Composite active material and manufacturing method of composite active material

Abstract

To provide a composite active material capable of suppressing the increase of battery resistance.SOLUTION: A disclosed composite active material has: an active material particle that has a core particle, a first coating layer that covers the core particle, and a second coating layer that covers the active material particle. The first coating layer contains a first solid electrolyte, and the second coating layer contains a carbon-based conductive material and a second solid electrolyte. In the active material particle, the proportion of the second coating layer that is in contact with the carbon-based conductive material (conductive material coverage rate) is 0.9% or more and less than 5.0%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to composite active materials and methods for making composite active materials. [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 a composite active material comprising composite particles containing an oxide-based solid electrolyte that covers all or part of the surfaces of the active material particles, and a sulfide-based solid electrolyte that further covers 76.0% or more of the surfaces of the composite particles.

[0004] Furthermore, Patent Document 2 discloses a method for producing a positive electrode material, which includes a first mixing step of mixing a positive electrode active material and a conductive additive to produce a first powder, a second mixing step of mixing a solid electrolyte and a conductive additive to produce a second powder, and a third mixing step of mixing the first powder and the second powder to produce a third powder. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-154407 [Patent Document 2] Japanese Patent Application Publication No. 2023-150188 Summary of the Invention [Problem to be solved by the invention]

[0006] As in the above-mentioned Patent Document 1, composite active materials in which the surface of an active material is coated with a solid electrolyte have been studied. Such composite active materials are expected to have the effect of suppressing the deterioration of the active material and suppressing an increase in battery resistance. However, there is room for further improvement in suppressing an increase in battery resistance.

[0007] 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]

[0008] [1] active material particles having a core particle and a first coating layer coating the core particle; a second coating layer that coats the active material particles, the first coating layer contains a first solid electrolyte, the second coating layer contains a carbon-based conductive material and a second solid electrolyte, A composite active material, wherein the proportion of the portion of the second coating layer that is in contact with the carbon-based conductive material in the active material particles (conductive material coverage) is 0.9% or more and less than 5.0%.

[0009] [2] The composite active material according to [1], wherein the first coating layer contains LiNbO3 as the first solid electrolyte.

[0010] [3] The composite active material according to [1] or [2], wherein the second coating layer contains a sulfide solid electrolyte as the second solid electrolyte.

[0011] [4] The composite active material according to any one of [1] to [3], wherein the proportion of the portion of the second coating layer that is in contact with the second solid electrolyte (solid electrolyte coverage) of the active material particles is 95% or more and 99% or less.

[0012] [5] A method for producing a composite active material according to any one of [1] to [4], a first step of preparing the active material particles; a second step of subjecting a mixture containing the active material particles, the second solid electrolyte, and the carbon-based conductive material to a compressive shear treatment to obtain the composite active material. [Effects of the Invention]

[0013] The present disclosure has an effect of providing a composite active material that can suppress an increase in battery resistance. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view illustrating a composite active material according to the present disclosure. [Figure 2] FIG. 1 is a flow diagram illustrating a method for producing a composite active material according to the present disclosure. [Figure 3] 1 is a surface SEM image of the composite active material obtained in Example 1. [Figure 4] 10 is a graph showing the measurement results of the conductive material coverage rate and the resistance increase rate. DETAILED DESCRIPTION OF THE INVENTION

[0015] The composite active material and the method for producing the composite active material according to the present disclosure will be described in detail below.

[0016] A. Composite active material FIG. 1 is a schematic cross-sectional view illustrating an example of a composite active material according to the present disclosure. Note that FIG. 1 is a schematic illustration of the composite active material according to the present disclosure, and the size and shape of each part are appropriately exaggerated for ease of understanding. The composite active material 20 shown in FIG. 1 includes active material particles 10 having a core particle 1 and a first coating layer 2 coating the core particle 1, and a second coating layer 11 coating the active material particles 10. The first coating layer 2 contains a first solid electrolyte, and the second coating layer 11 contains a carbon-based conductive material and a second solid electrolyte. In the active material particles 10, the proportion of the portion of the second coating layer 11 in contact with the carbon-based conductive material (conductive material coverage) is 0.9% or more and less than 5.0%.

