Electrode material and battery

Abstract

An electrode material 1000 comprises a particle group of a coated active material 130. The coated active material 130 includes: an active material 110; and a coating layer 111 that covers at least a portion of the surface of the active material 110 and includes a first solid electrolyte. The electrode material 1000 satisfies at least one of (i) to (iii) below.　(i) The thickness Tc of the coating layer, calculated by averaging the median values in a thickness distribution of the coating layers of a plurality of particles, is 1.0 to 100.0 nm.　(ii) The thickness Ta of the coating layer, calculated by averaging the average values in a thickness distribution of the coating layers of a plurality of particles, is 9.0 to 100.0 nm.　(iii) The thickness Tq of the coating layer, calculated by averaging the first quartiles in a thickness distribution of the coating layers of a plurality of particles, is 2.5-50.0 nm.

Description

Electrode materials and batteries

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

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

[0003] International Publication No. 2021 / 187391

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

[0005] The electrode material of the present disclosure is an electrode material including a particle group of coated active material, wherein the coated active material particles include an active material and a coating layer that coats at least a portion of the surface of the active material, and the electrode material satisfies at least one selected from the group consisting of the following requirements (i), (ii), and (iii): (i) The thickness Tc of the coating layer calculated by averaging the median value in the thickness distribution of the coating layer of a plurality of the particles is 1.0 nm or more and 100.0 nm or less; (ii) The thickness Ta of the coating layer calculated by averaging the average value in the thickness distribution of the coating layer of a plurality of the particles is 9.0 nm or more and 100.0 nm or less; and (iii) The thickness Tq of the coating layer calculated by averaging the first quartile in the thickness distribution of the coating layer of a plurality of the particles is 2.5 nm or more and 50.0 nm or less.

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

[0007] FIG. 1 is a cross-sectional view showing a schematic configuration of an electrode material in embodiment 1. FIG. 2 is a cross-sectional view of a coated active material for explaining the measurement position of the thickness of the coating layer. FIG. 3 is a cross-sectional view showing another schematic configuration of the electrode material in embodiment 1. FIG. 4 is a cross-sectional view showing a schematic configuration of a battery in embodiment 2. FIG. 5 is a graph showing the thickness measurement results obtained for one particle of the coated active material in example 1. FIG. 6 is an electron microscope image of a cross-section of the coated active material in example 1. FIG. 7 is an electron microscope image of a cross-section of the coated active material in comparative example 1.

[0008] (Findings that form the basis of the present disclosure) For example, when an active material and a solid electrolyte are in contact with each other, the solid electrolyte may undergo oxidative decomposition during charging of the battery. This tendency is particularly pronounced when the solid electrolyte has poor oxidation stability, such as a sulfide solid electrolyte. To solve this problem, the surface of the active material is coated with a coating material that has excellent oxidation stability, such as a halide solid electrolyte.

[0009] The present inventors have discovered that even when the coating material has the same composition, differences in battery resistance occur. The present inventors have found that this difference is related to the distribution of the coating layer thickness, and have arrived at the present disclosure.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0011] In this specification, "average" means the arithmetic mean, and "averaging" means "calculating the arithmetic mean."

[0012] 1 is a cross-sectional view showing a schematic configuration of an electrode material 1000 according to a first embodiment. The electrode material 1000 includes a particle group of a coated active material 130. The particles of the coated active material 130 include an active material 110 and a coating layer 111. The active material 110 has, for example, a particulate shape. The coating layer 111 coats at least a portion of the surface of the active material 110.

[0013] The coating layer 111 may be a layer containing a first solid electrolyte. The coating layer 111 is provided on the surface of the active material 110. When the coating layer 111 contains the first solid electrolyte, the ionic conduction resistance of the coated active material 130 can be reduced.

[0014] The first solid electrolyte contains, for example, Li, M, and F. M is at least one element selected from the group consisting of metal elements and metalloid elements other than Li.

[0015] "Metalloid elements" include B, Si, Ge, As, Sb, and Te.

[0016] The term "metal element" includes 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 inorganic compounds with halogen elements.

[0017] The first solid electrolyte may be a solid electrolyte containing fluorine as an element. A solid electrolyte containing fluorine is also called a fluoride solid electrolyte. A fluoride solid electrolyte has excellent oxidation resistance due to the high electronegativity of fluorine. Therefore, by covering the surface of the active material 110 with the first solid electrolyte, it is possible to suppress oxidative decomposition of other solid electrolytes in contact with the active material 110. This reduces the resistance of the battery.

[0018] In the present disclosure, the resistance of a battery can be measured by the following method. After fabrication of the battery, the battery is placed in a thermostatic chamber at 25°C and subjected to charge and discharge processes. The battery is then charged to a desired charging voltage and discharged at a desired rate. A constant current discharge is then performed for several seconds at a desired current amount. The resistance value is defined as the difference between the open circuit voltage before discharge and the voltage at the end of discharge divided by the discharge current amount.

[0019] The coating layer 111 may uniformly coat the active material 110 .

[0020] The coating layer 111 may cover only a portion of the surface of the active material 110. In this case, particles of the active material 110 are in direct contact with each other via the portion not covered by the coating layer 111, improving the electronic conductivity between the particles of the active material 110. As a result, high-power operation of the battery is possible.

[0021] In this embodiment, the electrode material 1000 satisfies at least one selected from the group consisting of the following requirements (i), (ii), and (iii): (i) The thickness Tc of the coating layer calculated by averaging the median values ​​in the thickness distribution of the coating layer of a plurality of the particles is 1.0 nm or more and 100.0 nm or less; (ii) The thickness Ta of the coating layer calculated by averaging the average values ​​in the thickness distribution of the coating layer of a plurality of the particles is 9.0 nm or more and 100.0 nm or less; and (iii) The thickness Tq of the coating layer calculated by averaging the first quartiles in the thickness distribution of the coating layer of a plurality of the particles is 2.5 nm or more and 50.0 nm or less.

