Electrode material and battery

Abstract

An electrode material 1000 according to the present disclosure includes a particle group of a coated active material 100. Each particle of the coated active material 100 includes: a composite particle 130 which includes an active material 110 and a first coating layer 120 that covers at least a part of the surface of the active material 110; and a second coating layer 140 that covers at least a part of the surface of the composite particle 130. The electrode material 1000 satisfies at least one requirement that is selected from the group consisting of the requirements (i) to (v) described below with respect to the thickness distribution of the second coating layer 140.　(i) The value Tc obtained by averaging the median values is 1.0-200.0 nm inclusive.　(ii) The value Ta obtained by averaging the average values is 1.0-250.0 nm inclusive.　(iii) The value Tq obtained by averaging the first quartiles is 1.0-80.0 nm inclusive.　(iv) The value Tm obtained by averaging the maximum values is 50.0-1,000.0 nm inclusive.　(v) The value CV obtained by averaging the coefficients of variation is 50.0-150.0% inclusive.

Description

Electrode materials and batteries

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

[0002] Patent Document 1 discloses a composite active material having an oxide active material, an oxide solid electrolyte layer covering the surface of the oxide active material, and a sulfide solid electrolyte layer covering the surface of the oxide solid electrolyte layer, wherein the specific surface area of ​​the sulfide solid electrolyte layer is 1.06 m 2 / g or more and 1.22m 2 / g or less, and the thickness of the sulfide solid electrolyte layer is in the range of 15 nm or more and 25 nm or less.

[0003] Japanese Patent Application Laid-Open No. 2017-152347

[0004] In the prior art, there is a need to improve the durability of batteries.

[0005] The present disclosure provides an electrode material comprising a particle group of coated active material, wherein the particles of the coated active material comprise: composite particles comprising an active material and a first coating layer coating at least a portion of the surface of the active material; and a second coating layer coating at least a portion of the surface of the composite particle, wherein the first coating layer comprises a first solid electrolyte, and the second coating layer comprises a second solid electrolyte having a different composition from the first solid electrolyte, and the electrode material satisfies at least one selected from the group consisting of the following requirements (i) to (v): (i) A value Tc calculated by calculating the median of the thickness distribution of the second coating layer for one particle of the coated active material and averaging the median for the particle group of the coated active material is 1.0 nm or more and 200.0 nm or less. (ii) The value Ta calculated by calculating the average value of the thickness distribution of the second coating layer for one of the particles of the coated active material and averaging the average value for the particle group of the coated active material is 1.0 nm or more and 250.0 nm or less. (iii) The value Tq calculated by calculating the first quartile of the thickness distribution of the second coating layer for one of the particles of the coated active material and averaging the first quartile for the particle group of the coated active material is 1.0 nm or more and 80.0 nm or less. (iv) The value Tm calculated by calculating the maximum value of the thickness distribution of the second coating layer for one of the particles of the coated active material and averaging the maximum value for the particle group of the coated active material is 50.0 nm or more and 1000.0 nm or less. (v) The coefficient of variation of the thickness distribution of the second coating layer is calculated for one of the particles of the coated active material, and the value CV calculated by averaging the coefficient of variation for the particle group of the coated active material is 50.0% or more and 150.0% or less.

[0006] According to the technology of the present disclosure, the durability of the battery can be improved.

[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 showing a schematic configuration of another example of the electrode material in embodiment 1. Fig. 3 is a cross-sectional view showing a schematic configuration of a battery in embodiment 2. Fig. 4 is a cross-sectional secondary electron image of a representative particle of the coated active material of Examples 1 to 6. Fig. 5 is a graph showing the measurement results of the thickness of the second coating layer obtained for one particle of the coated active material of Example 1.

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

[0009] In addition, in order to improve the durability of an all-solid-state battery, it is important that the interface between the composite particles in the electrode and the surrounding bulk solid electrolyte is well adhered and a sufficient ion conduction path is secured even after the battery has been used for a long time. Therefore, as disclosed in Patent Document 1, a method has been proposed in which the composite particles are additionally coated with a different type of solid electrolyte to assist the interfacial bonding between the composite particles and the bulk solid electrolyte.

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

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

[0012] In this specification, "average" means the arithmetic mean, and "averaging" means "calculating the arithmetic mean."

[0013] (Embodiment 1) FIG. 1 is a cross-sectional view showing a schematic configuration of an electrode material 1000 in embodiment 1. The electrode material 1000 includes a particle group of coated active material 100. The particles of the coated active material 100 include composite particles 130 including an active material 110 and a first coating layer 120, and a second coating layer 140. The active material 110 has, for example, a particulate shape. The first coating layer 120 coats at least a portion of the surface of the active material 110. The second coating layer 140 coats at least a portion of the surface of the composite particle 130. The first coating layer 120 includes a first solid electrolyte. The second coating layer 140 includes a second solid electrolyte having a different composition from the first solid electrolyte. The electrode material 1000 satisfies at least one selected from the group consisting of the following requirements (i) to (v):

[0014] (i) The value Tc calculated by calculating the median of the thickness distribution of the second coating layer 140 for one particle of the coated active material 100 and averaging the median for a group of particles of the coated active material 100 is 1.0 nm or more and 200.0 nm or less. (ii) The value Ta calculated by calculating the average value of the thickness distribution of the second coating layer 140 for one particle of the coated active material 100 and averaging the average value for a group of particles of the coated active material 100 is 1.0 nm or more and 250.0 nm or less. (iii) The value Tq calculated by calculating the first quartile of the thickness distribution of the second coating layer 140 for one particle of the coated active material 100 and averaging the first quartile for a group of particles of the coated active material 100 is 1.0 nm or more and 80.0 nm or less. (iv) The value Tm calculated by calculating the maximum value of the thickness distribution of the second coating layer 140 for one particle of the coated active material 100 and averaging the maximum value for a group of particles of the coated active material 100 is 50.0 nm or more and 1000.0 nm or less. (v) The value CV calculated by calculating the coefficient of variation of the thickness distribution of the second coating layer 140 for one particle of the coated active material 100 and averaging the coefficient of variation for a group of particles of the coated active material 100 is 50.0% or more and 150.0% or less.

[0015] The electrode material 1000 of this embodiment is suitable for improving the durability of a battery.

[0016] In this specification, the durability of a battery is evaluated by the degree of increase in the resistance of the battery after a durability test relative to the resistance of the battery before the durability test. The degree of increase in the resistance of the battery is expressed by the index "(R2 / R1) x 100 (%)." (R2 / R1) is the value obtained by dividing the resistance R2 after the durability test by the resistance R1 before the durability test. A durability test is, for example, a test in which a battery is stored 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 an electrode material 1000 containing a 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. Thereafter, a constant-current discharge is 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. Next, a durability test is performed under appropriate conditions. After the durability test, the charge and discharge processes are performed as described above. Next, the battery is charged and discharged to a predetermined voltage. After that, it is discharged at a constant current of a predetermined current value for 1 to 10 seconds. The voltage drop at this time is divided by the discharge current value to calculate the resistance R2 after the durability test.

