Composite active material

Abstract

Provided is a composite active material in which the allowable amount of moisture contained in a composite active material layer can be increased, and deterioration of the active material of the composite active material with respect to moisture can be suppressed compared to conventional active materials. This composite active material is used in a solid-state battery and comprises: an active material; a first coating layer containing a first solid electrolyte containing a fluoride, the first coating layer coating at least a portion of a surface of the active material; and a second coating layer that contains a second solid electrolyte containing a sulfide and a solvent, and that coats at least a portion of the first coating layer, the composite active material having a water content of 823 ppm or less at 200 DEG C as measured by a Karl Fischer moisture meter.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a composite active material. BACKGROUND

[0002] A technique for reducing the resistance by forming a coated active material having a positive electrode active material and a coating layer that coats at least a part of the surface of the positive electrode active material, the amount of moisture of the positive electrode active material per unit mass being more than 0 ppm and less than 250 ppm is disclosed in Patent Literature 1. PRIOR ART DOCUMENTS PATENT LITERATURE

[0003] Patent Literature 1: WO2023 / 037775 SUMMARY PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] The more the moisture of the positive electrode active material, the more a part of the coating layer deteriorates when coated with a material containing lithium-containing fluoride, and a resistance layer is generated at the interface, so there is a problem that the output resistance becomes large. In addition, when moisture is adsorbed to the positive electrode active material, a resistance layer is also generated at the interface, so there is a problem that the output resistance becomes large.

[0005] In view of the above problems, the present disclosure aims to provide a composite active material that can increase the allowable amount of moisture contained in the composite active material layer and suppress the deterioration of the active material of the composite active material with respect to moisture compared to the past. TECHNICAL MEANS FOR SOLVING THE PROBLEMS

[0006] The present application discloses a composite active material for a solid-state battery, the composite active material comprising: an active material; a first coating layer containing a first solid electrolyte containing a fluoride, coating at least a part of the surface of the active material; and a second coating layer containing a second solid electrolyte containing a sulfide and a solvent, coating at least a part of the first coating layer, the amount of moisture of the composite active material at 200°C in a measurement using a Karl Fischer moisture meter being 823 ppm or less.

[0007] Here, the "amount of moisture of the composite active material at 200°C in a measurement using a Karl Fischer moisture meter" is a value obtained using a Karl Fischer device (Karl Fischer moisture meter) as follows. Under a dry nitrogen atmosphere, the introduction portion of the composite active material as a measurement sample is preheated to 300°C, and the device is stabilized by air firing. After the device is stabilized, the temperature of the introduction portion is set to 200°C. When the temperature of the introduction portion becomes 200°C, the amount of moisture emission (μg / sec) of the background is measured. The temperature of the introduction section was set to 25°C. After the temperature of the introduction section became 25°C, the composite active material as a measurement sample was introduced into the introduction section. The composite active material as a measurement sample was heated from 25°C to 200°C at a temperature increase rate of 10°C per minute, and the moisture contained in the composite active material as a measurement sample was vaporized. The amount of moisture after vaporization was quantified by coulometric titration to a value below the moisture emission amount at which the background became constant, and the amount of moisture was calculated. The amount of moisture quantified at this time was defined as the "amount of moisture at 200°C".

[0008] In addition, it can also be that the amount of moisture at 200°C of the composite active material is 10 ppm or more in a measurement using a Karl Fischer moisture meter.

[0009] In addition, it can also be that the amount of moisture contained in the composite active material is contained more in the second coating layer than in the first coating layer. EFFECT 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 the degradation of the active material caused by moisture. This is because, by containing more moisture in the second coating layer, it is possible to reduce the adsorption of moisture to the active material, and the composite active material as a whole can tolerate more moisture than before. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0013] In the present disclosure, "solid-state battery" means a battery that uses at least a solid electrolyte as an electrolyte. Therefore, the solid-state battery can also use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. In addition, in the present disclosure, the solid-state battery can also be a full solid-state battery, i.e., a battery that uses only a solid electrolyte as an electrolyte.

