Coated active material, electrode material, and battery

Abstract

A coated active material 100 according to the present disclosure comprises: composite particles 130 that include an active material 110 and a first coating layer 120 which covers at least part of the surface of the active material 110; and a second coating layer 140 that covers the surface of the composite particles 130 at a coverage ratio of 15.0-75.0%. The first coating layer 120 contains a first solid electrolyte. The second coating layer 140 contains a second solid electrolyte having a composition differing from that of the first solid electrolyte. The ratio of the average roundness of the coated active material 100 to the average roundness of the active material 110 is less than 1.30.

Description

Coated active material, electrode material, and battery

[0001] The present disclosure relates to coated active materials, electrode materials, and batteries.

[0002] Patent Document 1 discloses a composite positive electrode active material for an all-solid-state secondary battery, which comprises a particulate positive electrode active material and a sulfide-based solid electrolyte coating the surface of the particulate positive electrode active material, and the composite positive electrode active material has an average roundness 1.3 times or more of that of the positive electrode active material at the core of the composite positive electrode active material. Patent Document 1 also discloses a composite positive electrode active material in which the sulfide solid electrolyte layer covers 50% or more of the surface of the positive electrode active material.

[0003] International Publication No. 2018 / 038037

[0004] In the prior art, there is a need to reduce the resistance of the battery.

[0005] The present disclosure provides a coated active material comprising: a composite particle including an active material and a first coating layer that coats at least a portion of the surface of the active material; and a second coating layer that coats the surface of the composite particle at a coverage rate of 15.0% or more and 75.0% or less, wherein the first coating layer includes a first solid electrolyte, and the second coating layer includes a second solid electrolyte having a different composition from the first solid electrolyte, and the ratio of the average roundness of the coated active material to the average roundness of the active material is less than 1.30.

[0006] According to the technology of the present disclosure, the resistance of the battery can be reduced.

[0007] Fig. 1 is a cross-sectional view showing a schematic configuration of a coated active material in embodiment 1. Fig. 2 is a cross-sectional view showing a schematic configuration of an electrode material in embodiment 2. Fig. 3 is a cross-sectional view showing a schematic configuration of a battery in embodiment 3. Fig. 4 is a cross-sectional secondary electron image of a representative particle of the coated active material in examples 1 to 5 and comparative example 2.

[0008] (Findings forming the basis of the present disclosure) In a battery, when the potential window of the electrolyte is narrower than the operating potential range of the battery, in order to suppress an increase in the resistance of the battery due to decomposition of the electrolyte, it is effective to use composite particles in which the surface of an active material is coated with a coating layer containing the solid electrolyte, so that a solid electrolyte with a wide potential window is present at the interface between the active material and the electrolyte, in place of single active material particles.

[0009] In addition, in all-solid-state batteries, in order to reduce the resistance of the battery, it is important that the interface between the composite particles in the electrode and the surrounding bulk solid electrolyte is well adhered to ensure a sufficient ion conduction path. Therefore, as disclosed in Patent Document 1, a method has been proposed in which the composite particles are additionally coated with a different type of solid electrolyte at a high coverage rate to promote interfacial bonding between the composite particles and the bulk solid electrolyte.

[0010] On the other hand, the present inventors have found that differences in battery resistance also occur in batteries using coated active materials in which the above-mentioned composite particles are coated with a different type of solid electrolyte. As a result of extensive research, the present inventors have found that there is a correlation between the coating form of the composite particles with the different type of solid electrolyte, particularly the coverage rate and roundness, and the battery resistance, and have arrived at the technology of the present disclosure.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0012] (Embodiment 1) FIG. 1 is a cross-sectional view showing a schematic configuration of a coated active material according to embodiment 1. The coated active material 100 according to embodiment 1 includes a composite particle 130 including an active material 110 and a first coating layer 120, and a second coating layer 140. In the composite particle 130, the first coating layer 120 includes a first solid electrolyte and coats at least a portion of the surface of the active material 110. The second coating layer 140 includes a second solid electrolyte and coats the surface of the composite particle 130 containing the active material 110 and the first coating layer 120 at a coverage of 15.0% or more and 75.0% or less. The second solid electrolyte has a different composition from the first solid electrolyte. The ratio of the average roundness of the coated active material 100 to the average roundness of the active material 110 is less than 1.30. That is, the first coating layer 120 and the second coating layer 140 coat the active material 110 so that the ratio of the average roundness of the coated active material 100 to the average roundness of the active material 110 is less than 1.30. Hereinafter, the ratio of the average roundness of the coated active material 100 to the average roundness of the active material 110 will be referred to as the average roundness ratio.

[0013] The coated active material 100 in this embodiment is suitable for reducing battery resistance because the second coating layer 140 coats the surface of the composite particle 130 at a coverage rate of 15.0% or more and 75.0% or less, and has a configuration in which the average roundness ratio is less than 1.30.

[0014] By having an average roundness ratio of less than 1.30, the interface between the coated active material 100 and other electrolytes in the electrode can be well adhered within the battery electrode. That is, within the battery electrode, both an ionic conduction path from the external electrolyte to the composite particles 130 (i.e., contact between the composite particles 130 and other electrolytes in the electrode) and an electronic conduction path (i.e., contact between the composite particles 130 themselves or between the composite particles 130 and the conductive additive) can be sufficiently secured. This reduces the battery resistance. Here, the other electrolyte within the electrode refers to an electrolyte present around the coated active material 100 within the electrode, such as a bulk solid electrolyte (corresponding to the third solid electrolyte contained in the electrode material in the second embodiment described below) present around the coated active material 100 within the electrode.

[0015] In this specification, the average roundness of the active material 110 and the average roundness of the coated active material 100 are defined by the following formulas (I) and (II) in Patent Document 1 as the average roundness R of the composite positive electrode active material and the positive electrode active material of the core of the composite positive electrode active material. ave This is a value that is defined in the same way as In the above formulas (I) and (II), N p is the number of measured particles, R j is the roundness of each particle, median() is the median of the values ​​in the parentheses, r1, r2, ... r n is the radius of curvature of each convex part in the two-dimensional projection of the particle to be measured, n is the total number of convex parts whose radius of curvature is to be measured, r A represents the circle-equivalent radius of the particle to be measured.

[0016] The average roundness of the active material 110 and the average roundness of the coated active material 100 are determined by the method described in Patent Document 1. For example, the average roundness of the active material 110 and the average roundness of the coated active material 100 can be measured by observing a cross section of the coated active material 100 with a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM).

[0017] For example, when measuring the average roundness ratio from a cross-sectional image of the coated active material 100 taken by SEM, the cross-sectional image of any 100 particles of the coated active material 100 is tri-valued into the active material 110, the first coating layer 120 (i.e., the composite particle 130), the second coating layer 140, and other regions, and the average roundness is calculated for the surfaces of the composite particle 130 and the second coating layer 140 according to formulas (I) and (II), and the ratio is then calculated to determine the average roundness ratio.

[0018] By covering the surface of the composite particle 130 with the second coating layer 140 at a coverage rate of 15.0% or more and 75.0% or less, it is possible to sufficiently ensure both an ionic conduction path from the external electrolyte to the composite particle 130 (i.e., contact between the composite particle 130 and other electrolytes in the electrode) and an electronic conduction path (i.e., contact between the composite particles 130 themselves or between the composite particle 130 and the conductive additive) within the battery electrode, thereby reducing the battery resistance. Here, the other electrolyte within the electrode refers to an electrolyte present around the coated active material 100 within the electrode, such as a bulk solid electrolyte (corresponding to the third solid electrolyte contained in the electrode material in Embodiment 2 described below) present around the coated active material 100 within the electrode.