[0017] When the second coating layer 140 coats the surface of the composite particle 130 so as to satisfy at least one selected from the group consisting of the above requirements (i) to (v), the second coating layer 140, in which an increase in resistance is suppressed, is present with a sufficient thickness on the surface of the composite particle 130. When at least one selected from the group consisting of the above requirements (i) to (v) is satisfied, the increase in resistance of the second coating layer 140 is suppressed because, in the electrode of the battery, the second solid electrolyte contained in the second coating layer 140 is less likely to undergo oxidation-reduction decomposition even when it comes into contact with, for example, a conductive additive contained in the electrode, and a decrease in ionic conductivity during long-term durability is suppressed.

[0018] Furthermore, when the second coating layer 140 coats the surface of the composite particle 130 so as to satisfy at least one selected from the group consisting of the above requirements (i) to (v), the second coating layer 140 can sufficiently alleviate distortion caused by volume changes of the composite particle 130 accompanying charge and discharge within the battery electrode. This makes it possible to ensure long-term adhesion between the external solid electrolyte and the composite particle, thereby improving the durability of the battery.

[0019] It should be noted that if the second coating layer has a thickness exceeding the upper limit values ​​of the above values ​​Tc, Ta, Tq, and Tm specified in the requirements (i) to (iv), the presence of the second coating layer 140 may inhibit the electron conduction path to the composite particle 130, thereby increasing the resistance of the battery, which is not preferable. In other words, by having the second coating layer have values ​​equal to or less than the upper limit values ​​of the above values ​​Tc, Ta, Tq, and Tm specified in the requirements (i) to (iv), it is possible to suppress, for example, an increase in the initial resistance of the battery.

[0020] The thickness distribution of the second coating layer 140 can be measured, for example, by observing a cross section of the coated active material 100 with a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM).

[0021] For example, when measuring the thickness distribution of the second coating layer 140 from a cross-sectional image of the coated active material 100 captured by SEM, the local film thickness of the second coating layer 140 is first measured for any 100 particles of the coated active material 100. The local film thickness of the second coating layer 140 is determined by dividing the cross-sectional SEM image of the coated active material 100 into 360° sections starting from the center of gravity of the active material 110 and measuring the thickness of the second coating layer 140 every 1°. In other words, 360 local film thickness values ​​can be obtained for each particle of the coated active material 100. From the obtained local film thickness of the second coating layer 140, the median, mean, first quartile, and maximum value are calculated for each particle for portions with a film thickness of 0 nm or more. Next, the above values ​​Tc, Ta, Tq, and Tm can be determined by averaging the median, mean, first quartile, and maximum local film thickness for each of any 100 particles of coated active material 100, respectively.

[0022] The coefficient of variation of the thickness distribution of the second coating layer 140 means the value obtained by dividing the square root of the unbiased variance by the average value. In detail, first, the thickness distribution of the second coating layer 140 is obtained for each particle of the coated active material 100. The average value Xa is calculated from this thickness distribution. In addition, the square root of the unbiased variance σa is calculated from this thickness distribution. Then, the coefficient of variation CVa is calculated by CVa = σa / Xa. 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 multiple particles of the coated active material 100.

[0023] Hereinafter, the components and manufacturing method of the coated active material 100 in the electrode material 1000 of this embodiment will be described in detail.

[0024] <Composite Particles> (Active Material) The active material 110 includes a material that has the property of absorbing and releasing metal ions (for example, lithium ions).

[0025] Examples of materials that can be used as the active material 110 include lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, transition metal oxynitrides, metal materials, carbon materials, oxides, nitrides, tin compounds, and silicon compounds. Using a lithium-containing transition metal oxide as the active material 110 can reduce the manufacturing cost of the battery. Examples of lithium-containing transition metal oxides include Li(Ni, Co, Al)O, Li(Ni, Co, Mn)O, and LiCoO.

[0026] 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.

[0027] 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.

[0028] The median diameter of the active material 110 may be 0.1 μm or more and 100 μm or less. When the median diameter of the active material 110 is 0.1 μm or more, the coated active material 100 and the above-mentioned bulk solid electrolyte (corresponding to the third solid electrolyte contained in the separate electrode material in the first embodiment described later) can form a well-dispersed state within the electrode. As a result, the charge / discharge characteristics of the battery are improved. When the median diameter of the active material 110 is 100 μm or less, the diffusion rate of lithium within the active material 110 is sufficiently ensured. Therefore, the battery can operate at high power.

[0029] The active material 110 may be a positive electrode active material. In this case, a sufficient ion conduction path can be provided near the interface between the positive electrode active material and the electrolyte, which generally has high charge transfer resistance, and the resistance of the battery can be reduced.

[0030] The active material 110 may contain Li, Ni, and O. In this case, the energy density of the battery can be increased.

[0031] <First Coating Layer> As described above, the first coating layer 120 covers at least a part of the surface of the active material 110. The first coating layer 120 is in direct contact with the active material 110, for example.

[0032] The first coating layer 120 includes a first solid electrolyte. The first solid electrolyte has ion conductivity. The ion conductivity is typically lithium ion conductivity.

[0033] The first solid electrolyte may contain Li, M, and at least one element selected from the group consisting of F and O. M is at least one element selected from the group consisting of metal elements other than Li and metalloid elements. A first solid electrolyte having such a composition has excellent oxidation-reduction resistance. Therefore, it is possible to suppress the oxidation-reduction of the second solid electrolyte contained in the second coating layer 140 that contacts the first coating layer 120. This makes it possible to suppress an increase in the resistance of the battery.

[0034] In this disclosure, "metalloid elements" include B, Si, Ge, As, Sb, and Te. "Metal elements" include all elements in groups 1 to 12 of the periodic table except hydrogen, and all elements in groups 13 to 16 of the periodic table except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se.

[0035] The first solid electrolyte contains Li, M1, M2, and F, where M1 is at least one selected from the group consisting of Al and Y, and M2 may be at least one selected from the group consisting of Ti, Zr, Mg, Ca, Si, and Sn. In a first solid electrolyte having such a composition, a cationic framework suitable for ion conduction can be formed within the crystal lattice. Therefore, the first solid electrolyte exhibits high ionic conductivity. High ionic conductivity is, for example, 1.0 × 10 -8 That is, the first solid electrolyte has a specific resistance of, for example, 1.0×10 -8 The ionic conductivity may be 100 S / cm or more.

[0036] M1 may be Al and M2 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): Li(4-x-4y+my)(Ti 1-x-y Al x M3 y ) b F 6-2z O z... (1) In the composition formula (1), M3 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the valence of M3, and 0.1 < x < 0.9, 0 ≦ y < 0.1, 0 ≦ z < 0.1, and 0.8 < b ≦ 1.2 are satisfied. A first solid electrolyte having such a composition has high ionic conductivity and can be produced by a method with high industrial productivity.

