Living Substance Composite Particles, Secondary Battery, and Method for Producing Living Substance Composite Particles

Abstract

To provide an active material composite particle containing Si that is excellent in cycle characteristic under low restraint.SOLUTION: An active material composite particle contains Si and a resin. Here, in a case where a cross section of the composite particle is observed, an area rate of the resin that occupies a surface layer part of the composite particle is higher than an area rate of the resin that occupies a central part of the composite particle.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] This application discloses active material composite particles, a secondary battery, and a method for manufacturing the active material composite particles.

Background Art

[0002] Patent Document 1 discloses a negative electrode active material having a small amount of expansion during charging, which is composed of non-woven fabric-like particles containing Si fibers, has a predetermined average particle diameter (D50), and is amorphous. Further, Patent Document 2 discloses a negative electrode active material having a small initial irreversible capacity, which has secondary particles of Si-based particles and a fluorinated layer formed on the surface of the secondary particles.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional active materials containing Si have room for improvement, for example, in cycle characteristics under low constraints.

Means for Solving the Problems

[0005] As means for solving the above problems, this application discloses the following multiple aspects. <Aspect 1> Active material composite particles, comprising Si and a resin, when observing a cross-section of the composite particles, the area ratio of the resin in the surface layer portion of the composite particles is higher than the area ratio of the resin in the central portion of the composite particles, Active material composite particles. <Aspect 2> When observing the cross-section of the composite particles, the porosity in the central portion of the composite particles is higher than the porosity in the surface layer portion of the composite particles. The active material composite particles of Embodiment 1. <Embodiment 3> When observing the cross-section of the composite particles, the area ratio of Si in the central portion of the composite particles is higher than the area ratio of Si in the surface layer portion of the composite particles. The active material composite particles of Embodiment 1 or 2. <Embodiment 4> The surface layer portion is made of the resin. The active material composite particles of any one of Embodiments 1 to 3. <Embodiment 5> The central portion contains a plurality of Si particles. The active material composite particles of any one of Embodiments 1 to 4. <Embodiment 6> The Si particles are porous. The active material composite particles of Embodiment 5. <Embodiment 7> The composite particles have a surface layer portion containing the resin and a central portion containing a plurality of the Si particles and voids. The active material composite particles of Embodiment 5 or 6. <Embodiment 8> A secondary battery having a positive electrode, an electrolyte layer, and a negative electrode. The negative electrode contains the active material composite particles of any one of Embodiments 1 to 7. Secondary battery. <Embodiment 9> At least one of the positive electrode, the electrolyte layer, and the negative electrode contains a solid electrolyte. The secondary battery of Embodiment 8. <Embodiment 10> Atomizing a slurry containing Si particles, a resin, and a solvent to obtain slurry droplets, and Airflow drying the slurry droplets in a heated gas to obtain an active material composite containing Si particles and a resin. A method for manufacturing active material composite particles, including the above steps. <Embodiment 11> By spray drying, atomization of the slurry and airflow drying of the slurry droplets are performed. The manufacturing method of Mode 10.

Advantages of the Invention

[0006] The active material composite particles of the present disclosure are excellent in cycle characteristics under low restraint.

Brief Description of the Drawings

[0007]

Figure 1A

Figure 1B

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5A

Figure 5B

Figure 6

Modes for Carrying Out the Invention

[0008] 1. Active material composite particles FIG. 1A schematically shows the cross-sectional structure of active material composite particles 1 according to one embodiment. The active material composite particles 1 contain Si and resin. Here, when observing the cross section of the composite particles 1, the area ratio of the resin in the surface layer part 1x of the composite particles 1 is higher than the area ratio of the resin in the central part 1y of the composite particles 1.

[0009] 1.1 Surface part and central part In the present application, the "surface part" and "central part" of the active material composite particles are defined as follows. That is, when observing the cross-section of the active material composite particle 1, if a boundary is observed between the outermost resin-rich layer and the inner layer, the outermost layer outside the boundary is regarded as the surface part 1x, and the inner layer inside the boundary is regarded as the central part 1y. On the other hand, when observing the cross-section of the active material composite particle 1, if no boundary is observed between the surface part 1x and the central part 1y inside it, the surface part 1x and the central part 1y shall be distinguished as follows. Specifically, the surface part 1x of the active material composite particle 1 is specified as follows. That is, as shown in FIG. 1B, the cross-section of the active material composite particle is observed with a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc. to obtain a two-dimensional image of the cross-section of the active material composite particle. When the area of the region X from the surface of the active material composite particle to a predetermined depth in the two-dimensional image is a1 and the area of the entire particle is a1 + a2, the region X where a1 / (a1 + a2) = 0.5 is regarded as the "surface part of the active material composite particle". The part (inner part) deeper than the "surface part of the active material composite particle" specified in this way can be the "central part of the active material composite particle".

[0010] 1.1.1 Area ratio of resin When observing the cross-section of the active material composite particle 1, the area ratio of the resin in the surface layer portion 1x of the composite particle 1 is higher than the area ratio of the resin in the central portion 1y of the composite particle 1. For example, the active material composite particle 1 may have a resin-rich portion in the surface layer portion 1x, or the surface layer portion 1x may be made of resin, that is, the surface layer portion 1x may be a resin layer 2. Thus, when Si expands due to charging, the high ratio of resin in the surface layer portion 1x of the composite particle 1 relaxes the volume change of the entire composite particle 1 by the resin in the surface layer portion 1x, and the shape of the entire composite particle 1 is easily maintained. Also, when Si expands due to charging, the high ratio of resin in the surface layer portion 1x causes the resin in the surface layer portion 1x to function as a cushioning material, and cracks and gaps are less likely to occur in the materials around the composite particle 1. Therefore, excellent cycle characteristics are likely to be exhibited under both high and low confinement pressures.

[0011] The area ratio AR of the resin in the surface layer portion 1x of the active material composite particle 1 1 and the area ratio AR of the resin in the central portion 1y of the composite particle 1 2 The ratio AR 1 / AR 2 is not particularly limited. For example, the ratio AR 1 / AR 2 may be greater than 1.0, 1.5 or more, 2.0 or more, 2.5 or more, 3.0 or more, 3.5 or more, 4.0 or more, 4.5 or more, or 5.0 or more. The upper limit of the ratio AR 1 / AR 2 is not particularly limited, and AR 2 may be 0%. Also, the value of the area ratio AR 1 of the resin in the surface layer portion 1x of the composite particle 1 is not particularly limited. For example, when observing the cross-section of the composite particle 1, assuming the total area of the surface layer portion 1x is 100 area%, the area ratio AR 1 of the resin contained in the surface layer portion 1x may be 70 area% or more and 100 area% or less, 80 area% or more and 100 area% or less, or 90 area% or more and 100 area% or less. Further, the area ratio AR 2is not particularly limited. For example, when observing the cross-section of the composite particle 1, with the total area of the central portion 1y being 100 area%, the area ratio AR of the resin contained in the central portion 1y 2 may be 0 area% or more and 30 area% or less, 0 area% or more and 20 area% or less, or 0 area% or more and 10 area%.

[0012] In addition, the area ratio AR of the resin in the surface layer portion 1x of the active material composite particle 1 1 and the area ratio AR of the resin in the central portion 1y of the composite particle 1 2 can be obtained by performing elemental analysis on the cross-section of the composite particle 1 by means of EDX or the like and identifying the region where the resin exists in the cross-section.