[0014] 1. Composite active material The composite active material is a material that becomes a raw material for an electrode, and has a shape such as a spherical shape, an ellipsoidal shape, a flaky shape, or a fibrous shape. As a form, it can be formed into a granular shape, a powder shape, or a clay shape, etc. The D50 of the composite active material may, for example, be 1 μm or more and 30 μm or less, 3 μm or more and 20 μm or less, or 5 μm or more and 15 μm or less. Here, "D50" means the particle diameter at which the cumulative frequency of the frequency distribution on a volume basis reaches 50% from the smaller particle diameter side. The D50 can be measured by a laser diffraction type particle size distribution measuring device. Figure 1 FIG. 1 is a conceptual diagram schematically showing the configuration of a composite active material 10 according to one embodiment in cross section. The composite active material 10 is configured to have an active material 11, a first coating layer 12, and a second coating layer 13. These will be described in more detail below.

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

[0016] The active material 11 can have any shape. The active material may, for example, be spherical, ellipsoidal, flaky, or fibrous, or the like. The active material can be either a solid particle or a hollow particle. Here, a "solid particle" means a particle in which the area of the hollow in the center portion in a cross-sectional image of the particle is less than 30% of the cross-sectional area of the entire particle. On the other hand, a "hollow particle" means a particle in which the area of the hollow in the center portion in a cross-sectional image (e.g., a cross-sectional SEM image, or the like) of the particle is 30% or more of the cross-sectional area of the entire particle.

[0017] The active material 11 may, for example, be a positive electrode active material. The positive electrode active material can undergo a positive electrode reaction. The positive electrode active material can include any component. The positive electrode active material may, for example, include 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" means that the total of the composition ratios within the parentheses is 1. The amounts of the respective components are arbitrary as long as the total is 1. Li(NiCoMn)O2 may, for example, include LiNiO2, LiCoO2, and LiMnO2 in amounts such that the total of the composition ratios of Ni, Co, and Mn is 1. Li(NiCoAl)O2 may, for example, include LiNiO2, LiCoO2, and LiAlO2 in amounts such that the total of the composition ratios of Ni, Co, and Al is 1. Li(NiCoMnAl)O2 may, for example, include LiNiO2, LiCoO2, LiMnO2, and LiAlO2 in amounts such that the total of the composition ratios of Ni, Co, Mn, and Al is 1. 1 / 3 Co 1 / 3 Mn 1 / 3O2, 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 O2 0.8 Co 0.15 Al 0.05 O2, and the like.

[0018] The positive electrode active material may, for example, be represented by 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, for example, include at least one selected from the group consisting of Co, Mn, and Al. x may, for example, be 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more.

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

[0020] On the other hand, the active material can also be a negative electrode active material. The negative electrode active material can undergo a negative electrode reaction. The negative electrode active material can contain any component. The negative electrode active material may, for example, contain at least one selected from the group consisting of 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 consisting of natural graphite, artificial graphite, soft carbon, hard carbon, Si, SiO x (0 < x < 2) may, for example, be doped with Mg or the like. The alloy-based active material (for example, Si or the like) can form a composite material by being supported on a carbon-based active material (for example, graphite or the like).

[0021] 1.2. First Coating Layer The first coating layer 12 is a layer that coats at least a part of the outer periphery of the active material 11, and is a layer based on a first solid electrolyte composed of a fluoride (fluoride solid electrolyte). The fluoride solid electrolyte is interposed between the active material 11 and a sulfide solid electrolyte contained in the second coating layer 13 described later. The fluoride solid electrolyte can also promote the formation of an interface with the sulfide solid electrolyte in the presence of a solvent. The fluoride solid electrolyte coats at least a part of the surface of the active material 11.