[0019] The coverage of the second coating layer 140 can be measured, for example, by observing a cross section of the coated active material 100 with an SEM or STEM.

[0020] For example, when measuring the coverage of the second coating layer 140 from a cross-sectional image of the coated active material 100 taken by SEM, the coverage can be determined by dividing the cross-sectional image of any 100 particles of the coated active material 100 into 360° sections starting from the center of gravity of the active material 110, determining the presence or absence of the second coating layer 140 every 1°, and calculating the proportion of the second coating layer 140 present.

[0021] In the present disclosure, the coverage of the surface of the composite particle 130 with the second coating layer 140 is defined as the average value of the coverage of any 100 particles of the coated active material 100 .

[0022] Hereinafter, the components and manufacturing method of coated active material 100 in this embodiment will be described in detail.

[0023] <Composite Particles> (Active Material) The active material 110 includes a material that has the property of absorbing and releasing metal ions (for example, lithium ions).

[0024] Examples of materials that can be used as the active material 110 include lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, transition metal oxynitrides, metal materials, carbon materials, oxides, nitrides, tin compounds, and silicon compounds. Using a lithium-containing transition metal oxide as the active material 110 can reduce the manufacturing cost of the battery. Examples of lithium-containing transition metal oxides include Li(Ni, Co, Al)O, Li(Ni, Co, Mn)O, and LiCoO.

[0025] In the present disclosure, when an element in a formula is expressed as "(Ni, Co, Al)," this notation indicates at least one element selected from the group of elements in the parentheses. That is, "(Ni, Co, Al)" is synonymous with "at least one selected from the group consisting of Ni, Co, and Al." The same applies to other elements.

[0026] The active material 110 has, for example, a particle shape. There are no particular limitations on the shape of the particles of the active material 110. The shape of the particles of the active material 110 can be spherical, oval, scaly, or fibrous.

[0027] The median diameter of the active material 110 may be 0.1 μm or more and 100 μm or less. When the median diameter of the active material 110 is 0.1 μm or more, the coated active material 100 and the above-mentioned bulk solid electrolyte (corresponding to the third solid electrolyte contained in the electrode material in the second embodiment described later) can form a well-dispersed state in the electrode. As a result, the charge / discharge characteristics of the battery are improved. When the median diameter of the active material 110 is 100 μm or less, the diffusion rate of lithium inside the active material 110 is sufficiently ensured. Therefore, the battery can operate at high power.

[0028] The active material 110 may be a positive electrode active material. In this case, a sufficient ion conduction path can be provided near the interface between the positive electrode active material and the electrolyte, which generally has high charge transfer resistance, and the resistance of the battery can be reduced.

[0029] The active material 110 may contain Li, Ni, and O. In this case, the energy density of the battery can be increased.

[0030] <First Coating Layer> As described above, the first coating layer 120 covers at least a part of the surface of the active material 110. The first coating layer 120 is in direct contact with the active material 110, for example.

[0031] The first coating layer 120 includes a first solid electrolyte. The first solid electrolyte has ion conductivity. The ion conductivity is typically lithium ion conductivity.

[0032] The first solid electrolyte may contain Li, M, and at least one element selected from the group consisting of F and O. M is at least one element selected from the group consisting of metal elements other than Li and metalloid elements. A first solid electrolyte having such a composition has excellent oxidation-reduction resistance. Therefore, it is possible to suppress the oxidation-reduction of the second solid electrolyte contained in the second coating layer 140 that contacts the first coating layer 120. This reduces the resistance of the battery.

[0033] In this disclosure, "metalloid elements" include B, Si, Ge, As, Sb, and Te. "Metal elements" include all elements in groups 1 to 12 of the periodic table except hydrogen, and all elements in groups 13 to 16 of the periodic table except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se.

[0034] The first solid electrolyte contains Li, M1, M2, and F, where M1 is at least one selected from the group consisting of Al and Y, and M2 may be at least one selected from the group consisting of Ti, Zr, Mg, Ca, Si, and Sn. In a first solid electrolyte having such a composition, a cationic framework suitable for ion conduction can be formed within the crystal lattice. Therefore, the first solid electrolyte exhibits high ionic conductivity. High ionic conductivity is, for example, 1.0 × 10 -8 That is, the first solid electrolyte has a specific resistance of, for example, 1.0×10 -8 The ionic conductivity may be 100 S / cm or more.

[0035] M1 may be Al and M2 may be Ti. A first solid electrolyte having such a composition exhibits even higher ionic conductivity.

[0036] The first solid electrolyte may consist essentially of Li, Ti, Al, and F. In the present disclosure, "the first solid electrolyte consists essentially of Li, Ti, Al, and F" means that the molar ratio (i.e., molar fraction) of the total amount of substance of Li, Ti, Al, and F to the total amount of substance of all elements constituting the first solid electrolyte is 90% or more. As an example, the molar ratio (i.e., molar fraction) may be 95% or more. The first solid electrolyte may consist only of Li, Ti, Al, and F.

[0037] The first solid electrolyte may be represented by the following composition formula (1): Li(4-x-4y+my)(Ti 1-x-y Al x M3 y ) b F 6-2z O z ... (1) In the composition formula (1), M3 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the valence of M3, and 0.1 < x < 0.9, 0 ≦ y < 0.1, 0 ≦ z < 0.1, and 0.8 < b ≦ 1.2 are satisfied. A first solid electrolyte having such a composition has high ionic conductivity and can be produced by a method with high industrial productivity.

[0038] In the composition formula (1), the following may be satisfied: 0.1<x<0.9, y=0, z=0, and 0.8<b≦1.2. A first solid electrolyte having such a composition has higher ionic conductivity.

[0039] In the composition formula (1), 0.1≦x≦0.7 may be satisfied.

[0040] The upper and lower limits of the range of x in composition formula (1) can be defined by any combination selected from the following numerical values: 0.1, 0.3, 0.4, 0.5, 0.6, 0.65, 0.67, 0.7, 0.8, and 0.9.

[0041] The upper and lower limits of the range of b in composition formula (1) can be defined by any combination selected from the following numerical values: 0.8, 0.9, 0.94, 1.0, 1.06, 1.1, and 1.2.

[0042] The first solid electrolyte may contain Li, Nb, and O. A first solid electrolyte having such a composition may also form a cationic framework structure suitable for ion conduction within the crystal lattice. Therefore, the first solid electrolyte exhibits high ionic conductivity. High ionic conductivity is, for example, 1.0×10 -8 That is, the first solid electrolyte has a specific resistance of, for example, 1.0×10 -8 The ionic conductivity may be 100 S / cm or more.

[0043] The first solid electrolyte may be crystalline or amorphous.

[0044] The shape of the first solid electrolyte is not particularly limited. The shape of the first solid electrolyte is, for example, needle-like, spherical, film-like, or ellipsoidal. The shape of the first solid electrolyte may also be particulate.

[0045] When the first solid electrolyte has a particulate (e.g., spherical) shape, the first solid electrolyte may have a median diameter of 0.01 μm or more and 100 μm or less.

[0046] In the present disclosure, the term "median diameter" refers to the particle size at which the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measurement device or an image analysis device.