[0039] 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.

[0040] In the composition formula (1), 0.1≦x≦0.7 may be satisfied.

[0041] 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.

[0042] 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.

[0043] The first solid electrolyte may contain Li, Nb, and O. A first solid electrolyte having such a composition may also form a cationic framework structure suitable for ion conduction within the crystal lattice. Therefore, the first solid electrolyte exhibits high ionic conductivity. High ionic conductivity is, for example, 1.0×10 -8 That is, the first solid electrolyte has a specific resistance of, for example, 1.0×10 -8 The ionic conductivity may be 100 S / cm or more.

[0044] The first solid electrolyte may be crystalline or amorphous.

[0045] The shape of the first solid electrolyte is not particularly limited. The shape of the first solid electrolyte is, for example, needle-like, spherical, film-like, or ellipsoidal. The shape of the first solid electrolyte may also be particulate.

[0046] When the first solid electrolyte has a particulate (eg, spherical) shape, the first solid electrolyte may have a median diameter of 0.01 μm or more and 100 μm or less.

[0047] In the present disclosure, 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.

[0048] The first coating layer 120 may contain the first solid electrolyte as a main component, or may contain only the first solid electrolyte. In the present disclosure, "main component" refers to the component that is contained in the largest amount by mass. "Containing only the first solid electrolyte" means that, with the exception of inevitable impurities, no materials other than the first solid electrolyte are intentionally added. For example, the raw materials of the first solid electrolyte and by-products generated during the production of the first solid electrolyte are included as inevitable impurities. The mass ratio of the inevitable impurities to the total mass of the first coating layer 120 may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0049] The first coating layer 120 may not contain sulfur.

[0050] The first coating layer 120 may uniformly coat the active material 110 .

[0051] The first coating layer 120 may cover only a portion of the surface of the active material 110. In this case, particles of the active material 110 can come into direct contact with each other via the portion not covered by the first coating layer 120, improving the electronic conductivity between particles of the active material 110. As a result, high-power operation of the battery is possible.

[0052] The shape of the first solid electrolyte contained in the first coating layer 120 is not particularly limited. For example, a thin film formed by the accumulation of fine particles of the first solid electrolyte, such as plate-like, needle-like, spherical, or oval-spherical, may cover at least a portion of the surface of the active material 110.

[0053] The thickness of the thin film of the first coating layer 120 is, for example, 1 nm or more and 1000 nm or less. When the thickness of the thin film of the first coating layer 120 is appropriately adjusted, contact between the active material 110 and the second solid electrolyte can be sufficiently suppressed. The thickness of the thin film of the first coating layer 120 can be determined, for example, by observing the cross section of a particle of the coated active material 100 with a scanning electron microscope. The average value of the thicknesses of the thin film of the first coating layer 120 measured at multiple arbitrary positions (for example, five points) can be considered to be the thickness of the thin film of the first coating layer 120.

[0054] <Second Coating Layer> As described above, the second coating layer 140 coats the surface of the composite particle 130 with a thickness distribution that satisfies at least one selected from the group consisting of the above requirements (i) to (v). The second coating layer 140 is in contact with the composite particle 130, for example.

[0055] The second coating layer 140 includes a second solid electrolyte. The second solid electrolyte has ion conductivity. The ion conductivity is typically lithium ion conductivity.

[0056] Tc may be 40.0 nm or more, 41.0 nm or more, or 41.3 nm or more. With this configuration, a layer of the second solid electrolyte, in which an increase in resistance is suppressed, is present on the surface of the composite particle 130 with a more appropriate thickness. Furthermore, within the battery electrode, the second coating layer 140 can more efficiently alleviate distortion caused by volumetric changes in the composite particle 130 associated with charging and discharging. These effects can further improve the durability of the battery.

[0057] Tc may be 140.0 nm or less, 139.0 nm or less, or 138.7 nm or less. With this configuration, the second coating layer 140 is less likely to obstruct the electron conduction path to the composite particle 130, thereby further reducing the resistance of the battery. Furthermore, even if the ionic conductivity of the second solid electrolyte is low, the resistance of the battery can be reduced.

[0058] Ta may be 60.0 nm or more, 64.0 nm or more, or 64.4 nm or more. With this configuration, a layer of the second solid electrolyte, in which an increase in resistance is suppressed, is present on the surface of the composite particle 130 with a more appropriate thickness. Furthermore, within the battery electrode, the second coating layer 140 can more efficiently alleviate distortion caused by volumetric changes in the composite particle 130 associated with charging and discharging. These effects can further improve the durability of the battery.

[0059] Ta may be 200.0 nm or less, 190.0 nm or less, or 189.0 nm or less. With this configuration, the second coating layer 140 is less likely to obstruct the electron conduction path to the composite particle 130, thereby further reducing the battery resistance. Furthermore, even if the ionic conductivity of the second solid electrolyte is low, the battery resistance can be reduced.

[0060] Tq may be 10.0 nm or more, 13.0 nm or more, or 13.5 nm or more. With this configuration, a layer of the second solid electrolyte, in which an increase in resistance is suppressed, is present on the surface of the composite particle 130 with a more appropriate thickness. Furthermore, within the battery electrode, the second coating layer 140 can more efficiently alleviate distortion caused by volume changes in the composite particle 130 associated with charging and discharging. These effects can further improve the durability of the battery.

[0061] Tq may be 65.0 nm or less, 60.0 nm or less, or 59.2 nm or less. With this configuration, the second coating layer 140 is less likely to obstruct the electron conduction path to the composite particle 130, thereby further reducing the battery resistance. Furthermore, even if the ionic conductivity of the second solid electrolyte is low, the battery resistance can be reduced.

[0062] Tm may be 230.0 nm or more, 239.0 nm or more, or 239.4 nm or more. With this configuration, a layer of the second solid electrolyte, in which an increase in resistance is suppressed, is present on the surface of the composite particle 130 with a more appropriate thickness. Furthermore, within the battery electrode, the second coating layer 140 can more efficiently alleviate distortion caused by volume changes in the composite particle 130 associated with charging and discharging. These effects can further improve the durability of the battery.

[0063] Tm may be 720.0 nm or less, 716.0 nm or less, or 715.9 nm or less. With this configuration, the second coating layer 140 is less likely to obstruct the electron conduction path to the composite particle 130, thereby further reducing the battery resistance. Furthermore, even if the ionic conductivity of the second solid electrolyte is low, the battery resistance can be reduced.

[0064] The CV may be 120.0% or less, 112.0% or less, or 111.7% or less. With this configuration, a layer of the second solid electrolyte, which suppresses an increase in resistance, is present on the surface of the composite particle 130 with a more appropriate thickness. Furthermore, within the battery electrode, the second coating layer 140 can more efficiently alleviate strain caused by volume changes in the composite particle 130 associated with charging and discharging. These effects can further improve the durability of the battery.