[0022] The thickness of the first coating layer 12 may, for example, be 1 nm or more and 100 nm or less, or 1 nm or more and 50 nm or less. The amount of the fluoride solid electrolyte may, for example, be 1 part by mass or more and 10 parts by mass or less, or 2 parts by mass or more and 3 parts by mass or less, with respect to 100 parts by mass of the active material 11. Here, the "thickness of the coating" can be measured by the following procedure. A test sample is prepared by embedding the active material 11 coated with the first coating layer 12 in a resin material. Cross-section processing is performed on the test sample using an ion milling device. For example, a product of Hitachi High-Technologies Corporation, product name "Arblade (registered trademark) 5000" (or an equivalent product) can be used. The cross-section of the test sample is observed using an SEM (Scanning Electron Microscope). For example, a product of Hitachi High-Technologies Corporation, product name "SU8030" (or an equivalent product) can be used. The thickness of the fluoride SE is measured at 20 fields of view for 10 composite particles, respectively. The arithmetic mean of the thicknesses of 200 is regarded as the thickness of the coating. Further, the thickness of the coating based on the fluoride solid electrolyte can also be referred to as the "thickness of the buffer layer". Alternatively, the thickness of the coating can also be measured in an elemental mapping image based on SEM-EDX (Energy Dispersive X-ray Spectrometry). In the elemental mapping image, an element representing each portion is selected.

[0023] The first coating layer 12 can coat all of the surface of the active material 11, or can coat a part of the surface. The first coating layer 12 can be distributed in an island shape on the surface of the active material 11. The coating rate can 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, the more, for example, a decrease in the initial resistance can be expected. The "coating rate" is measured by the following procedure. As with the test sample for measuring the thickness of the coating, a cross-sectional test 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 outline of the active material is measured. The length (L1) of the portion of the outline of the active material 11 coated with the first coating layer 12 is measured. The percentage of the value obtained by dividing L1 by L0 is the coating rate. The coating rate is measured for 20 composite particles, respectively. The arithmetic mean of the 20 coating rates is regarded as the "coating rate". For example, L0 and L1 can be calculated by performing image processing on the elemental mapping image based on SEM-EDX.

[0024] The fluoride solid electrolyte (first solid electrolyte) can have any composition as long as it contains F. The fluoride solid electrolyte can contain Li and F, for example. The fluoride solid electrolyte can be represented by the following formula, for example. Li 6-nx Mx F6 In this formula, x satisfies 0 < x < 2. M is at least one selected from the group consisting of a semi-metal atom and a metal atom other than Li. n represents the oxidation number of M. In this formula, M can be composed of a single atom or a plurality of atoms. In the case where M is composed of a plurality of atoms, n represents a weighted average of the oxidation numbers of the respective atoms. For example, in the case where M includes Ti (oxidation number = +4) and Al (oxidation number = +3), the molar ratio of Ti to Al is "Ti / Al = 3 / 7", and x = 1, n is 3.3 according to the formula "n = 0.3 x 4 + 0.7 x 3". x may, for example, satisfy 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. M may, for example, include an atom having an oxidation number of +4. M may, for example, include an atom having an oxidation number of +3. M may, for example, include an atom having an oxidation number of +4 and an atom having an oxidation number of +3. M may, for example, include at least one selected from the group consisting of Ca, Mg, Al, Y, Ti, and Zr. M may, for example, include at least one selected from the group consisting of Al, Y, and Ti. M may, for example, include at least one selected from the group consisting of Al and Ti.

[0025] The fluoride solid electrolyte may, for example, be represented by the following formula. Li 3-x Ti x Al 1-x F6 In the above formula, x may, for example, satisfy 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 by the first coating layer 12, and is a layer based on a second solid electrolyte composed of a sulfide (sulfide solid electrolyte) and a solvent.

[0027] 1.3.1. Sulfide solid electrolyte (second solid electrolyte) The sulfide solid electrolyte adheres to the outer surface of the active material 11 coated by the first coating layer 12 together with a solvent. The sulfide solid electrolyte is in a particulate form, and the D50 thereof can 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 blending amount of the sulfide solid electrolyte can 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, with respect to 100 parts by mass of the active material 11.

