Coated active substance, positive electrode material, and battery

Abstract

This coated active substance comprises: a positive electrode active substance; and a coating material that includes a first solid electrolyte and covers at least a part of the surface of the positive electrode active substance. The first solid electrolyte contains Li, M, and X. M is at least one element selected from the group consisting of a metal element other than Li and a metalloid element, and X is a halogen element. When the integrated value of the amount of moisture released from the coated active substance when the coated active substance is heated to raise the temperature thereof from 25°C to 120°C is divided by the total mass of the coated active substance, the quotient obtained is defined as MC120. In this case, MC120, which is the amount of moisture, satisfies 0 ppm < MC120 ≤ 600 ppm.

Description

Coated active material, positive electrode material, and battery

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

[0002] Patent Document 1 discloses a cathode material including a cathode active material and a first solid electrolyte material that coats at least a portion of the surface of the cathode active material. The first solid electrolyte material includes Li, Ti, M1, and F, where M1 is at least one element selected from the group consisting of Ca, Mg, Al, Y, and Zr.

[0003] Non-Patent Document 1 describes that when a layered positive electrode material is heated, the moisture generated from the positive electrode material can exist in various forms, such as adsorbed water on the surface of the positive electrode material, adsorbed water, and a reaction product between CO2 and the positive electrode material.

[0004] International Publication No. 2021 / 187391

[0005] Journal of The Electrochemical Society, 164 (14) A3727-A3741 (2017)

[0006] In the prior art, it is required to suppress the increase in the resistance of the battery.

[0007] The coated active material of the present disclosure is a coated active material comprising: a positive electrode active material; and a coating material including a first solid electrolyte and coating at least a part of a surface of the positive electrode active material, wherein the first solid electrolyte includes Li, M, and X, M is at least one element selected from the group consisting of metal elements other than Li and metalloid elements, and X is a halogen element, and MC is a value obtained by dividing the integrated value of the amount of water released from the coated active material when the coated active material is heated from 25°C to 120°C by the total mass of the coated active material. 120 When defined as above, 0 ppm < MC 120 ≦600 ppm.

[0008] According to the present disclosure, an increase in the resistance of the battery can be suppressed.

[0009] 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 a positive electrode material in embodiment 2. Fig. 3 is a cross-sectional view showing a schematic configuration of a battery in embodiment 3.

[0010] (Findings underlying the present disclosure) For example, when a positive electrode active material and a solid electrolyte are in contact with each other in a positive electrode, the solid electrolyte may undergo oxidative decomposition during charging of the battery. Oxidative decomposition tends to occur more easily when a solid electrolyte with poor oxidative stability, such as a sulfide solid electrolyte, is used. To address this issue, it has been proposed to coat the surface of the positive electrode active material with a coating material containing a solid electrolyte with excellent oxidative stability, such as a halide solid electrolyte.

[0011] On the other hand, the present inventors have discovered that even if the composition of the solid electrolyte contained in the coating material is the same, differences occur in the durability of the battery, specifically, the degree of increase in the resistance of the battery after a durability test. As a result of extensive research, the present inventors have found that there is a correlation between the amount of water released when a positive electrode active material whose surface is coated with a coating material containing a solid electrolyte is heated and the degree of increase in the resistance of the battery after a durability test, and have arrived at the technology of the present disclosure.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0013] 1 is a cross-sectional view showing a schematic configuration of a coated active material according to embodiment 1. Coated active material 100 according to embodiment 1 includes a positive electrode active material 11 and a coating material 12. Coating material 12 includes a first solid electrolyte, and coats at least a portion of the surface of positive electrode active material 11.

[0014] The value obtained by dividing the integrated amount of moisture released from the coated active material 100 when the temperature of the coated active material 100 is increased from 25° C. to 120° C. by the total mass of the coated active material 100 is MC. 120 At this time, the moisture content MC 120 , 0 ppm < MC 120In this disclosure, "ppm" means mass fraction, i.e., wtppm (mass / mass).

[0015] The coated active material 100 may contain moisture physically adsorbed on its surface and moisture chemically bonded to it. Examples of moisture chemically bonded to the coated active material 100 include crystal water and intermediate-like compounds formed by the reaction of Li, CO2, and HO near the surfaces of the positive electrode active material 11 and / or coating material 12. The specific form of moisture released from the coated active material 100 when the coated active material 100 is heated from 25°C to 120°C is not entirely clear. However, it is presumed that moisture desorbed from the coated active material 100 in the relatively low temperature range up to 120°C is primarily moisture physically adsorbed on its surface. When the second solid electrolyte described below is a highly hydrophilic solid electrolyte such as a sulfide solid electrolyte, such moisture may desorb from the surface of the coated active material 100 even upon contact with the second solid electrolyte. The desorbed moisture may undergo a side reaction with another material present in the vicinity of the coated active material 100, thereby forming a reaction layer at the interface between the two. The other material may be, for example, a second solid electrolyte described below.