[0047] The first coating layer 120 may contain the first solid electrolyte as a main component, or may contain only the first solid electrolyte. In the present disclosure, "main component" refers to the component that is contained in the largest amount by mass. "Containing only the first solid electrolyte" means that, with the exception of inevitable impurities, no materials other than the first solid electrolyte are intentionally added. For example, the raw materials of the first solid electrolyte and by-products generated during the production of the first solid electrolyte are included as inevitable impurities. The mass ratio of the inevitable impurities to the total mass of the first coating layer 120 may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0048] The first coating layer 120 may not contain sulfur.

[0049] The first coating layer 120 may uniformly coat the active material 110 .

[0050] The first coating layer 120 may cover only a portion of the surface of the active material 110. In this case, particles of the active material 110 can come into direct contact with each other via the portion not covered by the first coating layer 120, improving the electronic conductivity between particles of the active material 110. As a result, high-power operation of the battery is possible.

[0051] The shape of the first solid electrolyte contained in the first coating layer 120 is not particularly limited. For example, a thin film formed by the accumulation of fine particles of the first solid electrolyte, such as plate-like, needle-like, spherical, or oval-spherical, may cover at least a portion of the surface of the active material 110.

[0052] The thickness of the thin film of the first coating layer 120 is, for example, 1 nm or more and 1000 nm or less. When the thickness of the thin film of the first coating layer 120 is appropriately adjusted, contact between the active material 110 and the second solid electrolyte can be sufficiently suppressed. The thickness of the thin film of the first coating layer 120 can be determined, for example, by observing the cross section of a particle of the coated active material 100 with a scanning electron microscope. The average value of the thicknesses of the thin film of the first coating layer 120 measured at multiple arbitrary positions (for example, five points) can be considered to be the thickness of the thin film of the first coating layer 120.

[0053] <Second Coating Layer> As described above, the second coating layer 140 covers the surface of the composite particle 130 at a coverage rate of 15.0% or more and 75.0% or less. The second coating layer 140 is in contact with the composite particle 130, for example.

[0054] The second coating layer 140 includes a second solid electrolyte. The second solid electrolyte has ion conductivity. The ion conductivity is typically lithium ion conductivity.

[0055] The coverage of the surface of the composite particle 130 with the second coating layer 140 may be 20.0% or more, 23.0% or more, or 23.8% or more. In this case, a large amount of electrolyte is in close contact with the composite particle 130, so that a wider ion conduction path to the composite particle 130 can be ensured. As a result, the resistance of the battery can be further reduced.

[0056] The coverage of the surface of the composite particle 130 with the second coating layer 140 may be 72.0% or less, 71.0% or less, or 70.0% or less. In this case, a moderate amount of the surface of the composite particle 130 where the second coating layer 140 is not present exists, so that a wider electron conduction path to the composite particle 130 can be ensured. As a result, the resistance of the battery can be further reduced.

[0057] The coverage of the surface of the composite particle 130 with the second coating layer 140 may be 61.5% or less. In this case, a more appropriate portion of the surface of the composite particle 130 where the second coating layer 140 is not present exists, so that an even wider electron conduction path to the composite particle 130 can be secured. As a result, the resistance of the battery can be reduced more efficiently.

[0058] The coefficient of variation of the coverage of the surface of the composite particle 130 with the second coating layer 140 may be 20.0% or more, 21.0% or more, or 21.5% or more. In this case, the presence of both composite particles 130 with a comparatively low coverage of the second coating layer 140 and composite particles 130 with a relatively high coverage makes it easier to effectively utilize the active material 110 during charge and discharge, even when the state of charge of the active material 110 changes and the ease of electronic conduction and the ease of ionic conduction change. As a result, the input / output characteristics of the battery can be improved.

[0059] The coefficient of variation of the coverage of the surface of the composite particle 130 with the second coating layer 140 may be 65.0% or less, 64.5% or less, or 64.3% or less. In this case, the proportion of active material with an appropriate coverage of the second coating layer 140 increases, and the resistance of the battery can be kept extremely low.

[0060] The coefficient of variation of the coverage of the composite particle surface with the second coating layer 140 can be calculated by taking the ratio of the unbiased square root of the coverage of any 100 particles of the coated active material 100 to the average value.

[0061] The second solid electrolyte contained in the second coating layer 140 may contain S. With this configuration, the second solid electrolyte has high ionic conductivity. Here, the high ionic conductivity of the second solid electrolyte is, for example, 1.0×10 -4 That is, the second solid electrolyte has an ionic conductivity of 1.0×10 -4 The ionic conductivity may be 100 S / cm or more.

[0062] The second solid electrolyte may be crystalline or amorphous.

[0063] The shape of the second solid electrolyte is not particularly limited. The shape of the second solid electrolyte is, for example, needle-like, spherical, film-like, or oval-spherical. The shape of the second solid electrolyte may also be particulate.

[0064] When the second solid electrolyte is, for example, particulate (for example, spherical) in shape, the first solid electrolyte may have a median diameter of 0.01 μm or more and 100 μm or less.

[0065] In the second coating layer 140, the shape of the second solid electrolyte contained in the second coating layer 140 is not particularly limited. For example, at least a portion of the surface of the composite particle 130 may be covered with a thin film formed by the accumulation of fine particles of the second solid electrolyte having a shape such as a plate, needle, sphere, or oval sphere.

[0066] The second coating layer 140 may contain the second solid electrolyte as a main component, or may contain only the second solid electrolyte. In the present disclosure, "main component" refers to the component that is contained in the largest amount by mass. "Containing only the second solid electrolyte" means that, with the exception of inevitable impurities, no materials other than the second solid electrolyte are intentionally added. For example, the raw materials of the second solid electrolyte and by-products generated during the production of the second solid electrolyte are included as inevitable impurities. The mass ratio of the inevitable impurities to the total mass of the second solid electrolyte may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0067] The thickness of the thin film of the second coating layer 140 is, for example, 1 nm or more and 5000 nm or less. If the thickness of the thin film of the second coating layer 140 is appropriately adjusted, it is possible to appropriately ensure both an electron conduction path and an ion conduction path to the composite particle 130. The thickness of the thin film of the second coating layer 140 can be determined, for example, by observing the cross section of a particle of the coated active material 100 with a scanning electron microscope.

[0068] <Method for Producing First Solid Electrolyte> The first solid electrolyte contained in the coated active material 100 can be produced, for example, by the following method.

[0069] Two or more kinds of raw material powders are prepared to have the desired composition. For example, Li 2.7 Ti 0.3 Al 0.7 When F is produced, LiF, TiF, and AlF are prepared in a molar ratio of LiF:TiF:AlF=2.7:0.3:0.7. The raw material powders may be mixed in a pre-adjusted molar ratio to offset compositional changes that may occur during the synthesis process.

[0070] After mixing the raw material powders, the raw material powders are reacted with each other using a mechanochemical milling method in a mixing device such as a planetary ball mill to obtain a reaction product, which may then be calcined in an inert gas atmosphere or in vacuum.

[0071] Alternatively, a mixture of raw material powders may be fired in an inert gas atmosphere to react with each other to obtain a reactant. Examples of inert gases include helium, nitrogen, or argon. The firing may be performed in a vacuum. In the firing step, the mixture of raw material powders may be placed in a container and fired in a heating furnace. The container may be, for example, a crucible, a sealed container, or a vacuum sealed tube.

[0072] By these methods, the first solid electrolyte having the above-mentioned composition can be obtained.

[0073] The composition of the first solid electrolyte can be determined by, for example, high-frequency inductively coupled plasma atomic emission spectroscopy, ion chromatography, or the like.