[0028] The sulfide solid electrolyte can exhibit high ion conductivity. The sulfide solid electrolyte can have an arbitrary composition as long as it contains S (sulfur). The sulfide solid electrolyte can contain, for example, Li, P, and S. The sulfide solid electrolyte can further contain, for example, O, Ge, Si, or the like. The sulfide solid electrolyte can further contain, for example, halogen or the like. The sulfide solid electrolyte can further contain, for example, I, Br, or the like. The sulfide solid electrolyte can be, for example, a glass-ceramic type or a lechatelierite type. The sulfide SE can contain, for example, at least one selected from the group consisting of 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, Li7P3S 11 For example, “LiI-LiBr-Li3PS4” indicates a sulfide solid electrolyte generated by mixing LiI, LiBr, and Li3PS4 in an arbitrary molar ratio. The sulfide solid electrolyte can be generated, for example, by a mechanochemical method. “Li2S-P2S5” contains Li3PS4. Li3PS4 can be generated, for example, by mixing Li2S and P2S5 at “Li2S / P2S5 = 75 / 25 (molar ratio)”.

[0029] 1.3.2. Solvent The solvent is a liquid and promotes the adhesion of the active material 11 coated by the first coating layer 12 to the sulfide solid electrolyte at the time of thickening. The solvent can function as a dispersion medium in the slurry. The solvent can contain an arbitrary component, and can contain, for example, at least one selected from the group consisting of aromatic hydrocarbons, esters, alcohols, ketones, and lactams. The solvent can contain, for example, at least one selected from the group consisting of tetrahydronaphthalene (1,2,3,4-tetrahydronaphthalene, THN), butyl butyrate, heptane, and N-methyl-2-pyrrolidone (NMP). ​Compared to substances such as NMP, butyl butyrate is expected to make sulfide solid electrolytes less prone to degradation. THN, compared to butyl butyrate and NMP, is also expected to make sulfide solid electrolytes less prone to degradation. By including THN in the solvent, a reduction in initial resistance can be expected.

[0030] 1.4. Moisture Content Regarding the water content in the composite active material, the water content at 200°C is 823 ppm or less. Furthermore, the lower limit is preferably 10 ppm.

[0031] Here, the "moisture content at 200°C" is the value obtained using a Karl Fischer apparatus (Karl Fischer moisture meter) as follows. Under a dry nitrogen atmosphere, the inlet of the composite active substance (hereinafter referred to as the test sample) was preheated to 300°C, and the apparatus was stabilized by dry firing. After stabilization, the temperature of the inlet was set to 200°C. When the temperature of the inlet reached 200°C, the background moisture release (μg / second) was measured. The temperature of the inlet section is set to 25°C. Once the temperature of the inlet section reaches 25°C, the test sample is introduced into the inlet section. The test sample is heated from 25°C to 200°C at a heating rate of 10°C per minute, causing the water contained in the test sample to vaporize. The vaporized water is quantified by electrostatic titration to a value below the background water release, and the water content is determined. The water content quantified at this point is defined as "the water content at 200°C".

