production of First Solid Electrolyte]

[0138] In an argon glove box with a dew point below -60°C, LiF, TiF4, and AlF3, as raw material powders, were weighed in a molar ratio of LiF:TiF4:AlF3 = 2.5:0.5:0.5. They were pulverized and mixed in a mortar to obtain a mixture. The resulting mixture was then milled using a planetary ball mill at 500 rpm for 12 hours. Thus, a halide solid electrolyte powder was obtained as the first solid electrolyte of Example 1. The first solid electrolyte of Example 1 has a composition of Li... 2.5 Ti 0.5 Al 0.5 F6 (hereinafter referred to as "LTAF") represents the composition.

[0139] [Preparation of Coated Active Substances]

[0140] As the positive electrode active material, Li(NiCoAl)O2 powder (hereinafter referred to as "NCA") was prepared. A coating layer obtained by LTAF was formed on the surface of NCA. The coating layer was formed by shearing treatment using a particle mixing device (manufactured by BALANCE GRAN, FREUND-TURBO). Specifically, NCA and LTAF were weighed at a mass ratio of 98.9:1.1, and the mixture was treated at a rotation speed of 3100 rpm for a processing time of 1 hour. Thus, the coated active material of Example 1 was obtained.

[0141] The specific surface area of ​​the coated active material in Example 1 is 0.68 m². 2 / g.

[0142] [Preparation of the Second Solid Electrolyte]

[0143] In an argon glove box with a dew point below -60°C, Li₂S and P₂S₅ powders were weighed in a molar ratio of Li₂S:P₂S₅ = 75:25. They were pulverized and mixed in a mortar to obtain a mixture. The mixture was then ground using a planetary ball mill (Fritsch P-7 type) at 510 rpm for 10 hours. This yielded a glassy solid electrolyte. The glassy solid electrolyte was then heat-treated at 270°C for 2 hours in an inert atmosphere. This resulted in Li₂S-P₂S₅ (hereinafter referred to as "LPS"), a glass-ceramic-like sulfide solid electrolyte, as a second solid electrolyte.

[0144] [Production of cathode materials]

[0145] Inside an argon glove box, the coated active material and LPS of Example 1 were weighed at a volume ratio of 70:30, where the volume ratio of the coated active material to the sulfide solid electrolyte was 70:30. They were then mixed in an agate mortar to prepare the cathode material of Example 1.

[0146] <Example 2>

[0147] The mass ratio of NCA to LTAF was changed to 98.39:1.61, and the coated active material of Example 2 was obtained using the same method as in Example 1. The specific surface area of ​​the coated active material of Example 2 was 0.81 m². 2 / g.

[0148] Using the coated active material of Example 2, the cathode material of Example 2 was obtained in the same manner as in Example 1.

[0149] <Example 3>

[0150] The mass ratio of NCA to LTAF was changed to 97.55:2.45, and the coated active material of Example 3 was obtained using the same method as in Example 1. The specific surface area of ​​the coated active material of Example 3 was 1.10 m². 2 / g.

[0151] Using the coated active material of Example 3, the cathode material of Example 3 was obtained in the same manner as in Example 1.

[0152] <Example 4>

[0153] The mass ratio of NCA to LTAF was changed to 96.42:3.58, and the coated active material of Example 4 was obtained using the same method as in Example 1. The specific surface area of ​​the coated active material of Example 4 was 1.15 m². 2 / g.

[0154] Using the coated active material of Example 4, the cathode material of Example 4 was obtained in the same manner as in Example 1.

[0155] <Example 5>

[0156] The mass ratio of NCA to LTAF was changed to 95.99:4.01, and the coated active material of Example 5 was obtained using the same method as in Example 1. The specific surface area of ​​the coated active material of Example 5 was 1.16 m². 2 / g.

[0157] Using the coated active material of Example 5, the cathode material of Example 5 was obtained in the same manner as in Example 1.

[0158] <Comparative Example 1>

[0159] Uncoated LTAF NCA was used as the active material in Comparative Example 1. The specific surface area of ​​the active material in Comparative Example 1 was 0.55 m². 2 / g.

[0160] In the cathode materials of Examples 1 to 5 and Comparative Example 1, the ratio of the mass of LTAF to the total mass of NCA and LTAF is expressed as a percentage, as shown in Table 1. In Table 1, “LTAF / (LTAF+NCA)(mass%)” represents the ratio of the mass of LTAF to the total mass of NCA and LTAF.

[0161] [Battery Manufacturing]

[0162] The positive electrode material was weighed with 14 mg of NCA. LPS and the positive electrode material were sequentially stacked in an insulating outer cylinder. The resulting laminate was pressurized at 720 MPa. Next, lithium metal was placed in contact with the LPS layer, and the laminate was again pressurized at 40 MPa. This produced a laminate consisting of a positive electrode, a solid electrolyte layer, and a negative electrode. Next, stainless steel current collectors were placed on the top and bottom of the laminate. Current collector leads were installed on each current collector. Then, the outer cylinder was sealed using an insulating sleeve, thereby isolating the interior of the outer cylinder from the external air atmosphere. Following the above steps, batteries of Examples 1 to 5 and Comparative Example 1 were manufactured. A surface pressure of 150 MPa was applied to the battery by constraining it from top and bottom with four bolts.

