Composite active material and battery

Abstract

To provide a composite active material capable of suppressing the increase of battery resistance.SOLUTION: A disclosed composite active material includes: an electrode active material that contains silicon and has voids inside; and a coating layer that covers the surface of the electrode active material and contains a solid electrolyte. The BET specific surface area of the composite active material is 40 m2 / g or less. The coverage rate of the coating layer is 20% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, the development of batteries has been actively pursued. For example, in the automotive industry, development of batteries for use in electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and hybrid electric vehicles (HEVs) is underway. Furthermore, development of components and materials for use in these batteries is also underway.

[0003] For example, Patent Document 1 discloses an anode layer used in an all-solid-state battery, which contains Si-based particles having pores as an anode active material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-079684 Summary of the Invention [Problem to be solved by the invention]

[0005] Si has a large theoretical capacity and is effective in increasing the energy density of batteries. However, Si undergoes large volume changes during battery charging and discharging. In this regard, the use of Si-based particles with pores as an electrode active material has been studied, as in Patent Document 1. However, the presence of pores increases the specific surface area, which creates a new problem: it becomes particularly difficult to maintain a good interface with the solid electrolyte on the particle surface. If a good interface with the solid electrolyte is not maintained, a good ion conduction path cannot be maintained, which may increase battery resistance.

[0006] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a composite active material that can suppress an increase in battery resistance. [Means for solving the problem]

[0007] [1] an electrode active material containing Si element and having voids therein; A composite active material having a coating layer that coats the surface of the electrode active material and contains a solid electrolyte, The BET specific surface area of ​​the above composite active material is 40m 2 / g or less, The composite active material has a coverage of 20% or more with the coating layer.

[0008] [2] The composite active material according to [1], wherein the coverage is 30% or more.

[0009] [3] The BET specific surface area of ​​the composite active material is 20m 2 / g or more of the composite active material according to [1] or [2].

[0010] [4] When the coating layer is removed from the composite active material to expose the electrode active material, The BET specific surface area of ​​the exposed electrode active material is 40 m 2 / g or more of the composite active material according to any one of [1] to [3].

[0011] [5] A battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, The negative electrode active material layer of the battery contains the composite active material according to any one of [1] to [4]. [Effects of the Invention]

[0012] The present disclosure has the effect of suppressing an increase in battery resistance. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic cross-sectional view illustrating a composite active material according to the present disclosure. [Figure 2] 1 is a schematic cross-sectional view illustrating an example of an electrode active material according to the present disclosure. [Figure 3] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. [Figure 4] 1 is a graph summarizing the results of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0014] The composite active material and the battery according to the present disclosure will be described in detail below. Note that the drawings shown below are schematic illustrations, and the size and shape of each part are appropriately exaggerated for ease of understanding.

[0015] A. Composite active material FIG. 1 is a schematic cross-sectional view illustrating a composite active material according to the present disclosure. As will be described later, electrode active materials have voids inside, but the voids inside composite active material 10 (electrode active material 1) shown in FIG. 1 are omitted. The composite active material 10 shown in FIG. 1 comprises an electrode active material 1 containing Si element and having voids inside (not shown), and a coating layer 2 that coats the surface of the electrode active material 1 and contains a solid electrolyte. In addition, the BET specific surface area of ​​composite active material 10 is 40 m 2 / g or less, and the coverage by the coating layer 2 is 20% or more. Herein, the electrode active material may be referred to as porous Si (p-Si), and the composite active material may be referred to as composite porous Si (composite p-Si).

[0016] According to the present disclosure, a composite active material having porous Si and a coating layer has a BET specific surface area of ​​40 m 2 / g or less and the coverage is 20% or more, so that an increase in battery resistance can be suppressed.