[0065] The CV may be 65.0% or more, 68.0% or more, or 68.4% or more. With this configuration, the second coating layer 140 is less likely to obstruct the electron conduction path to the composite particle 130, thereby further reducing the battery resistance. Furthermore, even if the ionic conductivity of the second solid electrolyte is low, the battery resistance can be reduced.

[0066] The second solid electrolyte contained in the second coating layer 140 may contain S. With this configuration, the second solid electrolyte has high ionic conductivity. Here, the high ionic conductivity of the second solid electrolyte is, for example, 1.0×10 -4That is, the second solid electrolyte has an ionic conductivity of 1.0×10 -4 The ionic conductivity may be 100 S / cm or more.

[0067] The second solid electrolyte may be crystalline or amorphous.

[0068] The shape of the second solid electrolyte is not particularly limited. The shape of the second solid electrolyte is, for example, needle-like, spherical, film-like, or oval-spherical. The shape of the second solid electrolyte may also be particulate.

[0069] When the second solid electrolyte is, for example, particulate (for example, spherical) in shape, the first solid electrolyte may have a median diameter of 0.01 μm or more and 100 μm or less.

[0070] In the second coating layer 140, the shape of the second solid electrolyte contained in the second coating layer 140 is not particularly limited. For example, at least a portion of the surface of the composite particle 130 may be covered with a thin film formed by the accumulation of fine particles of the second solid electrolyte having a shape such as a plate, needle, sphere, or oval sphere.

[0071] The second coating layer 140 may contain the second solid electrolyte as a main component, or may contain only the second solid electrolyte. In the present disclosure, "main component" refers to the component that is contained in the largest amount by mass. "Containing only the second solid electrolyte" means that, with the exception of inevitable impurities, no materials other than the second solid electrolyte are intentionally added. For example, the raw materials of the second solid electrolyte and by-products generated during the production of the second solid electrolyte are included as inevitable impurities. The mass ratio of the inevitable impurities to the total mass of the second solid electrolyte may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0072] For example, the second coating layer 140 does not contain a conductive additive. With this configuration, the electrode material 1000 of this embodiment can further improve the durability of the battery.

[0073] <Method for Producing First Solid Electrolyte> The first solid electrolyte contained in the coated active material 100 can be produced, for example, by the following method.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] By these methods, the first solid electrolyte having the above-mentioned composition can be obtained.

[0078] 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.

[0079] <Method for Producing Composite Particles> The composite particles 130 in the first embodiment can be produced, for example, by the following method.

[0080] A powder of the active material 110 and a powder of a material for the first coating layer 120 containing the first solid electrolyte are prepared in a predetermined mass ratio. Here, an example of a method for producing composite particles in which the first coating layer 120 is made of the first solid electrolyte will be described.

[0081] For example, the active material 110 is a powder of Li(Ni, Co, Al)O2, and the first solid electrolyte is Li 2.7 Al 0.7 Ti 0.3A powder of F6 is prepared. Mechanical energy is applied to a mixture of these two materials using a dry process to coat at least a portion of the surface of the active material 110 with the first solid electrolyte, forming a first coating layer 120, thereby obtaining composite particles 130. For example, the two materials may be placed in a container and a rotating blade may be used to apply shear force to the two materials. For example, the two materials may be placed in a container and a jet stream may be used to collide the two materials. The powder of the active material 110 and the powder of the first solid electrolyte are mixed in an appropriate ratio.

[0082] 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.

[0083] The composite particles 130 may be manufactured by a dry particle compounding method, which includes applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to a mixture of the active material 110 powder and the first solid electrolyte powder.

[0084] The apparatus used in producing the composite particles 130 is not particularly limited. The apparatus may be an apparatus capable of applying mechanical energy such as impact, compression, and shear to a mixture of the powder of the active material 110 and the powder of the first solid electrolyte. Examples of apparatus capable of applying mechanical energy include a ball mill, a jet mill, a compression shear processing apparatus (particle composite apparatus) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation) and "Nobilta" (manufactured by Hosokawa Micron Corporation), a "Hybridization System (High-Speed ​​Airflow Impact Apparatus)" (manufactured by Nara Machinery Works), and a "Balance Gran" (manufactured by Freund Turbo Corporation).

[0085] "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.

[0086] "Nobilta" is a particle compositing device that uses dry mechanical compositing technology, an advanced form of particle compositing technology, to composite nanoparticles as raw materials. Nobilta produces composite particles 130 by applying mechanical energy of impact, compression, and shear to multiple raw material powders.

[0087] In the Nobilta, a rotor positioned to leave a predetermined gap between itself and the inner wall of a horizontal cylindrical mixing vessel rotates at high speed, forcing the raw material powder through the gap, a process that is repeated multiple times. This applies impact, compression, and shear forces to the mixture, producing composite particles 130 of active material 110 and first solid electrolyte. Conditions such as rotor rotation speed, processing time, and feed amount can be adjusted as needed.

[0088] In the "hybridization system," raw material powder is dispersed in a high-speed airflow while a force, primarily an impact, is applied, thereby producing composite particles 130 of active material 110 and first solid electrolyte.

[0089] The Balance Gran is equipped with a chopper that stirs the powder in a spiral from the outer periphery to the inner periphery, promoting convection, and an agitator scraper that rotates in the opposite direction to the chopper. The action of the chopper and agitator scraper disperses the mixture uniformly, allowing the production of composite particles 130 of the active material 110 and the first solid electrolyte.

[0090] However, processing using the above-mentioned apparatus is not essential. The composite particles may be produced by mixing a powder of the active material 110 and a powder of the first solid electrolyte using a mortar, a mixer, or the like. For example, the first coating layer 120 may be formed by depositing the first solid electrolyte on the surface of the active material 110 using a method such as mechanical mixing using a disperser.

[0091] Alternatively, the composite particles 130 may be manufactured using a wet (liquid phase) coating method or a vapor phase coating method without applying mechanical energy. Examples of the wet (liquid phase) coating method include an air suspension coating method, a spray method, a spray dry coating method, an electrodeposition method, and a dipping method. Examples of the vapor phase coating method include a pulsed laser deposition method, a vacuum evaporation method, a sputtering method, a thermal chemical vapor deposition method, and a plasma chemical vapor deposition method.

[0092] <Method for Producing Coated Active Material> The coated active material 100 in the first embodiment can be produced, for example, by the following method.

[0093] A powder of the composite particles 130 and a powder of a material for the second coating layer 140 containing the second solid electrolyte are prepared in a predetermined mass ratio. Here, an example of a method for manufacturing the coated active material 100 in which the second coating layer 140 is made of the second solid electrolyte will be described.