[0013] 1.1.2 Porosity When observing the cross-section of the active material composite particle 1, the porosity in the central portion 1y of the composite particle 1 may be higher than the porosity in the surface layer portion 1x of the composite particle 1. That is, the active material composite particle 1 may have voids 3 in the central portion 1y. Also, the active material composite particle 1 may or may not have voids 3 in the surface layer portion 1x. In this way, by having a higher porosity in the central portion 1y than in the surface layer portion 1x, even when Si expands due to charging, the expansion of the Si can be absorbed by the voids, the volume change of the entire composite particle 1 is alleviated, and the shape of the entire composite particle 1 is easily maintained. Further, by alleviating the volume change of the entire composite particle 1, cracks and gaps are less likely to occur in the materials around the composite particle 1. Therefore, excellent cycle characteristics are more likely to be exhibited under both high confinement pressure and low confinement.

[0014] The porosity P in the surface layer portion 1x of the active material composite particle 1 1 and the porosity P in the central portion 1y of the composite particle 1 2 The ratio P 1 / P 2 is not particularly limited. For example, the ratio P 1 / P 2may be less than 1.0, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. The ratio P 1 / P 2 has no particular lower limit and may be 0 (P 1 = 0%). Also, the porosity P 1 in the surface layer portion 1x of the composite particle 1 is not particularly limited. For example, when observing the cross-section of the composite particle 1, with the total area of the surface layer portion 1x being 100 area%, the area ratio P 1 of the voids contained in the surface layer portion 1x may be 0 area% or more and 10 area% or less, 0 area% or more and 7 area% or less, 0 area% or more and 5 area% or less, 0 area% or more and 3 area% or less, or 0 area% or more and 1 area% or less. Further, the porosity P 2 in the central portion 1y of the composite particle 1 is not particularly limited. For example, when observing the cross-section of the composite particle 1, with the total area of the central portion 1y being 100 area%, the area ratio P 2 of the voids contained in the central portion 1y may be more than 0 area% and 50 area% or less, 10 area% or more and 50 area% or less, or 20 area% or more and 50 area% or less.

[0015] Incidentally, the porosity P 1 in the surface layer portion 1x of the active material composite particle 1 and the porosity P 2 in the central portion 1y of the composite particle 1 can be determined by performing elemental analysis on the cross-section of the composite particle 1 by means of EDX or the like and identifying the regions where voids exist in the cross-section.

[0016] 1.1.3 Area ratio of Si When observing the cross-section of the active material composite particle 1, the area ratio of Si in the central portion 1y of the composite particle 1 may be higher than the area ratio of Si in the surface layer portion 1x of the composite particle 1. That is, the active material composite particle 1 may have an Si-rich portion in the central portion 1y. Further, the central portion 1y may contain a plurality of Si particles 4. Thus, when Si expands due to charging, since the area ratio of Si in the central portion 1y is higher than the area ratio of Si in the surface layer portion 1x, it is difficult for the expansion of the Si to reach the outside of the composite particle 1, the volume change of the entire composite particle 1 is alleviated, and the shape of the entire composite particle 1 is easily maintained. Further, since the volume change of the entire composite particle 1 is alleviated, cracks and gaps are less likely to occur in the material around the composite particle 1. Therefore, excellent cycle characteristics are more likely to be exhibited under both high and low confinement pressures.

[0017] The area ratio AR of Si in the surface layer portion 1x of the active material composite particle 1 3 and the area ratio AR of Si in the central portion 1y of the composite particle 1 4 The ratio AR 3 / AR 4 is not particularly limited. For example, the ratio AR 3 / AR 4 may be less than 1.0, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. The lower limit of the ratio AR 3 / AR 4 is not particularly limited and may be 0 (AR 3 = 0%). Further, the value of the area ratio AR of Si in the surface layer portion 1x of the composite particle 1 3 is not particularly limited. For example, when observing the cross-section of the composite particle 1, with the total area of the surface layer portion 1x being 100 area%, the area ratio AR of Si contained in the surface layer portion 1x 3 may be 0 area% or more and 30 area% or less, 0 area% or more and 20 area% or less, or 0 area% or more and 10 area% or less. Further, the area ratio AR of Si in the central portion 1y of the composite particle 1 4is not particularly limited. For example, when observing the cross-section of the composite particle 1, with the total area of the central portion 1y being 100 area%, the area ratio AR of Si contained in the central portion 1y 4 may be 50 area% or more and less than 100 area%, 50 area% or more and 90 area% or less, or 50 area% or more and 80 area% or less.

[0018] In addition, the area ratio AR of Si in the surface layer portion 1x of the active material composite particle 1 3 and the area ratio AR of Si in the central portion 1y of the composite particle 1 4 can be determined by performing elemental analysis on the cross-section of the composite particle 1 by means of EDX or the like and specifying the region where Si exists in the cross-section.

[0019] 1.2 Si The active material composite particle 1 contains Si. As shown in FIG. 1A, in the active material composite particle 1, Si may be contained, for example, as particles. The Si particles may exist as primary particles or as secondary particles. The composition of the Si particles is not particularly limited. The proportion of the Si element in all the elements contained in the Si particles may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. The Si particles may contain other elements such as Li element in addition to the Si element. Examples of other elements include, in addition to the Li element, Sn element, Fe element, Co element, Ni element, Ti element, Cr element, B element, P element, etc. Further, the Si particles may contain impurities such as oxides. The Si particles may be amorphous or crystalline. The crystal phase contained in the Si particles is not particularly limited.

[0020] When the Si contained in the active material composite particle 1 is in the form of particles, the number of Si particles contained in one active material composite particle 1 is not particularly limited. The number of Si particles may be 2 or more, 5 or more, 10 or more, 50 or more, or 100 or more, and may also be 10000 or less, 1000 or less, or 500 or less.

[0021] When the Si contained in the active material composite particle 1 is in the form of particles, its size is not particularly limited. The average primary particle diameter of the Si particles may be, for example, 10 nm or more, 30 nm or more, 50 nm or more, 100 nm or more, or 150 nm or more, and may be 10 μm or less, 5 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less. Also, the average secondary particle diameter of the Si particles may be, for example, 100 nm or more, 1 μm or more, or 2 μm or more, and may be 20 μm or less, 15 μm or less, or 10 μm or less. Incidentally, the average primary particle diameter and the average secondary particle diameter can be determined by observation with an electron microscope such as SEM. For example, they are determined as the average value of the maximum Feret diameters of each of a plurality of particles. The number of samples is preferably large, for example 20 or more, and may be 50 or more, or 100 or more. The average primary particle diameter and the average secondary particle diameter can be appropriately adjusted, for example, by appropriately changing the manufacturing conditions of the Si particles or performing a classification process.

[0022] When the Si contained in the active material composite particle 1 is in the form of particles, the Si particles may be porous. For example, when the central portion 1y contains a plurality of Si particles, the porosity of the Si particles can reduce the amount of expansion of Si during charging. There is no particular limitation on the form of the voids in the porous Si particles. The porous Si particles may be particles containing nanoporous silicon. Nanoporous silicon refers to silicon in which there are a plurality of pores having a pore diameter on the order of nanometers (less than 1000 nm, preferably 100 nm or less). The porous Si particles may contain pores with a diameter of 55 nm or less. Pores with a diameter of 55 nm or less are difficult to be crushed by pressing. That is, the porous Si particles containing pores with a diameter of 55 nm or less are likely to maintain their porosity even after pressing. For example, per 1 g of the porous Si particles, the pores with a diameter of 55 nm or less may be contained in an amount of 0.21 cc or more, 0.22 cc / g or more, or 0.23 cc / g or more, and may be contained in an amount of 0.30 cc / g or less, 0.28 cc / g or less, or 0.26 cc / g or less. The amount of pores with a diameter of 55 nm or less contained in the porous Si particles can be determined, for example, from the pore size distribution by the nitrogen gas adsorption method or the DFT method.

