Electrode mixture and solid-state battery

Abstract

To provide an electrode mixture that can achieve both low resistance and high volumetric energy density, and a solid-state battery containing such an electrode mixture.SOLUTION: An electrode mixture according to the present disclosure includes a layered rock salt type electrode active material, a sulfide solid electrolyte, and a conductive aid. The layered rock salt type electrode active material has a D50 particle size of 2.5 μm or more and 4.5 μm or less, and a ratio of a mass of the conductive aid to a mass of the sulfide solid electrolyte is 2 mass% or more and 11 mass% or less. A solid battery 100 according to the present disclosure includes a positive electrode current collector layer 110, a positive electrode active material layer 120, a solid electrolyte layer 130, a negative electrode active material layer 140, and a negative electrode current collector layer 150 in this order, and either the positive electrode active material layer or the negative electrode active material layer includes an electrode mixture according to the present disclosure.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an electrode composite material and a solid-state battery.

Background Art

[0002] In order to improve various characteristics of a battery, attention may be paid to the particle size of an electrode active material.

[0003] For example, Patent Document 1 discloses an all-solid-state secondary battery having a positive electrode, a negative electrode, and a solid electrolyte layer, wherein the positive electrode has a molded body of a positive electrode composite agent containing a positive electrode active material, a conductive auxiliary agent, and a sulfide-based solid electrolyte, the positive electrode active material has an Nb-containing oxide layer on its surface, and the particle size distribution of the positive electrode active material has a first frequency peak and a second frequency peak, the first frequency peak is in the range of 1 to 8 μm, and the second frequency peak is in the range of 15 to 35 μm.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, generally in a battery, it is preferable that the resistance value is small and the volume energy density is high.

[0006] An object of the present disclosure is to provide an electrode composite material capable of achieving both low resistance and high volume energy density, and a solid-state battery containing such an electrode composite material.

Means for Solving the Problems

[0007] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> An electrode composite material having a layered rock salt type electrode active material, a sulfide solid electrolyte, and a conductive assistant, wherein the D50 particle size of the layered rock salt type electrode active material is 2.5 μm or more and 4.5 μm or less, and the ratio of the mass of the conductive assistant to the mass of the sulfide solid electrolyte is 2.0% by mass or more and 11.0% by mass or less, an electrode composite material. <Aspect 2> The electrode composite material according to Aspect 1, wherein the ratio of the mass of the sulfide solid electrolyte to the total mass of the layered rock salt type electrode active material and the sulfide solid electrolyte is 10% by mass or more and 20% by mass or less. <Aspect 3> The electrode composite material according to Aspect 1 or 2, wherein the conductive assistant is fibrous carbon. <Aspect 4> The electrode composite material according to any one of Aspects 1 to 3, wherein the layered rock salt type electrode active material has a composition represented by the following formula (1): Li a (Ni x Co y M 1-x-y )O2… (1) (In the formula (1), a, x, y, and 1 - x - y are numbers satisfying 1.00 ≤ a ≤ 1.20, 0.30 ≤ x ≤ 0.90, 0.10 ≤ y ≤ 0.35, and 0 < 1 - x - y ≤ 0.10, and M is a metal element selected from aluminum and manganese.). <Aspect 5> The electrode composite material according to any one of Aspects 1 to 3, wherein the layered rock salt type electrode active material contains lithium, nickel, aluminum, and manganese. <Aspect 6> A solid battery having a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer in this order, and wherein either one of the positive electrode active material layer and the negative electrode active material layer contains the electrode composite material according to any one of Aspects 1 to 5. a solid battery. <Aspect 7> The solid battery according to Aspect 6, wherein the positive electrode active material layer contains the electrode composite material according to any one of Aspects 1 to 5. <Aspect 8> The solid-state battery according to Aspect 7, wherein the negative electrode active material layer contains a negative electrode active material having a silicon element.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide an electrode composite material capable of achieving both low resistance and high volumetric energy density, and a solid-state battery containing such an electrode composite material.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0010] 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 disclosure.