[0094] By applying mechanical energy to a mixture of two materials, a powder of the composite particle 130 and a powder of the second solid electrolyte, using a dry or wet method, the second solid electrolyte is coated on at least a portion of the surface of the composite particle 130 to form a second coating layer 140, thereby obtaining the coated active material 100. For example, the two materials may be placed in a container and a rotating blade may be used to apply shear force to the two materials. Alternatively, a mixture of the two materials and a solvent may be prepared and then shear force may be applied using a kneading method. The kneading method is a technique in which a solid and a liquid are mixed to knead a solid material that has a clay-like texture rather than a powdery state. When the coated active material 100 is produced using the kneading method, the mixture used for kneading may contain a binder or a dispersant.

[0095] As an apparatus for producing the coated active material 100, for example, when producing by a dry method or a wet method, the apparatus described in the method for producing the composite particles can be used. Alternatively, when producing by a kneading method, an apparatus such as a kneader or a planetary mixer can be used. In order to suppress side reactions of the materials, the production of the coated active material 100 may be carried out in a dry atmosphere or an inert atmosphere.

[0096] To enhance the electronic conductivity of the second coating layer, the second coating layer 140 of the coated active material 100 may contain a conductive additive. However, if the coverage of the composite particle 130 by the second coating layer 140 is appropriately adjusted, the coated active material 100 can maintain sufficient electronic conductivity even if the second coating layer 140 does not contain a conductive additive. When the second coating layer 140 does not contain a conductive additive, the coated active material 100 can be manufactured using a method with high industrial productivity. Examples of conductive additives include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black and ketjen black, conductive fibers such as carbon fiber or metal fiber, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can reduce costs.

[0097] <Another Example of Electrode Material in Embodiment 1> Fig. 2 is a cross-sectional view showing a schematic configuration of another example of the electrode material in Embodiment 1. Electrode material 2000 shown in Fig. 2 includes a particle group of coated active material 100 and third solid electrolyte 210. Like electrode material 1000, electrode material 2000 of the present embodiment is suitable for improving the durability of a battery.

[0098] The third solid electrolyte 210 may have a different composition than the second solid electrolyte.

[0099] The third solid electrolyte 210 may include at least one selected from the group consisting of a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. The third solid electrolyte 210 allows the electrode material 2000 to achieve high ionic conductivity.

[0100] Examples of halide solid electrolytes that can be used include Li3REX6, Li3(Al,Ga,In)X6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, Li(Ta,Nb)OX4, and LiI, where X is at least one selected from the group consisting of Cl, Br, and I, and RE is at least one selected from the group consisting of rare earth elements.

[0101] 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 These can be used in combination with LiX, LiO, MO 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.

[0102] 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.

[0103] 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.

[0104] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0105] The third solid electrolyte 210 may contain S. That is, it may be a sulfide-based solid electrolyte. With this configuration, the third solid electrolyte 210 has high ionic conductivity. Here, with respect to the third solid electrolyte, high ionic conductivity means, for example, 1.0×10 -4 That is, the third solid electrolyte 210 has an ionic conductivity of 1.0×10 S / cm or more. -4 The ionic conductivity may be 100 S / cm or more.

[0106] A solid electrolyte having the same composition as the second solid electrolyte may be included as the third solid electrolyte 210. With this configuration, the electrode material can be produced by a method with high industrial productivity.

[0107] When it is necessary to distinguish between the third solid electrolyte 210 and the second solid electrolyte contained in the second coating layer 140 of the coated active material 100 in the electrode material 2000, i.e., when it is necessary to identify the boundary between the second coating layer 140 of the coated active material 100 and the third solid electrolyte 210, the two can be distinguished, for example, as follows. When the constituent elements of the third solid electrolyte 210 and the second solid electrolyte are different, the two can be distinguished by performing elemental analysis of a cross section of the electrode using a technique such as energy dispersive X-ray spectroscopy (EDS). Furthermore, when the constituent elements of the third solid electrolyte 210 and the second solid electrolyte are similar, it is possible to identify the boundary between the second coating layer 140 of the coated active material 100 and the third solid electrolyte 210 by using an additive (e.g., a conductive additive, a binder, or a dispersant) that is not contained in the second coating layer 140 of the coated active material 100 but is contained in the portion of the electrode material 2000 other than the coated active material 100. In this case, by analyzing the cross section of the electrode using a method such as EDS to determine the presence or absence of elements (e.g., carbon) that are contained in the additive but not contained in the second solid electrolyte, it is possible to distinguish between the second solid electrolyte that does not contain the additive and exists as the second coating layer 140 and the third solid electrolyte 210 that exists in other locations.

[0108] The third solid electrolyte 210 may contain unavoidable impurities such as starting materials, by-products, and decomposition products used in synthesizing the solid electrolyte.

[0109] The shape of the third solid electrolyte 210 is not particularly limited, and may be needle-like, spherical, oval-spherical, etc. The shape of the third solid electrolyte 210 may be particulate.

[0110] When the third solid electrolyte 210 is, for example, particulate (e.g., spherical) in shape, the solid electrolyte may have a median diameter of 0.1 μm or more and 100 μm or less. When the solid electrolyte has a median diameter in this range, the coated active material 100 and the third solid electrolyte 210 are well dispersed in the electrode material 2000.

[0111] The median diameter of the third solid electrolyte 210 may be 10 μm or less. In this case, the dispersion state of the coated active material 100 and the third solid electrolyte 210 in the electrode material 2000 becomes better.

[0112] The median diameter of the third solid electrolyte 210 may be smaller than the median diameter of the coated active material 100. In this case, the coated active material 100 and the third solid electrolyte 210 are better dispersed in the electrode material 2000.

[0113] In the electrode material 2000, the coated active material 100 and the third solid electrolyte 210 may be in contact with each other. In this case, the second coating layer 140 and the third solid electrolyte 210 are in contact with each other.

[0114] The electrode material 2000 may include a plurality of particles of the third solid electrolyte 210 and a plurality of particles of the coated active material 100. In other words, the electrode material 2000 may be a mixture of a powder of the coated active material 100 and a powder of the third solid electrolyte 210.

[0115] In the electrode material 2000, the content of the coated active material 100 and the content of the third solid electrolyte 210 may be the same as or different from each other.

[0116] The electrode material 2000 is obtained by mixing the coated active material 100 and the third solid electrolyte 210. The method for mixing the coated active material 100 and the third solid electrolyte 210 is not particularly limited. The coated active material 100 and the third solid electrolyte 210 may be mixed using a tool such as a mortar, or may be mixed using a mixing device such as a ball mill. After forming the second coating layer 140 of the coated active material 100, the coated active material 100 and the third solid electrolyte 210 may be mixed by subsequently adding the third solid electrolyte to the same manufacturing device.

[0117] <Additives> The electrode material in this embodiment may contain a binder for the purpose of improving adhesion between particles. The binder is used to improve the binding 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 acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polycarbonate, polyethersulfone, polyetherketone, polyetheretherketone, polyphenylene sulfide, hexafluoropolypropylene, styrene-butadiene rubber, carboxymethyl cellulose, 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.