[0022] Regarding (i), first, a thickness distribution is obtained for each of the multiple particles of the coated active material 130. A median is calculated from this thickness distribution. The average value of the medians calculated for each of the multiple particles of the coated active material 130 is defined as Tc. In this case, Tc is 1.0 nm or more and 100.0 nm or less.

[0023] Regarding (ii), first, a thickness distribution is obtained for each of the multiple particles of the coated active material 130. An average value is calculated from this thickness distribution. The average value of the average values ​​calculated for each of the multiple particles of the coated active material 130 is defined as Ta. In this case, Ta is 9.0 nm or more and 100.0 nm or less.

[0024] Regarding (iii), first, a thickness distribution is obtained for each of the multiple particles of the coated active material 130. The first quartile is calculated from this thickness distribution. The average value of the first quartiles calculated for each of the multiple particles of the coated active material 130 is defined as Tq. In this case, Tq is 2.5 nm or more and 50.0 nm or less.

[0025] The thickness of the coating layer 111 can be measured, for example, by the following method.

[0026] FIG. 2 is a cross-sectional view of the coated active material 130 illustrating the measurement position of the thickness of the coating layer 111. First, a cross-section of a particle of the coated active material 130 is photographed with a scanning electron microscope (SEM). In the cross-sectional SEM image of the coated active material 130, the center of gravity G of the active material 110 is determined. Next, line segments Ra and Rb are defined that pass through this center of gravity G and extend in the radial direction of the coated active material 130. The central angle θ formed by these line segments Ra and Rb is 1°. Then, a region r of the coated active material 130 bounded by the line segments Ra and Rb is defined. The thickness R of the coating layer 111 is measured in this region r.

[0027] The above measurement is repeated in the circumferential direction of the coated active material 130 to measure the thickness R for each region r. As a result, 360 thickness values ​​can be obtained for one particle of the coated active material 130.

[0028] Next, the median, mean, and first quartile are calculated from the 360 ​​thickness values ​​of the coating layer 111 obtained from one particle of the coated active material 130, that is, the thickness distribution.

[0029] Next, for each of a plurality of arbitrary particles of the coated active material 130, the median, mean, and first quartile are calculated by the above-mentioned method.

[0030] Tc is calculated by averaging the median values ​​obtained for each of the plurality of particles of the coated active material 130. Ta is calculated by averaging the average values ​​obtained for each of the plurality of particles of the coated active material 130. Tq is calculated by averaging the first quartile values ​​obtained for each of the plurality of particles of the coated active material 130.

[0031] Here, the number of "any plurality of coated active material particles" is at least 4 or more. The number of "any plurality of coated active material particles" may be 10 or more, or may be 50 or more. The number of "any plurality of coated active material particles" may be 1000 or less, or may be 100 or less.

[0032] The electrode material 1000 includes a coated active material 130, which includes an active material 110 and a coating layer 111. Because the coated active material 130 includes the coating layer 111, the active material 110 is less likely to come into direct contact with other materials. This can prevent the other materials from oxidizing and decomposing. An example of the other materials is the second solid electrolyte described below. In this embodiment, the electrode material 1000 satisfies at least one selected from the group consisting of the above-described requirements (i), (ii), and (iii). In this case, the thickness distribution of the coating layer 111 is appropriately adjusted, which can prevent the active material 110 from coming into direct contact with other materials. In addition, because the thickness distribution of the coating layer 111 is appropriately adjusted, the coating layer 111 is less likely to become a resistor, thereby reducing the resistance of the battery.

[0033] If Tc exceeds 100 nm, Ta exceeds 100 nm, or Tq exceeds 50 nm, the battery may have significantly high resistance, which is not preferable. This is mainly due to the following two reasons. First, when a coating layer, which generally has low electronic conductivity, thickly coats the surface of the active material, electrons required for the electrode reaction may be difficult to supply to the active material, resulting in high battery resistance. Furthermore, if the ionic conductivity of the first solid electrolyte contained in the coating layer is not high, ions required for the electrode reaction may be difficult to supply to the active material, resulting in high battery resistance.

[0034] Tc may be 30.0 nm or less, or 27.3 nm or less. With this configuration, even if the ionic conductivity of the first solid electrolyte is low, the resistance of the battery can be further reduced.

[0035] Tc may be 10.0 nm or more, or 11.7 nm or more. In this case, the thickness of the coating layer 111 is sufficiently large, so that oxidative decomposition of other materials can be sufficiently suppressed. As a result, the resistance of the battery can be further reduced.

[0036] Tc may be 11.8 nm or more and 20.0 nm or less, or 11.8 nm or more and 14.9 nm or less. In this case, the thickness distribution of the coating layer 111 is appropriately adjusted, so that the resistance of the battery can be further reduced.

[0037] Ta may be 40.0 nm or less, or 38.8 nm or less. With this configuration, even if the ionic conductivity of the first solid electrolyte is low, the resistance of the battery can be further reduced.

[0038] Ta may be 20.0 nm or more, or 21.1 nm or more. In this case, the thickness of the coating layer 111 is sufficiently large, so that oxidative decomposition of other materials can be sufficiently suppressed. As a result, the resistance of the battery can be further reduced.

[0039] The coefficient of variation CV of the thickness of the coating layer 111 may be equal to or greater than 70% and less than 237%. With this configuration, the variation in the thickness of the coating layer 111 can be reduced.