[0032] In addition, in this method, the second coating layer 13 preferably contains more moisture than the first coating layer 12 in the composite active material. In the composite active material disclosed herein, a first coating layer 12 is formed to efficiently transfer electrons and lithium ions at the interface of the active material. In this disclosure, a second coating layer 13 exists on the outermost layer of the composite active material that is easily in contact with moisture. Therefore, moisture is easily retained in the second coating layer 13. Thus, it is preferable that the second coating layer 13 contains more moisture than the first coating layer 12. Details are as follows. In a case where the composite active material of the present disclosure and the composite active material not provided with the second coating layer 12 included in the present disclosure (a conventional composite active material) are exposed to an environment having a dew point of -5°C for 9 minutes, the composite active material of the present disclosure has less moisture present in the first coating layer than the conventional composite active material. This is made clear by performing EDS line analysis (line analysis based on energy dispersive X-ray spectroscopy) in a cross-section SEM image (image based on a scanning electron microscope) of the composite active material in a manner that traverses the active material, the first coating layer (and the second coating layer as necessary). More specifically, for the first coating layer, the elemental ratio of fluorine to oxygen is found at a point where fluorine originating from the fluoride solid electrolyte is most detected, and the composite active material of the present disclosure is compared with the conventional composite active material, and the moisture in the first coating layer of the composite active material of the present disclosure is less. Also, here, oxygen means an oxygen atom originating from a moisture molecule. Also, regarding the output resistance of a battery in which they are used in the positive electrode, the composite active material of the present disclosure is less than the conventional composite active material. In the composite active material of the present disclosure, the moisture included in the first coating layer 12 and the active material 11 can move to the second coating layer 13. The moisture within the second coating layer 13 can be removed by moving to the solvent contacted within the paste at the time of electrode production, or can be removed at the time of drying after the electrode is formed into a film.

[0033] 1.5. Effects and the like According to the composite active material of the present disclosure, the moisture resistance (a property in which the reaction resistance becomes high due to the deterioration of the active material by moisture.) of the composite active material 10 can be improved. Even if the composite active material of the present disclosure retains a moisture amount that is high to some extent, it has moisture resistance. It can be considered that this is because the moisture is preferentially included in the second solid electrolyte or the solvent of the second coating layer 13, so the deterioration of the first coating layer 12 and the active material 11 is suppressed. Also, the moisture included in the active material and the first coating layer can also move to the second coating layer as is. Also, as shown in the following examples, the effect in which the resistance increase rate is reduced even if the moisture amount is more than the reference value was also confirmed.

[0034] 2. Production of the composite active material In one example of the production method of the composite active material, the following processes are provided. Each process is described below. 2.1. Process of forming the first coating layer The first coating layer 12 is formed on the active material 11 by any method. For example, a dry mechanical chemical method can be given. More specifically, the active material 11 can be mixed with the fluoride solid electrolyte by using a particle compounding device. As an example of the particle compounding device, "NOBIL TA NOB-MINI" manufactured by Hosokawa Micron Co., Ltd. can be given. However, any mixing device, a granulating device, or the like can be used as long as compounding of the particles can be achieved.

[0035] 2.2. Pre-mixing process Before the pre-mixing process is performed, a material to be the second coating layer 13 is prepared. Specifically, for example, a dispersion liquid can be prepared by dispersing a sulfide solid electrolyte as a powder in a solvent as a liquid. A device for performing the dispersion is not particularly limited, but an ultrasonic homogenizer or the like can be given.

[0036] In the pre-mixing process, thickening and addition of the solvent are alternately performed 2 or more times. The pre-mixing is performed by stirring the active material 11 (powder) coated with the first coating layer 12 obtained in the process of forming the first coating layer with the dispersion liquid for the second coating layer 13 prepared as described above using a mixing device (for example, a self-rotation and revolution type stirrer). Thereby, the mixture starts to generate viscosity. For example, the mixture can be stirred at a rotation speed of 50 rpm or more and 100 rpm or less for 1 minute or more and 1 hour or less. In addition, the mixing conditions (rotation speed, mixing time, and the like) are sometimes different, for example, depending on the powder properties, the specifications of the device, and the like. By alternately repeating the thickening and the addition of the solvent, the second coating layer 13 can be more densely coated.

[0037] Before the thickening, 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, there is a tendency that absorption of the solvent into the active material 11 coated with the first coating layer 12 is difficult to proceed. In contrast, by performing the thickening, the surface properties of the active material 11 coated with the first coating layer 12 change, absorption of the solvent into the solid component is promoted, and a part of the solvent evaporates. Thereby, the solvent required for the thickening is insufficient. By performing the thickening with the addition of the solvent for the insufficient solvent, absorption of the solvent is further promoted. By repeating the thickening and the addition of the solvent, a coating layer based on a dense sulfide solid electrolyte is gradually formed, and becomes the second coating layer 13.