[0118] 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.

[0119] The electrode material in this embodiment may contain a conductive additive for the purpose of increasing electronic conductivity. As the conductive additive, the materials described in the method for producing a coated active material may be used.

[0120] (Embodiment 2) A battery according to embodiment 2 will be described below. Descriptions that overlap with embodiment 1 will be omitted as appropriate.

[0121] The battery according to the second embodiment includes a positive electrode, a separator, and a negative electrode. The separator is located between the positive electrode and the negative electrode. The positive electrode includes the electrode material according to the second embodiment. The electrode material includes a positive electrode active material, such as Li(Ni, Co, Al)O, as the active material 110. This configuration reduces the resistance of the battery.

[0122] The separator portion may be an electrolyte layer containing a solid electrolyte, or may be a separator impregnated with an electrolytic solution.

[0123] FIG. 3 is a cross-sectional view showing a schematic configuration of a battery 3000 according to the second embodiment.

[0124] Battery 3000 includes a positive electrode 310, an electrolyte layer 320, and a negative electrode 330. Electrolyte layer 320 is disposed between positive electrode 310 and negative electrode 330. In battery 3000, electrolyte layer 320 serves as a separator. At least one selected from the group consisting of positive electrode 310 and negative electrode 330 includes the electrode material of embodiment 1 (e.g., electrode material 1000). With this configuration, an increase in the resistance of battery 3000 is suppressed, thereby improving the durability of battery 3000.

[0125] The thickness of each of the positive electrode 310 and the negative electrode 330 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 310 and the negative electrode 330 is 10 μm or more, a sufficient energy density of the battery 3000 can be ensured. When the thickness of the positive electrode 310 and the negative electrode 330 is 500 μm or less, high-power operation of the battery 3000 can be achieved.

[0126] The positive electrode 310 includes, for example, the electrode material in the first embodiment (for example, the electrode material 1000).

[0127] The electrolyte layer 320 is a layer containing an electrolyte material. The electrolyte layer 320 may contain at least one solid electrolyte selected from the group consisting of a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. Details of each solid electrolyte are as described in the first embodiment.

[0128] The thickness of the electrolyte layer 320 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 320 is 1 μm or more, the positive electrode 310 and the negative electrode 330 can be more reliably separated. When the thickness of the electrolyte layer 320 is 300 μm or less, the battery 3000 can operate at high power.

[0129] The negative electrode 330 contains, as a negative electrode active material, a material that has the property of absorbing and releasing metal ions (for example, lithium ions).

[0130] 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.

[0131] The median diameter of the particles of the negative electrode active material may be 0.1 μm or more and 100 μm or less.

[0132] The negative electrode 330 may contain other materials such as a solid electrolyte. As the solid electrolyte, the solid electrolyte described in the first embodiment can be used.

[0133] The battery 3000 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.

[0134] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0135] (Technology 1) An electrode material comprising a particle group of coated active material, wherein the particles of the coated active material comprise: composite particles comprising an active material and a first coating layer coating at least a portion of the surface of the active material, and a second coating layer coating at least a portion of the surface of the composite particles, wherein the first coating layer comprises a first solid electrolyte, and the second coating layer comprises a second solid electrolyte having a different composition from the first solid electrolyte, and the electrode material satisfies at least one selected from the group consisting of the following requirements (i) to (v): (i) A value Tc calculated by calculating a median value of the thickness distribution of the second coating layer for one particle of the coated active material and averaging the median values ​​for the particle group of the coated active material is 1.0 nm or more and 200.0 nm or less. (ii) The value Ta calculated by calculating the average value of the thickness distribution of the second coating layer for one of the particles of the coated active material and averaging the average value for the particle group of the coated active material is 1.0 nm or more and 250.0 nm or less. (iii) The value Tq calculated by calculating the first quartile of the thickness distribution of the second coating layer for one of the particles of the coated active material and averaging the first quartile for the particle group of the coated active material is 1.0 nm or more and 80.0 nm or less. (iv) The value Tm calculated by calculating the maximum value of the thickness distribution of the second coating layer for one of the particles of the coated active material and averaging the maximum value for the particle group of the coated active material is 50.0 nm or more and 1000.0 nm or less. (v) The coefficient of variation of the thickness distribution of the second coating layer is calculated for one of the particles of the coated active material, and the value CV calculated by averaging the coefficient of variation for the particle group of the coated active material is 50.0% or more and 150.0% or less.

[0136] This configuration improves the durability of the battery.

[0137] (Technology 2) The electrode material according to Technology 1, wherein the Tc is 40.0 nm or more.

[0138] This configuration can further improve the durability of the battery.

[0139] (Technology 3) The electrode material according to Technology 1 or 2, wherein the Tc is 140.0 nm or less.

[0140] This configuration reduces the resistance of the battery.

[0141] (Technology 4) The electrode material according to any one of Techniques 1 to 3, wherein the Ta is 60.0 nm or more.

[0142] This configuration can further improve the durability of the battery.

[0143] (Technology 5) The electrode material according to any one of Technologies 1 to 4, wherein the Ta is 200.0 nm or less.

[0144] This configuration reduces the resistance of the battery.

[0145] (Technology 6) The electrode material according to any one of Techniques 1 to 5, wherein the Tq is 10.0 nm or more.

[0146] This configuration can further improve the durability of the battery.

[0147] (Technology 7) The electrode material according to any one of technologies 1 to 6, wherein the Tq is 65.0 nm or less.

[0148] This configuration reduces the resistance of the battery.

[0149] (Technology 8) The electrode material according to any one of Techniques 1 to 7, wherein the Tm is 230.0 nm or more.

[0150] This configuration can further improve the durability of the battery.

[0151] (Technology 9) The electrode material according to any one of Techniques 1 to 8, wherein the Tm is 720.0 nm or less.

[0152] This configuration reduces the resistance of the battery.

[0153] (Technology 10) The electrode material according to any one of Techniques 1 to 9, wherein the CV is 120.0% or less.

[0154] This configuration can further improve the durability of the battery.

[0155] (Technology 11) The electrode material according to any one of Techniques 1 to 10, wherein the CV is 65.0% or more.

[0156] This configuration reduces the resistance of the battery.

[0157] (Technology 12) The electrode material according to any one of Techniques 1 to 11, wherein the active material contains Li, Ni, and O.

[0158] This configuration can increase the energy density of the battery.

[0159] (Technology 13) The electrode material according to any one of Techniques 1 to 12, wherein the first solid electrolyte contains Li, M, and at least one selected from the group consisting of F and O, and the M is at least one element selected from the group consisting of metal elements and semimetal elements other than Li.

[0160] This configuration can suppress an increase in the resistance of the battery.