[0016] Until now, it has been thought that it is desirable to have as little moisture as possible in the coated active material. 2.7 Ti 0.3 Al 0.7 This is because it was thought that a reaction between a lithium-containing fluoride such as F6 and the moisture contained in the coated active material would cause a part of the coating layer to change in quality, and that this changed part would function as a resistance layer at the interface between the positive electrode active material and the coating layer. However, the inventors' investigations have newly revealed that it is actually preferable for the coated active material to contain a very small amount of water. The moisture content MC 120 is 0 ppm < MC 120If the moisture content MC is less than 600 ppm, a sufficient amount of moisture is present near the surface of the coated active material 100 so that a reaction layer having an appropriate thickness is formed at the interface between the coated active material 100 and a second solid electrolyte described later to prepare a positive electrode material. 120 If the content is greater than 60 ppm, the thickness of the formed reaction layer increases, which increases the resistance of the battery, leading to a significant increase in the battery resistance, which is not desirable. The reaction layer is formed by the reaction between water and the second solid electrolyte. A reaction layer with an appropriate thickness can suppress deterioration of the positive electrode containing the coated active material 100 and the second solid electrolyte, such as thermodynamic reactions caused by contact between the coated active material 100 and the second solid electrolyte, and oxidative decomposition of the second solid electrolyte caused by exposure to a high potential. Therefore, the coated active material 100 can suppress an increase in the battery resistance.

[0017] Moisture content MC 120 can be measured by, for example, the Karl Fischer method. 120 can be determined using a Karl Fischer apparatus (Karl Fischer moisture meter) as follows.

[0018] In a dry nitrogen gas atmosphere, the introduction portion of the coated active material 100 as a measurement sample is pre-baked at 300° C. to stabilize the device. The “coated active material 100 as a measurement sample” refers to a particle group of the coated active material 100.

[0019] After the device has stabilized, the temperature of the inlet is set to 120° C. When the temperature of the inlet reaches 120° C., the amount of water released as background (μg / sec) is measured.

[0020] Next, the temperature of the introduction section is set to 25°C. When the temperature of the introduction section reaches 25°C, the measurement sample is introduced into the introduction section. The measurement sample is heated from 25°C to 120°C at a temperature increase rate of 10°C per minute to vaporize the moisture contained in the measurement sample. The vaporized moisture is quantified by coulometric titration until it reaches a value below the background moisture release amount and integrated, thereby determining the integrated value of the moisture amount released from the measurement sample. The integrated value of the moisture amount is divided by the total mass of the measurement sample to determine the moisture amount MC 120 Ask for.

[0021] The degree of increase in battery resistance is expressed by the index "(R2 / R1) x 100 (%)." (R2 / R1) is the resistance R2 after the durability test divided by the resistance R1 before the durability test. A durability test involves, for example, storing a battery in a high-temperature environment for a certain period of time. The resistances R1 and R2 can be determined by the following method. A battery fabricated using a positive electrode material containing the coated active material 100 is placed in a thermostatic chamber at 25°C and charged and discharged. Next, the battery is charged and discharged to a predetermined voltage. A constant-current discharge is then performed at a predetermined current value for 1 second to 10 seconds. The voltage drop at this time, i.e., the difference between the open-circuit voltage before discharge and the open-circuit voltage at the end of discharge, is divided by the discharge current value to determine the resistance R1 before the durability test. A durability test is then performed under appropriate conditions. After the durability test, the battery is charged and discharged in the same manner as described above. Next, the battery is charged and discharged to a predetermined voltage. A constant-current discharge is then performed at a predetermined current value for 1 second to 10 seconds. The voltage drop at this time is divided by the discharge current value to determine the resistance R2 after the endurance test.

[0022] Moisture content MC 120 MC 120 ≦500 ppm. With this configuration, when the coated active material 100 and the second solid electrolyte are mixed to prepare a positive electrode material, a reaction layer having an appropriate thickness is likely to be formed on the surface of the coated active material 100. As a result, an increase in resistance in the initial stage of the battery can be suppressed.

[0023] Moisture content MC 120 MC 120 ≦490 ppm, MC 120 ≦480 ppm, MC 120 ≦470 ppm, and further, MC 120 ≦464 ppm. According to this configuration, as a result, an increase in resistance in the initial stage of the battery can be further suppressed.

[0024] Moisture content MC 120 0.5 ppm≦MC 120 and further, 1 ppm≦MC 120According to this configuration, when the coated active material 100 and the second solid electrolyte are mixed to prepare a positive electrode material, a reaction between water and the second solid electrolyte is likely to occur uniformly at various locations on the surface of the coated active material 100, and a reaction layer having a sufficient thickness is likely to be formed on the surface of the coated active material 100. As a result, an increase in the resistance of the battery can be suppressed.

[0025] Moisture content MC 120 5 ppm ≦ MC 120 and 10 ppm≦MC 120 and 20 ppm≦MC 120 and further, 24 ppm≦MC 120 According to this configuration, an increase in the resistance of the battery can be further suppressed.

[0026] Moisture content MC 120 30 ppm≦MC 120 and further, 34 ppm≦MC 120 According to this configuration, an increase in the resistance of the battery can be further suppressed.

[0027] Moisture content MC 120 40 ppm≦MC 120 and 50 ppm≦MC 120 and further, 63 ppm≦MC 120 According to this configuration, an increase in the resistance of the battery can be further suppressed.