[0038] 2.3. Main mixing process In the main kneading process, the kneading is continued from the pre-kneading process. In the main kneading process, although the stirring is continued from the pre-kneading process, the addition of the solvent is not performed. In addition, the main kneading process performs the kneading at a higher speed for a longer time than the pre-kneading process. Specifically, for example, the mixture can be stirred at a speed of 100 rpm or more and 200 rpm or less for 2 hours or more and 6 hours or less. Furthermore, in the main kneading, it is preferable to scrape off the material adhering to the edge of the device as necessary or regularly, while confirming the situation. Thus, the active material 11 coated with the first coating layer 12 and the second coating layer 13 is obtained.

[0039] 2.4. Process of adjusting the amount of moisture The amount of moisture of the active material 11 coated with the first coating layer 12 and the second coating layer 13 obtained in the main kneading process is adjusted so that the amount of moisture thereof is as described above, and the amount of moisture at 200°C (the meaning of the amount of moisture is as described above) becomes 823 ppm or less. The adjustment of the amount of moisture can be performed, for example, by placing the active material after the main kneading in a glove box in which the dew point is controlled to -5°C and exposing it to adsorb moisture. The amount of moisture is adjusted by an appropriate exposure time obtained by a preliminary test. Thus, the composite active material of the present disclosure is obtained.

[0040] 3. Production of electrode An electrode can be produced based on the composite active material 10 produced. Specifically, for example, a slurry containing the composite active material 10 is formed, the slurry is applied to the surface of a substrate and dried, thereby producing an electrode.

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

[0042] The electron-conducting material can form an electron-conducting path in the electrode. The amount of the electron-conducting material to be blended is arbitrary. The amount of the electron-conducting material to be blended can be, for example, 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the active material. The electron-conducting material can contain any component. The electron-conducting material can contain, for example, at least one selected from the group consisting of carbon black (CB), vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene flake (GF). The CB can contain, for example, at least one selected from the group consisting of acetylene black (AB), Ketjen black (registered trademark), and furnace black.

[0043] The ion-conducting material can form an ion-conducting path within the electrode. The ion-conducting material can be particulate. The ion-conducting material may, for example, have a D50 of 0.01 pm or more and 1 pm or less, 0.01 pm or more and 0.95 pm or less, or 0.1 pm or more and 0.9 pm or less. The amount of the ion-conducting material is arbitrary. The amount of the ion-conducting material may, for example, be 1 part by volume or more and 200 parts by volume or less, 50 parts by volume or more and 150 parts by volume or less, or 50 parts by volume or more and 100 parts by volume or less, with respect to 100 parts by volume of the active material. The ion-conducting material may, for example, include a sulfide SE, a fluoride SE, or the like. The sulfide SE and the fluoride SE included in the ion-conducting material may be the same kind as or different from the sulfide SE and the fluoride SE included in the electrode material.

[0044] The binder can bind the solid materials to each other. The amount of the binder may, for example, be 0.1 parts by mass or more and 10 parts by mass or less, with respect to 100 parts by mass of the active material. The binder can include an arbitrary component. The binder may, for example, include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), a polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), a styrene butadiene rubber (SBR), a butadiene rubber (BR), and a polytetrafluoroethylene (PTFE).

[0045] 3.2. Coating In the present production method, an arbitrary 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 the substrate. The substrate can have conductivity. The substrate can function as a current collector. The substrate may, for example, be in a sheet shape or a mesh shape. The substrate may, for example, have a thickness of 5 pm or more and 50 pm or less. The substrate may, for example, include a metal foil, a metal mesh, a porous metal body, or the like. The substrate may, for example, include at least one selected from the group consisting of Al, Cu, Ni, Cr, Ti, and Fe. The substrate may, for example, include an Al foil, an Al alloy foil, a Ni foil, a Cu foil, a Cu alloy foil, a Ti foil, a stainless steel foil, or the like. The surface of the metal foil can be coated with a carbon layer. The carbon layer may, for example, include a conductive carbon material (for example, AB or the like).

