Composite active material

Abstract

To provide a composite active material capable of increasing an allowable amount of moisture contained in a composite active material layer and suppressing degradation of an active material due to moisture in the composite active material as compared with the conventional art.SOLUTION: The composite active material for use in a solid-state battery includes: an active material; a first covering layer including a first solid electrolyte containing a fluoride and covering at least a part of a surface of the active material; and a second covering layer including a second solid electrolyte containing a sulfide and a solvent and covering at least a part of the first covering layer, the composite active material having a moisture content of 823 ppm or less at 200°C as measured by a Karl Fischer moisture meter.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to composite active materials. [Background technology]

[0002] Patent Document 1 discloses a technology for reducing resistance by providing a coated active material that includes a positive electrode active material and a coating layer that covers at least a portion of the surface of the positive electrode active material, and the moisture content of the positive electrode active material is more than 0 ppm and less than 250 ppm per unit mass. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2023 / 037775 Summary of the Invention [Problem to be solved by the invention]

[0004] The more moisture there is in the positive electrode active material, the more likely it is that a part of the coating layer will be altered when it is coated with a material containing lithium-containing fluoride, creating a resistive layer at the interface, resulting in a problem of increased output resistance.In addition, when moisture is generally adsorbed onto the positive electrode active material, a resistive layer is also created at the interface, resulting in a problem of increased output resistance.

[0005] In view of the above problems, the present disclosure aims to provide a composite active material that can increase the moisture tolerance contained in the composite active material layer and suppress deterioration of the active material due to moisture compared to conventional composite active materials. [Means for solving the problem]

[0006] The present application discloses a composite active material for use in a solid-state battery, the composite active material comprising: an active material; a first coating layer containing a first solid electrolyte containing a fluoride and coating at least a portion of the surface of the active material; and a second coating layer containing a second solid electrolyte containing a sulfide and a solvent and coating at least a portion of the first coating layer, wherein the composite active material has a moisture content of 823 ppm or less at 200°C as measured with a Karl Fischer moisture meter.

[0007] Here, "the amount of moisture of the composite active material at 200° C. as measured with a Karl Fischer moisture meter" is a value determined as follows using a Karl Fischer apparatus (Karl Fischer moisture meter). In a dry nitrogen gas atmosphere, the inlet of the composite active material (the measurement sample) is heated to 300°C in advance, and the device is stabilized by baking. After the device has stabilized, the temperature of the inlet is set to 200°C. Once the temperature of the inlet reaches 200°C, the background moisture release rate (μg / sec) is measured. The temperature of the inlet is set to 25°C. Once the temperature of the inlet reaches 25°C, the composite active material (measurement sample) is introduced into the inlet. The composite active material (measurement sample) is heated from 25°C to 200°C at a temperature increase rate of 10°C per minute to vaporize the moisture contained in the composite active material (measurement sample). The vaporized moisture is quantified by coulometric titration until the value is below the background moisture release amount, and the moisture content is determined. The moisture content determined at this time is defined as the "moisture content at 200°C."

[0008] The composite active material may have a moisture content of 10 ppm or more at 200° C. as measured by a Karl Fischer moisture meter.

[0009] Furthermore, the amount of water contained in the composite active material may be greater in the second coating layer than in the first coating layer. [Effects of the Invention]

[0010] According to the composite active material of the present disclosure, by providing two different coating layers on the surface of the active material, it is possible to suppress deterioration of the active material due to moisture. This is because the high moisture content of the second coating layer reduces moisture adsorption to the active material, allowing the composite active material as a whole to tolerate more moisture than before. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a conceptual diagram of a composite active material. [Figure 2] FIG. 1 is a diagram conceptually illustrating a layer structure of a solid-state battery. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present disclosure.

[0013] In the context of this disclosure, a "solid-state battery" refers to a battery that uses at least a solid electrolyte as the electrolyte. Thus, a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as the electrolyte. Also, in the context of this disclosure, a solid-state battery may be an all-solid-state battery, i.e., a battery that uses only a solid electrolyte as the electrolyte.