[0074] <Method for Producing Composite Particles> The composite particles 130 in the first embodiment can be produced, for example, by the following method.

[0075] A powder of the active material 110 and a powder of a material for the first coating layer 120 containing the first solid electrolyte are prepared in a predetermined mass ratio. Here, an example of a method for producing composite particles in which the first coating layer 120 is made of the first solid electrolyte will be described.

[0076] For example, the active material 110 is a powder of Li(Ni, Co, Al)O2, and the first solid electrolyte is Li 2.7 Al 0.7 Ti 0.3 A powder of F6 is prepared. Mechanical energy is applied to a mixture of these two materials using a dry process to coat at least a portion of the surface of the active material 110 with the first solid electrolyte, forming a first coating layer 120, thereby obtaining composite particles 130. For example, the two materials may be placed in a container and a rotating blade may be used to apply shear force to the two materials. For example, the two materials may be placed in a container and a jet stream may be used to collide the two materials. The powder of the active material 110 and the powder of the first solid electrolyte are mixed in an appropriate ratio.

[0077] Before applying mechanical energy to the mixture of the active material 110 powder and the first solid electrolyte powder, the mixture may be milled. A mixing device such as a ball mill may be used for the milling. To prevent side reactions of the materials, the milling may be performed in a dry or inert atmosphere.

[0078] The composite particles 130 may be manufactured by a dry particle compounding method, which includes applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to a mixture of the active material 110 powder and the first solid electrolyte powder.

[0079] The apparatus used in producing the composite particles 130 is not particularly limited. The apparatus may be an apparatus capable of applying mechanical energy such as impact, compression, and shear to a mixture of the powder of the active material 110 and the powder of the first solid electrolyte. Examples of apparatus capable of applying mechanical energy include a ball mill, a jet mill, a compression shear processing apparatus (particle composite apparatus) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation) and "Nobilta" (manufactured by Hosokawa Micron Corporation), a "Hybridization System (high-velocity airflow impact apparatus)" (manufactured by Nara Machinery Works), and "Balance Gran" (manufactured by Freund Turbo Corporation).

[0080] "Mechanofusion" is a particle compounding device that uses dry mechanical compounding technology by applying strong mechanical energy to particles of multiple different materials. In mechanofusion, powder raw materials are placed between a rotating container and a press head, and mechanical energy such as compression, shear, and friction is applied to them, causing the particles to compound.

[0081] "Nobilta" is a particle compositing device that uses dry mechanical compositing technology, an advanced form of particle compositing technology, to composite nanoparticles as raw materials. Nobilta produces composite particles 130 by applying mechanical energy of impact, compression, and shear to multiple raw material powders.

[0082] In the Nobilta, a rotor positioned to leave a predetermined gap between itself and the inner wall of a horizontal cylindrical mixing vessel rotates at high speed, forcing the raw material powder through the gap, a process that is repeated multiple times. This applies impact, compression, and shear forces to the mixture, producing composite particles 130 of active material 110 and first solid electrolyte. Conditions such as rotor rotation speed, processing time, and feed amount can be adjusted as needed.

[0083] In the "hybridization system," raw material powder is dispersed in a high-speed airflow while a force, primarily an impact, is applied, thereby producing composite particles 130 of active material 110 and first solid electrolyte.

[0084] The Balance Gran is equipped with a chopper that stirs the powder in a spiral from the outer periphery to the inner periphery, promoting convection, and an agitator scraper that rotates in the opposite direction to the chopper. The action of the chopper and agitator scraper disperses the mixture uniformly, allowing the production of composite particles 130 of the active material 110 and the first solid electrolyte.

[0085] However, processing using the above-mentioned apparatus is not essential. The composite particles may be produced by mixing a powder of the active material 110 and a powder of the first solid electrolyte using a mortar, a mixer, or the like. For example, the first coating layer 120 may be formed by depositing the first solid electrolyte on the surface of the active material 110 using a method such as mechanical mixing using a disperser.

[0086] Alternatively, the composite particles 130 may be manufactured using a wet (liquid phase) coating method or a vapor phase coating method without applying mechanical energy. Examples of the wet (liquid phase) coating method include an air suspension coating method, a spray method, a spray dry coating method, an electrodeposition method, and a dipping method. Examples of the vapor phase coating method include a pulsed laser deposition method, a vacuum evaporation method, a sputtering method, a thermal chemical vapor deposition method, and a plasma chemical vapor deposition method.

[0087] <Method for Producing Coated Active Material> The coated active material 100 in the first embodiment can be produced, for example, by the following method.

[0088] A powder of the composite particles 130 and a powder of a material for the second coating layer 140 containing the second solid electrolyte are prepared in a predetermined mass ratio. Here, an example of a method for manufacturing the coated active material 100 in which the second coating layer 140 is made of the second solid electrolyte will be described.

[0089] By applying mechanical energy to a mixture of two materials, a powder of the composite particle 130 and a powder of the second solid electrolyte, using a dry or wet method, the second solid electrolyte is coated on at least a portion of the surface of the composite particle 130 to form a second coating layer 140, thereby obtaining the coated active material 100. For example, the two materials may be placed in a container and a rotating blade may be used to apply shear force to the two materials. Alternatively, a mixture of the two materials and a solvent may be prepared and then shear force may be applied using a kneading method. The kneading method is a technique in which a solid and a liquid are mixed to knead a solid material that has a clay-like texture rather than a powdery state. When the coated active material 100 is produced using the kneading method, the mixture used for kneading may contain a binder or a dispersant.

[0090] As an apparatus for producing the coated active material 100, for example, when producing by a dry method or a wet method, the apparatus described in the method for producing the composite particles can be used. Alternatively, when producing by a kneading method, an apparatus such as a kneader or a planetary mixer can be used. In order to suppress side reactions of the materials, the production of the coated active material 100 may be carried out in a dry atmosphere or an inert atmosphere.

[0091] To enhance the electronic conductivity of the second coating layer, the second coating layer 140 of the coated active material 100 may contain a conductive additive. However, if the coverage of the composite particle 130 by the second coating layer 140 is appropriately adjusted, the coated active material 100 can maintain sufficient electronic conductivity even if the second coating layer 140 does not contain a conductive additive. When the second coating layer 140 does not contain a conductive additive, the coated active material 100 can be manufactured using a method with high industrial productivity. Examples of conductive additives include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black and ketjen black, conductive fibers such as carbon fiber or metal fiber, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can reduce costs.

[0092] Second Embodiment Hereinafter, an electrode material in a second embodiment will be described. Descriptions that overlap with those in the first embodiment will be omitted as appropriate.

[0093] FIG. 2 is a cross-sectional view showing a schematic configuration of an electrode material 200 according to the second embodiment.

[0094] The electrode material 200 includes the coated active material 100 according to the first embodiment. The electrode material 200 is suitable for reducing the resistance of a battery because it includes the coated active material 100. The electrode material 200 may further include, for example, a third solid electrolyte 210.

[0095] In the coated active material 100, the ratio of the average roundness of the coated active material 100 to the average roundness of the active material 110 is less than 1.30. When the average roundness ratio is less than 1.30, the contact area between the coated active material 100 and the third solid electrolyte 210 at the interface between the coated active material 100 and the third solid electrolyte 210 increases. This makes it easier for the coated active material 100 and the third solid electrolyte 210 to adhere to each other sufficiently. Therefore, when the average roundness ratio is less than 1.30, it becomes easier to ensure a good ion conduction path within the electrode, which is effective in reducing the resistance of the battery.