[0163] [Preservation Experiment]

[0164] The battery was placed in a constant-temperature bath at 25°C. It was then charged at a constant current of 147 μA at a 0.05C rate (20-hour rate) relative to its theoretical capacity until the voltage reached 4.3V. Next, it was discharged at a constant current of 147 μA at a 0.05C rate (20-hour rate) relative to its theoretical capacity until the voltage reached 3.7V. Finally, it was discharged at a constant current of 0.136 A at a 46.4C rate relative to its theoretical capacity for 0.1 seconds. The voltage drop at this point was used to determine the battery's resistance before the storage test.

[0165] Next, the internal temperature of the constant temperature bath was changed to 80°C, and the battery was stored for one week while charged to 4.1V.

[0166] Next, the internal temperature of the constant temperature bath was restored to 25°C, and the battery was charged at a constant current of 147 μA at a 0.05C rate (20-hour rate) relative to the battery's theoretical capacity until the voltage reached 4.3V. Then, the battery was discharged at a constant current of 147 μA at a 0.05C rate (20-hour rate) relative to the battery's theoretical capacity until the voltage reached 3.7V. Then, a constant current discharge was performed for 0.136 A at a 46.4C rate relative to the battery's theoretical capacity for 0.1 seconds, and the resistance value of the battery after the storage test was calculated from the voltage drop at this time.

[0167] The results of the preservation test are shown in Table 1. In Table 1, the "resistance increase rate" is the value calculated using the mathematical formula: 100 × (resistance value after preservation test) / (resistance value before preservation test).

[0168] [Table 1]

[0169]

[0170] <Inspection>

[0171] As shown in Table 1, in Examples 1-5, where the positive electrode active material was coated with a first solid electrolyte that served as a halide solid electrolyte, the increase in resistance due to storage was suppressed. Furthermore, the resistance values ​​of Examples 1-5 before the storage test were lower than those of Comparative Example 1. This is presumably because the reaction between oxygen extracted from the positive electrode active material and the sulfide solid electrolyte was suppressed. Thus, in Examples 1-5, the internal resistance of the battery and the increase in internal resistance due to storage were suppressed.

[0172] It should be noted that when using at least one of the metal elements and half-metal elements selected from the group consisting of elements other than Li and Ti, such as Ca, Mg, Al, Y, or Zr instead of Al, it has also been confirmed that the halide solid electrolyte exhibits the same level of ionic conductivity (e.g., Japanese Patent Application 2020-048461). Therefore, a halide solid electrolyte containing at least one of these elements can be used instead of or in conjunction with Al. In this case, battery charging and discharging can also be performed, achieving the effect of suppressing the oxidation reaction of the sulfide solid electrolyte and thus suppressing the increase in resistance.

[0173] Furthermore, the oxidation of sulfide solid electrolytes is mainly caused by the sulfide solid electrolyte contacting the positive electrode active material and thus losing electrons from the sulfide solid electrolyte. Therefore, according to the technology disclosed herein, even when using active materials other than NCA, the oxidation of sulfide solid electrolytes can be suppressed.

[0174] Industrial applicability

[0175] The techniques disclosed herein are useful, for example, for all-solid-state lithium secondary batteries.

Claims

1. A positive electrode material includes a coated active material and a second solid electrolyte, The coated active material includes a positive electrode active material and a coating layer. The coating layer includes a first solid electrolyte and coats at least a part of the surface of the positive electrode active material. The first solid electrolyte includes Li, Ti, M, and X. M is at least one selected from the group consisting of metal elements and metalloid elements other than Li and Ti. X is at least one selected from the group consisting of F, Cl, Br, and I. The second solid electrolyte includes Li and S. The ratio of the mass of the first solid electrolyte to the total mass of the positive electrode active material and the first solid electrolyte is 1.00% or more and 4.10% or less.

2. The cathode material according to claim 1, wherein, The ratio is 1.6% or more and 3.6% or less.

3. The cathode material according to claim 1, wherein, Specific surface area is 0.6 m² 2 / g or more and 1.4m 2 / g or less.

4. The cathode material according to claim 1, wherein, M includes at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr.

5. The cathode material according to claim 1, wherein, M includes Al.

6. The cathode material according to claim 1, wherein, The first solid electrolyte is represented by the following compositional formula (1). Li α Ti β M γ X δ Composition formula (1) In the compositional formula (1), α, β, γ, and δ are each independently values greater than 0.

7. The cathode material according to claim 1, wherein, The first solid electrolyte is represented by the following compositional formula (2). Li 6-(4-x-my)b (Ti 1-x-y Al x M2 y ) b F 6-2z O z Composition formula (2) In the compositional formula (2), M2 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the valence of M2, and 0.1 < x < 0.9, 0 ≤ y < 0.1, 0 ≤ z < 0.1, and 0.8 < b ≤ 1.2 are satisfied.

8. A positive electrode includes the positive electrode material according to any one of claims 1 to 7.

9. A battery includes the positive electrode according to claim 8.

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