[0011] 《Electrode Composite Material》 The electrode composite material of the present disclosure has a layered rock salt type electrode active material, a sulfide solid electrolyte, and a conductive auxiliary agent. The D50 particle size of the layered rock salt type electrode active material is 2.5 μm or more and 4.5 μm or less, and the ratio of the mass of the conductive auxiliary agent to the mass of the sulfide solid electrolyte is 2% by mass or more and 11% by mass or less.

[0012] In order to increase the volumetric energy density of the battery, if the content of the conductive auxiliary agent in the electrode composite material is reduced, the resistance value of the battery increases.

[0013] In this regard, the present inventors unexpectedly found that by reducing the proportion of the conductive aid for the sulfide solid electrolyte and reducing the particle size of the electrode active material, a battery with a low resistance value and a high volume energy density can be obtained. Although not intending to be bound by any theory, the reason is presumed as follows. That is, considering the electron conductivity in the electrode composite, the electron conductivity of the electrode active material is considered to be smaller than that of the conductive aid. On the other hand, when the particle size of the electrode active material is small, the distance between the electrode active materials becomes short, and thus it is considered that a good conductive path is easily formed between the electrode active materials in the electrode composite. Therefore, when the particle size of the electrode active material is small, even if a part of the conductive aid in the electrode composite is replaced with an electrode active material having lower electron conductivity, that is, even if the proportion of the conductive aid with respect to the sulfide solid electrolyte is reduced, the electron conductivity does not extremely decrease, and as a result, an increase in the resistance value is suppressed. Further, it is considered that the volume energy density of the battery is improved by reducing the content of the conductive aid, that is, relatively increasing the content of the electrode active material.

[0014] Regarding the present disclosure, "electrode composite" means a composition that can constitute an electrode active material layer as it is or by further containing other components. Further, regarding the present disclosure, "electrode composite slurry" means a slurry that contains a dispersion medium in addition to the "electrode composite" and can form an electrode active material layer by coating and drying it.

[0015] The electrode composite of the present disclosure has a layered rock salt type electrode active material, a sulfide solid electrolyte, and a conductive aid, and optionally has a binder.

[0016] The D50 particle size of the layered rock salt type electrode active material is 2.5 μm or more and 4.5 μm or less. This D50 particle size may be 2.5 μm or more and 4.0 μm or less. Further, this D50 particle size may be 2.6 μm or more, 2.7 μm or more, 2.8 μm or more, 2.9 μm or more, or 3.0 μm or more, and may be 3.8 μm or less, 3.6 μm or less, 3.5 μm or less, 3.4 μm or less, 3.3 μm or less, 3.2 μm or less, 3.1 μm or less, or 3.0 μm or less.

[0017] Regarding the present disclosure, the D50 particle size of the layered rock salt type electrode active material can be obtained by obtaining the particle size distribution of the layered rock salt type electrode active material using a laser diffraction / scattering particle size distribution measuring device LA-920 (manufactured by Horiba, Ltd.), and when the particles are divided into the larger particle size side and the smaller particle size side from a certain particle size, it can be calculated as the particle size at which the number of particles on the larger particle size side and the smaller particle size side becomes equal.

[0018] The ratio of the mass of the conductive assistant to the mass of the sulfide solid electrolyte is 2.0 mass% or more and 11.0 mass% or less. This ratio may be 3.0 mass% or more, 4.0 mass% or more, 5.0 mass% or more, 6.0 mass% or more, or 7.0 mass% or more, and may be 10.0 mass% or less, 9.0 mass% or less, 8.0 mass% or less, 7.0 mass% or less, 6.0 mass% or less, 5.0 mass% or less, or 4.0 mass% or less.

[0019] The ratio of the mass of the sulfide solid electrolyte to the total mass of the layered rock salt type electrode active material and the sulfide solid electrolyte may be 10 mass% or more and 20 mass% or less. This ratio may be 12 mass% or more, 14 mass% or more, or 16 mass% or more, and may be 18 mass% or less, 16 mass% or less, 14 mass% or less, 12 mass% or less, or 10 mass% or less.