[0017] FIG. 2 is a schematic cross-sectional view illustrating an example of an electrode active material (porous Si) according to the present disclosure. Note that, as in FIG. 1, internal voids are omitted in FIG. 2 as well. As shown in FIG. 2, minute voids H (depressions, holes) resulting from internal voids are likely to form on the surface of the electrode active material 1, and the BET specific surface area tends to be large. When such an electrode active material is used, a good interface may not be formed between the solid electrolyte and the electrode active material. Furthermore, when the electrode active material expands and contracts during battery charging and discharging, a good interface with the solid electrolyte may not be maintained. As a result, a good ion conduction path may not be formed or maintained, and battery resistance may increase.

[0018] In contrast, in the composite active material of the present disclosure, the surface of the porous Si is covered with a coating layer having a solid electrolyte at a coverage rate of 20% or more, and the BET specific surface area is 40 m 2 / g or less. In other words, in the composite active material of the present disclosure, it is believed that the solid electrolyte fills the fine voids on the surface of the porous Si described above. As a result, it is believed that a good interface with the solid electrolyte is formed and maintained, and an increase in battery resistance can be suppressed. Furthermore, because the composite active material of the present disclosure contains porous Si, expansion and contraction of Si can be suppressed. As a result, it is believed that cracking of the electrode layer can be prevented, and an increase in battery resistance can be further suppressed.

[0019] In the composite active material of the present disclosure, the BET specific surface area is 40 m 2 / g or less. The BET specific surface area is 35m 2 / g or less, and 2 / g or less, and 2 On the other hand, the BET specific surface area may be, for example, 15 m 2 / g or more, and 20m 2 / g or more. If the BET specific surface area is too small, the expansion and contraction (volume change) of Si may not be sufficiently suppressed. The BET specific surface area can be calculated by the BET method using a pore size distribution analyzer.

[0020] Furthermore, in the composite active material of the present disclosure, the coverage of the coating layer is 20% or more. The coverage may be 25% or more, or 30% or more. On the other hand, the coverage may be, for example, 85% or less, 80% or less, 70% or less, 60% or less, 50% or less, or 40% or less. If the coverage is too high, the BET specific surface area of ​​the composite active material may become too small, and the effect of suppressing volume change by p-Si may not be fully exerted. The coverage can be calculated by observation with a scanning electron microscope (SEM). More specifically, the method described in the Examples may be used. Details of the coating layer will be described later.

[0021] 1. Electrode active material The electrode active material according to the present disclosure contains Si element and has voids inside.

[0022] The electrode active material is a so-called Si-based active material. Examples of Si-based active materials include simple Si, Si alloys, and Si oxides. Examples of Si alloys include Si-Al alloys, Si-Sn alloys, Si-In alloys, Si-Ag alloys, Si-Pb alloys, Si-Sb alloys, Si-Bi alloys, Si-Mg alloys, Si-Ca alloys, Si-Ge alloys, and Si-Pb alloys. The Si alloy may be a binary alloy or a multi-component alloy of three or more components. Examples of Si oxides include SiO.

[0023] Furthermore, the electrode active material according to the present disclosure has voids inside (particularly inside the primary particles). The porosity is, for example, 4% or more, and may be 10% or more. The porosity is, for example, 40% or less, and may be 20% or less. The porosity can be determined, for example, by the following procedure. First, a cross section of an electrode layer containing the electrode active material is prepared by ion milling. The cross section is then observed with a scanning electron microscope (SEM) to obtain a photograph of the particles. From the obtained photograph, the silicon portion and the void portion are clearly distinguished and binarized using image analysis software. The areas of the silicon portion and the void portion are determined, and the porosity (%) is calculated using the following formula. When the electrode active material is a Si alloy, the porosity can be calculated by using the silicon portion area in the formula below as the metal portion area. Porosity (%) = 100 × (area of ​​void part) / ((area of ​​silicon part) + (area of ​​void part))

[0024] In addition, in the electrode active material, the pore volume of pores having a pore diameter of 50 nm or less is, for example, 0.05 cc / g or more and 0.30 cc / g or less.