[0017] According to the present disclosure, the composite active material has the predetermined first and second coating layers, and the conductive material coating rate is 0.9% or more and less than 5.0%, so that an increase in battery resistance can be suppressed.

[0018] As described above, composite active materials having a solid electrolyte layer formed on their surfaces have been investigated. However, in an electrode layer prepared by mixing such a composite active material with a conductive material, composite active materials that are in good contact with the conductive material (active materials with sufficient electron conduction paths) and composite active materials that are not in good contact with the conductive material (active materials with insufficient electron conduction paths) are mixed, which may result in uneven reactions in the electrode layer. Furthermore, the electrode layer may expand and contract during battery charging and discharging. In this regard, if the expansion and contraction of the electrode layer disrupts the electron conduction paths of the active material that is reacting locally, battery resistance may increase significantly. Furthermore, in the active material that is reacting locally, deterioration of the active material may be accelerated, resulting in an increase in battery resistance. In contrast, in the composite active material disclosed herein, a second coating layer containing a second solid electrolyte and a carbon-based conductive material is formed on the surface of the active material particles. Therefore, an electrode prepared using such a composite active material can increase the proportion of composite active materials with sufficient electron conduction paths. As a result, uneven reactions can be suppressed. Furthermore, because the conductive material coverage is 0.9% or more and less than 5.0%, it is presumed that the composite active material has a good balance between the electronic conduction path and the ionic conduction path, and these factors are presumed to be the reasons why the composite active material of the present disclosure can suppress an increase in battery resistance.

[0019] 1.Active material particles The active material particles have a core particle and a first coating layer that coats the core particle.

[0020] (1) Core particle The core particles are not particularly limited as long as they are active materials commonly used in batteries. Examples of the core particles include oxide active materials and metal active materials. Examples of oxide active materials include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and LiNi 0.8 Co 0.15 Al 0.05Examples of active materials include rock salt layered active materials such as O2, spinel active materials such as LiMn2O4 and lithium titanate, and olivine active materials such as LiFePO4. Examples of oxide active materials include SiO2. Examples of metal active materials include simple metals such as Si and alloys.

[0021] Average particle diameter of core particles D 50 is, for example, 100 nm or more, may be 1 μm or more, or may be 5 μm or more. On the other hand, the average particle diameter D of the core particles 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 analyzer. The core particle may be a primary particle or a secondary particle formed by aggregation of primary particles.

[0022] (2) First coating layer The first coating layer is a layer that coats the above-mentioned core particles and contains a first solid electrolyte.

[0023] The first solid electrolyte may be, for example, a lithium ion conductive oxide such as LiNbO3, Li4Ti5O, or Li3PO4, among which LiNbO3 is preferred.

[0024] The proportion of the first solid electrolyte in the first coating layer is not particularly limited, but is, for example, 90% by weight or more and 100% by weight or less. Here, the first coating layer may or may not contain a conductive material.

[0025] The coverage rate of the first coating layer is not particularly limited, but may be, for example, 50% or more, 60% or more, or 75% or more. On the other hand, the coverage rate may be 100% or less. The coverage rate may be 95% or less, 90% or less, or 80% or less. The coverage rate can be determined, for example, by observation with a scanning electron microscope (SEM).

[0026] The thickness of the first coating layer is not particularly limited, but is, for example, 1 nm or more and 100 nm or less. The thickness of the first coating layer can be determined, for example, from a cross-sectional SEM image.

[0027] (3) Active material particles Average particle diameter of active material particles (D 50 ) is not particularly limited, but is, for example, 100 nm or more and 50 μm or less. 50 The above is as stated above.

[0028] 2.Second coating layer The second coating layer is a layer that coats the above-mentioned active material particles, and contains a carbon-based conductive material and a second solid electrolyte.

[0029] Examples of carbon-based conductive materials include particulate carbon such as acetylene black (AB) and ketjen black (KB); and fibrous carbon such as carbon fiber (CF), carbon nanotube (CNT), and carbon nanofiber (CNF).

[0030] The proportion of the carbonaceous conductive material in the second coating layer is not particularly limited, but is, for example, 2% by weight or more and 10% by weight or less.