[0020] 〈Layered rock salt type electrode active material〉 The layered rock salt type electrode active material may have a composition represented by the following formula (1): Li a (Ni x Co y M 1-x-y )O2… (1) (In formula (1), a, x, y, and 1 - x - y are numbers satisfying 1.00 ≤ a ≤ 1.20, 0.30 ≤ x ≤ 0.90, 0.10 ≤ y ≤ 0.35, and 0 < 1 - x - y ≤ 0.10, and M is a metal element selected from aluminum and manganese.).

[0021] The layered rock salt type electrode active material may particularly be an NCA - type positive electrode active material in which M is aluminum.

[0022] The layered rock salt type electrode active material may contain lithium, nickel, aluminum, and manganese.

[0023] The method for manufacturing the layered rock salt type electrode active material is not particularly limited, but for example, it can be manufactured by the following method. That is, first, an alkaline aqueous solution is prepared. Next, nickel, cobalt, and metal element M, or nickel, cobalt, aluminum, and manganese are dissolved in water to prepare a mixed aqueous solution. Then, the mixed aqueous solution is dropped into the alkaline aqueous solution at a predetermined rate and stirred at a predetermined rate to form a precipitate, and the precipitate is dried to obtain a precursor. Further, the precursor and a lithium compound are mixed and fired to obtain a layered rock salt type electrode active material.

[0024] The D50 particle size of the layered rock salt type electrode active material can be adjusted, for example, by the pH of the alkaline aqueous solution, the dropping rate of the mixed aqueous solution, and the stirring rate of the aqueous solution after dropping the mixed aqueous solution, etc.

[0025] Regarding the present disclosure, the "electrode active material" can be used as both a "positive electrode active material" and a "negative electrode active material", and is particularly used as a "positive electrode active material".

[0026] When using a layered rock salt type electrode active material as the positive electrode active material, a material showing a lower potential than the layered rock salt type electrode active material can be used as the negative electrode active material. As such a negative electrode active material, known active materials may be used. For example, when constructing a lithium ion battery, as the negative electrode active material, silicon-based active materials such as silicon element, silicon alloy, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium, lithium alloy, etc. can be used. The negative electrode active material may be, for example, in a particulate form, and its size is not particularly limited.

[0027] 〈Sulfide solid electrolyte〉 Examples of the sulfide solid electrolyte include, but are not limited to, sulfide amorphous solid electrolytes, sulfide crystalline solid electrolytes, or argyrodite type solid electrolytes, etc. Specific examples of the sulfide solid electrolyte include Li2S-P2S5 systems (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2 (Li 13 GeP3S 16 , Li 10 GeP2S 12 , etc.), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x PS 6-x Cl x , etc.; or combinations thereof can be cited, but are not limited thereto.

[0028] The sulfide solid electrolyte may be a glass or a crystallized glass (glass ceramic).

[0029] 〈Conductive assistant〉 As the conductive additive, there is no particular limitation, and it may be a carbon material. Examples of the carbon material include particulate carbon such as acetylene black (AB) and ketjen black (KB), and fibrous carbon such as single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), and vapor-grown carbon fibers (VGCF). When the conductive additive is fibrous carbon, it is likely to contribute to the formation of a good conductive path between the electrode active materials in the electrode composite material.

[0030] 〈Binder〉 The binder is not particularly limited as long as it is commonly used as a binder for the electrode active material layer. For example, it may be a material such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, polyvinyl pyrrolidone, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, regenerated cellulose, polyethylene, polypropylene, starch, butadiene rubber (BR), styrene-butadiene rubber (SBR), fluororubber, or a combination thereof, but is not limited thereto. The binder may particularly be in the state of colloidal particles.

[0031] The method for producing the electrode composite material of the present disclosure is not particularly limited. For example, there is exemplified a method in which a layered rock salt type electrode active material, a sulfide solid electrolyte, and a conductive additive, and optionally a binder, are mixed in a dispersion medium to obtain a slurry-like electrode composite material (electrode composite material slurry).