[0025] Here, when the coating layer is removed from the composite active material to expose the electrode active material, the BET specific surface area of ​​the exposed electrode active material (also simply referred to as the BET specific surface area of ​​the electrode active material) is usually larger than the BET specific surface area of ​​the composite active material. The BET specific surface area of ​​the electrode active material is usually 40 m 2 / g, and 42m 2 / g or more, and 2 On the other hand, the BET specific surface area of ​​the electrode active material may be, for example, 100 m 2 / g or less. The BET specific surface area of ​​the electrode active material can be calculated by, for example, removing the coating layer from the composite active material by washing with water or the like, drying the resulting electrode active material, and then subjecting the resulting electrode active material to a BET method using a pore size distribution analyzer. Furthermore, when the BET specific surface area of ​​the composite active material is X and the BET specific surface area of ​​the electrode active material is Y, X / Y is, for example, 0.5 or more, or may be 0.6 or more, or may be 0.7 or more. On the other hand, X / Y is, for example, 0.9 or less, or may be 0.8 or less.

[0026] The electrode active material may have a diamond-type crystalline phase, a clathrate I-type crystalline phase, or a clathrate II-type crystalline phase. In the clathrate I-type or II-type crystalline phase, multiple Si elements form a polyhedron (cage) containing pentagons or hexagons. This polyhedron has spaces inside that can encapsulate Li ions, thereby suppressing volume changes due to charge and discharge.

[0027] The electrode active material is usually in the form of particles. The electrode active material may be in the form of primary particles or secondary particles formed by aggregation of primary particles. The average particle diameter D of the electrode active material 50 is not particularly limited, but may be, for example, 1 nm or more, 10 nm or more, or 100 nm or more. 50 is, for example, 50 μm or less, and may be 20 μm or less. 50 refers to the cumulative 50% particle size in the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer.

[0028] 2.Coating layer The coating layer in the present disclosure is a layer that coats the electrode active material and contains a solid electrolyte. The coating layer has a coverage of 20% or more. The coverage is as described above.

[0029] Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, and complex hydrides. Among these, sulfide solid electrolytes are particularly preferred because of their high ionic conductivity. Sulfide solid electrolytes typically contain sulfur (S) as the main anion element. Oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes typically contain oxygen (O), nitrogen (N), and halogen (X), respectively, as the main anion element.

[0030] The sulfide solid electrolyte preferably contains, for example, Li, X (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and a halogen element.

[0031] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (where m and n are positive numbers. Z is Ge, Zn, or Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In.)

[0032] The sulfide solid electrolyte may be crystalline, amorphous (glass), or crystallized glass (glass ceramics).

[0033] The coating layer in the present disclosure may also contain at least one of a conductive material and a binder. Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF). Examples of binders include rubber-based binders and fluoride-based binders. When the coating layer contains at least one of a conductive material and a binder, the proportion of the solid electrolyte in the coating layer is, for example, 90% by weight or more and 98% by weight or less. On the other hand, the coating layer does not necessarily contain a conductive material or a binder.

[0034] The thickness of the coating layer is not particularly limited, but may be, for example, 1 nm to 100 nm, or may be 5 nm to 50 nm, or may be 10 nm to 30 nm. The thickness of the coating layer is determined as the average thickness of multiple samples (e.g., 100 or more samples) observed by, for example, a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0035] 3.Composite active material The composite active material of the present disclosure is typically used in batteries. The composite active material may be used as a positive electrode active material or a negative electrode active material in the battery, but the latter is preferred because it allows for a battery with a higher capacity to be obtained.

[0036] The composite active material is usually in the form of particles. The average particle size (D 50 ) is the average particle size (D 50 ), but is not particularly limited thereto, and is, for example, 1 μm or more and 50 μm or less.

[0037] The composite active material can be produced by subjecting a mixture containing an electrode active material and a solid electrolyte to a compressive shear treatment to form the coating layer. Examples of the compressive shear treatment include placing the mixture in a container and mixing it with a crushing medium such as a blade, beads, or balls, and applying compressive shear energy to the mixture present between the container wall and the mixture.