[0031] In the present disclosure, the proportion of the active material particles in contact with the carbon-based conductive material in the second coating layer is referred to as the conductive material coverage. The conductive material coverage is 0.9% or more and less than 5.0%. The conductive material coverage may be 1.0% or more, or 2.0% or more. On the other hand, the conductive material coverage may be 4.9% or less, 4.0% or less, or 3.0% or less. The conductive material coverage can be calculated by observation with a SEM (scanning electron microscope). More specifically, the method described in the Examples can be used.

[0032] The second solid electrolyte is typically an electrolyte having a different main anion element from the first solid electrolyte. Examples of the second solid electrolyte 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.

[0033] 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.

[0034] 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.)

[0035] The sulfide solid electrolyte may be glass (amorphous) or glass ceramics.

[0036] The proportion of the second solid electrolyte in the second coating layer is not particularly limited, but is, for example, 90% by weight or more and 98% by weight or less.

[0037] Here, the ratio of the portion of the active material particle in contact with the second solid electrolyte in the second coating layer is referred to as the solid electrolyte coverage. The solid electrolyte coverage is not particularly limited, but may be, for example, 75% or more, 90% or more, 95% or more, 96% or more, or 97% or more. On the other hand, the solid electrolyte coverage is, for example, 99% or less. The method for calculating the solid electrolyte coverage can be the same as the method for calculating the conductive material coverage described above.

[0038] The thickness of the second coating layer is not particularly limited, but is, for example, 0.1 μm or more and 10 μm or less. The thickness of the second coating layer can be determined, for example, from a cross-sectional SEM image.

[0039] The second coating layer may be formed on a part or the entire surface of the first particle. The coverage of the second coating layer is not particularly limited, but is, for example, 75% or more and 100% or less. Here, the surface of the first particle can be understood as the surface of the first coating layer and the surface of the core particle on which the first coating layer is not formed. Furthermore, the second coating layer may be formed on the surface of the core particle, as long as it is formed at least on the surface of the first coating layer of the first particle. In other words, the second coating layer may be formed on the surface of the core particle that is not coated with the first coating layer.

[0040] 3.Composite active material The composite active material is typically in the form of particles. The average particle diameter (D 50 ) is, for example, 1 μm or more and 50 μm or less.

[0041] The composite active material is usually used in batteries. In particular, the composite active material of the present disclosure is preferably used in an all-solid-state battery. The composite active material may be used as a positive electrode active material or a negative electrode active material in the battery, with the former being preferred. The materials and configuration of the battery may be conventionally known materials and configurations.

[0042] B. Method for manufacturing composite active material Fig. 2 is a flow diagram illustrating a method for producing a composite active material according to the present disclosure. As shown in Fig. 2, first, active material particles having core particles and a first coating layer coating the core particles are prepared (step 1). Next, a mixture containing the active material particles, the second solid electrolyte, and the carbon-based conductive material is subjected to a compressive shear treatment to obtain the composite active material (step 2).

[0043] According to the present disclosure, by subjecting a mixture containing active material particles, a second solid electrolyte, and a carbon-based conductive material to a compressive shear treatment, a second coating layer is formed on the surface of the active material particles, and a composite active material exhibiting the above-mentioned conductive material coverage can be produced.

[0044] 1.First step The first step is to prepare the active material particles described above. The active material particles are the same as those described in "A. Composite active material."

[0045] The active material particles can be prepared by forming a first coating layer on the surface of core particles using, for example, a sol-gel method or a spray-drying method. In the sol-gel method, for example, a composition containing raw materials for the first solid electrolyte and a dispersion medium is spray-coated onto the surface of the core particles using a tumbling fluidized bed coating device, and then the active material particles can be obtained by firing. In addition, the spray-drying method can be described in the examples below.

[0046] 2.Second process The second step is a step of subjecting a mixture containing the active material particles, the second solid electrolyte, and the carbon-based conductive material to a compressive shear treatment to obtain the composite active material. The second solid electrolyte and the carbon-based conductive material are the same as those described in "A. Composite active material."