[0014] 1.Composite active material The composite active material is a material that serves as a raw material for an electrode, and has a shape such as a sphere, ellipsoid, flake, or fiber. The composite active material can also have a granular, powdery, or clay-like form. The D50 of the composite active material may be, for example, 1 μm to 30 μm, 3 μm to 20 μm, or 5 μm to 15 μm. Here, "D50" refers to the particle size at which the cumulative frequency of smaller particle sizes reaches 50% in a volume-based particle size distribution. D50 can be measured using a laser diffraction particle size distribution analyzer. 1 conceptually shows a cross-sectional view of a composite active material 10 according to one example (spherical) of the present invention. The composite active material 10 comprises an active material 11, a first coating layer 12, and a second coating layer 13. This will be explained in more detail below.

[0015] 1.1.Active material The active material 11 is a core material of the composite active material 10 and is particulate. The active material may be, for example, secondary particles. The secondary particles are aggregates of primary particles. The D50 of the secondary particles may be, for example, 1 μm to 30 μm, 3 μm to 20 μm, or 5 μm to 15 μm. The average Feret diameter of the primary particles may be, for example, 0.01 μm to 3 μm. The "average Feret diameter" is measured in a two-dimensional image of the particles and is the arithmetic mean value of the maximum Feret diameters of 20 or more particles.

[0016] The active material 11 may have any shape. For example, the active material may be spherical, ellipsoidal, flake-like, fibrous, etc. The active material may be solid particles or hollow particles. Here, a "solid particle" refers to a particle in which the area of ​​the cavity in the center in a cross-sectional image of the particle is less than 30% of the cross-sectional area of ​​the entire particle, while a "hollow particle" refers to a particle in which the area of ​​the cavity in the center in a cross-sectional image of the particle (e.g., a cross-sectional SEM image) is 30% or more of the cross-sectional area of ​​the entire particle.

[0017] The active material 11 may be, for example, a positive electrode active material. The positive electrode active material can cause a positive electrode reaction. The positive electrode active material can contain any component. The positive electrode active material may contain, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, Li(NiCoMnAl)O2, and LiFePO4. For example, "(NiCoMn)" in "Li(NiCoMn)O2" indicates that the sum of the composition ratios in parentheses is 1. As long as the sum is 1, the amount of each component is arbitrary. Li(NiCoMn)O2 can be, for example, LiNi 1 / 3 Co 1 / 3 Mn1 / 3 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, and LiNi 0.9 Co 0.05 Mn 0.05 Li(NiCoAl)O2 may contain at least one selected from the group consisting of LiNi 0.8 Co 0.15 Al 0.05 It may contain O2 etc.

[0018] The positive electrode active material may be represented by, for example, the following formula: Li 1-y Ni x M 1-x O2 0.5≦x≦1 -0.5≦y≦0.5 In the above formula (3), M may contain, for example, at least one selected from the group consisting of Co, Mn, and Al. x may be, for example, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more.

[0019] The positive electrode active material may contain, for example, an additive. The additive may be, for example, a substitutional solid solution atom, an interstitial solid solution atom, or the like. The additive may be an adherent adhering to the surface of the positive electrode active material (primary particles). The adherent may be, for example, an element, an oxide, a carbide, a nitride, a halide, or the like. The addition amount may be, for example, 0.01 to 0.1, 0.02 to 0.08, or 0.04 to 0.06. The addition amount indicates the ratio of the amount of the additive to the amount of the positive electrode active material. The additive may contain, for example, at least one selected from the group consisting of B, C, N, a halogen, Sc, Ti, V, Cu, Zn, Ga, Ge, Se, Sr, Y, Zr, Nb, Mo, In, Sn, W, and a lanthanoid.

[0020] On the other hand, the active material may be a negative electrode active material. The negative electrode active material can cause a negative electrode reaction. The negative electrode active material can contain any component. The negative electrode active material may be, for example, natural graphite, artificial graphite, soft carbon, hard carbon, Si, SiO x (0 < x < 2), Si-based alloy, Sn, SnO x (0 < x < 2), Li, Li-based alloy, and Li4Ti5O 12 and may contain at least one selected from the group consisting of. SiO x (0 < x < 2) may be doped with, for example, Mg or the like. A composite material may be formed by supporting an alloy-based active material (such as Si) on a carbon-based active material (such as graphite).