[0028] Moisture content MC 120 100 ppm≦MC 120 and 200 ppm≦MC 120 and further, 300 ppm≦MC 120 The moisture content MC 120 300 ppm≦MC 120 ≦600 ppm. With this configuration, an increase in the resistance of the battery can be further suppressed.

[0029] (Coating Material) The coating material 12 is in direct contact with the positive electrode active material 11. The coating material 12 includes a first solid electrolyte. The first solid electrolyte has ion conductivity. The ion conductivity is typically lithium ion conductivity.

[0030] The first solid electrolyte contains Li, M, and X. M is at least one element selected from the group consisting of metal elements other than Li and metalloid elements. X is a halogen element. A first solid electrolyte having such a composition has excellent oxidation resistance. Therefore, oxidation of the second solid electrolyte in contact with the positive electrode active material 11 can be suppressed. This can suppress an increase in battery resistance.

[0031] In the present 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 excluding hydrogen, and all elements in Groups 13 to 16 of the periodic table excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metal elements are a group of elements that can become cations when forming an inorganic compound with a halogen element.

[0032] As described above, the first solid electrolyte contains a halogen element. A solid electrolyte containing a halogen element is also called a halide solid electrolyte. A halide solid electrolyte has excellent oxidation resistance.

[0033] X may be F. A halide solid electrolyte containing F has excellent oxidation resistance due to the high electronegativity of F. Therefore, by covering at least a portion of the surface of the positive electrode active material 11 with the coating material 12 containing the first solid electrolyte, oxidation of the second solid electrolyte in contact with the positive electrode active material 11 can be further suppressed. This can further suppress an increase in the resistance of the battery.

[0034] M may include M1 and M2. In this case, M1 may be at least one selected from the group consisting of Ti and Zr, and M2 may be at least one selected from the group consisting of Al, Y, Mg, and Ca. In a first solid electrolyte having such a composition, a cationic framework structure suitable for ion conduction can be formed in the crystal lattice. Therefore, the first solid electrolyte exhibits high ionic conductivity. The 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] M2 may be Al. The first solid electrolyte having such a composition exhibits even higher ionic conductivity.

[0036] M1 may be Ti. A first solid electrolyte having such a composition exhibits even higher ionic conductivity.

[0037] 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.

[0038] The first solid electrolyte may be represented by the following composition formula (1):

[0039] Li6-(4-x-4y+my)b (Ti 1-x-y Al x M3 y ) b F 6-2z O z ...(1)

[0040] where M3 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the valence of M3, and satisfies 0.1<x<0.9, 0≦y<0.1, 0≦z<0.1, and 0.8<b≦1.2. A first solid electrolyte having such a composition has high ionic conductivity and can be produced by a method with high industrial productivity.

[0041] 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.

[0042] In the composition formula (1), 0.1≦x≦0.7 may be satisfied.

[0043] 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.

[0044] 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.

[0045] The first solid electrolyte may be crystalline or amorphous.

[0046] The shape of the first solid electrolyte is not particularly limited. The shape of the first solid electrolyte is, for example, needle-like, spherical, or oval-spherical. The shape of the first solid electrolyte may also be particulate.

[0047] 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.

[0048] 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.

[0049] The coating material 12 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, except for inevitable impurities, no materials other than the first solid electrolyte are intentionally added. For example, the inevitable impurities include raw materials for the first solid electrolyte and by-products generated during the production of the first solid electrolyte. The mass ratio of the inevitable impurities to the total mass of the coating material 12 may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0050] The coating material 12 may be sulfur-free.

[0051] The coating material 12 may uniformly coat the positive electrode active material 11 .

[0052] The coating material 12 may cover only a portion of the surface of the positive electrode active material 11. In this case, particles of the positive electrode active material 11 are in direct contact with each other via the portion not covered by the coating material 12, improving the electronic conductivity between the particles of the positive electrode active material 11. As a result, high-power operation of the battery is possible.

[0053] The shape of the coating material 12 itself is not particularly limited. For example, at least a portion of the surface of the positive electrode active material 11 may be covered with a thin film formed by the accumulation of fine particles of the coating material 12, such as plate-like, needle-like, spherical, or oval-spherical shapes.

[0054] The thickness of the thin film of the coating material 12 is, for example, 1 nm or more and 500 nm or less. When the thickness of the thin film of the coating material 12 is appropriately adjusted, contact between the positive electrode active material 11 and the second solid electrolyte can be sufficiently suppressed. The thickness of the thin film of the coating material 12 can be determined, for example, by observing the cross section of a particle of the coated active material 100 with a scanning electron microscope (SEM). The average value of the thicknesses of the thin film of the coating material 12 measured at any multiple positions (for example, five points) can be considered to be the thickness of the thin film of the coating material 12.

[0055] (Positive Electrode Active Material) The positive electrode active material 11 includes a material capable of absorbing and releasing metal ions (e.g., lithium ions). Examples of the positive electrode active material 11 include lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. Using a lithium-containing transition metal oxide as the positive electrode active material 11 can reduce the manufacturing cost of the battery and improve the average discharge voltage of the battery. Examples of lithium-containing transition metal oxides include Li(Ni, Co, Al)O, Li(Ni, Co, Mn)O, and LiCoO.