[0047] The proportions of the active material particles, second solid electrolyte, and carbonaceous conductive material in the mixture are adjusted appropriately so as to obtain the above-mentioned conductive material coverage and solid electrolyte coverage.

[0048] The compressive shear treatment may be carried out by placing the mixture in a container, 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. The compressive shear energy is appropriately adjusted so that the second coating layer described above is formed.

[0049] 3.Composite active material The composite active material produced by the above-mentioned process is the same as that described in "A. Composite active material."

[0050] 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]

[0051] [Example 1] (Preparation of composite active material) First, the core particles (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The surface of the active material particles was coated with lithium niobate (LiNbO3). Specifically, hydrogen peroxide (30% by mass), ion-exchanged water, and niobic acid (Nb2O5·3H2O) were placed in a container, and then ammonia water (28% by mass) was added and stirred. Lithium hydroxide monohydrate (LiOH·H2O) was then added and dissolved. This prepared the coating solution. The core particles and the coating liquid were mixed to prepare a suspension. This suspension was dried using a BUCHI Mini Spray Dryer B-290 to obtain a solid component. The solid component was then heat-treated at 200°C for 5 hours. This resulted in core particles (active material particles) coated with LiNbO3.

[0052] Next, the active material particles, sulfide solid electrolyte (LiI-Li2S-P2S5; glass ceramics), and carbon-based conductive material (carbon black) were mixed under shear force (compression shear treatment) using a dry particle composite device (Nobilta) manufactured by Hosokawa Micron Corporation. This resulted in a composite active material in which a second coating layer containing the sulfide solid electrolyte and carbon black was formed on the surface of the active material particles.

[0053] (Preparation of evaluation battery) The composite active material, sulfide solid electrolyte (LiI-Li2S-P2S5; glass ceramics), binder (styrene butadiene rubber (SBR)), conductive material (carbon nanotubes), and dispersion medium (1,2,3,4-tetrahydronaphthalene) were mixed to obtain a positive electrode slurry. The weight ratio of the composite active material, sulfide solid electrolyte, binder, and conductive material in the positive electrode slurry was 81.2:16.5:0.3:1.9. The positive electrode slurry was applied to a positive electrode current collector (Al foil) and dried to obtain a positive electrode having a positive electrode active material layer and a positive electrode current collector.

[0054] In addition, the negative electrode active material (Li4Ti5O 12The negative electrode slurry was obtained by mixing the negative electrode active material, sulfide solid electrolyte (LiI-Li2S-P2S5; glass ceramics), binder (SBR), conductive material (carbon nanotubes), and dispersion medium (diisobutyl ketone). The weight ratio of the negative electrode active material, sulfide solid electrolyte, binder, and conductive material in the negative electrode slurry was 72.2:24.3:1.8:2.4. 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. The size of the negative electrode was adjusted to be larger than the size of the positive electrode.

[0055] 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.

[0056] 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).

[0057] [Example 2] A composite active material and a test battery were prepared in the same manner as in Example 1, except that the proportions of the active material particles, sulfide solid electrolyte, and carbon-based conductive material in the compressive shear treatment were changed as shown in Table 1. Ta.

[0058] [Table 1]

[0059] [Comparative Example 1] A test battery was fabricated in the same manner as in Example 1, except that the positive electrode was fabricated using the above-described active material particles instead of the composite active material.

[0060] Comparative Example 2 The active material particles and a sulfide solid electrolyte (LiI-Li2S-P2S5; glass ceramics) were mixed under shear using a dry particle compositing device (Nobilta) manufactured by Hosokawa Micron Corporation. This resulted in composite particles in which a second coating layer not containing a carbon-based conductive material was formed on the surface of the active material particles. A test battery was fabricated in the same manner as in Example 1, except that a positive electrode was fabricated using these composite particles.

[0061] Comparative Example 3 The active material particles and a carbon-based conductive material (carbon nanotubes) were mixed under shear using a dry particle compositing device (Nobilta) manufactured by Hosokawa Micron Corporation. This resulted in composite particles in which a second coating layer not containing a sulfide solid electrolyte was formed on the surface of the active material particles. A test battery was fabricated in the same manner as in Example 1, except that a positive electrode was fabricated using these composite particles.