[0021] 1.2. The first coating layer The first coating layer 12 is a layer that coats at least a portion of the outer periphery of the active material 11 and is a layer made of a first solid electrolyte (fluoride solid electrolyte) made of fluoride. The fluoride solid electrolyte is interposed between the active material 11 and the sulfide solid electrolyte contained in the second coating layer 13, which will be described later. The fluoride solid electrolyte can promote interface formation with the sulfide solid electrolyte even in the presence of a solvent. The fluoride solid electrolyte coats at least a portion of the surface of the active material 11.

[0022] The thickness of the first coating layer 12 may be, for example, 1 nm to 100 nm, or 1 nm to 50 nm. The amount of the fluoride solid electrolyte mixed may be, for example, 1 part by mass to 10 parts by mass, or 2 parts by mass to 3 parts by mass, relative to 100 parts by mass of the active material 11. Here, the "coating thickness" can be measured by the following procedure. A sample is prepared by embedding the active material 11 coated with the first coating layer 12 in a resin material. The sample is cross-sectioned using an ion milling device. For example, a Hitachi High-Technologies Corporation product named "Arblade (registered trademark) 5000" (or an equivalent product) may be used. The cross-section of the sample is observed using a SEM (Scanning Electron Microscope). For example, a Hitachi High-Technologies Corporation product named "SU8030" (or an equivalent product) may be used. The thickness of the fluoride SE is measured in 20 fields of view for each of 10 composite particles. The arithmetic average of the thicknesses at 200 locations in total is considered to be the coating thickness. The thickness of the fluoride solid electrolyte coating may also be referred to as the "buffer layer thickness." Alternatively, the thickness of the coating may be measured in an elemental mapping image obtained by SEM-EDX (Energy Dispersive X-ray Spectrometry), in which an element representative of each portion is selected.

[0023] The first coating layer 12 may cover the entire surface of the active material 11 or may cover a part of the surface. The first coating layer 12 may be distributed in an island shape on the surface of the active material 11. The coating rate may be, for example, 50% or more and 100% or less, 60% or more and 100% or less, 70% or more and 100% or less, 80% or more and 100% or less, or 90% or more and 100% or less. The higher the coating rate, for example, the more the reduction of the initial resistance is expected. The "coating rate" is measured by the following procedure. Similar to the sample for measuring the coating thickness, a cross-sectional sample of the active material 11 coated with the first coating layer 12 is prepared. In the cross-sectional SEM image, the length (L0) of the contour line of the active material is measured. Among the contour lines of the active material 11, the length (L1) of the portion covered by the first coating layer 12 is measured. The percentage of the value obtained by dividing L1 by L0 is the coating rate. For 20 composite particles, the coating rate is measured for each. The arithmetic mean of the 20 coating rates is regarded as the "coating rate". For example, L0 and L1 may be calculated by subjecting the element mapping image by SEM-EDX to image processing.

[0024] The fluoride solid electrolyte (the first solid electrolyte) can have any composition as long as it contains F. The fluoride solid electrolyte may contain, for example, Li and F. The fluoride solid electrolyte may be represented, for example, by the following formula. Li 6-nx M x F6 In this formula, x satisfies 0 < x < 2. M is at least one selected from the group consisting of a semimetal atom and a metal atom other than Li. n indicates the oxidation number of M. In this formula, M may consist of a single atom or may consist of a plurality of types of atoms. When M consists of a plurality of types of atoms, n indicates the weighted average of the oxidation numbers of each atom. For example, when M contains Ti (oxidation number = +4) and Al (oxidation number = +3), the molar ratio of Ti to Al is "Ti / Al = \alpha / 7", and x = 1, n becomes 3.3 according to the formula "n = 0.3×4 + 0.7×3". x may satisfy, for example, 0.1≦x≦1.9, 0.2≦x≦1.8, 0.3≦x≦1.7, 0.4≦x≦1.6, 0.5≦x≦1.5, 0.6≦x≦1.4, 0.7≦x≦1.3, 0.8≦x≦1.2, or 0.9≦x≦1.1. For example, M may include an atom having an oxidation number of +4. For example, M may include an atom having an oxidation number of +3. For example, M may include an atom having an oxidation number of +4 and an atom having an oxidation number of +3. M may include, for example, at least one selected from the group consisting of Ca, Mg, Al, Y, Ti, and Zr. M may include, for example, at least one selected from the group consisting of Al, Y, and Ti. M may include, for example, at least one selected from the group consisting of Al and Ti.