[0046] On the surface of the substrate, the active material layer is formed by drying the slurry. In the present production method, an arbitrary drying device can be used. For example, a hot plate, a hot air dryer, an infrared dryer, or the like can be used.

[0047] After drying of the slurry, the electrode can also be subjected to press working. For example, cold press working can be performed, or hot press working can be performed. In the present production method, any press device can be used. For example, a roll press device or the like can be used. In the case where hot press working is performed, the press temperature can be adjusted, for example, depending on the kind of the binder or the like. The press temperature can be, for example, 80°C or higher and 180°C or lower. After the press working, the thickness of the active material layer can be, for example, 10 μm or more and 200 μm or less. After the press working, the density of the active material layer can be, for example, 2 g / cm 3 and 4 g / cm 3 or more.

[0048] 4. Production of all-solid-state battery Figure 2 is a conceptual diagram showing a layer structure of a power generating element 20 included in an all-solid-state battery. Further, in this example, the production of an all-solid-state battery is described, but as described above, the present disclosure is directed to a battery using at least a solid electrolyte as an electrolyte, and can also be a battery using a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. The power generating element 20 can be formed by laminating the positive electrode 21, the spacer layer 22, and the negative electrode 23. At least one of the positive electrode 21 and the negative electrode 23 is the electrode obtained as described above. The spacer layer 22 is disposed between the positive electrode 21 and the negative electrode 23. The spacer layer 22 can include, for example, an ion-conducting material and a binder. The spacer layer 22 can be formed, for example, by applying the slurry to the surface of at least one of the positive electrode 21 and the negative electrode 23. After the formation of the power generating element 20, the power generating element 20 can be subjected to hot press working. By the hot press working, it is expected that the power generating element 20 becomes denser. The power generating element 20 can be connected to a lead tab, an external terminal, or the like, for example. The power generating element 20 is housed in an exterior body (not shown). The exterior body can be sealed. By housing the power generating element 20 in the exterior body, the all-solid-state battery can be completed. The exterior body can have any form. The exterior body can be, for example, a bag made of a metal foil laminated film or the like. The exterior body can also be, for example, a case made of metal or the like. The exterior body can include, for example, Al or the like. The exterior body can house one power generating element 20 alone, or can house a plurality of power generating elements 20. The plurality of power generating elements 20 can form a series circuit, or can form a parallel circuit. [Example]

[0049] 5. Example In the example, the moisture adsorbed to the composite active material produced was investigated, and the relationship between the amount of moisture and the increase in resistance was investigated. Specifically, as follows. However, the present disclosure is not limited to the example.

[0050] 5.1. Production of composite active material As the active material, Li(NiCoAl)O2was used. Hereinafter, "Li(NiCoAl)O2" is abbreviated as "NCA". LiF, TiF4, and AlF3were mixed by using a planetary ball mill, and a fluoride solid electrolyte was synthesized. The fluoride solid electrolyte had a composition of Li 2.7 Ti 0.3 Al 0.7 F6. Hereinafter, "Li 2.7 Ti 0.3 Al 0.7 F6" is abbreviated as "LTAF". As the particle-complexing device, "NOBILTANOB-MINI (Mitsui Miike Kogyo Co., Ltd.)" was used. In the particle-complexing device, by subjecting 48.7 parts by mass of NCA and 1.3 parts by mass of LTAF to complexing treatment, an active material coated with a first coating layer was formed. The operating conditions of the device were that the power was 12 W per 1 g of material, the rotation speed was 6000 rpm, and the treatment time was 30 minutes.

[0051] Next, for the second coating layer, Li2S-P2S5 (glass ceramic, hereinafter "LPS") was prepared as a sulfide solid electrolyte, and THN was prepared as a solvent. Then, the following was performed in an environment in which the dew point temperature was controlled to be -70°C or lower.