[0161] (Technology 14) The electrode material according to any one of technologies 1 to 12, wherein the first solid electrolyte contains Li, M1, M2, and F, wherein M1 is at least one selected from the group consisting of Al and Y, and wherein M2 is at least one selected from the group consisting of Ti, Zr, Mg, Ca, Si, and Sn.

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

[0163] (Technology 15) The electrode material according to Technology 14, wherein M1 is Al and M2 is Ti.

[0164] This configuration allows the first solid electrolyte to exhibit even higher ionic conductivity.

[0165] (Technology 16) 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 F6-2z O z ...(1) Here, in the above composition formula (1), M3 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is a valence of M3, and the following conditions are satisfied: 0.1<x<0.9, 0≦y<0.1, 0≦z<0.1, and 0.8<b≦1.2.

[0166] This configuration allows the first solid electrolyte to exhibit high ionic conductivity.

[0167] (Technology 17) The electrode material according to any one of Techniques 1 to 12, wherein the first solid electrolyte contains Li, Nb, and O.

[0168] This configuration allows the first solid electrolyte to exhibit high ionic conductivity.

[0169] (Technology 18) The electrode material according to any one of Techniques 1 to 17, wherein the second solid electrolyte contains S.

[0170] This configuration allows the second solid electrolyte to exhibit high ionic conductivity.

[0171] (Technology 19) A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode and the negative electrode contains the electrode material according to any one of technologies 1 to 18.

[0172] This configuration improves the durability of the battery.

[0173] The present disclosure will be described in more detail below with reference to examples and comparative examples, although the present invention is not limited to the following examples.

[0174] Example 1 Positive Electrode Active Material Li(Ni,Co,Al)O2 (hereinafter referred to as NCA) having a median diameter of 5 μm was used as the positive electrode active material.

[0175] [Preparation of First Solid Electrolyte] In an argon glove box with a dew point of -60°C or less, raw material powders of LiF, TiF4, and AlF3 were weighed in a molar ratio of LiF:TiF4:AlF3 = 2.7:0.3:0.7. These were pulverized and mixed in a mortar to obtain a mixture. The obtained mixed powder was milled at 500 rpm for 12 hours using a planetary ball mill (Fritsch, P-7 model). In this way, a halide solid electrolyte powder was obtained. The obtained halide solid electrolyte contained Li, 2.7 Ti 0.3 Al 0.7 The resulting LTAF was used as the material for the first coating layer (first solid electrolyte) of Example 1.

[0176] [Preparation of Composite Particles] A first coating layer made of LTAF was formed on the surface of the NCA. The first coating layer was formed by compressive shear treatment using a particle compositer (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, in an argon glove box with a dew point of -60°C or less, the NCA and LTAF were weighed out to a mass ratio of NCA:LTAF = 97.3:2.7, and treated under the conditions of a blade clearance of 2 mm, a rotation speed of 6000 rpm, and a treatment time of 50 minutes. In this manner, composite particles composed of the positive electrode active material of Example 1 and a first coating layer formed from the first solid electrolyte were prepared.

[0177] [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.

[0178] [Preparation of Coated Active Material] A second coating layer made of LPS was formed on the surface of the composite particles. The second coating layer was formed by a kneading method using a planetary mixer (Hibismix 2P-1, manufactured by Primix Corporation). Specifically, in an argon glove box with a dew point of -60°C or less, the composite particles and LPS were weighed out so that the mass ratio of composite particles to LPS was 91.6:8.4, and then tetralin, the solvent, was weighed out so that the solids ratio was 78.5%. These were then placed in a planetary mixer and kneaded at a rotation speed of 70 rpm for a processing time of 30 minutes. In this manner, a kneaded composition containing the coated active material of Example 1 was prepared.

[0179] [Preparation of Third Solid Electrolyte] A third solid electrolyte was prepared in the same manner as in the preparation of the second solid electrolyte. That is, LPS was used as the third solid electrolyte of Example 1.

[0180] [Preparation of Positive Electrode Material] In an argon glove box with a dew point of -60°C or less, a kneaded composition containing the coated active material and LPS as a third solid electrolyte were weighed out so that the mass ratio of the coated active material to the LPS was 71.1:28.9. Furthermore, a fibrous conductive additive (VGCF (registered trademark)-H, manufactured by Resonac Packaging Co., Ltd.) was weighed out so that the amount was 1.5 mass% relative to the mass of the NCA. This mixture was dispersed in tetralin, a solvent, using an ultrasonic homogenizer to prepare a slurry. The slurry was applied to a current collector to form a coating film, which was then dried on a hot plate. The positive electrode material of Example 1 was thus prepared.

[0181] Example 2 When preparing the coated active material, the material was kneaded using a planetary mixer at a rotation speed of 70 rpm for a treatment time of 30 minutes, and then further kneaded at a rotation speed of 100 rpm for a treatment time of 2 hours. A positive electrode material of Example 2 was prepared in the same manner as in Example 1.

[0182] Example 3 When preparing the coated active material, the material was kneaded using a planetary mixer at a rotation speed of 70 rpm for a treatment time of 30 minutes, and then further kneaded at a rotation speed of 100 rpm for a treatment time of 4 hours. A positive electrode material of Example 3 was prepared in the same manner as in Example 1.

[0183] Example 4 When preparing the coated active material, the composite particles and LPS were weighed to have a mass ratio of composite particles:LPS = 76.0:24.0. Furthermore, after kneading using a planetary mixer at a rotation speed of 70 rpm and a processing time of 30 minutes, the mixture was further kneaded at a rotation speed of 100 rpm and a processing time of 3 hours. Furthermore, when preparing the positive electrode material, no third solid electrolyte was added. The positive electrode material of Example 4 was prepared in the same manner as in Example 1.

[0184] Example 5 When preparing the coated active material, the composite particles and LPS were weighed out so that the mass ratio of the composite particles to the LPS was 91.0:9.0, and then the solvent tetralin was weighed out so that the solid content was 83.5%. Subsequently, these were placed in a kneader (manufactured by Irie Shokai, PBV-0.1) and kneaded at a rotation speed of 60 rpm for a processing time of 1 hour and 40 minutes. Furthermore, when preparing the positive electrode material, the kneaded composition containing the coated active material and the LPS as the third solid electrolyte were weighed out so that the mass ratio of the coated active material to the LPS was 79.5:20.5. The positive electrode material of Example 5 was prepared in the same manner as in Example 1.