[0056] 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.

[0057] The positive electrode active material 11 has, for example, a particle shape. There are no particular limitations on the shape of the particles of the positive electrode active material 11. The shape of the particles of the positive electrode active material 11 may be spherical, oval, scaly, or fibrous.

[0058] The median diameter of the positive electrode active material 11 may be 0.1 μm or more and 100 μm or less. When the median diameter of the positive electrode active material 11 is 0.1 μm or more, the coated active material 100 and the second solid electrolyte can be well dispersed. As a result, the charge / discharge characteristics of the battery are improved. When the median diameter of the positive electrode active material 11 is 100 μm or less, the diffusion rate of lithium inside the positive electrode active material 11 is sufficiently ensured. Therefore, the battery can operate at high power.

[0059] The positive electrode active material 11 may contain lithium nickel cobalt aluminum oxide, which may be Li(Ni, Co, Al)O. This configuration can increase the energy density of the battery.

[0060] Li(Ni,Co,Al)O2 includes those containing at least one additional element in addition to Li, Ni, Co, and Al. The additional element may be at least one or more elements selected from boron (B), sodium (Na), magnesium (Mg), silicon (Si), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), tin (Sn), tungsten (W), lanthanum (La), and cerium (Ce).

[0061] <Method for Producing First Solid Electrolyte> The first solid electrolyte contained in the coating material 12 can be produced, for example, by the following method.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] By these methods, the first solid electrolyte having the above-mentioned composition can be obtained.

[0066] 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.

[0067] <Method for Producing Coated Active Material> The coated active material 100 in the first embodiment can be produced, for example, by the following method.

[0068] A powder of the positive electrode active material 11 and a powder of the coating material 12 containing the first solid electrolyte are prepared in a predetermined mass ratio. For example, the positive electrode active material 11 is a powder of Li(Ni, Co, Al)O2, and the coating material 12 is a powder of the first solid electrolyte Li. 2.7 Al 0.7 Ti 0.3 A powder of F6 is prepared. By applying mechanical energy to a mixture of these two materials, at least a portion of the surface of the positive electrode active material 11 is coated with the coating material 12, 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. 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 positive electrode active material 11 and the powder of the coating material 12 are mixed in an appropriate ratio.

[0069] Before applying mechanical energy to the mixture of the powder of the positive electrode active material 11 and the powder of the coating material 12, 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 atmosphere or an inert atmosphere.

[0070] The coated active material 100 may be manufactured by a dry particle compounding method. The treatment by the dry particle compounding method includes applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to a mixture of powder of the positive electrode active material 11 and powder of the coating material 12.

[0071] The apparatus used in the production of the coated active material 100 is not particularly limited. The apparatus can be an apparatus capable of applying mechanical energy such as impact, compression, and shear to a mixture of powder of the positive electrode active material 11 and powder of the coating material 12. 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-speed airflow impact apparatus)" (manufactured by Nara Machinery Works), and a "Balance Gran" (manufactured by Freund Turbo Corporation).

[0072] "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.

[0073] "Nobilta" is a particle compounding device that uses dry mechanical compounding technology, an advanced form of particle compounding technology, to compound nanoparticles as raw materials. Nobilta produces composite particles by applying mechanical energy of impact, compression, and shear to multiple raw material powders.

[0074] 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 of positive electrode active material 11 and coating material 12. Conditions such as rotor rotation speed, processing time, and feed amount can be adjusted as needed.

[0075] In the "hybridization system," raw material powder is dispersed in a high-speed airflow while a force, mainly consisting of an impact, is applied, thereby producing composite particles of positive electrode active material 11 and coating material 12.

[0076] 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 uniformly disperses the mixture, allowing composite particles of the positive electrode active material 11 and the coating material 12 to be produced.

[0077] However, the treatment using the above-mentioned apparatus is not essential. The coated active material 100 may be produced by mixing a powder of the positive electrode active material 11 and a powder of the coating material 12 using a mortar, a mixer, or the like. The coating material 12 may be deposited on the surface of the positive electrode active material 11 by various methods such as a spraying method, a spray-dry coating method, an electrodeposition method, an immersion method, or a mechanical mixing method using a disperser.

[0078] For example, by carrying out the manufacturing process of the coated active material 100 in an environment with low environmental moisture, the moisture content MC 120 Within the above range (0 ppm < MC 120 For example, the manufacturing process of the coated active material 100 may be performed in a dry air environment with a dew point of −30° C. or less. The manufacturing process of the coated active material 100 may be performed in a dry air environment with a dew point of −50° C. or less.

[0079] For example, after at least a portion of the surface of the positive electrode active material 11 is coated with the coating material 12, the positive electrode active material 11 is temporarily stored in an environment with low environmental moisture, whereby the moisture content MC 120 Within the above range (0 ppm < MC 120 For example, after at least a portion of the surface of positive electrode active material 11 is coated with coating material 12, it may be stored in a sealed container in a dry air environment with a dew point of −30° C. or less. It may also be stored in a sealed container in a dry air environment with a dew point of −50° C. or less.

[0080] Second Embodiment Hereinafter, a second embodiment will be described. Descriptions that overlap with the first embodiment will be omitted as appropriate.