[0025] The fluoride solid electrolyte may be represented, for example, by the following formula: Li 3-x Ti x Al 1-x F6 In the above formula, x may satisfy, for example, 0≦x≦1, 0.1≦x≦0.9, 0.2≦x≦0.8, 0.3≦x≦0.7, or 0.4≦x≦0.6.

[0026] 1.3.Second coating layer The second coating layer 13 is a layer that further coats the active material 11 coated with the first coating layer 12, and is a layer made of a second solid electrolyte (sulfide solid electrolyte) made of a sulfide and a solvent.

[0027] 1.3.1. Sulfide Solid Electrolyte (Second Solid Electrolyte) The sulfide solid electrolyte, together with the solvent, is adhered to the outer surface of the active material 11 coated with the first coating layer 12. The sulfide solid electrolyte is particulate, and its D50 may be, for example, 0.01 μm or more and 1 μm or less, or 0.1 μm or more and 0.9 μm or less. The amount of the sulfide solid electrolyte mixed per 100 parts by mass of the active material 11 may be, for example, 0.1 parts by mass or more and 20 parts by mass or less, or 0.5 parts by mass or more and 15 parts by mass or less.

[0028] The sulfide solid electrolyte can exhibit high ionic conductivity. The sulfide solid electrolyte can have any composition as long as it contains S (sulfur). The sulfide solid electrolyte may contain, for example, Li, P, and S. The sulfide solid electrolyte may further contain, for example, O, Ge, Si, etc. The sulfide solid electrolyte may further contain, for example, a halogen, etc. The sulfide solid electrolyte may further contain, for example, I, Br, etc. The sulfide solid electrolyte may be, for example, a glass ceramic type or an argyrodite type. Sulfides SE include, for example, LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-GeS2-P2S5, Li2S-P2S5, Li4P2S6, and Li7P3S 11 and Li3PS4. For example, "LiI-LiBr-Li3PS4" refers to a sulfide solid electrolyte produced by mixing LiI, LiBr, and Li3PS4 in any molar ratio. For example, the sulfide solid electrolyte may be produced by a mechanochemical method. "Li2S-P2S5" includes Li3PS4. Li3PS4 can be produced, for example, by mixing Li2S and P2S5 in a molar ratio of Li2S / P2S5 = 75 / 25.

[0029] Solvents The solvent is liquid and promotes adhesion between the active material 11 coated with the first coating layer 12 and the sulfide solid electrolyte during kneading. The solvent can function as a dispersion medium in the slurry. The solvent can contain any component, and may include, for example, at least one selected from the group consisting of aromatic hydrocarbons, esters, alcohols, ketones, and lactams. The solvent may include, for example, at least one selected from the group consisting of tetralin (1,2,3,4-tetrahydronaphthalene, THN), butyl butyrate, heptane, and N-methyl-2-pyrrolidone (NMP). Butyl butyrate is expected to be less likely to deteriorate the sulfide solid electrolyte than, for example, NMP, etc. THN is expected to be less likely to deteriorate the sulfide solid electrolyte than butyl butyrate and NMP, etc. The inclusion of THN in the solvent is expected to reduce the initial resistance.

[0030] 1.4.Water content The composite active material contains water in an amount of 823 ppm or less at 200° C. The lower limit is preferably 10 ppm.

[0031] Here, the "moisture content at 200°C" is a value determined using a Karl Fischer apparatus (Karl Fischer moisture meter) as follows. In a dry nitrogen gas atmosphere, the inlet of the composite active material (hereinafter simply referred to as the measurement sample) is heated to 300°C in advance and the device is stabilized by baking. After the device has stabilized, the temperature of the inlet is set to 200°C. Once the temperature of the inlet reaches 200°C, the background moisture release rate (μg / sec) is measured. The temperature of the inlet is set to 25°C. Once the temperature of the inlet reaches 25°C, the measurement sample is introduced into the inlet. The measurement sample is heated from 25°C to 200°C at a rate of 10°C per minute to vaporize the moisture contained in the measurement sample. The vaporized moisture is quantified using coulometric titration until it reaches a value below the background moisture release amount, and the moisture content is determined. The moisture content determined at this time is defined as the "moisture content at 200°C."