[0040] The coefficient of variation CV means the value obtained by dividing the standard deviation by the mean value. Specifically, first, a thickness distribution is obtained for each of the multiple particles of the coated active material 130. The mean value Xa is calculated from this thickness distribution. In addition, the standard deviation σa is calculated from this thickness distribution. The coefficient of variation CVa is calculated from the mean value Xa and the standard deviation σa by CVa = σa / Xa.

[0041] The coefficient of variation CV is a value expressed as a percentage, which is the average value of the coefficients of variation CVa obtained for each of the plurality of particles of the coated active material 130 .

[0042] The coefficient of variation CV may be 80% or more. The coefficient of variation CV may be 230% or less, 210% or less, 199% or less, or 150% or less. With this configuration, the variation in the thickness of the coating layer 111 can be further reduced.

[0043] Tq may be 10.0 nm or less, or 9.1 nm or less. With this configuration, even if the ionic conductivity of the first solid electrolyte is low, the resistance of the battery can be further reduced.

[0044] <<Active Material 110>> The active material 110 includes a material that has the property of absorbing and releasing metal ions (e.g., lithium ions). The active material 110 is a positive electrode active material or a negative electrode active material. When the active material 110 is a positive electrode active material, the electrode material 1000 is a positive electrode material. When the active material 110 is a negative electrode active material, the electrode material 1000 is a negative electrode material.

[0045] When the active material 110 is a positive electrode active material, lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, transition metal oxynitrides, etc. can be used as the active material 110. In particular, when a lithium-containing transition metal oxide is used as the active material 110, the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased. Examples of lithium-containing transition metal oxides include lithium nickel cobalt aluminum oxide (Li(NiCoAl)O), lithium nickel cobalt manganese oxide (Li(NiCoMn)O), and lithium cobalt oxide (LiCoO).

[0046] When the active material 110 is a negative electrode active material, the material described below can be used as the active material 110 .

[0047] 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.

[0048] 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 130 and the other solid electrolyte can be well dispersed. 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.

[0049] In this specification, the term "median diameter" refers to the particle size when 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.

[0050] <<Coating Layer 111>> The coating layer 111 may include a first solid electrolyte. The first solid electrolyte has ion conductivity. The ion conductivity is typically lithium ion conductivity. The coating layer 111 may include the first solid electrolyte as a main component, or may include only the first solid electrolyte. Here, "main component" refers to the component that is most abundant in terms of mass ratio. "Includes only the first solid electrolyte" means that, except for unavoidable impurities, no materials other than the first solid electrolyte are intentionally added. For example, raw materials for the first solid electrolyte and by-products generated during the production of the first solid electrolyte are included as unavoidable impurities. The mass ratio of the unavoidable impurities to the total mass of the coating layer 111 may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0051] The first solid electrolyte may be a material containing Li, M, and F, where M is at least one selected from the group consisting of metal elements and semimetal elements other than Li. Such a material has excellent oxidation resistance. Therefore, the coated active material 130 having the coating layer 111 of the first solid electrolyte can improve the charge / discharge efficiency and thermal stability of the battery.

[0052] The first solid electrolyte may contain Li, M1, M2, and F. Here, 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. When having such a composition, the first solid electrolyte exhibits high ionic conductivity. Here, high lithium ion 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 first solid electrolyte can have a lithium ion conductivity of 1000 S / cm or more. When 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, the first solid electrolyte can form a cation framework structure within the crystal lattice that is suitable for lithium ion conduction. Therefore, the first solid electrolyte exhibits high lithium ion conductivity.

[0053] To further increase the ionic conductivity of the first solid electrolyte, M2 may be Al.

[0054] To further increase the ionic conductivity of the first solid electrolyte, M1 may be Ti.

[0055] To further increase the ionic conductivity of the first solid electrolyte, M2 may be Al and M1 may be Ti.

[0056] The first solid electrolyte may consist essentially of Li, Ti, Al, and F. Here, "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.

[0057] The composition of the first solid electrolyte may be represented by the following composition formula (1):

[0058] Li6-(4-x-4y+my)b (Ti 1-x-y Al x M3 y ) b F 6-2z O z ...(1)

[0059] In 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 the following conditions are satisfied: 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 higher ionic conductivity and can be produced by a method with high industrial productivity.

[0060] In composition formula (1), 0.1<x<0.9, y=0, z=0, and 0.8<b≦1.2 may be satisfied, in which case the first solid electrolyte has higher ionic conductivity.

[0061] In the composition formula (1), 0.1≦x≦0.7 may be satisfied.

[0062] 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.

[0063] 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.

[0064] The first solid electrolyte may be crystalline or amorphous.

[0065] The shape of the first solid electrolyte is not 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.

[0066] 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.

[0067] <<Method for Producing First Solid Electrolyte>> The first solid electrolyte according to the first embodiment can be produced, for example, by the following method.

[0068] Two or more types of raw material powders are mixed together to obtain a desired composition.

[0069] As an example, the desired composition is Li 2.7 Ti 0.3 Al 0.7 Assume that the raw material powder is F. In this case, raw material powders of LiF, TiF, and AlF are mixed to have a molar ratio of LiF:TiF:AlF=2.7:0.3:0.7. The raw material powders may be mixed at a molar ratio that is adjusted in advance to offset composition changes that may occur during the synthesis process.

[0070] The raw material powders are reacted mechanochemically in a mixing device such as a planetary ball mill to obtain a reactant. That is, the raw material powders are mixed and reacted using a mechanochemical milling method. The reactant thus obtained may be further calcined in an inert gas atmosphere or in a vacuum.