[0096] The third solid electrolyte 210 may have a different composition than the second solid electrolyte.

[0097] The third solid electrolyte 210 may include at least one selected from the group consisting of a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. The third solid electrolyte 210 allows the electrode material 200 to achieve high ionic conductivity.

[0098] Examples of halide solid electrolytes that can be used include Li3REX6, Li3(Al,Ga,In)X6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, Li(Ta,Nb)OX4, and LiI, where X is at least one selected from the group consisting of Cl, Br, and I, and RE is at least one selected from the group consisting of rare earth elements.

[0099] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 LiX, LiO, MO, etc. can be used. q , Li p MO q The element X in "LiX" is at least one element selected from the group consisting of F, Cl, Br, and I. q " and "Li p MO q " The element M is at least one element selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q In the above formula, p and q are independent natural numbers.

[0100] Examples of oxide solid electrolytes include NASICON-type solid electrolytes, such as LiTi2(PO4)3 and its elemental substitution products, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGeO 16 , Li4SiO4, LiGeO4 and their element substitution products, LiSICON type solid electrolytes, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as LiN and its element substitution products, LiN and its H-substituted products, LiPO and its N-substituted products, and glasses or glass ceramics based on Li-B-O compounds such as LiBO and LiBO, to which materials such as LiSO and LiCO are added can be used.

[0101] Examples of the polymer solid electrolyte include a compound of a polymer compound and a lithium salt. The polymer compound may have an ethylene oxide structure. The ethylene oxide structure allows the polymer compound to contain a large amount of lithium salt. This increases ionic conductivity. Examples of the lithium salt include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2CF2F5)2, LiN(SO2CF3)(SO2CF4F9), and LiC(SO2CF3)3. A single lithium salt selected from these may be used alone, or a mixture of two or more lithium salts selected from these may be used.

[0102] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0103] The third solid electrolyte 210 may contain S. That is, it may be a sulfide-based solid electrolyte. With this configuration, the third solid electrolyte 210 has high ionic conductivity. Here, with respect to the third solid electrolyte, high ionic conductivity means, for example, 1.0×10 -4 That is, the third solid electrolyte 210 has an ionic conductivity of 1.0×10 S / cm or more. -4The ionic conductivity may be 100 S / cm or more.

[0104] A solid electrolyte having the same composition as the second solid electrolyte may be included as the third solid electrolyte 210. With this configuration, the electrode material can be produced by a method with high industrial productivity.

[0105] When it is necessary to distinguish between the third solid electrolyte 210 and the second solid electrolyte contained in the second coating layer 140 of the coated active material 100 within the electrode material, i.e., when it is necessary to identify the boundary between the second coating layer 140 of the coated active material 100 and the third solid electrolyte 210, the two can be distinguished, for example, as follows. When the constituent elements of the third solid electrolyte 210 and the second solid electrolyte are different, the two can be distinguished by elemental analysis of a cross section of the electrode using a technique such as energy dispersive X-ray spectroscopy (EDS). Furthermore, when the constituent elements of the third solid electrolyte 210 and the second solid electrolyte are similar, it is possible to identify the boundary between the second coating layer 140 of the coated active material 100 and the third solid electrolyte 210 by using an additive (e.g., a conductive additive, a binder, or a dispersant) that is not contained in the second coating layer 140 of the coated active material 100 but is contained in the portion of the electrode material 200 other than the coated active material 100. In this case, by analyzing the cross section of the electrode using a method such as EDS to determine the presence or absence of elements (e.g., carbon) that are contained in the additive but not contained in the second solid electrolyte, it is possible to distinguish between the second solid electrolyte that does not contain the additive and exists as the second coating layer 140 and the third solid electrolyte 210 that exists in other locations.

[0106] The third solid electrolyte 210 may contain unavoidable impurities such as starting materials, by-products, and decomposition products used in synthesizing the solid electrolyte.

[0107] The shape of the third solid electrolyte 210 is not particularly limited, and may be needle-like, spherical, oval-spherical, etc. The shape of the third solid electrolyte 210 may be particulate.

[0108] When the third solid electrolyte 210 is, for example, particulate (e.g., spherical) in shape, the solid electrolyte may have a median diameter of 0.1 μm or more and 100 μm or less. When the solid electrolyte has a median diameter in this range, the coated active material 100 and the third solid electrolyte 210 are well dispersed in the electrode material 200.

[0109] The median diameter of the third solid electrolyte 210 may be 10 μm or less. In this case, the dispersion state of the coated active material 100 and the third solid electrolyte 210 in the electrode material 200 becomes better.

[0110] The median diameter of the third solid electrolyte 210 may be smaller than the median diameter of the coated active material 100. In this case, the coated active material 100 and the third solid electrolyte 210 are better dispersed in the electrode material 200.

[0111] In the electrode material 200, the coated active material 100 and the third solid electrolyte 210 may be in contact with each other. In this case, the second coating layer 140 and the third solid electrolyte 210 are in contact with each other.

[0112] The electrode material 200 may include a plurality of particles of the third solid electrolyte 210 and a plurality of particles of the coated active material 100. In other words, the electrode material 200 may be a mixture of a powder of the coated active material 100 and a powder of the third solid electrolyte 210.

[0113] In the electrode material 200, the content of the coated active material 100 and the content of the third solid electrolyte 210 may be the same as or different from each other.

[0114] The electrode material 200 may contain a binder to improve adhesion between particles. The binder is used to improve the binding properties of the materials constituting the positive electrode. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl ester of acrylic acid, polyethyl ester of acrylic acid, polyhexyl ester of acrylic acid, polymethacrylic acid, polymethyl ester of methacrylic acid, polyethyl ester of methacrylic acid, polyhexyl ester of methacrylic acid, polyvinyl acetate, polyvinylpyrrolidone, polyether, polycarbonate, polyethersulfone, polyetherketone, polyetheretherketone, polyphenylene sulfide, hexafluoropolypropylene, styrene-butadiene rubber, carboxymethyl cellulose, and ethyl cellulose. Also usable are copolymers of two or more monomers selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, butadiene, styrene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid ester, acrylic acid, and hexadiene. One selected from these may be used alone, or two or more may be used in combination.

[0115] The binder may be an elastomer because it has excellent binding properties. An elastomer is a polymer having rubber elasticity. The elastomer used as the binder may be a thermoplastic elastomer or a thermosetting elastomer. The binder may contain a thermoplastic elastomer. Examples of thermoplastic elastomers include styrene-ethylene-butylene-styrene (SEBS), styrene-ethylene-propylene-styrene (SEPS), styrene-ethylene-ethylene-propylene-styrene (SEEPS), butylene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), styrene-butylene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), hydrogenated isoprene rubber (HIR), hydrogenated butyl rubber (HIIR), hydrogenated nitrile rubber (HNBR), hydrogenated styrene-butylene rubber (HSBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), etc. One selected from these may be used alone, or two or more may be used in combination.

[0116] The electrode material 200 may contain a conductive additive for the purpose of increasing electronic conductivity. As the conductive additive, the materials described in the method for producing a coated active material in the first embodiment may be used.