[0081] [Positive Electrode Material] FIG. 2 is a cross-sectional view showing a schematic configuration of a positive electrode material 200 according to the second embodiment.

[0082] The positive electrode material 200 includes the coated active material 100 of the first embodiment and a second solid electrolyte 21. The positive electrode material 200 includes the coated active material 100, and is therefore suitable for suppressing an increase in the resistance of the battery.

[0083] The positive electrode active material 11 of the coated active material 100 is separated from the second solid electrolyte 21 by the coating material 12. The positive electrode active material 11 does not need to be in direct contact with the second solid electrolyte 21. This is because the coating material 12 has ion conductivity.

[0084] The second solid electrolyte 21 may have a different composition from the first solid electrolyte contained in the coating material 12 of the coated active material 100, or may have the same composition.

[0085] The second solid electrolyte 21 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 second solid electrolyte 21 may include a sulfide solid electrolyte. The second solid electrolyte 21 enables high ionic conductivity to be achieved in the positive electrode material 200.

[0086] Examples of halide solid electrolytes that can be used include Li3REX6, Li3(Al, Ga, In)X6, Li2MgX4, Li2FeX4, Li(Al, Ga, In)X4, 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0091] The second solid electrolyte 21 may contain two or more materials selected from the materials listed as solid electrolytes. For example, the second solid electrolyte 21 may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0092] The second solid electrolyte 21 may contain unavoidable impurities such as starting materials, by-products, and decomposition products used in synthesizing the solid electrolyte.

[0093] The shape of the second solid electrolyte 21 is not particularly limited, and may be needle-like, spherical, oval-spherical, etc. The second solid electrolyte 21 may also be particulate.

[0094] When the second solid electrolyte 21 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 second solid electrolyte 21 are well dispersed in the positive electrode material 200.

[0095] The median diameter of the second solid electrolyte 21 may be 10 μm or less. In this case, the dispersion state of the coated active material 100 and the second solid electrolyte 21 in the positive electrode material 200 becomes better.

[0096] The median diameter of the second solid electrolyte 21 may be smaller than the median diameter of the coated active material 100. In this case, the coated active material 100 and the second solid electrolyte 21 are better dispersed in the positive electrode material 200.

[0097] In the positive electrode material 200, the coated active material 100 and the second solid electrolyte 21 may be in contact with each other. In this case, the coating material 12 and the second solid electrolyte 21 are in contact with each other.

[0098] The positive electrode material 200 may include a plurality of particles of the second solid electrolyte 21 and a plurality of particles of the coated active material 100. In other words, the positive electrode material 200 may be a mixture of a powder of the coated active material 100 and a powder of the second solid electrolyte 21.

[0099] In the positive electrode material 200, the content of the coated active material 100 and the content of the second solid electrolyte 21 may be the same as or different from each other.

[0100] The positive 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.

[0101] 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.

[0102] The positive electrode material 200 may contain a conductive additive for the purpose of enhancing electronic conductivity. Examples of the conductive additive 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.

[0103] The above-mentioned conductive additive may be contained in the coating material 12 of the coated active material 100 .

[0104] <Method for manufacturing the positive electrode material> The positive electrode material 200 is obtained by mixing the coated active material 100 and the second solid electrolyte 21. There are no particular limitations on the method for mixing the coated active material 100 and the second solid electrolyte 21. The coated active material 100 and the second solid electrolyte 21 may be mixed using a tool such as a mortar, or the coated active material 100 and the second solid electrolyte 21 may be mixed using a mixing device such as a ball mill.

[0105] Third Embodiment Hereinafter, a third embodiment will be described. Descriptions that overlap with the first and second embodiments will be omitted as appropriate.

[0106] The battery according to 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 positive electrode material 200 according to the second embodiment. This configuration suppresses an increase in the resistance of the battery, thereby improving the durability of the battery.

[0107] The separator portion may be an electrolyte layer containing a solid electrolyte, or may be a separator impregnated with an electrolytic solution.

[0108] FIG. 3 is a cross-sectional view showing a schematic configuration of a battery 300 according to the third embodiment.

[0109] The battery 300 includes a positive electrode 31, an electrolyte layer 32, and a negative electrode 33. The electrolyte layer 32 is disposed between the positive electrode 31 and the negative electrode 33. In the battery 300, the separator portion is the electrolyte layer 32. The positive electrode 31 includes the positive electrode material 200 of the second embodiment. With this configuration, an increase in the resistance of the battery 300 is suppressed, thereby improving the durability of the battery 300.

[0110] The thickness of each of the positive electrode 31 and the negative electrode 33 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 31 and the negative electrode 33 is 10 μm or more, a sufficient energy density of the battery 300 can be ensured. When the thickness of the positive electrode 31 and the negative electrode 33 is 500 μm or less, high-power operation of the battery 300 can be realized.

[0111] The electrolyte layer 32 is a layer containing an electrolyte material. The electrolyte layer 32 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.

[0112] The thickness of the electrolyte layer 32 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 32 is 1 μm or more, the positive electrode 31 and the negative electrode 33 can be more reliably separated. When the thickness of the electrolyte layer 32 is 300 μm or less, the battery 300 can operate at high power.