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

[0072] By these methods, the first solid electrolyte according to the first embodiment is obtained.

[0073] The composition of the solid electrolyte can be determined, for example, by inductively coupled plasma optical emission spectroscopy or ion chromatography.

[0074] <<Method for Producing Coated Active Material>> When the active material 110 is coated with the first solid electrolyte, the coated active material can be produced, for example, by the following method.

[0075] A powder of the active material 110 and a powder of the first solid electrolyte are prepared in a predetermined mass ratio. For example, a powder of Li(Ni, Co, Al)O2 is used as the active material 110, and a powder of Li(Ni, Co, Al)O2 is used as the first solid electrolyte. 2.7 Al 0.7 Ti 0.3 First, powder of F6 is prepared. These two materials are placed in the same reaction vessel, and a rotating blade is used to apply shear force to the two materials. Alternatively, the two materials may be collided with each other using a jet stream. By applying mechanical energy, at least a portion of the surface of the active material 110 is coated with the first solid electrolyte, thereby obtaining a coated active material.

[0076] 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.

[0077] The coated active material may be manufactured by a dry particle composite method. The dry particle composite method involves applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to the active material 110 and the first solid electrolyte. The active material 110 and the first solid electrolyte are mixed in an appropriate ratio.

[0078] The apparatus used in producing the coated active material is not limited, and may be an apparatus capable of applying mechanical energy such as impact, compression, or shear to a mixture of the active material 110 and 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 compounding apparatus) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation) and "Nobilta" (manufactured by Hosokawa Micron Corporation), a high-speed mixing granulator such as "Balance Gran" (manufactured by Freund Turbo Corporation), and a "Hybridization System (high-velocity airflow impact apparatus)" (manufactured by Nara Machinery Works, Ltd.).

[0079] "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 fed 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.

[0080] "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.

[0081] 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 the active material 110 and the first solid electrolyte. Conditions such as the rotor rotation speed, processing time, and feed amount can be adjusted as needed.

[0082] The Balance Gran has a chopper that stirs the powder from the outer periphery to the inner periphery in a spiral motion, promoting convection, and an agitator scraper that rotates in the opposite direction to the chopper. These actions enable the mixture to be uniformly dispersed and composite particles to be produced.

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

[0084] However, treatment using the above-mentioned apparatus is not essential. The coated active material 130 may be produced by mixing the active material 110 and the first solid electrolyte using a mortar, a mixer, etc. The first solid electrolyte may be deposited on the surface of the active material 110 by various methods, such as a spray method, a spray-dry coating method, an electrodeposition method, an immersion method, or a mechanical mixing method using a disperser.

[0085] Tc, Ta, and Tq can be adjusted to a desired range by appropriately adjusting the mixing ratio of the active material 110 and the first solid electrolyte when producing the coated active material 130. Furthermore, Tc, Ta, and Tq can be adjusted to a desired range by appropriately adjusting the mechanical energy such as impact, compression, and shear.

[0086] 3 is a cross-sectional view showing another schematic configuration of the electrode material 1100 according to the first embodiment. The electrode material 1100 includes a particle group of the coated active material 130 and a second solid electrolyte 150. The electrode material 1100 according to the present embodiment is suitable for reducing the resistance of a battery.

[0087] The active material 110 contained in the coated active material 130 is separated from the second solid electrolyte 150 by the coating layer 111. The active material 110 does not need to be in direct contact with the second solid electrolyte 150. This is because the coating layer 111 has ion conductivity.

[0088] The second solid electrolyte 150 may be a solid electrolyte having a different composition from the first solid electrolyte. That is, the first solid electrolyte and the second solid electrolyte 150 may be made of different materials. With such a configuration, the electrode material 1100 contains the coated active material 130, and is therefore suitable for suppressing an increase in the resistance of the battery.

[0089] <<Second Solid Electrolyte>> The second solid electrolyte 150 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.

[0090] When the second solid electrolyte 150 is a halide solid electrolyte, examples of the halide solid electrolyte that can be used include LiREX, Li(Al, Ga, In)X, LiMgX, LiFeX, Li(Al, Ga, In)X, 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.

[0091] When the second solid electrolyte 150 is an oxide solid electrolyte, examples of the oxide solid electrolyte include NASICON-type solid electrolytes represented by LiTi2(PO4)3 and its element 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 those typified by LiN and its element substitution products, LiN and its H-substituted products, LiPO and its N-substituted products, and glasses and 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.

[0092] When the second solid electrolyte 150 is a polymer solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used as the polymer solid electrolyte. The polymer compound may have an ethylene oxide structure. By having an ethylene oxide structure, the polymer compound can contain a large amount of lithium salt. This can further increase 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. As the lithium salt, one type of lithium salt selected from these may be used alone, or a mixture of two or more types of lithium salts selected from these may be used.

[0093] When the second solid electrolyte 150 is a complex hydride solid electrolyte, for example, LiBH4-LiI, LiBH4-P2S5, or the like can be used as the complex hydride solid electrolyte.

[0094] The second solid electrolyte 150 may contain Li and S. In other words, the second solid electrolyte 150 may contain a sulfide solid electrolyte. The sulfide solid electrolyte has high ionic conductivity and can improve the charge / discharge efficiency of the battery. On the other hand, the sulfide solid electrolyte may have poor oxidation resistance. When a battery contains a sulfide solid electrolyte as the second solid electrolyte 150, applying the technology of the present disclosure can provide significant benefits.

[0095] When the second solid electrolyte 150 is a sulfide solid electrolyte, examples of the sulfide solid electrolyte 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 qThe 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.