[0185] Example 6: Lithium niobate (LiNbO3) was used as the first solid electrolyte. Lithium ethoxide and niobium pentaethoxide were dissolved in ethanol to prepare a coating solution. Using a tumbling fluidized bed granulation coating device, the coating solution was applied to the surface of the NCA by an air suspension coating method so that the average thickness of the LiNbO3 was 15 nm. The treated powder was placed in an alumina crucible and removed to an air atmosphere. The treated powder was then heat-treated at 220°C for 1 hour in an air atmosphere. The heat-treated powder was then crushed using an agate mortar to obtain the composite particles of Example 5. Furthermore, when preparing the coated active material, the composite particles and LPS were weighed to a mass ratio of composite particles:LPS = 91.0:9.0, and the solvent tetralin was weighed to a solids ratio of 82.0%. Next, these were placed in a kneader (PBV-0.1, manufactured by Irie Shokai Co., Ltd.) and kneaded at a rotation speed of 60 rpm for 1 hour. Furthermore, when preparing the positive electrode material, the kneaded composition containing the coated active material and LPS as the third solid electrolyte were weighed out so that the mass ratio of the coated active material to LPS was 79.5:20.5. The positive electrode material of Example 6 was prepared in the same manner as in Example 1, except for the above.

[0186] Comparative Example 1: After the composite particles were prepared, the second coating layer was not formed. Furthermore, when preparing the positive electrode material, the composite particles and LPS were weighed so that the mass ratio of the composite particles to the LPS serving as the third solid electrolyte was 76.0:24.0 (coated active material:LPS). The positive electrode material of Comparative Example 1 was prepared in the same manner as in Example 1.

[0187] In all examples and comparative examples, the positive electrode materials were prepared by adjusting the content of the positive electrode active material to be the same.

[0188] [Measurement of thickness distribution of the second coating layer of the coated active material] Cross-sectional secondary electron images were taken of 100 particles of each coated active material of the examples using a field emission scanning electron microscope (SU8230, manufactured by Hitachi High-Technologies Corporation). Figure 4 shows a cross-sectional secondary electron image of a representative particle of the coated active material of Examples 1 to 6.

[0189] Subsequently, the thickness distribution of the second coating layer was determined by image analysis of the cross-sectional image. The thickness distribution of the second coating layer was determined in accordance with the method described in Embodiment 1. The results are shown in Table 1.

[0190] Fig. 5 is a graph showing the measurement results of the thickness of the second coating layer 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 film thickness [nm] of the second coating layer at each angle.

[0191] [Fabrication of Battery] The following steps were carried out using each electrode material of the Examples and Comparative Examples.

[0192] 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.

[0193] (Evaluation of Battery Resistance) The battery resistance was measured under the following conditions using each of the batteries of the example and comparative example.

[0194] 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 3.69 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.

[0195] 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.

[0196] 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.

[0197] 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.

[0198]

[0199] <<Discussion>> As shown in Table 1, the batteries using the coated active materials of Examples 1 to 6, which satisfied at least one selected from the group consisting of requirements (i) to (v) described in embodiment 1, had a lower degree of increase in resistance (R2 / R1)×100(%) after the durability test than the battery of Comparative Example 1, and were therefore more durable.

[0200] The coated active materials of Examples 1 to 6 had Tc of 41.3 nm or more and 138.7 nm or less, Ta of 64.4 nm or more and 189.0 nm or less, Tq of 13.5 nm or more and 59.2 nm or less, Tm of 239.4 nm or more and 715.9 nm or less, and CV of 111.7% or less and 68.4% or more.

[0201] As is clear from a comparison between Examples 1 to 6 and Comparative Example 1, controlling the coating form of the second coating layer allowed suppressing an increase in battery resistance regardless of the type of first solid electrolyte. Therefore, it is expected that the same tendency as the results of this example will be observed even when, for example, other halide solid electrolytes or oxide solid electrolytes other than LTAF or LiNbO are used as the coating layer.

[0202] It is presumed that the improvement in battery durability due to the control of the coating morphology of the second coating layer is the effect of appropriately balancing the electron conduction path and the ion conduction path to the active material. Therefore, as the active material, other positive electrode materials such as Li(Ni, Co, Mn)O2, LiCoO2, and Li4Ti5O 12 It is presumed that the same tendency as the results of this example will be observed when negative electrode materials such as Ti2NbO7 and silicon compounds are used.

[0203] The technology of the present disclosure is useful for, for example, all-solid-state lithium-ion secondary batteries.

Claims

1. An electrode material comprising a particle group of coated active material, wherein the particles of the coated active material comprise: composite particles comprising an active material and a first coating layer coating at least a portion of the surface of the active material; and a second coating layer coating at least a portion of the surface of the composite particles, wherein the first coating layer comprises a first solid electrolyte, and the second coating layer comprises a second solid electrolyte having a different composition from the first solid electrolyte, and the electrode material satisfies at least one selected from the group consisting of the following requirements (i) to (v): (i) A value Tc calculated by calculating the median of the thickness distribution of the second coating layer for one particle of the coated active material and averaging the median for the particle group of the coated active material is 1.0 nm or more and 200.0 nm or less. (ii) The value Ta calculated by calculating the average value of the thickness distribution of the second coating layer for one of the particles of the coated active material and averaging the average value for the particle group of the coated active material is 1.0 nm or more and 250.0 nm or less. (iii) The value Tq calculated by calculating the first quartile of the thickness distribution of the second coating layer for one of the particles of the coated active material and averaging the first quartile for the particle group of the coated active material is 1.0 nm or more and 80.0 nm or less. (iv) The value Tm calculated by calculating the maximum value of the thickness distribution of the second coating layer for one of the particles of the coated active material and averaging the maximum value for the particle group of the coated active material is 50.0 nm or more and 1000.0 nm or less. (v) The coefficient of variation of the thickness distribution of the second coating layer is calculated for one of the particles of the coated active material, and the value CV calculated by averaging the coefficient of variation for the particle group of the coated active material is 50.0% or more and 150.0% or less.

2. The electrode material according to claim 1, wherein the Tc is 40.0 nm or more.

3. The electrode material according to claim 1, wherein the Tc is 140.0 nm or less.

4. The electrode material according to claim 1, wherein the Ta is 60.0 nm or more.

5. The electrode material according to claim 1, wherein the Ta is 200.0 nm or less.

6. The electrode material according to claim 1, wherein Tq is 10.0 nm or more.

7. The electrode material according to claim 1, wherein the Tq is 65.0 nm or less.

8. The electrode material according to claim 1, wherein the Tm is 230.0 nm or more.

9. The electrode material according to claim 1, wherein the Tm is 720.0 nm or less.

10. The electrode material according to claim 1, wherein the CV is 120.0% or less.

11. The electrode material according to claim 1, wherein the CV is 65.0% or more.

12. The electrode material according to claim 1, wherein the active material comprises Li, Ni, and O.

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

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

15. The electrode material according to claim 14, wherein M1 is Al and M2 is Ti.

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

2. The electrode material according to claim 1 .

17. The electrode material according to claim 1, wherein the first solid electrolyte contains Li, Nb, and O.

18. The electrode material according to claim 1, wherein the second solid electrolyte contains S.

19. A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein at least one selected from the group consisting of the positive electrode and the negative electrode comprises the electrode material according to any one of claims 1 to 18.

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