[0113] The negative electrode 33 contains, as a negative electrode active material, a material that has the property of absorbing and releasing metal ions (for example, lithium ions).

[0114] 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.

[0115] The median diameter of the particles of the negative electrode active material may be 0.1 μm or more and 100 μm or less.

[0116] The negative electrode 33 may contain other materials such as a solid electrolyte. As the solid electrolyte, the materials described in the second embodiment can be used.

[0117] 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.

[0118] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0119] (Technology 1) A coated active material comprising: a positive electrode active material; and a coating material containing a first solid electrolyte and coating at least a part of a surface of the positive electrode active material, wherein the first solid electrolyte contains Li, M, and X, M is at least one element selected from the group consisting of metal elements other than Li and metalloid elements, and X is a halogen element, and MC is a value obtained by dividing an integrated value of the amount of water released from the coated active material when the coated active material is heated from 25°C to 120°C by the total mass of the coated active material. 120 When defined as above, 0 ppm < MC 120 ≦600 ppm.

[0120] The coated active material of Technology 1 can suppress an increase in the resistance of the battery.

[0121] (Technology 2) MC 120 ≦500 ppm. With this configuration, an increase in resistance in the initial stage of the battery can be suppressed.

[0122] (Technology 3) 1ppm≦MC 120 10. The coated active material according to claim 1, wherein the coated active material satisfies the above condition. 11. According to this configuration, an increase in the resistance of the battery can be suppressed.

[0123] (Technology 4) 20ppm≦MC 120 The coated active material according to any one of Techniques 1 to 3 satisfies the above. According to this configuration, an increase in the resistance of the battery can be further suppressed.

[0124] (Technology 5) 30ppm≦MC 120 5. The coated active material according to any one of Techniques 1 to 4, which satisfies the above condition. With this configuration, an increase in the resistance of the battery can be further suppressed.

[0125] (Technology 6) The coated active material according to any one of Technologies 1 to 5, wherein X is F. With this configuration, oxidation of another solid electrolyte in contact with the positive electrode active material can be suppressed, thereby suppressing an increase in the resistance of the battery.

[0126] (Technology 7) The coated active material according to any one of Technologies 1 to 6, wherein M includes M1 and M2, M1 being at least one selected from the group consisting of Ti and Zr, and M2 being at least one selected from the group consisting of Al, Y, Mg, and Ca. With this configuration, the first solid electrolyte exhibits high ionic conductivity.

[0127] (Technology 8) The coated active material according to Technology 7, wherein M2 is Al. With this configuration, the first solid electrolyte exhibits even higher ionic conductivity.

[0128] (Technology 9) The coated active material according to Technology 7 or 8, wherein M1 is Ti. With this configuration, the first solid electrolyte exhibits even higher ionic conductivity.

[0129] (Technology 10) 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) wherein M3 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the 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. According to this configuration, the first solid electrolyte has high ionic conductivity and can be produced by a method with high industrial productivity.

[0130] (Technology 11) The coated active material according to Technology 10, which satisfies 0.1<x<0.9, y=0, z=0, and 0.8<b≦1.2. With this configuration, the first solid electrolyte has higher ionic conductivity.

[0131] (Technology 12) A positive electrode material comprising: the coated active material according to any one of technologies 1 to 11; and a second solid electrolyte having a composition different from that of the first solid electrolyte.

[0132] The positive electrode material of Technology 12 includes a coated active material, and is therefore suitable for suppressing an increase in the resistance of the battery.

[0133] (Technology 13) The positive electrode material according to Technology 12, wherein the second solid electrolyte includes a sulfide solid electrolyte. With this configuration, high ionic conductivity can be achieved in the positive electrode material.

[0134] (Technology 14) A battery having a positive electrode containing the positive electrode material according to Technology 12.

[0135] According to the battery of Technique 14, an increase in the resistance of the battery is suppressed, and therefore the durability of the battery is improved.

[0136] (Technology 15) A battery comprising: a positive electrode containing the positive electrode material according to Technology 12; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode.

[0137] According to the battery of Technique 15, an increase in the resistance of the battery is suppressed, and therefore the durability of the battery is improved.

[0138] The present disclosure will be described in detail below using examples and reference examples, but the present invention is not limited to the following examples.

[0139] Example 1 Positive Electrode Active Material Li(NiCoAl)O2 (hereinafter referred to as NCA) having a median diameter of 5 μm was used as the positive electrode active material.

[0140] [Preparation of Coating Material (First Solid Electrolyte)] In an argon glove box with a dew point of -60°C or less, raw material powders of LiF, TiF, and AlF were weighed out in a molar ratio of LiF:TiF:AlF = 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 coating material (first solid electrolyte) of Example 1.

[0141] [Preparation of Coated Active Material] The surface of NCA as a positive electrode active material was coated with LTAF as a coating material. A thin film of LTAF was formed by compressive shear treatment using a particle compositer (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, NCA and LTAF were weighed to a weight ratio of 97.3:2.7, and treated under conditions of blade clearance: 2 mm, rotation speed: 6000 rpm, and treatment time: 50 minutes. In this way, a thin film was formed by coating the surface of NCA with LTAF. Thereafter, the coated active material was allowed to stand in a draft chamber at a temperature of approximately 20°C and a humidity of approximately 20% for 48 hours, thereby adjusting the moisture content of the coated active material. As a result, the coated active material of Example 1 was obtained.