[0023] When the active material composite particles 1 contain porous Si particles, the porous Si particles may have a predetermined porosity. The porosity of the porous Si particles may be, for example, 1% or more, 5% or more, 10% or more, or 20% or more, and may be 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, or 30% or less. The porosity of the Si particles can be determined, for example, by observation using a scanning electron microscope (SEM). It is preferable that the number of samples is large, for example, 100 or more. The porosity can be the average value obtained from these samples.

[0024] 1.3 Resin The active material composite particles 1 contain a resin. The resin may have a function as a binder that binds Si particles to each other, for example. The type of resin is not particularly limited. As the resin, various binders known as constituent materials of secondary batteries may be employed. For example, it may be selected from butadiene rubber (BR)-based binders, isobutylene rubber (IIR)-based binders, acrylate butadiene rubber (ABR)-based binders, styrene butadiene rubber (SBR)-based binders, polyvinylidene fluoride (PVdF)-based binders, polytetrafluoroethylene (PTFE)-based binders, polyimide (PI)-based binders, carboxymethyl cellulose (CMC)-based binders, polyacrylate-based binders, polyacrylate ester-based binders, etc. In particular, the performance of PVdF-based binders is high. The PVdF-based binder may be a copolymer having units derived from monomers other than VdF. Only one type of resin may be used alone, or two or more types may be used in combination.

[0025] When the Si particles are included in the active material composite particles 1, the mass ratio of the Si particles in the active material composite particles 1 is not particularly limited. For example, the active material composite particles 1 may contain 70% by mass or more and 90% by mass or less of the Si particles. The mass ratio of the resin in the active material composite particles 1 is not particularly limited. For example, the active material composite particles 1 may contain 10% by mass or more and 30% by mass or less of the resin. Furthermore, the ratio of the Si particles and the resin contained in the active material composite particles 1 is not particularly limited as long as the composite particles 1 can be formed. For example, the ratio of the resin in the total of the Si particles and the resin may be 1% by mass or more, 5% by mass or more, or 8% by mass or more, and may be 30% by mass or less, 28% by mass or less, 26% by mass or less, 24% by mass or less, or 22% by mass or less. When the ratio of the resin in the total of the Si particles and the resin is 1% by mass or more and 30% by mass or less, it is easier to secure a larger charge-discharge capacity.

[0026] 1.4 Other Components The active material composite particles 1 may consist only of the above-mentioned Si and resin (and voids), or may contain other components other than these. Examples of the other components include various solid components and liquid components.

[0027] 1.5 Particle Size of Active Material Composite Particles The active material composite particle 1 can be regarded as a secondary particle in which a plurality of Si particles are aggregated via a resin. The average particle diameter of the composite particle 1 is not particularly limited. The average particle diameter of the composite particle 1 may be 100 nm or more, 1 μm or more, 2 μm or more, or 3 μm or more, and may also be 20 μm or less, 15 μm or less, or 10 μm or less. The average particle diameter of the composite particle 1 can be determined by observation with an electron microscope such as SEM. For example, it can be determined as the average value of the maximum Feret diameters of a plurality of composite particles. The number of samples is preferably large, for example, 20 or more, and may be 50 or more, or 100 or more. Alternatively, only the composite particle 1 is taken out, and the average particle diameter (D50, median diameter) of the composite particle 1 measured using a laser diffraction particle size distribution measuring device may be 100 nm or more, 1 μm or more, 2 μm or more, or 3 μm or more, and may also be 20 μm or less, 15 μm or less, or 10 μm or less.

[0028] 1.6 Structure and Shape of Active Material Composite Particles As described above, the active material composite particle 1 may have the surface layer portion 1x containing the resin and the central portion 1y containing the plurality of Si particles and voids. Further, the active material composite particle 1 may have a major axis and a minor axis, for example, in a state before being applied to a secondary battery. The ratio of the major axis to the minor axis (major axis / minor axis) may be, for example, 1.0 or more or 1.1 or more, and may also be 1.3 or less or 1.2 or less. On the other hand, as will be described later, when the active material composite particle 1 is applied to the negative electrode active material layer of a secondary battery, the negative electrode active material layer can be formed by pressing the negative electrode active material composite material containing the active material composite particle 1. At this time, the composite particle 1 can be crushed in the pressing direction and have an aspect ratio of a predetermined value or more. By pressing the composite particle 1 to have an aspect ratio of a predetermined value or more, the contact resistance within the composite particle, the contact resistance between composite particles, and the contact resistance between the composite particle and other materials are likely to be reduced. Specifically, from the viewpoint that the resistance of the negative electrode described later becomes even smaller, when observing the cross-section of the negative electrode active material layer, more than half (50% or more in terms of the number ratio) of the plurality of composite particles 1 extracted by the following extraction method may have an aspect ratio of 1.5 or more.

[0029] Extraction method: Observe the cross-section of the active material layer, extract the composite particles contained in the cross-section in descending order of cross-sectional area, and end the extraction when the total area of the extracted composite particles exceeds 80% of the total area of all the composite particles contained in the cross-section.

[0030] In addition, the above extraction method may be performed by image analysis based on the cross-sectional image of the active material layer obtained by SEM or the like. In the image analysis, the composite particles contained in the image may be approximated by an ellipse, and the aspect ratio of each composite particle may be specified.

[0031] 2. Secondary battery Fig. 2 schematically shows the configuration of a secondary battery 100 according to an embodiment. As shown in Fig. 2, the secondary battery 100 has a positive electrode 10, an electrolyte layer 20, and a negative electrode 30, and the negative electrode 30 contains the above-mentioned active material composite particles 1. In the secondary battery 100, at least one of the positive electrode 10, the electrolyte layer 20, and the negative electrode 30 may contain a solid electrolyte. Also, all of the positive electrode 10, the electrolyte layer 20, and the negative electrode 30 of the secondary battery 100 may contain a solid electrolyte. Further, the secondary battery 100 may be a solid battery. A solid battery refers to one in which an electrolyte having carrier ion conductivity is mainly composed of a solid electrolyte. However, a liquid component may be included at the additive level. Alternatively, the secondary battery 100 may be an all-solid battery substantially free of liquid components.

[0032] 2.1 Positive electrode The positive electrode 10 may be any one that can function properly as the positive electrode of a secondary battery, and its configuration is not particularly limited. As shown in Fig. 2, the positive electrode 10 may include a positive electrode active material layer 11 and a positive electrode current collector 12.

[0033] 2.1.1 Positive electrode active material layer The positive electrode active material layer 11 contains at least a positive electrode active material, and may further optionally contain an electrolyte, a conductive assistant, a binder, etc. The positive electrode active material layer 11 may also contain various other additives. The content of each component in the positive electrode active material layer 11 may be appropriately determined according to the intended battery performance. For example, taking the entire positive electrode active material layer 11 (the entire solid content) as 100% by mass, the content of the positive electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, and may also be 100% by mass or less or 90% by mass or less. The shape of the positive electrode active material layer 11 is not particularly limited, and for example, it may be a sheet-shaped positive electrode active material layer having a substantially flat surface. The thickness of the positive electrode active material layer 11 is not particularly limited, and for example, it may be 0.1 μm or more, 1 μm or more, or 10 μm or more, and may also be 2 mm or less, 1 mm or less, or 500 μm or less.