[0096] The second solid electrolyte 150 may contain two or more materials selected from the materials listed as solid electrolytes. The second solid electrolyte 150 may contain, for example, a halide solid electrolyte and a sulfide solid electrolyte.

[0097] The second solid electrolyte 150 may contain unavoidable impurities such as starting materials, by-products, and decomposition products used in synthesizing the solid electrolyte.

[0098] The shape of the second solid electrolyte is not particularly limited, and may be needle-like, spherical, oval-spherical, etc. The shape of the second solid electrolyte 150 may be particulate.

[0099] When the second solid electrolyte 150 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 130 and the second solid electrolyte 150 are well dispersed in the electrode material 1100.

[0100] In the present embodiment, the median diameter of the second solid electrolyte 150 may be 10 μm or less. In this case, the dispersion state of the coated active material 130 and the second solid electrolyte 150 in the electrode material 1100 becomes better.

[0101] In the present embodiment, the median diameter of the second solid electrolyte 150 may be smaller than the median diameter of the coated active material 130. In this case, the coated active material 130 and the second solid electrolyte 150 are better dispersed in the electrode material 1100.

[0102] In the electrode material 1100, the second solid electrolyte 150 and the coated active material 130 may be in contact with each other. In this case, the coating layer 111 and the second solid electrolyte 150 are in contact with each other.

[0103] The electrode material 1100 may include a plurality of particles of the second solid electrolyte 150 and a plurality of particles of the coated active material 130. In other words, the electrode material 1100 may be a mixed powder of a powder of the coated active material 130 and a powder of the second solid electrolyte 150.

[0104] In the electrode material 1100, the content of the second solid electrolyte 150 and the content of the coated active material 130 may be the same as or different from each other.

[0105] Other Materials The electrode material 1000 or the electrode material 1100 may contain a binder to improve adhesion between particles. The binder is used to improve the binding properties of the materials constituting the 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.

[0106] 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.

[0107] The electrode material 1000 or the electrode material 1100 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 and metal fiber, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide and 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.

[0108] The conductive additive may be contained in the coating layer 111 .

[0109] <<Method of Manufacturing Electrode Material>> The electrode material 1100 is obtained by mixing the particle group of the coated active material 130 with the second solid electrolyte 150. The method of mixing the particle group of the coated active material 130 with the second solid electrolyte 150 is not limited. The particle group of the coated active material 130 and the second solid electrolyte 150 may be mixed using a tool such as a mortar, or the particle group of the coated active material 130 and the second solid electrolyte 150 may be mixed using a mixing device such as a ball mill.

[0110] Second Embodiment Hereinafter, a second embodiment will be described. Descriptions that overlap with the first embodiment will be omitted as appropriate.

[0111] The battery in the second embodiment includes a first electrode, a separator portion, and a second electrode. The separator portion is located between the first electrode and the second electrode. The first electrode includes the electrode material 1000 in the first embodiment. The first electrode may also include the electrode material 1100. With this configuration, an increase in the resistance of the battery is suppressed, thereby improving the durability of the battery.

[0112] The first electrode is an electrode having the opposite polarity to the second electrode. When the first electrode is a positive electrode, the second electrode is a negative electrode. When the first electrode is a negative electrode, the second electrode is a positive electrode.

[0113] The separator portion may be an electrolyte layer containing a solid electrolyte, or may be a separator impregnated with an electrolytic solution.

[0114] FIG. 4 is a cross-sectional view showing a schematic configuration of a battery 2000 according to embodiment 2. The battery 2000 includes a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203. In the battery 2000, the separator portion is the electrolyte layer 32. The positive electrode 201 includes the electrode material 1000 described in embodiment 1. The positive electrode 201 may also include the electrode material 1100. This configuration can suppress an increase in the resistance of the battery 2000, thereby providing a battery with excellent durability. The negative electrode 203 may also include the electrode material 1000 or 1100.

[0115] The thickness of each of the positive electrode 201 and the negative electrode 203 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 201 and the negative electrode 203 is 10 μm or more, a sufficient energy density of the battery can be ensured. When the thickness of the positive electrode 201 and the negative electrode 203 is 500 μm or less, high-power operation of the battery 2000 can be achieved.

[0116] The electrolyte layer 202 is a layer containing an electrolyte material. The electrolyte layer 202 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 first embodiment.

[0117] The thickness of the electrolyte layer 202 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 202 is 1 μm or more, the positive electrode 201 and the negative electrode 203 can be more reliably separated. When the thickness of the electrolyte layer 202 is 300 μm or less, the battery 2000 can operate at high power.

[0118] The negative electrode 203 contains, as a negative electrode active material, a material that has the property of absorbing and releasing metal ions (for example, lithium ions).

[0119] 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.

[0120] The median diameter of the particles of the negative electrode active material may be 0.1 μm or more and 100 μm or less.

[0121] The negative electrode 203 may contain other materials such as a solid electrolyte. As the solid electrolyte, the materials described in the first embodiment can be used.

[0122] The battery 2000 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.

[0123] (Additional Note) From the above description, the following techniques are disclosed.

[0124] (Technology 1) An electrode material including a group of particles of coated active material, wherein the particles of the coated active material include an active material and a coating layer that coats at least a portion of the surface of the active material, and the electrode material satisfies at least one selected from the group consisting of the following requirements (i), (ii), and (iii): (i) The thickness Tc of the coating layer calculated by averaging the median value in the thickness distribution of the coating layer of a plurality of the particles is 1.0 nm or more and 100.0 nm or less; (ii) The thickness Ta of the coating layer calculated by averaging the average value in the thickness distribution of the coating layer of a plurality of the particles is 9.0 nm or more and 100.0 nm or less; (iii) The thickness Tq of the coating layer calculated by averaging the first quartile in the thickness distribution of the coating layer of a plurality of the particles is 2.5 nm or more and 50.0 nm or less.