[0038] B.Battery Fig. 3 is a schematic cross-sectional view illustrating a battery according to the present disclosure. Battery 20 shown in Fig. 3 includes a positive electrode active material layer 21, a negative electrode active material layer 22, a solid electrolyte layer 23 disposed between positive electrode active material layer 21 and negative electrode active material layer 22, a positive electrode current collector 24 that collects electrons from positive electrode active material layer 21, and a negative electrode current collector 25 that collects electrons from negative electrode active material layer 22. In particular, in battery 20 according to the present disclosure, negative electrode active material layer 22 contains the composite active material described above in "A. Composite active material."

[0039] According to the present disclosure, since the negative electrode active material layer contains the above-described composite active material, the battery is one in which an increase in resistance is suppressed.

[0040] 1.Negative electrode active material layer The negative electrode active material layer contains the composite active material described above. The negative electrode active material layer may also contain at least one of a conductive material, a binder, and a solid electrolyte, as needed. The conductive material, binder, and solid electrolyte are the same as those described in "A. Composite Active Material."

[0041] The thickness of the negative electrode active material layer is not particularly limited, but is, for example, 0.1 μm or more and 1000 μm or less. The negative electrode active material layer can be formed, for example, by a coating method. In the coating method, a slurry containing at least the above-mentioned composite active material is applied to a negative electrode current collector and then dried to form the negative electrode active material layer.

[0042] 2.Cathode active material layer The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer may also contain at least one of a conductive material, a binder, and a solid electrolyte, as needed. The conductive material, binder, and solid electrolyte are the same as those described in "A. Composite Active Material."

[0043] The positive electrode active material may be, for example, an oxide active material, such as LiCoO2 or LiNi. 0.33 Co 0.33 Mn 0.33 O2 and LiNi 0.8 Co 0.15 Al 0.05 O2, etc., rock salt layered active materials, LiMn2O4 and Li4Ti5O 12 and olivine type active materials such as LiFePO4. The positive electrode active material is, for example, in the form of particles.

[0044] The positive electrode active material layer can be formed by the above-mentioned coating method. The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

[0045] 3.Solid electrolyte layer The solid electrolyte layer is a layer disposed between the positive electrode active material layer and the negative electrode active material layer, and contains at least a solid electrolyte.

[0046] Examples of the solid electrolyte include the inorganic solid electrolytes described in "A. Composite Active Material." Other examples of the solid electrolyte include organic solid electrolytes such as polymer electrolytes and gel electrolytes. The solid electrolyte layer may contain a liquid electrolyte (electrolytic solution) as the electrolyte. The thickness of the solid electrolyte layer is, for example, 1 μm or more and 500 μm or less.

[0047] 4. Other configurations The battery of the present disclosure typically includes a positive electrode current collector that collects current from the positive electrode active material layer and a negative electrode current collector that collects current from the negative electrode active material layer. Examples of materials for the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, and carbon. Examples of materials for the negative electrode current collector include stainless steel, copper, nickel, and carbon.

[0048] The battery according to the present disclosure may further include a restraining jig that applies a restraining pressure to the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer in the thickness direction. The restraining pressure is, for example, 0.1 MPa or more, or may be 1 MPa or more, or may be 5 MPa or more. Meanwhile, the restraining pressure is, for example, 100 MPa or less, or may be 50 MPa or less, or may be 20 MPa or less.

[0049] 5.Battery The type of battery in the present disclosure is not particularly limited, but is typically a lithium-ion battery. Furthermore, since the battery in the present disclosure has a solid electrolyte layer, it typically corresponds to a solid-state battery. The solid-state battery may be a semi-solid-state battery or an all-solid-state battery. Furthermore, the battery in the present disclosure may be a primary battery or a secondary battery, but a secondary battery is preferred. This is because it can be repeatedly charged and discharged and is useful, for example, as an on-board battery.

[0050] Examples of uses of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, it is preferable to use the battery as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), and may also be used as a power source for electrical appliances such as information processing devices.