[0117] <Method for manufacturing electrode material> The electrode material 200 is obtained by mixing the coated active material 100 and the third solid electrolyte 210. The method for mixing the coated active material 100 and the third solid electrolyte 210 is not particularly limited. The coated active material 100 and the third solid electrolyte 210 may be mixed using a tool such as a mortar, or may be mixed using a mixing device such as a ball mill. After forming the second coating layer 140 of the coated active material 100, the coated active material 100 and the third solid electrolyte 210 may be mixed by subsequently adding the third solid electrolyte to the same manufacturing device.

[0118] (Embodiment 3) A battery according to embodiment 3 will be described below. Descriptions that overlap with embodiments 1 and 2 will be omitted where appropriate.

[0119] The battery of the third embodiment includes a positive electrode, a separator, and a negative electrode. The separator is located between the positive electrode and the negative electrode. The positive electrode includes the electrode material 200 of the second embodiment. The electrode material 200 includes a positive electrode active material, such as Li(Ni, Co, Al)O, as the active material 110. This configuration can reduce the resistance of the battery.

[0120] The separator portion may be an electrolyte layer containing a solid electrolyte, or may be a separator impregnated with an electrolytic solution.

[0121] FIG. 3 is a cross-sectional view showing a schematic configuration of a battery 300 according to the third embodiment.

[0122] Battery 300 includes a positive electrode 310, an electrolyte layer 320, and a negative electrode 330. Electrolyte layer 320 is disposed between positive electrode 310 and negative electrode 330. In battery 300, electrolyte layer 320 serves as a separator. At least one selected from the group consisting of positive electrode 310 and negative electrode 330 includes electrode material 200 according to the second embodiment. With this configuration, an increase in the resistance of battery 300 is suppressed, thereby improving the durability of battery 300.

[0123] The thickness of each of the positive electrode 310 and the negative electrode 330 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 310 and the negative electrode 330 is 10 μm or more, a sufficient energy density of the battery 300 can be ensured. When the thickness of the positive electrode 310 and the negative electrode 330 is 500 μm or less, high-power operation of the battery 300 can be achieved.

[0124] The positive electrode 310 includes, for example, the electrode material 200 in the second embodiment.

[0125] The electrolyte layer 320 is a layer containing an electrolyte material. The electrolyte layer 320 may contain at least one solid electrolyte selected from the group consisting of a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. Details of each solid electrolyte are as described in the second embodiment.

[0126] The thickness of the electrolyte layer 320 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 320 is 1 μm or more, the positive electrode 310 and the negative electrode 330 can be more reliably separated. When the thickness of the electrolyte layer 320 is 300 μm or less, the battery 300 can operate at high power.

[0127] The negative electrode 330 contains, as a negative electrode active material, a material that has the property of absorbing and releasing metal ions (for example, lithium ions).

[0128] Examples of the negative electrode active material that can be used include metal materials, carbon materials, oxides, nitrides, tin compounds, and silicon compounds. The metal material may be a single metal. Alternatively, the metal material may be an alloy. Examples of the metal material include lithium metal and lithium alloys. Examples of the carbon material include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, and tin compounds can be preferably used.

[0129] The median diameter of the particles of the negative electrode active material may be 0.1 μm or more and 100 μm or less.

[0130] The negative electrode 330 may contain other materials such as a solid electrolyte. As the solid electrolyte, the solid electrolyte described in the second embodiment can be used.

[0131] The battery 300 can be configured as a battery of various shapes, such as a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminated type.

[0132] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0133] (Technology 1) A coated active material comprising: composite particles including an active material and a first coating layer that coats at least a portion of the surface of the active material; and a second coating layer that coats the surface of the composite particles at a coverage rate of 15.0% or more and 75.0% or less, wherein the first coating layer includes a first solid electrolyte, and the second coating layer includes a second solid electrolyte having a different composition from the first solid electrolyte, and the ratio of the average roundness of the coated active material to the average roundness of the active material is less than 1.30.

[0134] This configuration can reduce the resistance of the battery.

[0135] (Technology 2) The coated active material according to Technology 1, wherein the coverage of the surface of the composite particle with the second coating layer is 20.0% or more.

[0136] This configuration can further reduce the resistance of the battery.

[0137] (Technology 3) The coated active material according to Technology 1 or 2, wherein the coverage of the surface of the composite particle with the second coating layer is 72.0% or less.

[0138] This configuration can further reduce the resistance of the battery.

[0139] (Technology 4) The coated active material according to any one of Technologies 1 to 3, wherein a coefficient of variation of the coverage of the surface of the composite particle with the second coating layer is 20.0% or more.

[0140] This configuration can improve the input / output characteristics of the battery.

[0141] (Technology 5) The coated active material according to any one of Technologies 1 to 4, wherein a coefficient of variation of the coverage of the surface of the composite particle with the second coating layer is 65.0% or less.

[0142] This configuration can further reduce the resistance of the battery.

[0143] (Technology 6) The coated active material according to any one of Technologies 1 to 5, wherein the active material is a positive electrode active material.

[0144] This configuration can reduce the resistance of the battery.

[0145] (Technology 7) The coated active material according to any one of Technologies 1 to 6, wherein the active material contains Li, Ni, and O.

[0146] This configuration can increase the energy density of the battery.

[0147] (Technology 8) The coated active material according to any one of Technologies 1 to 7, wherein the first solid electrolyte contains Li, M, and at least one selected from the group consisting of F and O, and the M is at least one element selected from the group consisting of metal elements and semimetal elements other than Li.

[0148] This configuration can reduce the resistance of the battery.

[0149] (Technology 9) The coated active material according to any one of Technologies 1 to 7, wherein the first solid electrolyte contains Li, M1, M2, and F, wherein M1 is at least one selected from the group consisting of Al and Y, and wherein M2 is at least one selected from the group consisting of Ti, Zr, Mg, Ca, Si, and Sn.

[0150] This configuration allows the first solid electrolyte to exhibit high ionic conductivity.

[0151] (Technology 10) The coated active material according to Technology 9, wherein M1 is Al and M2 is Ti.

[0152] This configuration allows the first solid electrolyte to exhibit higher ionic conductivity.

[0153] (Technology 11) The first solid electrolyte is represented by the following composition formula (1): Li6-(4-x-4y+my)b(Ti 1-x-y Al x M3 y ) b F 6-2z O z... (1) Here, in the above composition formula (1), M3 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is a valence of M3, and the following conditions are satisfied: 0.1<x<0.9, 0≦y<0.1, 0≦z<0.1, and 0.8<b≦1.2.

[0154] With this configuration, the first solid electrolyte has high ionic conductivity and can be produced by a method with high industrial productivity.

[0155] (Technology 12) The coated active material according to any one of Technologies 1 to 7, wherein the first solid electrolyte contains Li, Nb, and O.

[0156] This configuration allows the first solid electrolyte to exhibit high ionic conductivity.

[0157] (Technology 13) The coated active material according to any one of Techniques 1 to 12, wherein the second solid electrolyte contains S.

[0158] This configuration allows the second solid electrolyte to exhibit high ionic conductivity.

[0159] (Technology 14) An electrode material comprising the coated active material according to any one of technologies 1 to 13.

[0160] This configuration can reduce the resistance of the battery.

[0161] (Technology 15) The electrode material according to Technology 14, further comprising a third solid electrolyte, wherein the third solid electrolyte contains S.

[0162] This configuration allows the third solid electrolyte to exhibit high ionic conductivity.

[0163] (Technology 16) The electrode material according to Technology 14 or 15, further comprising a third solid electrolyte, wherein the third solid electrolyte includes a solid electrolyte having the same composition as the second solid electrolyte.

[0164] This configuration allows the electrode material to be produced by a method with high industrial productivity.