[0125] The electrode material of Technology 1 can reduce the resistance of the battery.

[0126] (Technology 2) The electrode material according to Technology 1, wherein the Tc is 30.0 nm or less. With this configuration, even if the ionic conductivity of the first solid electrolyte is low, the resistance of the battery can be further reduced.

[0127] (Technology 3) The electrode material according to Technology 1 or 2, wherein the Tc is 10.0 nm or more. With this configuration, the thickness of the coating layer is sufficiently large, so that oxidative decomposition of other materials can be sufficiently suppressed. As a result, the resistance of the battery can be further reduced.

[0128] (Technology 4) The electrode material according to any one of Technologies 1 to 3, wherein the Tc is 11.8 nm or more and 20.0 nm or less. With this configuration, the thickness distribution of the coating layer is appropriately adjusted, so that the resistance of the battery can be further reduced.

[0129] (Technology 5) The electrode material according to any one of Technologies 1 to 4, wherein the Ta is 40.0 nm or less. With this configuration, even if the ionic conductivity of the first solid electrolyte is low, the resistance of the battery can be further reduced.

[0130] (Technology 6) The electrode material according to any one of Technologies 1 to 5, wherein the Ta is 20.0 nm or more. With this configuration, the coating layer is sufficiently thick, so that oxidative decomposition of other materials can be sufficiently suppressed. As a result, the resistance of the battery can be further reduced.

[0131] (Technology 7) The electrode material according to any one of Technologies 1 to 6, wherein the Tq is 10.0 nm or less. With this configuration, even if the ionic conductivity of the first solid electrolyte is low, the resistance of the battery can be further reduced.

[0132] (Technology 8) The electrode material according to any one of Technologies 1 to 7, wherein the coating layer has a coefficient of variation of thickness of 70% or more and less than 237%. With this configuration, it is possible to reduce the variation in thickness of the coating layer.

[0133] (Technology 9) The electrode material according to any one of Technologies 1 to 8, wherein the coating layer includes a first solid electrolyte.

[0134] (Technology 10) The electrode material according to Technology 9, wherein the first solid electrolyte contains Li, M, and F, and the M is at least one element selected from the group consisting of metal elements and semimetal elements other than Li.

[0135] (Technology 11) The electrode material according to Technology 9 or 10, wherein the first solid electrolyte contains Li, M1, M2, and F, where 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. With this configuration, the first solid electrolyte exhibits high lithium ion conductivity.

[0136] (Technology 12) The electrode material according to Technology 11, wherein M2 is Al. With this configuration, the first solid electrolyte exhibits higher lithium ion conductivity.

[0137] (Technology 13) The electrode material according to Technology 11 or 12, wherein M1 is Ti. With this configuration, the first solid electrolyte exhibits higher lithium ion conductivity.

[0138] (Technology 14) The electrode material according to any one of Techniques 9 to 13, wherein the first solid electrolyte is represented by the following composition formula (1), where 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. With this configuration, the first solid electrolyte has higher ionic conductivity and can be produced by a method with high industrial productivity. Li6-(4-x-4y+my)b(Ti 1-x-y Al x M3 y ) b F 6-2z O z ...(1)

[0139] (Technology 15) The electrode material according to Technology 14, wherein 0.1<x<0.9, y=0, z=0, and 0.8<b≦1.2 are satisfied. With this configuration, the first solid electrolyte exhibits higher lithium ion conductivity.

[0140] (Technology 16) The electrode material according to any one of Technologies 9 to 15, further comprising a second solid electrolyte that is a material different from the first solid electrolyte. According to this configuration, the electrode material includes a coated active material, and is therefore suitable for suppressing an increase in the resistance of the battery.

[0141] (Technology 17) The electrode material according to Technology 16, wherein the second solid electrolyte contains Li and S. According to this configuration, the sulfide solid electrolyte has high ionic conductivity, and therefore the charge / discharge efficiency of the battery can be improved.

[0142] (Technology 18) The electrode material according to any one of technologies 1 to 17, wherein the active material is a positive electrode active material, and the electrode material is a positive electrode material.

[0143] (Technology 19) A battery comprising an electrode containing the electrode material according to any one of technologies 1 to 18.

[0144] According to the battery of Technology 19, an increase in the resistance of the battery is suppressed, and therefore the durability of the battery is improved.

[0145] (Technology 20) A battery comprising: a first electrode containing the electrode material according to any one of technologies 1 to 18; a second electrode; and an electrolyte layer disposed between the first electrode and the second electrode.

[0146] According to the battery of Technique 20, an increase in the resistance of the battery is suppressed, and therefore the durability of the battery is improved.

[0147] Hereinafter, the present disclosure will be described in detail using examples and comparative examples. However, the present disclosure is not limited to the following examples.

[0148] Example 1 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 out 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 for 12 hours at 500 rpm using a planetary ball mill (Fritsch, Model P-7). In this way, a powder of a halide solid electrolyte material according to Example 1 was obtained. The solid electrolyte material according to Example 1 contained Li, 2.7 Ti 0.3 Al 0.7 F6 (hereinafter referred to as "LTAF").

[0149] [Preparation of Coated Active Material] A powder of Li(NiCoAl)O2 (hereinafter referred to as "NCA") was prepared as a positive electrode active material. A coating layer made of LTAF was formed on the surface of the NCA. This resulted in a coated active material (hereinafter referred to as "LTAF-coated NCA") having a coating layer made of LTAF on the surface of the NCA. The coating layer was formed using a high-speed mixer granulator (BG-2L, manufactured by Freund Turbo). Specifically, NCA and LTAF were weighed out to a weight ratio of 95.94:4.06 and charged into the high-speed mixer granulator, where the chopper rotation speed was 3000 rpm and the processing time was 60 minutes.