[0032] In the composite active material of this embodiment, it is preferable that the second coating layer 13 contains more moisture than the first coating layer 12. In the composite active material of the present disclosure, the first coating layer 12 is formed to efficiently exchange electrons and lithium ions at the active material interface, and in the present disclosure, the second coating layer 13 is present as the outermost layer of the composite active material, which is most susceptible to contact with moisture, so moisture is likely to remain in the second coating layer 13.As a result, it is preferable that the second coating layer 13 contains more moisture than the first coating layer 12. More details are as follows. When the composite active material of the present disclosure and a conventional composite active material without the second coating layer 12 included in the present disclosure were compared after nine minutes of exposure to an environment with a dew point of −5°C, the composite active material of the present disclosure contained less moisture in the first coating layer than the conventional composite active material. This was revealed by EDS line analysis (energy dispersive X-ray spectroscopy) across the active material and the first coating layer (and, if necessary, the second coating layer) in a cross-sectional SEM image (image taken with a scanning electron microscope) of the composite active material. More specifically, the elemental ratio of fluorine to oxygen was calculated at the point where the highest amount of fluorine derived from the fluoride solid electrolyte was detected in the first coating layer. Comparing the composite active material of the present disclosure and the conventional composite active material, the composite active material of the present disclosure contained less moisture in the first coating layer. Note that, here, oxygen refers to oxygen atoms derived from water molecules. Furthermore, the output resistance of batteries using these as positive electrodes was also lower for the composite active material of the present disclosure than for the conventional composite active material. In the composite active material of the present disclosure, moisture contained in the first coating layer 12 and the active material 11 can transfer to the second coating layer 13. The moisture in the second coating layer 13 may be removed by transferring to a solvent that comes into contact with the layer in the paste during electrode production, or may be removed during drying after the electrode is formed.

[0033] 1.5. Effects etc. The composite active material of the present disclosure can improve the moisture resistance of the composite active material 10 (the property of resisting moisture-induced degradation of the active material and increased reaction resistance). The composite active material of the present disclosure remains moisture-resistant even when it retains a relatively high moisture content. This is thought to be because moisture can be preferentially contained in the second solid electrolyte or solvent of the second coating layer 13, thereby suppressing deterioration of the first coating layer 12 and the active material 11. Furthermore, moisture originally contained in the active material and the first coating layer can also migrate to the second coating layer. As will be shown later in the Examples, it was also confirmed that a water content greater than the reference value actually had the effect of reducing the rate of increase in resistance.

[0034] 2. Preparation of composite active material One example of a method for producing a composite active material includes the following steps, each of which will be described below. 2.1. Process for forming the first coating layer The first coating layer 12 can be formed on the active material 11 by any method. For example, a dry mechanochemical method can be used. More specifically, the active material 11 and the fluoride solid electrolyte can be mixed using a particle compounding device. An example of a particle compounding device is the "Nobilta NOB-MINI" manufactured by Hosokawa Micron Corporation. However, any mixing device, granulating device, etc. can be used as long as it is capable of compounding particles.

[0035] 2.2.Pre-mixing process Prior to the pre-kneading step, a material to become the second coating layer 13 is prepared. Specifically, for example, a dispersion liquid may be prepared by dispersing a sulfide solid electrolyte, which is a powder, in a liquid solvent. The device for dispersion is not particularly limited, but an ultrasonic homogenizer or the like may be used.

[0036] In the pre-kneading step, kneading and solvent addition are alternately performed two or more times. The pre-kneading is performed by stirring the active material 11 (powder) coated with the first coating layer 12 obtained in the first coating layer formation step and the dispersion liquid for the second coating layer 13 prepared as described above in a kneading device (e.g., a planetary mixer). This causes the mixture to become viscous. For example, the mixture may be stirred at a rotation speed of 50 rpm to 100 rpm for one minute to one hour. Note that the mixing conditions (rotation speed, mixing time, etc.) may vary depending on, for example, the powder properties, the specifications of the device, etc. By alternately repeating kneading and solvent addition, the second coating layer 13 can be coated more densely.