[0142] [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.

[0143] [Preparation of Positive Electrode Material] In an argon glove box, the coated active material and LPS as the second solid electrolyte were weighed out so that the volume ratio of the coated active material to LPS was 60:40. 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. These were mixed in an agate mortar to prepare the positive electrode material of Example 1.

[0144] Example 2 After coating the surface of the NCA with LTAF, the coated active material was left to stand for 5 minutes in a dry air environment at a temperature of about 20°C and a dew point of about -30°C, thereby adjusting the moisture content of the coated active material. Except for this, the coated active material of Example 2 was obtained in the same manner as in Example 1. The positive electrode material of Example 2 was produced in the same manner as in Example 1 using the coated active material of Example 2.

[0145] Example 3 After coating the surface of the NCA with LTAF, the coated active material was left to stand for 1 hour in a dry air environment at a temperature of about 20°C and a dew point of about -30°C, thereby adjusting the moisture content of the coated active material. Except for this, the coated active material of Example 3 was obtained in the same manner as in Example 1. The positive electrode material of Example 3 was produced using the coated active material of Example 3 in the same manner as in Example 1.

[0146] Example 4 After coating the surface of the NCA with LTAF, the coated active material was left to stand for 6 hours in a dry air environment at a temperature of about 20°C and a dew point of about -30°C, thereby adjusting the moisture content of the coated active material. Except for this, the coated active material of Example 4 was obtained in the same manner as in Example 1. The positive electrode material of Example 4 was produced in the same manner as in Example 1 using the coated active material of Example 4.

[0147] Example 5 After coating the surface of the NCA with LTAF, the coated active material was left to stand for 12 hours in a dry air environment at a temperature of about 20°C and a dew point of about -30°C, thereby adjusting the moisture content of the coated active material. Except for this, the coated active material of Example 5 was obtained in the same manner as in Example 1. The positive electrode material of Example 5 was produced in the same manner as in Example 1 using the coated active material of Example 5.

[0148] Example 6 After coating the surface of the NCA with LTAF, the coated active material was left to stand in a draft chamber at a temperature of about 20°C and a humidity of about 20% for 24 hours to adjust the moisture content of the coated active material. Except for this, the coated active material of Example 6 was obtained in the same manner as in Example 1. The positive electrode material of Example 6 was produced using the coated active material of Example 6 in the same manner as in Example 1.

[0149] Comparative Example 1 A material in which LTAF was coated on the surface of NCA was used as the coated active material of Comparative Example 1. That is, in Comparative Example 1, after LTAF was coated on the surface of NCA, the moisture content was not adjusted. A positive electrode material of Comparative Example 1 was produced using the coated active material of Comparative Example 1 in the same manner as in Example 1.

[0150] (Measurement of Moisture Content of Coated Active Material) For each of the coated active materials in the Examples and Comparative Examples, the moisture content MC was measured by the Karl Fischer method described in the first embodiment. 120 The moisture content of the coated active material was measured using a Karl Fischer moisture meter (HIRANUMA Corporation, EV-2010). The results are shown in Table 1.

[0151] The moisture content of the coated active material of Comparative Example 1, MC 120 This indicates that the amount of water contained in the coated active material of Comparative Example 1 was below the detection limit of the Karl Fischer moisture meter.

[0152] [Fabrication of Battery] The following steps were carried out using each of the coated active materials of the Examples and Comparative Examples.

[0153] 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.

[0154] (Measurement of Battery Resistance) The battery resistance was measured under the following conditions using each of the batteries of the example and comparative example.

[0155] The battery was placed in a thermostatic chamber at 25°C. The battery was charged at a constant current of 50 μA, which corresponds to a 0.05 C rate (20-hour 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, which corresponds to a 0.05 C rate (20-hour rate) relative to the theoretical capacity of the battery, until the voltage reached 3.75 V. The battery was then discharged at a constant current of 46.4 mA for 2 seconds, which corresponds to a 46.4 C rate relative to the theoretical capacity of the battery. The resistance R1 before the durability test was calculated by dividing the voltage drop by the discharge current value.

[0156] Next, a durability test was carried out. First, the temperature of the thermostatic chamber was changed from 25° C. to 60° C., and the battery was stored in a charged state of 4.02 V for one week.

[0157] After storage, the temperature of the thermostatic chamber was changed to 25°C, and the battery was charged at a constant current of 50 μA, which corresponds to a 0.05 C rate (20-hour 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, which corresponds to a 0.05 C rate (20-hour rate) relative to the theoretical capacity of the battery, until the voltage reached 3.75 V. The battery was then discharged at a constant current of 46.4 mA for 2 seconds, which corresponds to a 46.4 C rate relative to the theoretical capacity of the battery. The resistance R2 after the durability test was calculated by dividing the voltage drop at this time by the discharge current value.

[0158] The resistance R2 after the durability test was divided by the resistance R1 before the durability test, and the result (R2 / R1) x 100 (%) is shown in Table 1.