[0062] [evaluation] (Surface observation of composite active material) The composite active material of Example 1 was subjected to SEM observation and EDX analysis to observe the surface. The SEM image is shown in FIG. 3. As shown in FIG. 3, it was confirmed that the sulfide solid electrolyte was disposed on the surface of the composite active material. Furthermore, the results of the EDX analysis confirmed that carbon elements derived from the carbonaceous conductive material were disposed on the surface of the composite active material.

[0063] (Measurement of coverage) Surface SEM images were taken for the composite active materials of Examples 1 and 2 and Comparative Example 3. From the obtained images, binary images of the conductive material-coated and uncoated areas were created. The image analysis software "ImageJ" was used to create the binary images. The image analysis software was then used to determine the area of ​​the coated and uncoated areas within the images. These values ​​were used to calculate the conductive material coverage rate according to the following formula. The results are shown in Table 2. In the formula below, the area of ​​the coated and uncoated areas refers to the area of ​​the entire active material particle. Similarly, the proportion of the area coated with sulfide solid electrolyte (solid electrolyte coverage rate) was calculated for the composite active materials of Examples 1 and 2. The results are shown in Table 2.

[0064]

number

[0065] (Charge / discharge evaluation: cycle test) The test batteries obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were activated by CCCV charging at 1 / 3C to 2.95V at 25°C and then CCCV discharging at 1 / 3C to 1.5V at 25°C. A cycle test was performed on the activated test batteries at a voltage range of 1.5V to 2.95V, 60°C, and 1C. 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 results are shown in Table 2. For resistance values, the 5-second discharge resistance was measured for batteries adjusted to an SOC of 20%. Specifically, the voltage change ΔV when a current of 2.5C was applied at 25°C was read, and the resistance value was calculated using Ohm's law (V = IR). The results of the conductive material coverage and resistance increase rate are summarized in Figure 4. In Figure 4, the conductive material coverage rates of Comparative Examples 1 and 2 are shown as 0%.

[0066] (Electron conductivity measurement) Furthermore, the electronic conductivity was measured for the positive electrodes produced in Examples 1 and 2 and Comparative Example 1. The results are shown in Table 2.

[0067] [Table 2]

[0068] As shown in Table 2 and Figure 4, it was confirmed that the resistance increase rate was smaller in all Examples than in the Comparative Examples, and the increase in battery resistance was suppressed. Furthermore, in Comparative Example 3, although the conductive material coverage was high, the absence of a sulfide solid electrolyte in the second coating layer precluded the formation of a good interface between the composite active material and the electrolyte in the positive electrode active material layer, which is thought to have resulted in an increase in resistance. Note that the solid electrolyte coverage rate for the composite active material of Comparative Example 2 was not calculated, but it is presumed to be higher than the solid electrolyte coverage rates of Examples 1 and 2. [Explanation of symbols]

[0069] 1...core particle 2...First coating layer 10...Active material particles 11...Second coating layer 20…Composite active material

Claims

1. active material particles having a core particle and a first coating layer coating the core particle; a second coating layer that coats the active material particles, the first coating layer contains a first solid electrolyte, the second coating layer contains a carbon-based conductive material and a second solid electrolyte, A composite active material, wherein the ratio of the portion of the second coating layer that is in contact with the carbon-based conductive material in the active material particles (conductive material coating rate) is 0.9% or more and less than 5.0%.

2. The first coating layer contains LiNbO as the first solid electrolyte. ３ The composite active material of claim 1 , comprising:

3. The composite active material according to claim 1 , wherein the second coating layer contains a sulfide solid electrolyte as the second solid electrolyte.

4. 2. The composite active material according to claim 1, wherein a ratio of a portion of the second coating layer that is in contact with the second solid electrolyte in the active material particles (solid electrolyte coverage) is 95% or more and 99% or less.

5. A method for producing a composite active material according to any one of claims 1 to 4, a first step of preparing the active material particles; a second step of subjecting a mixture containing the active material particles, the second solid electrolyte, and the carbon-based conductive material to a compressive shear treatment to obtain the composite active material.

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