[0037] Before the kneading, the first coating layer 12 is covered with the solvent of the second coating layer 13, and the sulfide solid electrolyte of the second coating layer 13 is dispersed in the solvent. In this state, the active material 11 coated with the first coating layer 12 tends to absorb the solvent less easily. In contrast, by performing the kneading, the surface properties of the active material 11 coated with the first coating layer 12 change, promoting the absorption of the solvent into the solid components and evaporating some of the solvent. This results in a shortage of solvent required for the kneading. By adding solvent to make up for this shortage and performing the kneading, the absorption of the solvent further progresses. By repeating this kneading and addition of solvent, a dense coating layer of sulfide solid electrolyte is gradually formed, which becomes second coating layer 13.

[0038] 2.3. Main kneading process In the main kneading step, kneading is carried out following the pre-kneading step. In the main kneading step, solid kneading is also carried out following the pre-kneading step, but no solvent is added. Furthermore, in the main kneading step, kneading is carried out for a longer period of time at a faster rotation speed than in the pre-kneading step. Specifically, for example, the mixture may be stirred at a rotation speed of 100 rpm or more and 200 rpm or less for 2 hours or more and 6 hours or less. In addition, in the main kneading step, it is preferable to scrape off the material adhering to the edges of the apparatus as needed or periodically and check the condition while carrying out the kneading. As a result, the active material 11 coated with the first coating layer 12 and the second coating layer 13 is obtained.

[0039] 2.4. Moisture adjustment process The moisture content of the active material 11 coated with the first coating layer 12 and the second coating layer 13 obtained in this kneading step is adjusted so that the moisture content at 200°C (the meaning of this moisture content is as described above) is 823 ppm or less. The moisture content can be adjusted, for example, by placing the active material after this kneading in a glove box with a controlled dew point of -5°C and exposing it to moisture to adsorb it. The moisture content is adjusted by an appropriate exposure time determined in advance by testing. In this way, the composite active material of the present disclosure is obtained.

[0040] 3. Electrode Fabrication An electrode can be manufactured from the prepared composite active material 10. Specifically, for example, a slurry containing the composite active material 10 is formed, and the slurry is applied to the surface of a substrate and dried to manufacture an electrode.

[0041] 3.1.Slurry For example, a slurry is formed by mixing the composite active material 10, an electron conductor, an ion conductor, a binder, and a solvent. At this time, the mixture may be subjected to a dispersion treatment using an ultrasonic homogenizer or the like. The solid content concentration of the slurry may be 50% by mass or more and 70% by mass.

[0042] The electronic conductive material can form an electronic conduction path within the electrode. The amount of the electronic conductive material can be any amount. The amount of the electronic conductive material can be, for example, 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the active material. The electronic conductive material can contain any component. The electronic conductive material can include, for example, at least one selected from the group consisting of carbon black (CB), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF). The CB can include, for example, at least one selected from the group consisting of acetylene black (AB), Ketjen Black (registered trademark), and furnace black.

[0043] The ion conductive material can form an ion conduction path within the electrode. The ion conductive material may be particulate. The ion conductive material may have a D50 of, for example, 0.01 μm to 1 μm, 0.01 μm to 0.95 μm, or 0.1 μm to 0.9 μm. The amount of the ion conductive material to be added is arbitrary. For example, the amount of the ion conductive material to be added may be 1 part by volume to 200 parts by volume, 50 parts by volume to 150 parts by volume, or 50 parts by volume to 100 parts by volume, per 100 parts by volume of the active material. The ion conductive material may contain, for example, a sulfide SE, a fluoride SE, or the like. The sulfide SE and fluoride SE contained in the ion conductive material may be the same or different from the sulfide SE and fluoride SE contained in the electrode material.

[0044] The binder can bind solid materials together. The amount of binder may be, for example, 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of active material. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), styrene butadiene rubber (SBR), butadiene rubber (BR), and polytetrafluoroethylene (PTFE).

[0045] 3.2. Coating In this manufacturing method, any coating device can be used. For example, a die coater, a roll coater, or the like can be used. The slurry can be coated on the surface of a substrate. The substrate may be conductive. The substrate may function as a current collector. The substrate may be, for example, in the form of a sheet or a mesh. The substrate may have a thickness of, for example, 5 μm or more and 50 μm or less. The substrate may include, for example, a metal foil, a metal mesh, a porous metal body, or the like. The substrate may include, for example, at least one selected from the group consisting of Al, Cu, Ni, Cr, Ti, and Fe. The substrate may include, for example, Al foil, Al alloy foil, Ni foil, Cu foil, Cu alloy foil, Ti foil, stainless steel foil, or the like. The surface of the metal foil may be coated with a carbon layer. The carbon layer may include, for example, a conductive carbon material (e.g., AB, etc.).