[0034] As the positive electrode active material, those known as the positive electrode active material of a secondary battery may be used. Among the known active materials, a material having a relatively noble potential (charge-discharge potential) for occluding and releasing a predetermined carrier ion (for example, lithium ion) can be used as the positive electrode active material. The positive electrode active material may be, for example, at least one selected from various lithium-containing compounds, elemental sulfur, sulfur compounds, etc. The lithium-containing compound as the positive electrode active material is lithium cobaltate, lithium nickelate, Li 1±α Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O 2±δ , lithium manganate, spinel-type lithium compounds (Li 1+x Mn 2-x-y M y O 4 (M is one or more selected from Al, Mg, Co, Fe, Ni, and Zn), such as hetero-element-substituted Li-Mn spinel with a composition represented thereby), lithium titanate, lithium metal phosphate (LiMPO 4Etc., M may be various lithium-containing oxides such as one or more selected from Fe, Mn, Co, and Ni. In particular, when the positive electrode active material contains a lithium-containing oxide including at least Li, at least one of Ni, Co, and Mn, and O as constituent elements, a higher effect can be expected. Only one type of positive electrode active material may be used alone, or two or more types may be used in combination.

[0035] The shape of the positive electrode active material may be a general shape as a positive electrode active material of a battery. The positive electrode active material may be, for example, particulate. The positive electrode active material may be solid, hollow, may have voids, or may be porous. The positive electrode active material may be primary particles or secondary particles in which a plurality of primary particles are aggregated. The average particle diameter D50 of the positive electrode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Note that the average particle diameter D50 referred to in the present application is the particle diameter (median diameter) at the integrated value 50% in the volume-based particle size distribution determined by the laser diffraction / scattering method.

[0036] A protective layer containing an ion-conductive oxide may be formed on the surface of the positive electrode active material. Thereby, reactions between the positive electrode active material and sulfides (for example, the sulfide solid electrolyte described later) are likely to be suppressed. Examples of the ion-conductive oxide include Li 3 BO 3 、LiBO 2 、Li 2 CO 3 、LiAlO 2 、Li 4 SiO 4 、Li 2 SiO 3 、Li 3 PO 4 、Li 2 SO 4 、Li 2 TiO 3 、Li 4 Ti 5 O 12 、Li 2 Ti2 O 5 , Li 2 ZrO 3 , LiNbO 3 , Li 2 MoO 4 , Li 2 WO 4 and the like. The ion conductive oxide may be one in which some elements are substituted by doping elements such as P and B. The coverage rate (area ratio) of the protective layer on the surface of the positive electrode active material may be, for example, 70% or more, 80% or more, or 90% or more. The thickness of the protective layer may be, for example, 0.1 nm or more or 1 nm or more, or 100 nm or less or 20 nm or less.

[0037] The electrolyte that can be included in the positive electrode active material layer 11 may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. In particular, when the positive electrode active material layer 11 contains at least a solid electrolyte as the electrolyte, a higher effect is likely to be obtained.

[0038] As the solid electrolyte, those known as solid electrolytes for secondary batteries may be used. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, inorganic solid electrolytes have high ionic conductivity and excellent heat resistance. Examples of inorganic solid electrolytes include lithium lanthanum zirconate, LiPON, Li 1+X Al X Ge 2-X (PO 4 ) 3 , oxide solid electrolytes such as Li-SiO-based glass and Li-Al-S-O-based glass; Li 2 S-P 2 S 5 , Li 2 S-SiS 2 , LiI-Li 2 S-SiS 2 , LiI-Si 2 S-P 2 S 5 , Li 2 S-P 2 S 5 , -LiI-Li 2S-P 2 S 5 、LiI-Li 2 S-P 2 O 5 、LiI-Li 3 PO 4 -P 2 S 5 、Li 2 S-P 2 S 5 -GeS 2 Examples of the sulfide solid electrolyte include S-P, 2 S, 5 , LiI-Li, 2 S-P, 2 O, 5 , LiI-Li, 3 PO, 4 -P, 2 S, 5 , Li, 2 S-P, 2 S, 5 -GeS, 2 and the like. In particular, the sulfide solid electrolyte, especially the sulfide solid electrolyte containing at least Li, S, and P as constituent elements, has high performance. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be, for example, particulate. Only one kind of the solid electrolyte may be used alone, or two or more kinds may be used in combination.

[0039] The electrolytic solution may contain a predetermined carrier ion (for example, lithium ion). The electrolytic solution may be, for example, a non-aqueous electrolytic solution. The composition of the electrolytic solution may be the same as that known as the composition of the electrolytic solution of the secondary battery. For example, as the electrolytic solution, a solution in which a lithium salt is dissolved in a carbonate solvent at a predetermined concentration can be used. Examples of the carbonate solvent include fluoroethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC), and the like. Examples of the lithium salt include LiPF 6 and the like.

[0040] Examples of the conductive auxiliary agent that may be included in the positive electrode active material layer 11 include carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotube (CNT), and carbon nanofiber (CNF); and metal materials such as nickel, aluminum, and stainless steel. The conductive auxiliary agent may be, for example, particulate or fibrous, and its size is not particularly limited. Only one kind of the conductive auxiliary agent may be used alone, or two or more kinds may be used in combination.

[0041] Examples of the binder that can be included in the positive electrode active material layer 11 include, for example, butadiene rubber (BR)-based binders, isobutylene rubber (IIR)-based binders, acrylate butadiene rubber (ABR)-based binders, styrene butadiene rubber (SBR)-based binders, polyvinylidene fluoride (PVdF)-based binders, polytetrafluoroethylene (PTFE)-based binders, polyimide (PI)-based binders, and the like. Only one type of binder may be used alone, or two or more types may be used in combination.

[0042] 2.1.2 Positive Electrode Current Collector As shown in FIG. 2, the positive electrode 10 may include a positive electrode current collector 12 that contacts the above-described positive electrode active material layer 11. Any of the commonly used materials for the positive electrode current collector of a battery can be adopted as the positive electrode current collector 12. Also, the positive electrode current collector 12 may be in the form of a foil, a plate, a mesh, a punched metal, a foam, or the like. The positive electrode current collector 12 may be composed of a metal foil or a metal mesh. In particular, a metal foil is excellent in terms of handleability and the like. The positive electrode current collector 12 may be composed of a plurality of foils. Examples of the metal constituting the positive electrode current collector 12 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. In particular, from the viewpoint of ensuring oxidation resistance, etc., the positive electrode current collector 12 may contain Al. The positive electrode current collector 12 may have some coating layer on its surface for the purpose of adjusting resistance or the like. Also, the positive electrode current collector 12 may be a metal foil or a substrate on which the above-described metal is plated or vapor-deposited. Further, when the positive electrode current collector 12 is composed of a plurality of metal foils, there may be some layer between the plurality of metal foils. The thickness of the positive electrode current collector 12 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, and may be 1 mm or less or 100 μm or less.