[0165] (Technology 17) A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode and the negative electrode comprises the electrode material according to any one of technologies 14 to 16.

[0166] This configuration can reduce the resistance of the battery.

[0167] The present disclosure will be described in more detail below with reference to examples and comparative examples, although the present invention is not limited to the following examples.

[0168] Example 1 Positive Electrode Active Material Li(Ni,Co,Al)O2 (hereinafter referred to as NCA) having a median diameter of 5 μm was used as the positive electrode active material.

[0169] [Preparation of First Solid Electrolyte] In an argon glove box with a dew point of -60°C or less, raw material powders of LiF, TiF4, and AlF3 were weighed in a molar ratio of LiF:TiF4:AlF3 = 2.7:0.3:0.7. These were pulverized and mixed in a mortar to obtain a mixture. The obtained mixed powder was milled at 500 rpm for 12 hours using a planetary ball mill (Fritsch, P-7 model). In this way, a halide solid electrolyte powder was obtained. The obtained halide solid electrolyte contained Li, 2.7 Ti 0.3 Al 0.7 The resulting LTAF was used as the material for the first coating layer (first solid electrolyte) of Example 1.

[0170] [Preparation of Composite Particles] A first coating layer made of LTAF was formed on the surface of the NCA. The first coating layer was formed by compressive shear treatment using a particle compositer (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, in an argon glove box with a dew point of -60°C or less, the NCA and LTAF were weighed out to a mass ratio of NCA:LTAF = 97.3:2.7, and treated under the conditions of a blade clearance of 2 mm, a rotation speed of 6000 rpm, and a treatment time of 50 minutes. In this manner, composite particles composed of the positive electrode active material of Example 1 and a first coating layer formed from the first solid electrolyte were prepared.

[0171] [Preparation of Second Solid Electrolyte] In an argon glove box with a dew point of −60°C or less, raw material powders LiS and PS were weighed out to a molar ratio of LiS:PS = 75:25. These were pulverized and mixed in a mortar to obtain a mixture. The mixture was then milled for 10 hours at 510 rpm using a planetary ball mill (Fritsch, Model P-7). This resulted in a glassy solid electrolyte. The glassy solid electrolyte was then heat-treated in an inert atmosphere at 270°C for 2 hours. This resulted in a glass-ceramic sulfide solid electrolyte, LiS-PS (hereinafter referred to as LPS). The resulting LPS was used as the second solid electrolyte of Example 1.

[0172] [Preparation of Coated Active Material] A second coating layer made of LPS was formed on the surface of the composite particles. The second coating layer was formed by a kneading method using a planetary mixer (Hibismix 2P-1, manufactured by Primix Corporation). Specifically, in an argon glove box with a dew point of -60°C or less, the composite particles and LPS were weighed out so that the mass ratio of composite particles to LPS was 91.6:8.4, and then tetralin, the solvent, was weighed out so that the solids ratio was 78.5%. These were then placed in a planetary mixer and kneaded at a rotation speed of 70 rpm for a processing time of 30 minutes. In this manner, a kneaded composition containing the coated active material of Example 1 was prepared.

[0173] [Preparation of Third Solid Electrolyte] A third solid electrolyte was prepared in the same manner as in the preparation of the second solid electrolyte. That is, LPS was used as the third solid electrolyte of Example 1.

[0174] [Preparation of Positive Electrode Material] In an argon glove box with a dew point of -60°C or less, a kneaded composition containing the coated active material and LPS as a third solid electrolyte were weighed out so that the mass ratio of the coated active material to the LPS was 71.1:28.9. Furthermore, a fibrous conductive additive (VGCF (registered trademark)-H, manufactured by Resonac Packaging Co., Ltd.) was weighed out so that the amount was 1.5 mass% relative to the mass of the NCA. This mixture was dispersed in tetralin, a solvent, using an ultrasonic homogenizer to prepare a slurry. The slurry was applied to a current collector to form a coating film, which was then dried on a hot plate. The positive electrode material of Example 1 was thus prepared.

[0175] Example 2 When preparing the coated active material, the material was kneaded using a planetary mixer at a rotation speed of 70 rpm for a treatment time of 30 minutes, and then further kneaded at a rotation speed of 100 rpm for a treatment time of 2 hours. A positive electrode material of Example 2 was prepared in the same manner as in Example 1.

[0176] Example 3 When preparing the coated active material, the material was kneaded using a planetary mixer at a rotation speed of 70 rpm for a treatment time of 30 minutes, and then further kneaded at a rotation speed of 100 rpm for a treatment time of 4 hours. A positive electrode material of Example 3 was prepared in the same manner as in Example 1.

[0177] Example 4 When preparing the coated active material, the composite particles and LPS were weighed to have a mass ratio of composite particles:LPS = 76.0:24.0. Furthermore, after kneading using a planetary mixer at a rotation speed of 70 rpm and a processing time of 30 minutes, the mixture was further kneaded at a rotation speed of 100 rpm and a processing time of 3 hours. Furthermore, when preparing the positive electrode material, no third solid electrolyte was added. The positive electrode material of Example 4 was prepared in the same manner as in Example 1.

[0178] Example 5: Lithium niobate (LiNbO3) was used as the first solid electrolyte. Lithium ethoxide and niobium pentaethoxide were dissolved in ethanol to prepare a coating solution. Using a tumbling fluidized bed granulation coating device, the coating solution was applied to the surface of the NCA by an air suspension coating method so that the average thickness of the LiNbO3 was 15 nm. The treated powder was placed in an alumina crucible and removed to an air atmosphere. The treated powder was heat-treated at 220°C for 1 hour in an air atmosphere. The heat-treated powder was then crushed using an agate mortar to obtain the composite particles of Example 5. Furthermore, when preparing the coated active material, the composite particles and LPS were weighed to a mass ratio of composite particles:LPS = 91.0:9.0, and the solvent tetralin was weighed to a solids ratio of 82.0%. Next, these were placed in a kneader (PBV-0.1, manufactured by Irie Shokai Co., Ltd.) and kneaded at a rotation speed of 60 rpm for 1 hour. Furthermore, when preparing the positive electrode material, the kneaded composition containing the coated active material and LPS as the third solid electrolyte were weighed out so that the mass ratio of the coated active material to LPS was 79.5:20.5. The positive electrode material of Example 5 was prepared in the same manner as in Example 1, except for the above.

[0179] Comparative Example 1: After the composite particles were prepared, the second coating layer was not formed. Furthermore, when preparing the positive electrode material, the composite particles and LPS were weighed so that the mass ratio of the composite particles to the LPS serving as the third solid electrolyte was 76.0:24.0 (coated active material:LPS). The positive electrode material of Comparative Example 1 was prepared in the same manner as in Example 1.

[0180] Comparative Example 2 When preparing the coated active material, the composite particles and LPS were weighed out to a mass ratio of composite particles:LPS = 91.0:9.0, and then the solvent tetralin was weighed out to a solid content ratio of 83.5%. Subsequently, these were placed in a kneader and kneaded at a rotation speed of 60 rpm and a processing time of 1 hour and 40 minutes. Furthermore, when preparing the positive electrode material, the kneaded composition containing the coated active material and LPS were weighed out so that the mass ratio of the coated active material to the LPS serving as the third solid electrolyte was 79.5:20.5. The positive electrode material of Comparative Example 2 was prepared in the same manner as in Example 1.

[0181] In all examples and comparative examples, the positive electrode materials were prepared by adjusting the content of the positive electrode active material to be the same.