[0032] 《Solid Battery》 As illustrated in FIG. 1, the solid battery 100 of the present disclosure has a positive electrode current collector layer 110, a positive electrode active material layer 120, a solid electrolyte layer 130, a negative electrode active material layer 140, and a negative electrode current collector layer 150 in this order, and either one of the positive electrode active material layer and the negative electrode active material layer contains the electrode composite material of the present disclosure.

[0033] Regarding the present disclosure, the "solid-state battery" means a battery that uses at least a solid electrolyte as an electrolyte. Therefore, the solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as the electrolyte. Further, the solid-state battery of the present disclosure may be an all-solid-state battery, that is, a battery that uses only a solid electrolyte as the electrolyte.

[0034] 〈Positive current collector layer, and negative current collector layer〉 The positive current collector layer and the negative current collector layer are not particularly limited as long as they can be used as the current collector layer of the battery. For example, when constructing a lithium-ion battery, it may be an aluminum foil, a copper foil, or the like.

[0035] 〈Positive electrode active material layer〉 The positive electrode active material layer contains a positive electrode active material, and optionally a positive electrode composite material containing a solid electrolyte, a conductive aid, and a binder. In particular, the positive electrode composite material may be the electrode composite material of the present disclosure. That is, the positive electrode active material layer may contain the electrode composite material of the present disclosure. For the electrode composite material of the present disclosure, reference can be made to the above description regarding the electrode composite material of the present disclosure.

[0036] 〈Negative electrode active material layer〉 The negative electrode active material layer contains a negative electrode active material, and optionally a negative electrode composite material containing a solid electrolyte, a conductive aid, and a binder. When the positive electrode active material layer contains the electrode composite material of the present disclosure, the negative electrode active material layer contains a negative electrode active material having a silicon element. In this case, for the solid electrolyte, the conductive aid, and the binder, reference can be made to the above description regarding the electrode composite material of the present disclosure.

[0037] 〈Solid electrolyte layer〉 The solid electrolyte layer contains a solid electrolyte, and optionally contains a conductive aid and a binder. For the solid electrolyte, the conductive aid, and the binder, reference can be made to the above description regarding the electrode composite material of the present disclosure.

[0038] As a method for manufacturing the solid-state battery of the present disclosure, a method including forming an electrode active material layer containing the electrode composite material of the present disclosure is exemplified.

[0039] As a method for forming an electrode active material layer, there may be exemplified a method of providing an electrode composite material slurry containing an electrode composite material and a dispersion medium, applying the electrode composite material slurry to a substrate, and then drying and removing the dispersion medium.

Examples

[0040] 《Production Example 1》 〈Production of layered rock salt type electrode active material〉 In a reaction vessel, 2.5 L of an aqueous ammonia solution at 5 g / L was prepared. While maintaining the temperature in the tank at 40°C, an initial aqueous solution was prepared by using an aqueous sodium hydroxide solution to adjust the pH to 11.5 based on a liquid temperature of 25°C. Further, nickel sulfate (NiSO4), cobalt sulfate (CoSO4), and aluminum sulfate (Al2(SO4)3) were dissolved in pure water so that Ni:Co:Al = 0.82:0.15:0.03 (mol), and a mixed aqueous solution with a concentration of 2.0 mol / L was prepared. The mixed aqueous solution was dropped into the initial aqueous solution in the reaction tank at a predetermined dropping rate and stirred at a predetermined stirring rate to form a precipitate. After the recovered slurry was filtered and washed, it was dried to obtain a precursor of the electrode active material. Lithium carbonate (Li2CO3) and the obtained precursor of the electrode active material were mixed so that Li:Ni+Co+Al = 1.10:1.00 (mol), and then fired in an oxygen atmosphere at 750°C for 10 hours to obtain the layered rock salt type electrode active material of Production Example 1.

[0041] 《Production Examples 2 and 3, and Comparative Production Examples 1 and 2》 Layered rock salt type electrode active materials of Production Examples 2 and 3, and Comparative Production Examples 1 and 2 were obtained in the same manner as in Production Example 1, except that the pH, dropping rate, and stirring rate of the initial aqueous solution were changed to prepare the precursor of the electrode active material.