[0150] [Preparation of Second Solid Electrolyte] In an argon glove box with a dew point of −60°C or less, raw material powders LiS and P2S5 were weighed out to a molar ratio of LiS:P2S5 = 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, P-7 model). 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 solid electrolyte, Li2S-P2S5 (hereinafter referred to as "LPS").

[0151] [Preparation of Positive Electrode Material] In an argon glove box, the LTAF-coated NCA and LPS were weighed out so that the volume ratio of the LTAF-coated NCA to the LPS was 60:40. Furthermore, a fibrous conductive additive (VGCF-H, manufactured by Resonac Packaging Co., Ltd.) was weighed out so that the amount was 1.5% by mass relative to the mass of the NCA. These were mixed in an agate mortar to prepare the positive electrode material of Example 1.

[0152] Example 2 A positive electrode material of Example 2 was produced in the same manner as Example 1, except that in producing the coated active material, NCA and LTAF were weighed out to give a weight ratio of 96.52:3.48.

[0153] Example 3 A positive electrode material of Example 3 was produced in the same manner as Example 1, except that in producing the coated active material, NCA and LTAF were weighed out to give a weight ratio of 97.31:2.69.

[0154] Example 4 In producing the coated active material, NCA and LTAF were weighed out to a weight ratio of 97.31:2.69 and charged into a high-speed mixer granulator, and processed under the conditions of chopper rotation speed: 3000 rpm and processing time: 80 minutes. A positive electrode material of Example 4 was produced in the same manner as in Example 1 except for the above.

[0155] Example 5 In producing the coated active material, NCA and LTAF were weighed out to a weight ratio of 97.31:2.69 and charged into a high-speed mixer granulator, and processed under the conditions of chopper rotation speed: 3000 rpm and processing time: 20 minutes. A positive electrode material of Example 5 was produced in the same manner as in Example 1 except for the above.

[0156] Example 6 A positive electrode material of Example 6 was produced in the same manner as Example 1, except that in producing the coated active material, NCA and LTAF were weighed out to give a weight ratio of 98.26:1.74.

[0157] Comparative Example 1 A positive electrode material of Comparative Example 1 was produced in the same manner as in Example 1, except that in producing the coated active material, NCA and LTAF were weighed out to give a weight ratio of 98.84:1.16.

[0158] [Measurement of the thickness of the coating layer in the coated active material] For each of the examples and comparative examples, a cross-sectional image of the coated active material was taken using a field emission scanning electron microscope (SU8230, manufactured by Hitachi High-Tech Corporation). The thickness of the coating layer was measured for each coated active material. The thickness measurement method was as described above.

[0159] Next, for each of the four particles of the coated active material, 360 thickness values ​​were obtained by the above-mentioned method, and the median, mean, and first quartile of this thickness distribution were calculated.

[0160] Tc was calculated by averaging the median values ​​obtained for each of the four particles of coated active material.

[0161] Ta was calculated by averaging the average values ​​obtained for each of the four particles of the coated active material.

[0162] The Tq was calculated by averaging the first quartile values ​​obtained for each of the four particles of coated active material. The results are shown in Table 1.

[0163] The average value Xa and standard deviation σa were calculated from the thickness distribution obtained for each of the four particles of the coated active material. The coefficient of variation CVa was calculated from the average value Xa and standard deviation σa by CVa = σa / Xa. The coefficient of variation CV of the thickness of the coating layer was calculated by averaging the coefficients of variation CVa calculated for each of the four particles of the coated active material and calculating the value obtained as a percentage. The results are shown in Table 1.

[0164] Fig. 5 is a graph showing the thickness measurement results obtained for one particle of the coated active material according to Example 1. Fig. 5 shows the thickness distribution obtained for one particle of the coated active material according to Example 1. In Fig. 5, the horizontal axis represents the angle [°] in the circumferential direction of the particle of the coated active material on a circumference centered on the center of gravity of the positive electrode active material. In Fig. 5, the vertical axis represents the thickness [nm] of the coating layer at each angle.

[0165] FIG. 6 is an electron microscope image of a cross section of the coated active material according to Example 1. As shown in FIG. 6, the coated active material 130 according to Example 1 had a positive electrode active material 110 and a coating layer 111. The coated active material 130 according to Example 1 was placed on a support 200 for cross-section observation. As shown in FIG. 6, in Example 1, the coating layer 111 coated at least a portion of the surface of the positive electrode active material 110. In Example 1, the coating layer 111 had an appropriate thickness. In addition, in Example 1, a coating layer 111 having a smaller coefficient of variation was formed than in Comparative Example 1, which will be described later.

[0166] Fig. 7 is an electron microscope image of a cross section of the coated active material according to Comparative Example 1. As shown in Fig. 7, in Comparative Example 1, there were many thin portions of the coating layer 111. In addition, in Comparative Example 1, the coating layer 111 formed had a larger coefficient of variation than in Example 1.

[0167] [Fabrication of Battery] Using each of the coated active materials of the Examples and Comparative Examples, batteries were fabricated by carrying out the following steps.

[0168] 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. The LPS and 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, a solid 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. Next, the outer cylinder was sealed using an insulating ferrule to isolate the interior of the outer cylinder from the ambient atmosphere. Through these processes, the batteries of Examples 1 to 5 and Comparative Example 1 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.