[0043] 2.2 Electrolyte Layer The electrolyte layer 20 is disposed between the positive electrode 10 and the negative electrode 30 and can function as a separator. The electrolyte layer 20 contains at least an electrolyte, and may further optionally contain a binder or the like. The electrolyte layer 20 may further contain various additives. The content of each component in the electrolyte layer 20 is not particularly limited and may be appropriately determined according to the intended battery performance. The shape of the electrolyte layer 20 is not particularly limited, and for example, it may be in the form of a sheet having a substantially flat surface. The thickness of the electrolyte layer 20 is not particularly limited, and for example, it may be 0.1 μm or more or 1 μm or more, and may be 2 mm or less or 1 mm or less.

[0044] 2.2.1 Electrolyte The electrolyte contained in the electrolyte layer 20 may be appropriately selected from among those exemplified as the electrolytes that can be contained in the above-described positive electrode active material layer. In particular, the performance of the electrolyte layer 20 containing a solid electrolyte, especially a sulfide solid electrolyte, and among them, a sulfide solid electrolyte containing at least Li, S, and P as constituent elements is high. When the electrolyte is a solid electrolyte, the solid electrolyte may be amorphous or crystalline. When the electrolyte is a solid electrolyte, the solid electrolyte may be, for example, in the form of particles. Only one kind of electrolyte may be used alone, or two or more kinds may be used in combination.

[0045] 2.2.2 Binder The binder that can be contained in the electrolyte layer 20 may be appropriately selected from among those exemplified as the binders that can be contained in the above-described positive electrode active material layer.

[0046] 2.3 Negative Electrode The negative electrode 30 may contain the above-described active material composite particles 1 and may be any that can function properly as the negative electrode of the secondary battery, and its configuration is not particularly limited. As shown in FIG. 2, the negative electrode 30 may include a negative electrode active material layer 31 and a negative electrode current collector 32.

[0047] 2.3.1 Negative Electrode Active Material Layer The negative electrode active material layer 31 contains at least the active material composite particles 1, and may further optionally contain other active materials, electrolytes, conductive aids, binders, and the like. The negative electrode active material layer 31 may also contain various additives. The content of each component in the negative electrode active material layer 31 may be appropriately determined according to the target battery performance. For example, taking the entire negative electrode active material layer 31 (total solid content) as 100% by mass, the content of the active material composite particles 1 may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, and may also be 100% by mass or less or 90% by mass or less. The shape of the negative electrode active material layer 31 is not particularly limited, and for example, it may be a sheet-shaped negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer 31 is not particularly limited, and for example, it may be 0.1 μm or more, 1 μm or more, or 10 μm or more, and may also be 2 mm or less, 1 mm or less, or 500 μm or less.

[0048] Regarding the active material composite particles 1, it is as described above. In the negative electrode active material layer 31, the active material composite particles 1 may be included in a pressed state. That is, when applying the active material composite particles 1 to the negative electrode active material layer 31 of the secondary battery 100, the negative electrode active material layer 31 can be formed by pressing the negative electrode active material composite material containing the active material composite particles 1. At this time, the composite particles 1 can be crushed in the pressing direction and have an aspect ratio of a predetermined value or more. By pressing the composite particles 1 to have an aspect ratio of a predetermined value or more, the contact resistance within the composite particles 1, the contact resistance between the composite particles 1, and the contact resistance between the composite particles 1 and other materials are likely to be reduced. An example of the aspect ratio of the composite particles 1 in this case is as described above.

[0049] As the negative electrode active material other than the active material composite particles 1, those known as the negative electrode active material of a secondary battery may be used. Among the known active materials, a material having a relatively low potential (charge-discharge potential) for occluding and releasing a predetermined carrier ion (for example, lithium ion) can be used as the negative electrode active material. Only one type of the other negative electrode active materials may be used alone, or two or more types may be used in combination. From the viewpoint of further improving the performance of the secondary battery, it is preferable that the ratio of the active material composite particles 1 in the entire negative electrode active material contained in the negative electrode active material layer 31 is higher. For example, assuming that the total of the active material composite particles 1 and the other negative electrode active materials is 100% by mass, the active material composite particles 1 may be contained in an amount of 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more. The upper limit is 100% by mass.

[0050] The electrolyte that can be contained in the negative electrode active material layer 31 may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. In particular, when the negative electrode active material layer 31 contains at least a solid electrolyte as the electrolyte, a higher effect is more easily obtained. The negative electrode active material layer 31 may contain a solid electrolyte, among which a sulfide solid electrolyte, and among which a sulfide solid electrolyte containing Li, S, and P as constituent elements. Examples of the conductive auxiliary agent that can be contained in the negative electrode active material layer 31 include the above-described carbon material and the above-described metal material. The binder that can be contained in the negative electrode active material layer 31 may be appropriately selected from, for example, those exemplified as the binder that can be contained in the positive electrode active material layer 11 described above.

[0051] 2.3.2 Negative electrode current collector As shown in FIG. 2, the negative electrode 30 may include a negative electrode current collector 32 that contacts the above-described negative electrode active material layer 31. Any of the commonly used ones as the negative electrode current collector of the battery can be adopted for the negative electrode current collector 32. Further, the negative electrode current collector 32 may be in the form of a foil, a plate, a mesh, a punched metal, a foam, or the like. The negative electrode current collector 32 may be a metal foil or a metal mesh, or may be a carbon sheet. In particular, the metal foil is excellent in handleability and the like. The negative electrode current collector 32 may be composed of a plurality of foils or sheets. Examples of the metal constituting the negative electrode current collector 32 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. In particular, from the viewpoints of ensuring reduction resistance and being difficult to alloy with lithium, the negative electrode current collector 32 may contain at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector 32 may have some coating layer on its surface for the purpose of adjusting resistance or the like. Further, the negative electrode current collector 32 may be a metal foil or a substrate on which the above metal is plated or vapor-deposited. Further, when the negative electrode current collector 32 is composed of a plurality of metal foils, there may be some layer between the plurality of metal foils. The thickness of the negative electrode current collector 32 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, and may be 1 mm or less or 100 μm or less.

[0052] 2.4 Other configurations The secondary battery 100 may be one in which each of the above-described configurations is housed inside the exterior body. Any of the known ones as the exterior body of the battery can be adopted for the exterior body. Further, a plurality of secondary batteries 100 may be arbitrarily electrically connected and arbitrarily stacked to form a battery pack. In this case, the battery pack may be housed inside a known battery case. The secondary battery 100 may further include obvious configurations such as necessary terminals. Examples of the shape of the secondary battery 100 include a coin type, a laminate type, a cylindrical type, and a rectangular type.

[0053] 3. Manufacturing method of secondary battery The secondary battery 100 can be manufactured by applying a known method. For example, it can be manufactured as follows. However, the manufacturing method of the secondary battery 100 is not limited to the following method. For example, each layer may be formed by dry pressing or the like. (1) Dispersing active material composite particles or the like constituting the negative electrode active material layer in a solvent to obtain a negative electrode slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. Then, using a doctor blade or the like, the negative electrode slurry is coated on the surface of the negative electrode current collector or the electrolyte layer described later, and then dried to form a negative electrode active material layer on the surface of the negative electrode current collector or the electrolyte layer, thereby obtaining a negative electrode. Here, the negative electrode active material layer may be press-molded. (2) Dispersing the positive electrode active material or the like constituting the positive electrode active material layer in a solvent to obtain a positive electrode slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. Then, using a doctor blade or the like, the positive electrode slurry is coated on the surface of the positive electrode current collector or the electrolyte layer described later, and then dried to form a positive electrode active material layer on the surface of the positive electrode current collector or the electrolyte layer, thereby obtaining a positive electrode. Here, the positive electrode active material layer may be press-molded. (3) Stacking the layers so that the electrolyte layer is sandwiched between the negative electrode and the positive electrode to obtain a laminate having a negative electrode current collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order. The electrolyte layer may be, for example, obtained by molding an electrolyte binder containing an electrolyte and a binder, or may be obtained by press-molding. Here, the laminate may be further press-molded. Other members such as terminals are attached to the laminate as necessary. When an electrolytic solution is used, a separator may be employed for the electrolyte layer. (4) A secondary battery is obtained by housing the laminate in a battery case and sealing it.