[0042] The layered rock salt type electrode active materials obtained in each production example were used as the positive electrode active material.

[0043] 《Comparative Example 1》 〈Preparation of coated positive electrode active material〉 10.8 g of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in 166.0 g of ion-exchanged water. Then, lithium hydroxide monohydrate (LiOH·H₂O) was added so that the Li / P (mol) ratio became 0.45 to prepare a coating solution. 53.7 g of the coating solution was added to 50.0 g of the layered rock salt type electrode active material of Comparative Production Example 1 as the positive electrode active material to obtain a slurry. The obtained slurry was spray-dried to obtain a coated positive electrode active material.

[0044] 〈Preparation of Positive Electrode Composite Material〉 The obtained coated positive electrode active material and a sulfide solid electrolyte (Li₂S-P₂S₅-based glass ceramics containing LiI, D50 = 0.8 μm) were weighed so that the volume ratio became 80:20. Also, when the coated positive electrode active material was 100 parts by mass, 0.2 parts by mass of vapor-grown carbon fiber (VGCF) as a conductive assistant and 0.4 parts by mass of butadiene rubber as a binder were weighed. Each of the weighed components was put into tetralin. Then, these were mixed and further sufficiently dispersed with an ultrasonic homogenizer (manufactured by SMT, UH-50) to obtain a slurry-like positive electrode composite material (positive electrode composite material slurry).

[0045] 〈Fabrication of Positive Electrode Laminate〉 The obtained positive electrode composite material slurry was coated on an aluminum (Al) foil as a positive electrode current collector, and the coated film was dried at 100 °C for 30 minutes to form a positive electrode active material layer on the positive electrode current collector. Then, the laminate composed of the positive electrode current collector and the positive electrode active material layer was punched out into a size of 1 cm 2 to obtain a positive electrode laminate.

[0046] 〈Preparation of Negative Electrode Composite Material〉 A sulfide solid electrolyte (Li₂S-P₂S₅-based glass ceramics containing LiI, D50 = 0.8 μm), 1% by mass of VGCF as a conductive assistant, 2% by mass of butadiene rubber as a binder, and heptane were put into a kneading container of a Filmix apparatus (manufactured by Primix, 30-L type) and stirred at 20000 rpm for 30 minutes. Then, a negative electrode active material (Li₄Ti₅O 12Particles (D50 = 1 μm) and the solid electrolyte were weighed so that the volume ratio became 7:3. These were put into a kneading container and stirred at 15,000 rpm for 60 minutes with a film mixing apparatus to obtain a negative electrode mixture slurry.

[0047] <Fabrication of Negative Electrode Laminate> The obtained negative electrode mixture slurry was coated on a copper foil, and the coated film was dried at 100 °C for 30 minutes to form a negative electrode active material layer on the negative electrode current collector. Thereafter, the laminate composed of the negative electrode current collector and the negative electrode active material layer was punched out into a size of 1 cm 2 to obtain a negative electrode laminate.

[0048] <Fabrication of Solid Electrolyte Layer> 64.8 mg of a sulfide solid electrolyte (Li2S-P2S5-based glass ceramic containing LiI, D50 = 2.5 μm) was put into a cylindrical ceramic having an inner diameter cross-sectional area of 1 cm 2 . After smoothing, it was pressed at 1 ton / cm 2 to fabricate a solid electrolyte layer.

[0049] <Fabrication of Battery> A positive electrode laminate was placed on one surface of the solid electrolyte layer, and a negative electrode laminate was placed on the other surface, and pressed at 6 ton / cm 2 for 1 minute. Each laminate was arranged so that the positive electrode active material layer and the negative electrode active material layer were in contact with the solid electrolyte layer. Next, stainless steel rods were inserted into both electrodes and constrained with 1 ton to obtain an all-solid-state lithium-ion battery of Comparative Example 1.