[0046] The active material layer is formed on the surface of the substrate by drying the slurry. In this production method, any drying device can be used. For example, a hot plate, a hot air dryer, an infrared dryer, etc. may be used.

[0047] After drying the slurry, the electrode may be subjected to press working. For example, cold press working may be performed, or hot press working may be performed. In this manufacturing method, any press device may be used. For example, a roll press device or the like may be used. When hot press working is performed, the press temperature may be adjusted depending on, for example, the type of binder. The press temperature may be, for example, 80°C or higher and 180°C or lower. After press working, the thickness of the active material layer may be, for example, 10 μm or higher and 200 μm or lower. After press working, the density of the active material layer may be, for example, 2 g / cm 3 More than 4g / cm 3 It may be the following:

[0048] 4. Manufacturing of all-solid-state batteries 2 is a conceptual diagram showing the layer structure of one power generating element 20 included in an all-solid-state battery. Note that, although the manufacture of an all-solid-state battery will be described here as an example, as described above, the present disclosure is directed to a battery that uses at least a solid electrolyte as the electrolyte, and may also be a battery that uses a combination of a solid electrolyte and a liquid electrolyte as the electrolyte. The power generating element 20 can be formed by laminating a positive electrode 21, a separator layer 22, and a negative electrode 23. At least one of the positive electrode 21 and the negative electrode 23 is the electrode obtained above. The separator layer 22 is disposed between the positive electrode 21 and the negative electrode 23. The separator layer 22 may contain, for example, an ion conductive material and a binder. The separator layer 22 can be formed, for example, by applying a slurry to the surface of at least one of the positive electrode 21 and the negative electrode 23. After the power generating element 20 is formed, the power generating element 20 may be subjected to hot pressing. It is expected that the power generating element 20 will become dense by hot pressing. For example, a lead tab, an external terminal, or the like may be connected to the power generating element 20. The power generating element 20 is housed in an exterior body (not shown). The exterior body may be sealed. By housing the power generating element 20 in the exterior body, an all-solid-state battery can be completed. The exterior body may have any shape. For example, the exterior body may be a pouch made of a metal foil laminated film. For example, the exterior body may be a metal case. For example, the exterior body may contain Al or the like. The exterior body may house a single power generating element 20, or may house multiple power generating elements 20. The multiple power generating elements 20 may form a series circuit or a parallel circuit. [Example]

[0049] 5. Working Example In the examples, moisture was adsorbed into the prepared composite active material to examine the relationship between the moisture content and the increase in resistance. Specifically, the following is the result. However, the present disclosure is not limited to the examples.

[0050] 5.1. Preparation of composite active material The active material used was Li(NiCoAl)O2, hereafter abbreviated as "NCA." A fluoride solid electrolyte was synthesized by mixing LiF, TiF4, and AlF3 in a planetary ball mill. 2.7 Ti 0.3 Al 0.7 The composition of the compound was F6. 2.7 Ti 0.3 Al 0.7 "F6" is abbreviated as "LTAF." The particle compositing device used was the "Nobilta NOB-MINI" (manufactured by Hosokawa Micron Corporation). 48.7 parts by mass of NCA and 1.3 parts by mass of LTAF were subjected to a compositing process in the particle compositing device to form an active material coated with a first coating layer. The operating conditions of the device were: power 12 W per 1 g of material, rotation speed 6000 rpm, and processing time 30 minutes.

[0051] Next, for the second coating layer, Li2S-P2S5 (glass ceramics, hereafter referred to as "LPS") was prepared as a sulfide solid electrolyte and THN was prepared as a solvent. The following procedures were then carried out in an environment where the dew point temperature was controlled to -70°C or below.

[0052] The subsequent operations were carried out in an environment where the dew point temperature was controlled to be below -70° C. An ultrasonic homogenizer was prepared as a dispersion device, and a dispersion liquid was prepared by dispersing 98.4 parts by mass of the sulfide solid electrolyte in 229.6 parts by mass of a solvent.