[0054] 4. Method for manufacturing active material composite particles The active material composite particles of the present disclosure can be produced, for example, in the process shown in FIG. 3. That is, as shown in FIG. 3, the method for producing the active material composite particles of the present disclosure includes atomizing a slurry containing Si particles, a resin, and a solvent to obtain slurry droplets (step S1), and subjecting the slurry droplets to airflow drying in a heated gas to obtain an active material composite containing Si particles and a resin (step S2). In the production method of the present disclosure, as will be described later, atomization of the slurry and airflow drying of the slurry droplets may be performed by spray drying.

[0055] 4.1 Step S1 In step S1, a slurry containing Si particles, a resin, and a solvent is atomized to obtain slurry droplets. The Si particles and the resin are as described above. The solvent may be any one that can disperse Si particles and dissolve the resin. For example, various organic solvents such as dimethyl carbonate can be employed.

[0056] The "slurry" in step S1 is a suspension or suspension liquid containing Si particles, a resin, and a solvent, and it may have fluidity sufficient for atomization. In step S1, the slurry may have fluidity sufficient for atomization, for example, by using a spray nozzle or a rotary atomizer. Incidentally, the slurry may contain some solid components or liquid components in addition to the above-described Si particles, resin, and solvent.

[0057] The "atomization" of the slurry in step S1 means turning the slurry containing Si particles, a resin, and a solvent into particles containing Si particles, a resin, and a solvent. In step S1, the method for atomizing the slurry containing Si particles, a resin, and a solvent is not particularly limited. For example, a method of atomizing the slurry by spraying can be mentioned. When spraying the slurry, a spray nozzle may be used. Examples of the method of spraying the slurry using a spray nozzle include, but are not limited to, the pressure nozzle method and the two-fluid nozzle method.

[0058] When spraying the slurry using a spray nozzle, the nozzle diameter is not particularly limited. The nozzle diameter may be, for example, 0.1 mm or more or 1 mm or more, and may also be 10 mm or less or 1 mm or less. Also, the spraying speed of the slurry (the supply speed of the slurry to the spray nozzle) is not particularly limited. The spraying speed may be adjusted according to the viscosity and solid content concentration of the slurry, the nozzle dimensions, etc.

[0059] As a method for atomizing the slurry, in addition to the method of spraying the slurry using the spray nozzle as described above, for example, a method of supplying a slurry containing Si particles, resin, and solvent onto a rotating disk at a constant speed and atomizing it by centrifugal force can also be exemplified. Also in this case, the supply speed of the slurry may be adjusted according to the viscosity and solid content concentration of the slurry, etc. Alternatively, a method of applying a high voltage to the surface of a slurry containing Si particles, resin, and solvent to atomize it can also be adopted.

[0060] In the manufacturing method of the present disclosure, for example, a spray dryer may be used to atomize the slurry (step S1) and perform the subsequent airflow drying (step S2). The type of the spray dryer is not particularly limited, and examples include the method using the above spray nozzle and the method using a rotating disk.

[0061] A "slurry droplet" is a particle of a slurry containing Si particles, resin, and solvent. The size of the slurry droplet is not particularly limited. The diameter (equivalent spherical diameter) of the slurry droplet may be, for example, 0.5 μm or more or 5 μm or more, and may also be 5000 μm or less or 1000 μm or less. The diameter of the slurry droplet can be measured, for example, using a two-dimensional image obtained by imaging the slurry droplet, or can also be measured using a laser diffraction particle size distribution analyzer. Alternatively, the droplet diameter can also be estimated from the operating conditions of the device for forming the slurry droplet, etc.

[0062] 4.2 Step S2 In step S2, the slurry droplets are dried by airflow in a heated gas to obtain an active material composite containing Si particles and resin.

[0063] In the manufacturing method of the present disclosure, "airflow drying" means drying while suspending slurry droplets in a high-temperature airflow. "Airflow drying" may include not only drying but also accompanying operations by using a dynamic airflow. By continuously applying hot air to the slurry droplets by airflow drying, a force is continuously applied to the slurry droplets. Utilizing this, for example, step S2 may include disintegrating (crushing) the slurry droplets or granulated bodies by airflow drying. In other words, in the method of the present disclosure, even when granulation of the slurry droplets occurs, the granulated bodies can be disintegrated by airflow drying. Therefore, a slurry with a low solid content concentration can also be used, and it is easy to increase the processing speed. In step S2, the above drying and disintegration may be performed simultaneously or separately. In step S2, a first airflow drying in which drying of the slurry droplets is dominant and a second airflow drying in which disintegration of the granulated bodies is dominant may be performed. Also, step S2 may be repeated.

[0064] In step S2, the temperature of the heated gas may be any temperature at which it is possible to volatilize the solvent from the slurry droplets. For example, it may be 100°C or higher, 110°C or higher, 120°C or higher, or 130°C or higher, and may also be 180°C or lower, 170°C or lower, 160°C or lower, or 150°C or lower.

[0065] In step S2, the supply amount (flow rate) of the heated gas can be appropriately set in consideration of the size of the apparatus used, the supply amount of the slurry droplets, etc. For example, the flow rate of the heated gas is 0.10m 3 / min or more, 0.15m 3 / min or more, 0.20m 3 / min or more, 0.25m 3 / min or more, 0.30m 3 / min or more, 0.35m 3 / min or more, 0.40m 3 / min or more, 0.45m 3 / min or more, or 0.50m 3It may be above / minute, and also 5.00 m 3 / minute or less, 4.00 m 3 / minute or less, 3.00 m 3 / minute or less, 2.00 m 3 / minute or less, or 1.00 m 3 It may be / minute or less.

[0066] In step S2, the supply rate (flow rate) of the heating gas can also be appropriately set in consideration of the size of the device used, the supply amount of the slurry droplets, etc. For example, the flow rate of the heating gas may be 1 m / s or more or 5 m / s or more in at least a part of the system, and may be 50 m / s or less or 10 m / s or less.

[0067] In step S2, the treatment time (drying time) by the heating gas can also be appropriately set in consideration of the size of the device used, the supply amount of the slurry droplets, etc. For example, the treatment time may be 5 seconds or less, or 1 second or less.

[0068] In step S2, a heating gas that is substantially inert to Si particles, resin, and solvent may be used. For example, an oxygen-containing gas such as air, an inert gas such as nitrogen or argon, dry air with a low dew point, etc. can be used. The dew point in that case may be -10°C or less, -50°C or less, or -70°C or less.

[0069] As a device for performing flash drying, for example, a spray dryer can be used, but it is not limited thereto.