[0182] [Measurement of Coverage Ratio of the Second Coating Layer of the Coated Active Material] Cross-sectional secondary electron images were taken of 100 particles of each of the coated active materials of the Examples and Comparative Examples using a field emission scanning electron microscope (SU8230, manufactured by Hitachi High-Technologies Corporation). Figure 4 shows cross-sectional secondary electron images of representative particles of the coated active materials of Examples 1 to 5 and Comparative Example 2.

[0183] Subsequently, the coverage of the second coating layer and its coefficient of variation were determined by image analysis of the cross-sectional image. The coverage of the second coating layer and its coefficient of variation were determined according to the method described in Example 1. The results are shown in Table 1.

[0184] Furthermore, the average roundness of the active material and the average roundness of the coated active material were determined by image analysis, and the ratio of the average roundness of the coated active material to the average roundness of the active material was determined. The average roundness of the active material and the average roundness of the coated active material were determined in accordance with the method described in embodiment 1, i.e., the method described in Patent Document 1. However, the number of active materials and coated active materials measured was 100. The results are shown in Table 1.

[0185] [Fabrication of Battery] The following steps were carried out using each electrode material of the Examples and Comparative Examples.

[0186] In an argon glove box with a dew point of -60°C or less, the positive electrode material was weighed so that it contained 5 mg of NCA. LPS and the positive electrode material were stacked in this order inside an insulating outer cylinder. The resulting stack was press-molded at a pressure of 720 MPa. Next, metallic lithium was placed in contact with the LPS layer, and the stack was again press-molded at a pressure of 40 MPa. This produced a stack consisting of a positive electrode, an electrolyte layer, and a negative electrode. Next, stainless steel current collectors were placed on the top and bottom of the stack. Current collector leads were attached to each current collector. The outer cylinder was then sealed using an insulating ferrule to isolate the interior of the outer cylinder from the ambient atmosphere. Through these processes, batteries of the examples and comparative examples were fabricated. The battery was restrained from above and below with four bolts, and a surface pressure of 150 MPa was applied to the battery.

[0187] (Evaluation of Battery Resistance) The battery resistance was measured under the following conditions using each of the batteries of the example and comparative example.

[0188] The battery was placed in a thermostatic chamber at 25°C. The battery was charged at a constant current of 50 μA, corresponding to a 0.05 C rate relative to the theoretical capacity of the battery, until the voltage reached 4.25 V. The battery was then discharged at a constant current of 50 μA, corresponding to a 0.05 C rate relative to the theoretical capacity of the battery, until the voltage reached 3.69 V. The battery was then discharged at a constant current of 72.0 mA for 2 seconds, corresponding to a 72.0 C rate relative to the theoretical capacity of the battery. The battery resistance was calculated by dividing the voltage drop by the discharge current. The results are shown in Table 1.

[0189]

[0190] <<Discussion>> As shown in Table 1, the batteries using the coated active materials of Examples 1 to 5, in which the coverage rate with the second coating layer was 15.0% or more and 75.0% or less and the average roundness ratio was less than 1.30, had lower resistance than the batteries of Comparative Examples 1 and 2.

[0191] In the coated active materials of Examples 1 to 5, the coefficient of variation of the coverage by the second coating layer was 21.5% or more and 64.3% or less.

[0192] In the coated active materials of Examples 1 to 5, the coverage rate with the second coating layer was 23.8% or more and 70.0% or less.

[0193] As is clear from a comparison of Examples 1 to 3 with Examples 4 and 5, the battery resistance was further reduced when a coated active material with a coverage of 61.5% or less was used. This is thought to be because an appropriate region where the second coating layer was not present existed on the surface of the coated active material, thereby forming an appropriate electron conduction path within the positive electrode.

[0194] As is clear from a comparison of Examples 1 to 5 with Comparative Examples 1 and 2, controlling the coating morphology of the second coating layer allowed the battery resistance to be reduced regardless of the type of first solid electrolyte. Therefore, it is presumed that, similar to the results of this example, the battery resistance can be reduced by controlling the coating morphology of the second coating layer even when, for example, other halide solid electrolytes and oxide solid electrolytes other than LTAF and LiNbO are used as the coating layer.

[0195] It is presumed that the reduction in battery resistance due to the control of the coating form of the second coating layer is an effect produced by appropriately balancing the electron conduction path and the ion conduction path to the active material. Therefore, other positive electrode materials such as Li(Ni, Co, Mn)O2, LiCoO2, Li4Ti5O2, etc., other than NCA, can be used as the active material. 12 It is presumed that the same tendency as the results of this example will be observed when negative electrode materials such as Ti2NbO7 and silicon compounds are used.

[0196] The technology of the present disclosure is useful for, for example, all-solid-state lithium-ion secondary batteries.

Claims

1. A coated active material comprising composite particles including an active material and a first coating layer that coats at least a portion of the surface of the active material, and a second coating layer that coats the surface of the composite particles at a coverage rate of 15.0% or more and 75.0% or less, wherein the first coating layer includes a first solid electrolyte, and the second coating layer includes a second solid electrolyte having a different composition from the first solid electrolyte, and the ratio of the average roundness of the coated active material to the average roundness of the active material is less than 1.

30.

2. The coated active material according to claim 1, wherein the coverage of the surface of the composite particle with the second coating layer is 20.0% or more.

3. The coated active material according to claim 1, wherein the coverage of the surface of the composite particle with the second coating layer is 72.0% or less.

4. The coated active material according to claim 1, wherein the coefficient of variation of the coverage of the surface of the composite particle with the second coating layer is 20.0% or more.

5. The coated active material according to claim 1, wherein the coefficient of variation of the coverage of the surface of the composite particle with the second coating layer is 65.0% or less.

6. The coated active material according to claim 1, wherein the active material is a positive electrode active material.

7. The coated active material according to claim 1, wherein the active material contains Li, Ni, and O.

8. The coated active material according to claim 1, wherein the first solid electrolyte contains Li, M, and at least one element selected from the group consisting of F and O, and M is at least one element selected from the group consisting of metal elements and semi-metal elements other than Li.

9. The coated active material according to claim 1, wherein the first solid electrolyte contains Li, M1, M2, and F, wherein M1 is at least one selected from the group consisting of Al and Y, and wherein M2 is at least one selected from the group consisting of Ti, Zr, Mg, Ca, Si, and Sn.

10. The coated active material according to claim 9, wherein M1 is Al and M2 is Ti.

11. The first solid electrolyte is represented by the following composition formula (1): Li6-(4-x-4y+my)b (Ti 1-x-y Al x M3 y ) b F 6-2z O z ...(1) Here, in the above composition formula (1), M3 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is a valence of M3, and the following conditions are satisfied: 0.1<x<0.9, 0≦y<0.1, 0≦z<0.1, and 0.8<b≦1.

2.

12. The coated active material according to claim 1, wherein the first solid electrolyte contains Li, Nb, and O.

13. The coated active material according to claim 1, wherein the second solid electrolyte contains S.

14. An electrode material comprising the coated active material according to any one of claims 1 to 13.

15. The electrode material according to claim 14, further comprising a third solid electrolyte, wherein the third solid electrolyte contains S.

16. The electrode material according to claim 14, further comprising a third solid electrolyte, wherein the third solid electrolyte comprises a solid electrolyte having the same composition as the second solid electrolyte.

17. A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode and the negative electrode comprises the electrode material according to claim 14.

Images