[0159]

[0160] <<Discussion>> As shown in Table 1, the moisture content MC 120 is 0 ppm < MC 120 In the batteries of Examples 1 to 6 that satisfy the condition of ≦600 ppm, the water content MC 120 Compared with the battery of Comparative Example 1, in which the water content MC was 0 ppm, (R2 / R1) × 100 was kept low. 120 It is presumed that by adjusting the temperature to an appropriate range, a homogeneous reaction layer is formed at the interface between the coated active material and the second solid electrolyte when they are mixed, thereby suppressing an increase in the resistance of the battery.

[0161] From the comparison between Example 2 and Comparative Example 1, the moisture content MC 120 It is understood that when the content of the second solid electrolyte is 1 ppm or more, an increase in the resistance of the battery is suppressed. This is presumably because the homogeneity of the reaction layer formed on the surface of the coated active material is improved when the coated active material and the second solid electrolyte are mixed.

[0162] When Example 3 is compared with Example 2 and Comparative Example 1, the moisture content MC 120 It is understood that when the content of the second solid electrolyte is 20 ppm or more, an increase in the resistance of the battery is further suppressed. This is presumably because the homogeneity of the reaction layer formed on the surface of the coated active material is further improved when the coated active material and the second solid electrolyte are mixed.

[0163] When Example 4 is compared with Examples 2 and 3 and Comparative Example 1, the moisture content MC 120 It is understood that when the content of the second solid electrolyte is 30 ppm or more, an increase in the resistance of the battery is further suppressed, which is presumably because the homogeneity of the reaction layer formed on the surface of the coated active material is further improved when the coated active material and the second solid electrolyte are mixed.

[0164] When Example 5 is compared with Examples 2 to 4 and Comparative Example 1, the moisture content MC 120 It is understood that when the content of the second solid electrolyte is 50 ppm or more, an increase in the resistance of the battery is further suppressed. This is presumably because the thickness of the reaction layer formed on the surface of the coated active material becomes relatively thick when the coated active material and the second solid electrolyte are mixed.

[0165] When Example 6 is compared with Examples 2 to 5 and Comparative Example 1, the moisture content MC 120 It is understood that when the content of the second solid electrolyte is 300 ppm or more, the increase in the resistance of the battery is further suppressed, which is presumably because the thickness of the reaction layer formed on the surface of the coated active material becomes sufficiently thick when the coated active material and the second solid electrolyte are mixed.

[0166] When Example 1 is compared with Examples 2 to 6 and Comparative Example 1, the moisture content MC 120 It is understood that when the content of the reactive carbon black is 460 ppm or more, the increase in the resistance of the battery is further suppressed. This is presumably because the uniformity and thickness of the reactive layer at each location of the coated active material are appropriate.

[0167] Moisture content MC 120 is the amount of moisture desorbed from the coated active material 100 in a relatively low temperature range up to 120°C. It is presumed that the moisture is mainly moisture physically adsorbed on the surface of the coated active material 100. Therefore, it is presumed that the same tendency as the results of this example will be observed even when, other than NCA, for example, Li(NiCoMn)O2, LiCoO2, etc. are used as the positive electrode active material.

[0168] The technology of the present disclosure is useful, for example, in lithium secondary batteries.

Claims

1. A coated active material comprising a positive electrode active material and a first solid electrolyte, the first solid electrolyte coating at least a part of the surface of the positive electrode active material, wherein the first solid electrolyte contains Li, M, and X, M is at least one element selected from the group consisting of a metal element other than Li and a semi-metal element, X is a halogen element, and when the integrated value of the amount of water released from the coated active material when the temperature of the coated active material is raised from 25°C to 120°C is divided by the total mass of the coated active material, the value is defined as MC 120 When defined as such, 0 ppm < MC 120 ≦ 600 ppm, satisfying the coated active material.

2. MC 120 The coated active material according to claim 1, satisfying ≦ 500 ppm.

3. 1 ppm ≤ MC 120 , satisfying the requirements of the coating active material according to claim 1.

4. 20 ppm ≤ MC 120 , which satisfies the requirements, the coated active material according to claim 1.

5. 30 ppm ≤ MC 120 , satisfying the requirements of the coating active material according to claim 1.

6. The coating active material according to claim 1, wherein X is F.

7. The coating active material according to claim 1, wherein M includes M1 and M2, M1 is at least one selected from the group consisting of Ti and Zr, and M2 is at least one selected from the group consisting of Al, Y, Mg, and Ca.

8. The coating active material according to claim 7, wherein M2 is Al.

9. The coating active material according to claim 7, wherein M1 is Ti.

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

2. The coated active material according to claim 1, which satisfies these conditions.

11. The coating active material according to claim 10, which satisfies 0.1 < x < 0.9, y = 0, z = 0, and 0.8 < b ≤ 1.

2.

12. A positive electrode material comprising the coating active material according to any one of claims 1 to 11 and a second solid electrolyte having a composition different from that of the first solid electrolyte.

13. The positive electrode material according to claim 12, wherein the second solid electrolyte includes a sulfide solid electrolyte.

14. A battery comprising a positive electrode including the positive electrode material according to claim 12.

15. A battery comprising a positive electrode including the positive electrode material according to claim 12, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode.

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