[0050] <<Example 1>> An all-solid-state lithium-ion battery of Example 1 was obtained in the same manner as in Comparative Example 1, except that the layered rock salt type electrode active material of Production Example 1 was used in the preparation process of the coated positive electrode active material.

[0051] <<Example 2>> In the step of preparing the coated positive electrode active material, the layered rock salt type electrode active material of Production Example 2 was used, and in the step of preparing the positive electrode composite material, except that the ratio of the mass of the conductive assistant to the mass of the solid electrolyte (conductive assistant / solid electrolyte) and the ratio of the mass of the solid electrolyte to the total mass of the positive electrode active material and the solid electrolyte (solid electrolyte / (positive electrode active material + solid electrolyte)) were changed as shown in Table 1, the all-solid-state lithium ion battery of Example 2 was obtained in the same manner as in Comparative Example 1.

[0052] 《Examples 3 to 5》 In the step of preparing the positive electrode composite material, except that the conductive assistant / solid electrolyte and the solid electrolyte / (positive electrode active material + solid electrolyte) were changed as shown in Table 1, the all-solid-state lithium ion batteries of Examples 3 to 5 were obtained in the same manner as in Example 2.

[0053] 《Comparative Examples 2 and 3》 In the step of preparing the coated positive electrode active material, the layered rock salt type electrode active material of Comparative Production Example 2 was used, and in the step of preparing the positive electrode composite material, except that the conductive assistant / solid electrolyte was changed as shown in Table 1, the all-solid-state lithium ion battery of Example 2 was obtained in the same manner as in Comparative Example 1.

[0054] 《Example 6》 In the step of preparing the coated positive electrode active material, the layered rock salt type electrode active material of Production Example 3 was used, and in the step of preparing the positive electrode composite material, except that the conductive assistant / solid electrolyte and the solid electrolyte / (positive electrode active material + solid electrolyte) were changed as shown in Table 1, the all-solid-state lithium ion battery of Example 6 was obtained in the same manner as in Comparative Example 1.

[0055] 《Examples 7 and 8》 In the step of preparing the positive electrode composite material, except that the conductive assistant / solid electrolyte and the solid electrolyte / (positive electrode active material + solid electrolyte) were changed as shown in Table 1, the all-solid-state lithium ion batteries of Examples 7 and 8 were obtained in the same manner as in Example 6.

[0056] 《Comparative Example 4》 In the process of preparing the coated positive electrode active material, except that the layered rock salt type electrode active material of Comparative Production Example 3 was used, and in the process of preparing the positive electrode composite material, the conductive assistant / solid electrolyte was changed as described in Table 1, a all-solid-state lithium-ion battery of Comparative Example 4 was obtained in the same manner as in Comparative Example 1.

[0057] 《Comparative Examples 5 and 6》 In the process of preparing the positive electrode composite material, except that the conductive assistant / solid electrolyte was changed as described in Table 1, all-solid-state lithium-ion batteries of Comparative Examples 5 and 6 were obtained in the same manner as in Comparative Example 4.

[0058] 《Evaluation》 〈D50 Particle Size of Layered Rock Salt Type Electrode Active Material〉 The D50 particle size of the layered rock salt type electrode active material as the positive electrode active material was obtained by using a laser diffraction / scattering particle size distribution measuring device LA-920 (manufactured by Horiba, Ltd.) to obtain the particle size distribution of the layered rock salt type electrode active material, and when the particles were divided into the larger and smaller particle size sides from a certain particle size, it was calculated as the particle size at which the number of particles on the larger and smaller particle size sides became equal. The results are shown in Table 1.

[0059] 〈Interparticle Distance of Layered Rock Salt Type Electrode Active Material〉 Using image analysis with the cross-sectional SEM image obtained by SEM, the distribution of the center-of-gravity distances of the layered rock salt type electrode active material as the positive electrode active material was represented by a histogram, and the average distance calculated based on this histogram was determined as the distance between the active materials. The results are shown in Figures 2 and 3.