[0053] A planetary mixer was prepared as a kneading device, and 1000 parts by mass of the active material coated with the first coating layer was supplied to the kneading device, followed by the dispersion liquid obtained above.

[0054] By alternately repeating "kneading" and "addition of solvent" in the order of (1) to (7) below, a composite active material was obtained, which was an active material coated with a first coating layer and a second coating layer.

[0055] (1) Stiff kneading: Rotation speed = 70 rpm, Time = 10 minutes (2) Addition of solvent: THN (34 parts by mass) (3) Stiff kneading: Rotation speed = 100 rpm, Time = 10 minutes (4) Addition of solvent: THN (37 parts by mass) (5) Stiff kneading: rotation speed = 100 rpm, time = 10 minutes (6) Addition of solvent: THN (23 parts by mass) (7) Stiff kneading: rotation speed = 100 rpm, time = 4 hours

[0056] Next, moisture was adsorbed onto the composite active material obtained for testing, and a plurality of composite active materials with different moisture contents at 200°C (the meaning of the moisture content is as described above) were produced. The specific moisture contents are shown in Table 1. The moisture content was adjusted by placing the composite active material in a glove box with a controlled dew point of -5°C and exposing the composite active material to absorb moisture, and the moisture content was adjusted by changing the exposure time. The specific time is also shown in Table 1.

[0057] Test Examples 1 to 7 were as described above, but Test Example 8 was an example in which the active material was coated only with the first coating layer without providing the second coating layer.

[0058] 5.2. Fabrication of all-solid-state batteries To test the battery performance of each composite active material, all-solid-state batteries were fabricated as follows. The composite active material, ionic conductor (LPS), and electronic conductor (AB+VGCF) were dispersed in a solvent (THN) using an ultrasonic homogenizer to prepare a slurry. The slurry was applied to the surface of a substrate and dried to produce a positive electrode.

[0059] It also contains a positive electrode and a negative electrode active material, Li4Ti5O 12 We then manufactured an all-solid-state battery enclosed in an exterior body made of aluminum laminate film.

[0060] 5.3. Battery Evaluation The all-solid-state battery was stored at 80% SOC (State of Charge) for 2 weeks in a 60°C atmosphere. The SOC (State of Charge) was then adjusted to 60% and the all-solid-state battery was discharged for 10 seconds at a 32C hourly rate. The discharge resistance (DC resistance) was calculated from the voltage drop and current during discharge. The discharge resistance was calculated after 2 seconds had elapsed. Furthermore, the all-solid-state battery was charged for 5 seconds at a time rate of 60 C. The initial charging resistance (DC resistance) was calculated from the voltage rise and current during charging. The charging resistance was calculated at each time point after 5 seconds had elapsed.

[0061] The discharge resistance and charge resistance in each example were expressed as a ratio (percentage) based on the discharge resistance and charge resistance in Example 1 (exposure time 0 minutes). Specifically, the resistance value in Test Example i was R i When [(R i The increase rate was calculated as [(-R1) / R1) × 100%. The results are shown in Table 1.

[0062] [Table 1]

[0063] When the composite active material of the test example according to the embodiment is used, it was found that, if the moisture content at 200°C at which the resistance increase rate during discharge becomes 0% is 823 ppm or less, a moisture content greater than the standard can reduce the resistance increase rate. Furthermore, in Test Example 8, which did not have a second coating layer, the moisture content was the same as in Test Example 5, but the resistance increase rate was higher. [Explanation of symbols]

[0064] 10... composite active material, 11... active material, 12... first coating layer, 13... second coating layer, 20... power generating element, 21... positive electrode, 22... separator layer, 23... negative electrode

Claims

1. A composite active material for use in a solid-state battery, An active material; a first coating layer containing a first solid electrolyte containing a fluoride and coating at least a portion of the surface of the active material; a second coating layer containing a second solid electrolyte containing a sulfide and a solvent, and coating at least a portion of the first coating layer; The composite active material has a moisture content of 823 ppm or less at 200°C as measured by a Karl Fischer moisture meter. Composite active material.

2. 2. The composite active material according to claim 1, wherein the composite active material has a moisture content of 10 ppm or more at 200°C as measured by a Karl Fischer moisture meter.

3. The composite active material according to claim 1 , wherein the second coating layer contains more water than the first coating layer.

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