[0070] According to the above manufacturing method, for example, slurry droplets containing a plurality of Si particles, a resin, and a solvent are dried by an air current, and as the solvent volatilizes, the resin can be concentrated on the surface layer of the composite particles. Also, a plurality of Si particles can be arranged at the center of the composite particles to form voids. As a result, the active material composite particles 1 of the present disclosure are obtained. That is, when observing the cross-section of the composite particles 1, the area ratio of the resin in the surface layer portion 1x of the composite particles 1 is higher than the area ratio of the resin in the central portion 1y of the composite particles 1. Further, when observing the cross-section of the composite particles 1, the porosity in the central portion 1y of the composite particles 1 tends to be higher than the porosity in the surface layer portion 1x of the composite particles 1, and the area ratio of the Si in the central portion 1y of the composite particles 1 tends to be higher than the area ratio of the Si in the surface layer portion 1x of the composite particles 1.

[0071] 5. Method for Charging and Discharging a Secondary Battery and Method for Improving Cycle Characteristics of a Secondary Battery When the active material composite particles of the present disclosure are included in the negative electrode of a secondary battery, the cycle characteristics of the secondary battery are likely to be improved. That is, the method for charging and discharging a secondary battery and the method for improving the cycle characteristics of a secondary battery of the present disclosure include repeating charging and discharging of the secondary battery, and the secondary battery has a positive electrode, an electrolyte layer, and a negative electrode, and the negative electrode is characterized by including the active material composite particles of the present disclosure.

[0072] 6. Vehicle Having a Secondary Battery As described above, when the active material composite particles of the present disclosure are included in the negative electrode of a secondary battery, improvement of the cycle characteristics of the secondary battery can be expected. A secondary battery having excellent charge and discharge cycle characteristics in this way can be suitably used, for example, in at least one type of vehicle selected from a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), and an electric vehicle (BEV). That is, the technology of the present disclosure also has an aspect as a vehicle having a secondary battery, where the secondary battery has a positive electrode, an electrolyte layer, and a negative electrode, and the negative electrode includes the active material composite particles of the present disclosure.

Examples

[0073] Hereinafter, while showing examples, the technology of the present disclosure will be described in more detail. However, the technology of the present disclosure is not limited to the following examples.

[0074] 1. Preparation of Anode Active Material 1.1 Comparative Example: Preparation of Nanoporous Si Particles 0.65 g of Si particles (particle size 0.5 μm, manufactured by Kojundo Chemical Laboratory Co., Ltd.) and 0.60 g of Li metal (manufactured by Honjo Metals Co., Ltd.) were mixed using an agate mortar under an Ar atmosphere to obtain a LiSi precursor. In a glass reactor under an Ar atmosphere, 1.0 g of the LiSi precursor and 125 ml of a dispersion medium (1,3,5-trimethylbenzene, manufactured by Nacalai Tesque) were mixed using an ultrasonic homogenizer (UH-50, manufactured by SMT). The LiSi precursor dispersion obtained after mixing was cooled to 0 °C, 125 ml of ethanol (manufactured by Nacalai Tesque) was added dropwise, and the mixture was reacted for 120 minutes. After the reaction, 50 ml of acetic acid (manufactured by Nacalai Tesque) was further added dropwise, and the mixture was reacted for 60 minutes. After the reaction, the liquid and the solid reactant (anode active material) were separated by suction filtration. The obtained solid reactant was vacuum-dried at 120 °C for 2 hours to recover nanoporous Si particles.

[0075] 1.2 Example: Preparation of Active Material Composite Particles Si particles (particle size 0.1 μm, manufactured by Kojundo Chemical Laboratory Co., Ltd.) and a PVdF-HFP binder (manufactured by Kuraray Co., Ltd.) were dispersed and dissolved in dimethyl carbonate (manufactured by Nacalai Tesque) at a mass ratio of Si particles: binder = 100:26.7 to obtain a slurry. This slurry was sprayed into a spray dryer under a nitrogen gas atmosphere at a temperature of 140 °C to form droplets while performing air flow drying. After air flow drying, active material composite particles containing Si particles and the PVdF-HFP binder as a resin were recovered.

[0076] 2. Preparation of Solid Electrolyte Li 2 0.550 g of S (manufactured by Furuchi Chemical) and P 2 S 50.887 g (manufactured by Aldrich), 0.285 g of LiI (manufactured by Nippo Chemical Industry Co., Ltd.), and 0.277 g of LiBr (manufactured by Kanto Chemical Co., Inc.) were mixed in an agate mortar for 5 minutes. To the obtained mixture, 4 g of n-heptane (dehydrated grade, manufactured by Kanto Chemical Co., Inc.) was added, and mechanical milling was performed for 40 hours using a planetary ball mill to obtain a sulfide solid electrolyte.

[0077] 3. Preparation of Cathode Composite Material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (manufactured by Nichia Chemical Industries, Ltd.) was surface-treated using LiNbO 3 to obtain a cathode active material. 1.5 g of this cathode active material, 0.023 g of a conductive assistant (VGCF, manufactured by Showa Denko K.K.), 0.239 g of the above sulfide solid electrolyte, 0.011 g of a binder (PVdF, manufactured by Kureha Corporation), and 0.8 g of butyl butyrate (manufactured by Kishida Chemical Co., Ltd.) were mixed using an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a cathode composite material.

[0078] 4. Preparation of Anode Composite Material 1.0 g of the anode active material according to the above comparative example or example, 0.04 g of a conductive assistant (VGCF, manufactured by Showa Denko K.K.), 0.776 g of the above sulfide solid electrolyte, 0.02 g of a binder (PVdF, manufactured by Kureha Corporation), and 1.7 g of butyl butyrate (manufactured by Kishida Chemical Co., Ltd.) were mixed using an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain an anode composite material.

[0079] 5. Preparation of Evaluation Battery 1 cm 2 0.065 g of the above sulfide solid electrolyte was placed in a ceramic mold of, and pressed at 1 ton / cm 2 to prepare a solid electrolyte layer. 0.018 g of the above cathode composite material was placed on one side and pressed at 1 ton / cm 2 to prepare a cathode active material layer. 0.0054 g of the above anode composite material was placed on the side opposite to the cathode active material layer and pressed at 4 ton / cm 2The negative electrode active material layer was fabricated by pressing. An Al foil was used for the positive electrode current collector, and a Cu foil was used for the negative electrode current collector. Thereby, an evaluation battery (all-solid-state battery) was fabricated.

[0080] 6. Evaluation 6.1 Cross-sectional Observation and Image Processing of Active Material Composite Particles Regarding the active material composite particles according to the examples, the cross-sectional structure before pressing and the cross-sectional structure after pressing were observed by SEM, the elements contained in the cross-section of the composite particles were analyzed by EDX, and the cross-sectional structure of the composite particles was specified by image processing. Figure 4A is a cross-sectional SEM image of the composite particles before pressing, Figure 4B is the result of image processing of Figure 4A, Figure 5A is a cross-sectional SEM image of the composite particles after pressing, and Figure 5B is the result of image processing of Figure 5A.

[0081] As shown in Figures 4A and B, the active material composite particles according to the examples contain a plurality of nanoporous Si particles and a binder. When observing the cross-section, a large amount of binder exists in the surface layer part of the composite particles (the black part in Figure 4B). On the other hand, it can be seen that there is almost no binder in the central part of the composite particles, and a plurality of nanoporous Si particles and voids exist (the gray part and the white part in Figure 4B). That is, when observing the cross-section of the active material composite particles according to the examples, (I) the area ratio of the resin occupying the surface layer part of the composite particles is higher than the area ratio of the resin occupying the central part of the composite particles. Also, (II) the porosity of the central part of the composite particles is higher than the porosity of the surface layer part of the composite particles, and (III) the area ratio of Si in the central part of the composite particles is higher than the area ratio of Si in the surface layer part of the composite particles.