[0060] 〈Evaluation of Battery Resistance〉 For each all-solid-state lithium-ion battery of each example, after performing constant current-constant voltage charging and discharging at a set voltage of 2.8 V or 1.5 V and a 1 / 3 C rate for 2 cycles, it was adjusted to SOC 40% at a 1 / 3 C rate. It was discharged with a direct current corresponding to a 2.5 C rate in a thermostatic bath maintained at 25°C, and the resistance value was calculated from the voltage drop amount after 5 seconds and the applied current with the voltage at 0 seconds as the initial value. The measured results are shown in Table 1 with the resistance value related to Comparative Example 1 as the reference (1.00) and the resistance values related to the other examples as relative values.

[0061] "Results" Table 1 shows the positive electrode active material (layered rock salt type electrode active material), the D50 particle size of the positive electrode active material, the conductive assistant / solid electrolyte, the solid electrolyte / (positive electrode active material + solid electrolyte), the resistance value, and the volume energy density.

[0062] "[Table 1]"

[0063] As shown in Table 1, in the batteries of the examples where the D50 particle size of the positive electrode active material is small and the ratio of the mass of the conductive assistant to the mass of the sulfide solid electrolyte is within a predetermined range, the resistance value is small and the volume energy density is high. In particular, in Examples 2 to 5 where the D50 particle size of the positive electrode active material is 3.0 μm, the resistance value is smaller and the volume energy density is higher. In contrast, in the battery of Comparative Example 1 where the D50 particle size of the positive electrode active material is smaller than within the range of the present disclosure, the resistance value is the largest. Although the D50 particle size of the positive electrode active material is within the range of the present disclosure, in the batteries of Comparative Examples 2 and 3 where the ratio of the mass of the conductive assistant to the mass of the sulfide solid electrolyte is large, the volume energy density is low. Furthermore, in the batteries of Comparative Examples 4 to 6 where the D50 particle size of the positive electrode active material is large, the resistance value is relatively large. When the D50 particle size of the positive electrode active material is large, as in Comparative Example 4, even if the ratio of the mass of the conductive assistant to the mass of the sulfide solid electrolyte is small, the volume energy density of the battery is low. "Explanation of Reference Numerals"

[0064] 100 Solid battery 110 Positive electrode current collector layer 120 Positive electrode active material layer 130 Solid electrolyte layer 140 Negative electrode active material layer 150 Negative electrode current collector layer

Claims

1. An electrode composite material having a layered rock salt type electrode active material, a sulfide solid electrolyte, and a conductive assistant, wherein the D50 particle diameter of the layered rock salt type electrode active material is 2.5 μm or more and 4.5 μm or less, and the ratio of the mass of the conductive assistant to the mass of the sulfide solid electrolyte is 2.0% by mass or more and 11.0% by mass or less, the electrode composite material.

2. The electrode composite material according to claim 1, wherein the ratio of the mass of the sulfide solid electrolyte to the total mass of the layered rock salt type electrode active material and the sulfide solid electrolyte is 10% by mass or more and 20% by mass or less.

3. The electrode composite material according to claim 1, wherein the conductive assistant is fibrous carbon.

4. The electrode composite material according to claim 1, wherein the layered rock salt type electrode active material has a composition represented by the following formula (1): Li ａ (Ni ｘ Co ｙ M １－ｘ－ｙ )O ２ … (1) (In the formula (1), a, x, y, and 1 - x - y are numbers satisfying 1.00 ≤ a ≤ 1.20, 0.30 ≤ x ≤ 0.90, 0.10 ≤ y ≤ 0.35, and 0 < 1 - x - y ≤ 0.10, and M is a metal element selected from aluminum and manganese.).

5. The electrode composite material according to claim 1, wherein the layered rock salt type electrode active material contains lithium, nickel, aluminum, and manganese.

6. A solid battery having a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer in this order, and either the positive electrode active material layer or the negative electrode active material layer contains the electrode composite material according to any one of claims 1 to 5. The solid battery.

7. The solid battery according to claim 6, wherein the positive electrode active material layer contains the electrode composite material according to any one of claims 1 to 5.

8. The solid battery according to claim 7, wherein the negative electrode active material layer contains a negative electrode active material having a silicon element.

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