[0051] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0052] [Example 1] (Preparation of composite active material) First, an electrode active material (porous Si particles: p-Si) containing Si element and having voids inside was prepared as follows. Si particles (27.7 g) were pulverized in a ball mill to adjust the particle size. The ball milling conditions were 1000 rpm and 3 h. Next, the crushed Si particles and metallic Li (32.5 g) were added to a mortar and mixed at room temperature to obtain a LiSi alloy. The mortar mixing conditions were 50 rpm and 20 min. The LiSi alloy was then added to mesitylene solvent (600 ml). While stirring at room temperature and 250 rpm, a total of 600 ml of ethanol at 0°C or below was added dropwise at a constant rate (1 drop / 5 sec). Furthermore, while stirring at 250 rpm, a total of 800 ml of acetic acid was added dropwise. The resulting solution was filtered under reduced pressure to recover the powder. The recovered powder was vacuum dried (-0.1 MPa, 12 h or more) to remove the solvent. This was followed by thermal drying (160°C, 12 h). This yielded porous Si particles.

[0053] The resulting porous Si particles were mixed with a sulfide solid electrolyte (LiI-Li2S-P2S5; glass ceramics) in a volume ratio of 100:81.8. The resulting mixture was mixed using a planetary mixer (two-axis planetary kneader) while applying shear force. This resulted in a composite active material (composite p-Si) in which a layer of sulfide solid electrolyte (coating layer) was formed on the surface of the electrode active material. Using the composite active material as the negative electrode active material, an evaluation battery (all-solid-state battery) was fabricated as described below.

[0054] (Preparation of evaluation battery) A conductive material (carbon nanotubes), a binder (styrene butadiene rubber (SBR)), and a dispersion medium (diisobutyl ketone) were further added to the composite active material and the sulfide solid electrolyte mixture and mixed to obtain a negative electrode slurry. The weight ratio of the composite active material, sulfide solid electrolyte, binder, and conductive material in the negative electrode slurry was 52.93:44.11:1.49:0.26. The negative electrode slurry was applied to a negative electrode current collector (Cu foil) and dried to obtain a negative electrode having a negative electrode active material layer and a negative electrode current collector.

[0055] In addition, the positive electrode active material (LiNi 0.8 Co 0.15 Al 0.05 A positive electrode slurry was prepared by mixing a composite active material (LiI-LiS-P2S5; glass ceramics), a sulfide solid electrolyte (LiI-LiS-P2S5; glass ceramics), a binder (styrene butadiene rubber (SBR)), a conductive material (carbon nanotubes), and a dispersion medium (1,2,3,4-tetrahydronaphthalene). The weight ratio of the composite active material, sulfide solid electrolyte, binder, and conductive material in the positive electrode slurry was 82.04:15.65:0.34:1.97. The positive electrode slurry was applied to a positive electrode current collector (Al foil) and dried to obtain a positive electrode with a positive electrode active material layer and a positive electrode current collector. The size of the positive electrode was adjusted to be smaller than that of the negative electrode.

[0056] In addition, a sulfide solid electrolyte (LiI-Li2S-P2S5; glass ceramics), a binder (acrylate butadiene rubber: ABR), and a dispersion medium (n-heptane, butyl butyrate) were mixed to obtain a slurry. The slurry was applied to a substrate (Al foil) and dried to obtain a transfer member with a solid electrolyte layer. The size of the solid electrolyte layer was the same as that of the negative electrode.

[0057] The negative electrode and the transfer member were stacked and pressed together so that the negative electrode active material layer and the solid electrolyte layer faced each other. The base material was then peeled off to transfer the solid electrolyte layer. The positive electrode was then stacked and pressed together so that the solid electrolyte layer and the positive electrode active material layer faced each other. A terminal was then attached, and the electrodes were constrained at a pressure of 5 MPa relative to the electrode surface area. This resulted in a battery for evaluation (all-solid-state battery).

[0058] [Examples 2 to 3] A test battery was fabricated in the same manner as in Example 1, except that the composite p-Si was fabricated by changing the ratio of porous Si particles and sulfide solid electrolyte so as to obtain a predetermined coverage rate.

[0059] [Comparative Example] Porous Si particles were prepared in the same manner as in Example 1. A test battery was prepared in the same manner as in Example 1, except that porous Si particles were used as the negative electrode active material.