[0052] The following operations were performed in an environment in which the dew point temperature was controlled to be -70°C or lower. As the dispersing device, an ultrasonic homogenizer was prepared, and thereby, by dispersing 98.4 parts by mass of the sulfide solid electrolyte in 229.6 parts by mass of the solvent, a dispersion liquid was prepared.

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

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

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

[0056] Next, the composite active material obtained for the purpose of the test was subjected to adsorption of moisture, and a plurality of composite active materials having different amounts of moisture at 200°C (the meaning of the amount of moisture is as described above) were prepared. The specific amounts of moisture are shown in Table 1. The adjustment of the amount of moisture was performed by placing the composite active material in a glove box in which the dew point was controlled to -5°C and allowing the composite active material to adsorb moisture by exposure, and the amount of moisture was adjusted by the exposure time. The specific time is also shown in Table 1.

[0057] Test Examples 1 to 7 are as described above, but Test Example 8 is an example in which the second coating layer is not provided and only the first coating layer is coated on the active material.

[0058] 5.2. Production of all-solid-state battery In order to perform a test on the battery performance based on each composite active material, an all-solid-state battery was produced. Specifically, as follows. A slurry was prepared by dispersing the composite active material, the ion-conducting material (LPS), and the electron-conducting material (AB + VGCF) in the solvent (THN) using an ultrasonic homogenizer. A positive electrode was manufactured by applying the slurry to the surface of a substrate and drying it.

[0059] Further, an all-solid-state battery including a positive electrode and a negative active material of Li4Ti5O 12 and a housing of an Al laminated film was manufactured.

[0060] 5.3. Evaluation of battery The SOC (State Of Charge) of the all-solid-state battery was set to 80%, and the all-solid-state battery was stored in a 60°C atmosphere for 2 weeks. Thereafter, the SOC (State Of Charge) of the all-solid-state battery was adjusted to 60%, and the all-solid-state battery was discharged at a time rate of 32C for 10 seconds. The discharge resistance (direct current resistance) was calculated from the voltage drop amount and the current during discharge. The discharge resistance was calculated at 2 seconds after the start of discharge. Further, the all-solid-state battery was charged at a time rate of 60C for 5 seconds. The initial charge resistance (direct current resistance) was calculated from the voltage rise amount and the current during charge. The charge resistance was calculated at 5 seconds after the start of charge.

[0061] The discharge resistance and the charge resistance of each example were expressed in terms of a ratio (percentage) with respect to the discharge resistance and the charge resistance at the time of Example 1 (exposure time 0 minutes) as a reference. Specifically, the resistance value in Test Example i was set to R iThe increase rate is calculated as [(Ri-Ri) / Ri] x 100%. The results are shown in Table 1.

[0062] [Table 1] (Table 1)

[0063] It is known that, in the case of the composite active material of the test example involved in the examples, if the moisture amount at 200°C at which the resistance increase rate in discharge becomes 0% is 823 ppm or less, the side having a larger moisture amount than the reference can reduce the resistance increase rate. In addition, in Test Example 8 in which the second coating layer is not provided, although the moisture amount is the same as that of Test Example 5, the resistance increase rate becomes high. Explanation of Reference Numerals

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

Claims

1. A composite active material for use in solid-state batteries, wherein, have: Active substances; A first coating layer, comprising a first solid electrolyte containing a fluoride, coating at least a portion of the surface of the active material; and The second coating layer contains a second solid electrolyte comprising a sulfide and a solvent, and coats at least a portion of the first coating layer. In measurements using a Karl Fischer moisture meter, the water content of the composite active substance at 200°C was below 823 ppm.

2. The composite active substance according to claim 1, wherein, In measurements using a Karl Fischer moisture meter, the water content of the composite active substance at 200°C was above 10 ppm.

3. The composite active substance according to claim 1 or 2, wherein, Regarding the water content of the composite active material, the second coating layer contains more water than the first coating layer.

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