[0082] In the central part of the images of FIGS. 5A and B, there are flat active material composite particles. As shown in FIGS. 5A and B, the active material composite particles according to the examples are crushed in the pressing direction by pressing, and have a large aspect ratio. As is clear from FIG. 5B, the flat active material composite particles have an outermost layer (black part) made of a binder, and further, there are voids (white part) inside (central part) the outermost layer, and it can be seen that a plurality of Si particles (gray part) exist together with the voids. That is, from FIGS. 5A and B, it can be seen that the active material composite particles according to the examples maintain the structures of (I) to (III) above even after pressing.

[0083] As shown in FIGS. 4A and B and FIGS. 5A and B, the active material composite particles according to the examples are clearly divided into a binder layer as the outermost layer and a central part inside the binder layer, which has a plurality of nanoporous Si particles and voids. For 14 composite particles after pressing and 7 composite particles before pressing, based on the cross-sectional SEM images, the area ratio of the outermost layer in the entire cross-section of the composite particle ([area of the outermost layer] / [area of the entire cross-section of the composite particle]), the area ratio of Si contained in the central part in the entire cross-section of the composite particle ([area of Si in the central part] / [area of the entire cross-section of the composite particle]), and the area ratio of voids contained in the central part in the entire cross-section of the composite particle ([area of voids in the central part] / [area of the entire cross-section of the composite particle]) were specified. The results are shown in Table 1 below.

[0084]

Table 1

[0085] From the results shown in Table 1, it can be seen that although the area ratios of the active material composite particles according to the examples change significantly before and after pressing, they maintain the structures of (I) to (III) above throughout before and after pressing.

[0086] 6.2 Durability Test of Evaluation Batteries Regarding the evaluation battery in the low constraint state (constraint pressure: 0.2 MPa) or high constraint state (constraint pressure: 5.0 MPa), after CC / CV charging at 0.3 mA up to 4.35 V, CC / CV discharge was performed at 0.3 mA down to 2.5 V. This was repeated 5 times. Then, the following DC-IR measurement was carried out to obtain the initial resistance value.

[0087] DC-IR measurement: After adjusting the voltage to 3.7 V, the resistance value was obtained from the voltage drop when a current of 10 mA was passed for 5 seconds.

[0088] Regarding the above evaluation battery, further, after CC charging at 1.4 mA up to 4.1 V, CC discharge at 1.4 mA down to 3.1 V was repeated 500 cycles with one cycle being defined as such. Then, DC-IR measurement was carried out in the same manner as in the initial case to obtain the resistance value after 500 cycles. The resistance increase rate was obtained from the following formula. [Resistance increase rate] = ((Resistance value after 500 cycles) / (Initial resistance value) - 1)×100

[0089] The results are shown in Figure 6. As shown in Figure 6, for the battery according to the comparative example, the resistance increase rate was high under both low and high constraint pressures, particularly high under low constraint pressure. In contrast, for the battery according to the example, the resistance increase rate could be suppressed low both under low constraint pressure and high constraint pressure. This is presumed to be due to the following mechanism.

[0090] As described above, for the active material composite particles according to the example, the area ratio of the resin in the surface layer part is higher than the area ratio of the resin in the central part. Thus, due to the high ratio of the resin in the surface layer part of the composite particles, even when Si expands due to charging, the volume change of the entire composite particles is relaxed by the resin in the surface layer part, and it is considered that the shape of the entire composite particles is maintained. Also, due to the high ratio of the resin in the surface layer part, even when Si expands due to charging, the resin in the surface layer part functions as a cushioning material, and it is considered that cracks and gaps were less likely to occur in the battery materials around the composite particles. Thereby, it is considered that excellent cycle characteristics were exhibited both under high constraint pressure and low constraint.

[0091] Alternatively, as described above, the active material composite particles according to the embodiment have a higher porosity in the central portion than in the surface layer portion. Thus, since the porosity in the central portion is higher than that in the surface layer portion, even when Si expands due to charging, the expansion of the Si can be absorbed by the voids, and it is considered that the volume change of the entire composite particle 1 is alleviated and the shape of the entire composite particle 1 is maintained. Further, since the volume change of the entire composite particle is alleviated, it is considered that cracks and gaps are less likely to occur in the battery material around the composite particle. Thereby, it is considered that excellent cycle characteristics are exhibited under both high confinement pressure and low confinement.

[0092] Alternatively, as described above, the active material composite particles according to the embodiment have a higher area ratio of Si in the central portion than in the surface layer portion. Thus, since the area ratio of Si in the central portion is higher than that in the surface layer portion, even when Si expands due to charging, the expansion of the Si hardly reaches the outside of the composite particle, and it is considered that the volume change of the entire composite particle is alleviated and the shape of the entire composite particle is maintained. Further, since the volume change of the entire composite particle is alleviated, it is considered that cracks and gaps are less likely to occur in the battery material around the composite particle. Thereby, it is considered that excellent cycle characteristics are exhibited under both high confinement pressure and low confinement.

[0093] In the above embodiment, the case where nanoporous Si particles are used as Si constituting the active material composite particles and a PVdF-based binder is used as the resin constituting the active material composite particles is exemplified, but the technology of the present disclosure is not limited to this form.

[0094] As described above, the active material composite particles containing Si and resin, when observing the cross section of the composite particles, those having a higher area ratio of the resin in the surface layer portion of the composite particles than the area ratio of the resin in the central portion of the composite particles can be said to have excellent cycle characteristics under low confinement.

Explanation of Reference Numerals

[0095] 1 Active material composite particle 2 Resin layer 3 Void 4 Si particle 10 Positive electrode 11 Positive electrode active material layer 12 Positive electrode current collector 20 Electrolyte layer 30 Negative electrode 31 Negative electrode active material layer 32 Negative electrode current collector 100 Secondary battery

Claims

1. A composite particle of active material, comprising a plurality of Si particles and a resin, when observing a cross-section of the composite particle, the area ratio of the resin in the surface layer portion of the composite particle is higher than the area ratio of the resin in the central portion of the composite particle, and when observing a cross-section of the composite particle, the porosity in the central portion of the composite particle is higher than the porosity in the surface layer portion of the composite particle, the composite particle of active material.

2. when observing a cross-section of the composite particle, the area ratio of the Si in the central portion of the composite particle is higher than the area ratio of the Si in the surface layer portion of the composite particle, the composite particle of active material according to Claim 1.

3. the surface layer portion is made of the resin, the composite particle of active material according to Claim 1.

4. the Si particles are porous, the composite particle of active material according to Claim 1.

5. the composite particle has a surface layer portion containing the resin and a central portion containing a plurality of the Si particles and voids, the composite particle of active material according to Claim 1.

6. A secondary battery, having a positive electrode, an electrolyte layer, and a negative electrode, the negative electrode contains the composite particle of active material according to any one of Claims 1 to 5, the secondary battery.

7. at least one of the positive electrode, the electrolyte layer, and the negative electrode contains a solid electrolyte, the secondary battery according to Claim 6.

8. atomizing a slurry containing Si particles, a resin, and a solvent to obtain slurry droplets, and airflow drying the slurry droplets in a heated gas to obtain a composite of active material containing Si particles and a resin, a method for manufacturing the composite particle of active material according to any one of Claims 1 to 5.

9. by spray drying, atomization of the slurry and airflow drying of the slurry droplets are performed, the manufacturing method according to Claim 8.

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