[0169] [Evaluation of Battery Characteristics] The battery was placed in a thermostatic chamber at 25°C. The battery was charged at a constant current of 50 μA until the voltage reached 4.25 V. The battery was then discharged at a constant current of 50 μA until the voltage reached 3.68 V. The battery was then discharged at a constant current of 46.4 mA for 2 seconds. The battery resistance was calculated by dividing the difference between the open circuit voltage before discharge and the voltage at the end of discharge by the discharge current. The results are shown in Table 1.

[0170]

[0171] <Discussion> As shown in Table 1, the batteries using the positive electrode materials of Examples 1 to 6, which satisfied at least one of the above-mentioned requirements (i), (ii), and (iii), had lower battery resistance than the battery using the positive electrode material of Comparative Example 1. In Examples 1 to 6, the thickness of the coating layer was neither too thin nor too thick. Therefore, it is presumed that oxidative decomposition of the second solid electrolyte was suppressed. As a result, the battery resistance of Examples 1 to 6 was lower than that of Comparative Example 1. In addition, the coating layer containing LTAF had an ionic conductivity of 1 / 1000 or less compared to that of LPS. In Examples 1 to 6, the Tc, Ta, and Tq of the coating layer were appropriately adjusted, which is presumed to have reduced the effect of the coating layer containing LTAF on the battery resistance. As a result, the battery resistance of Examples 1 to 6 was lower than that of Comparative Example 1.

[0172] As is clear from a comparison between Examples 1 to 5 and Example 6, when Tc was 11.7 nm or more, the resistance of the battery was further reduced. This is presumably because the coating layer was sufficiently thick, which further suppressed oxidation of the second solid electrolyte.

[0173] As is clear from a comparison of Examples 3 to 5 with Example 6, when Ta was 21.1 nm or more, the battery resistance was further reduced. This is presumably because the coating layer was sufficiently thick, which further suppressed oxidative decomposition of the second solid electrolyte.

[0174] As is clear from a comparison of Examples 3 and 4 with Examples 1, 2, 5, and 6, the battery resistance was further reduced when Tc was 11.8 nm or more and 14.9 nm or less. This is presumably because the thickness of the coating layer was in a more optimal range, which effectively suppressed oxidative decomposition of the second solid electrolyte and also sufficiently reduced the effect of the coating layer on the battery resistance.

[0175] The effects of Tc, Ta, and Tq on the battery resistance are presumed to be independent of the type of positive electrode active material, and therefore, it is expected that the same trends as in this example will be observed when using positive electrode active materials other than NCA, such as Li(NiCoMn)O2 and LiCoO2.

[0176] The above-mentioned effects can be obtained by appropriately adjusting Tc, Ta, and Tq in combination with the excellent oxidation resistance of the first solid electrolyte containing Li, M, and F. Therefore, it is presumed that the same effects can be obtained even when a first solid electrolyte having a composition other than LTAF is used, as long as it contains Li, M, and F.

[0177] The technology of the present disclosure is useful, for example, in all-solid-state lithium-ion secondary batteries.

Claims

1. An electrode material comprising a group of particles of a coated active material, wherein the particles of the coated active material include an active material and a coating layer covering at least a part of the surface of the active material, and satisfy at least one selected from the group consisting of the following requirements (i), (ii), and (iii). (i) The thickness Tc of the coating layer is 1.0 nm or more and 100.0 nm or less, calculated by averaging the median in the thickness distribution of the coating layers of the plurality of particles. (ii) The thickness Ta of the coating layer is 9.0 nm or more and 100.0 nm or less, calculated by averaging the average value in the thickness distribution of the coating layers of the plurality of particles. (iii) The thickness Tq of the coating layer is 2.5 nm or more and 50.0 nm or less, calculated by averaging the first quartile in the thickness distribution of the coating layers of the plurality of particles.

2. The electrode material according to claim 1, wherein Tc is 30.0 nm or less.

3. The electrode material according to claim 1, wherein Tc is 10.0 nm or more.

4. The electrode material according to claim 1, wherein Tc is 11.8 nm or more and 20.0 nm or less.

5. The electrode material according to claim 1, wherein Ta is 40.0 nm or less.

6. The electrode material according to claim 1, wherein Ta is 20.0 nm or more.

7. The electrode material according to claim 1, wherein Tq is 10.0 nm or less.

8. The electrode material according to claim 1, wherein the coefficient of variation of the thickness of the coating layer is 70% or more and less than 237%.

9. The electrode material according to claim 1, wherein the coating layer contains a first solid electrolyte.

10. The electrode material according to claim 9, wherein the first solid electrolyte contains Li, M, and F, and M is at least one element selected from the group consisting of metal elements and metalloid elements other than Li.

11. The electrode material according to claim 9, wherein the first solid electrolyte contains Li, M1, M2, and F, 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.

12. The electrode material according to claim 11, wherein M2 is Al.

13. The electrode material according to claim 11, wherein M1 is Ti.

14. 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 are satisfied. The electrode material according to claim 9.

15. The electrode material according to claim 14, wherein 0.1 < x < 0.9, y = 0, z = 0, and 0.8 < b ≦ 1.2 are satisfied.

16. The electrode material according to claim 9, further comprising a second solid electrolyte that is a material different from the first solid electrolyte.

17. The electrode material according to claim 16, wherein the second solid electrolyte contains Li and S.

18. The electrode material according to claim 1, wherein the active material is a positive electrode active material and the electrode material is a positive electrode material.

19. A battery comprising an electrode containing the electrode material according to claim 1.

20. A battery comprising a first electrode containing the electrode material according to claim 1, a second electrode, and an electrolyte layer disposed between the first electrode and the second electrode.