[0060] [evaluation] (SEM observation and coverage measurement) Surface SEM images were taken for the negative electrode active materials of Examples 1 to 3 and the comparative example. Furthermore, the coverage ratios for Examples 1 to 3 were calculated as follows. The results are shown in Table 1. First, a binarized image of the areas covered with the coating layer and the areas not covered was created from the obtained SEM images. The image analysis software "ImageJ" was used to create the binarized image. The areas of the covered and uncovered portions in the image were then calculated using the image analysis software. The coverage ratios were calculated using these values ​​according to the following formula:

[0061]

number

[0062] (BET specific surface area measurement) For the negative electrode active materials of Examples 1 to 3 and the Comparative Example, the BET specific surface area was calculated by the BET method using a pore size distribution analyzer. The results are shown in Table 1. In Examples 1 to 3, the p-Si was coated similarly to the Comparative Example, so the coating rate in the Comparative Example can be considered to be the specific surface area of ​​the negative electrode active materials of Examples 1 to 3 before coating.

[0063] (Cycle test) The test batteries obtained in Examples 1 to 3 and the Comparative Example were activated by CCCV charging at 1 / 3C to 4.05V at 25°C and then CCCV discharging at 1 / 3C to 2.5V at 25°C. A cycle test was performed on the activated test batteries at a voltage range of 2.5V to 4.05V, 60°C, and 1 / 3C. The resistance increase rate (the rate of increase in resistance after the cycle test relative to the resistance before the cycle test) was calculated from the resistance values ​​before and after the cycle test. The resistance value was measured by measuring the 5-second discharge resistance of a battery adjusted to 50% SOC. Specifically, the voltage change ΔV when a 6C rate current was applied at 25°C was read, and the resistance value was calculated using Ohm's law (V = IR). The results are shown in Table 1. The relationship between specific surface area and resistance increase rate is shown in Figure 4(a), and the relationship between coverage and resistance increase rate is shown in Figure 4(b). In FIG. 4(b), the coverage of the comparative example was set to 0%.

[0064] [Table 1]

[0065] From the SEM images, it was confirmed that fine voids were formed on the surface of the p-Si in the comparative example. In contrast, it was confirmed that a solid electrolyte was disposed on the surface of the composite p-Si in Examples 1 to 3, making the surface shape smooth. Furthermore, as shown in Table 1, in all Examples, the specific surface area was reduced by the solid electrolyte coating to the area before coating (42.19 m). 2 / g). Here, as shown in Figures 4(a) and (b) and Table 1, the coverage rate in Example 3 was greater than that in Example 2, but the specific surface area in Example 2 was smaller. Although the reason for this is unclear, it is presumed that the size of the voids on the surface of the p-Si was smaller in Example 3 than in Example 2, and therefore, although the coverage rate itself was large, the solid electrolyte was not able to sufficiently fill the voids on the surface of the p-Si.

[0066] As shown in Table 1 and FIGS. 4(a) and (b), the battery resistance increase rate was suppressed in Examples 1 to 3 compared to the comparative example, confirming that the composite active material of the present disclosure can suppress the increase in battery resistance. [Explanation of symbols]

[0067] 1...electrode active material 2...Covering layer 10…Composite active material 20...battery

Claims

1. an electrode active material containing Si element and having voids therein; A composite active material having a coating layer that coats the surface of the electrode active material and contains a solid electrolyte, The BET specific surface area of ​​the composite active material is 40 m ２ / g or less, A composite active material having a coverage of 20% or more with the coating layer.

2. The composite active material according to claim 1 , wherein the coverage is 30% or more.

3. The BET specific surface area of ​​the composite active material is 20 m ２ The composite active material according to claim 1 , wherein the Mo content is 1 / g or more.

4. When the coating layer is removed from the composite active material to expose the electrode active material, The exposed electrode active material has a BET specific surface area of ​​40 m ２ 10. The composite active material of claim 1, wherein the SiO2 content is greater than 1 / g.

5. A battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, A battery, wherein the negative electrode active material layer contains the composite active material according to any one of claims 1 to 4.

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