Active material composite particles, secondary battery, and method for manufacturing active material composite particles

Abstract

To disclose active material composite particles containing Si, which can reduce volume expansion during charging.SOLUTION: Active material composite particles of the present disclosure include a plurality of first particles and at least one second particle, the first particles include porous silicon, the reaction potential between the second particles and Li is lower than the reaction potential between the porous silicon and Li, and the ratio D2 / D1 of the particle diameter D2 of the second particle to the particle diameter D1 of the first particle is equal to or greater than 2.0.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a method for manufacturing a porous silicon material. Porous silicon materials are used, for example, as active materials in secondary batteries. Silicon materials used as active materials in secondary batteries undergo large volume changes with charging and discharging. For example, if the expansion amount of the silicon material as an active material is large, the confinement pressure of the secondary battery tends to increase significantly. In contrast, by making the silicon material porous and creating voids, it is thought that the expansion of the silicon material is mitigated by these voids, thereby reducing the increase in the confinement pressure of the secondary battery. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-150481 [Overview of the project] [Problems that the invention aims to solve]

[0004] New technologies are needed to further reduce the increase in the confinement pressure of secondary batteries. [Means for solving the problem]

[0005] This application discloses several embodiments as means for solving the above-mentioned problems. <Aspect 1> An active material composite particle comprising a plurality of first particles and at least one second particle, The first particle contains porous silicon, The reaction potential between the second particle and Li is lower than the reaction potential between the porous silicon and Li, and The ratio D2 / D1 of the particle diameter of the second particle to the particle diameter D1 of the first particle is 2.0 or greater. Active material composite particles. <Aspect 2> A composite particle of active material according to embodiment 1, The porous silicon constituting the first particle is amorphous, The second particle contains crystalline silicon, Active material composite particles. <Aspect 3> Active material composite particles of embodiment 2, The crystalline silicon constituting the second particle is porous. Active material composite particles. <Aspect 4> A composite particle of an active material according to any of embodiments 1 to 3, The second particle is located inside the first particle, Active material composite particles. <Aspect 5> A composite particle of an active material according to any of embodiments 1 to 4, The first particle and the second particle together include a binder, Active material composite particles. <Aspect 6> A composite particle of an active material according to any one of embodiments 1 to 5, The second particle is spherical. Active material composite particles. <Aspect 7> A secondary battery comprising a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The negative electrode active material layer contains active material composite particles according to any of embodiments 1 to 6. Secondary battery. <Aspect 8> A secondary battery as described in Embodiment 7, At least one of the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer includes a solid electrolyte. Secondary battery. <Pattern 9> A method for producing active material composite particles, To obtain slurry droplets by forming a slurry containing multiple first particles, at least one second particle, and a solvent into droplets, and, The process involves air-drying the slurry droplets in a heated gas to obtain an active material composite particle comprising a plurality of first particles and at least one second particle. The first particle contains porous silicon, The reaction potential between the second particle and Li is lower than the reaction potential between the porous silicon and Li, and The ratio D2 / D1 of the particle diameter of the second particle to the particle diameter D1 of the first particle is 2.0 or greater. Manufacturing method. <Aspect 10> A manufacturing method according to aspect 9, Spray drying is used to form droplets of the slurry and to perform air-flow drying of the slurry droplets. Manufacturing method. <Aspect 11> A manufacturing method according to embodiment 9 or 10, The slurry contains a binder along with the first and second particles. Manufacturing method. [Effects of the Invention]

[0006] According to the active material composite particles of this disclosure, the increase in the confinement pressure of a secondary battery is easily reduced. [Brief explanation of the drawing]

[0007] [Figure 1A] A schematic example of the cross-sectional shape of an active material composite particle is shown. [Figure 1B] A schematic example of the cross-sectional shape of an active material composite particle is shown. [Figure 2] This shows a schematic example of a secondary battery configuration. [Figure 3] This shows an example of a manufacturing process for active material composite particles. [Figure 4A] This is an SEM image of a cross-section of the active material composite particles according to Example 1. [Figure 4B]This is an EDS image showing the Si distribution in a cross-section of the active material composite particles according to Example 1. [Figure 5A] This is an SEM image of a cross-section of the active material composite particles according to Example 2. [Figure 5B] This is an EDS image showing the Si distribution in a cross-section of the active material composite particles according to Example 2. [Modes for carrying out the invention]

[0008] 1.Active material composite particles Figures 1A and 1B schematically show the cross-sectional structure of an active material composite particle 1 according to one embodiment. As shown in Figures 1A and 1B, the active material composite particle 1 includes a plurality of first particles 1a and at least one second particle 1b. The first particles 1a include porous silicon. The reaction potential between the second particle 1b and Li is lower than the reaction potential between the porous silicon and Li. The ratio D2 / D1 of the particle diameter D1 of the first particle 1a to the particle diameter D2 of the second particle 1b is 2.0 or greater.

[0009] 1.1 First particle The active material composite particle 1 contains a plurality of first particles 1a. Each first particle 1a contains porous silicon.

[0010] 1.1.1 Chemical composition of the first particle The chemical composition of the first particle 1a is not particularly limited. The proportion of Si element in all elements contained in the first particle 1a may be, for example, 50 mol% to 100 mol%, 70 mol% to 100 mol%, or 90 mol% to 100 mol%. The first particle 1a may contain other elements in addition to Si. The other elements may be at least one of Li, Sn, Fe, Co, Ni, Ti, Cr, Al, B, and P. When the first particle 1a is obtained by removing Li from Li-Si alloy particles, the first particle 1a may contain Li element along with Si element. Furthermore, the first particle 1a may contain impurities such as oxides.

[0011] 1.1.2 Crystallinity of the first particle The first particle 1a may be amorphous or crystalline. In particular, when the first particle 1a is amorphous, it is easier to obtain even higher performance as an active material. Among these, as will be described later, higher performance is easier to obtain when the porous silicon constituting the first particle 1a is amorphous and the second particle 1b contains crystalline silicon. Whether or not the first particle 1a is amorphous can be determined by X-ray diffraction measurement or the like.

[0012] 1.1.3 Pores and voids of the first particle The first particle 1a contains porous silicon. Because the first particle 1a is porous and has voids, these voids can absorb the expansion of the silicon, thereby reducing the increase in the confinement pressure of the secondary battery. The first particle 1a may, for example, be a particle containing nanoporous silicon. Nanoporous silicon refers to silicon having multiple pores with pore diameters on the order of nanometers (less than 1000 nm, preferably 100 nm or less). The first particle 1a may be a porous silicon particle containing pores with a diameter of 55 nm or less. Pores with a diameter of 55 nm or less are difficult to crush even by pressing. That is, porous silicon particles containing pores with a diameter of 55 nm or less tend to maintain their porous state even after pressing. For example, 1 g of the first particle 1a may contain 0.21 cc to 0.30 cc / g of pores with a diameter of 55 nm or less. The lower limit may be 0.22 cc / g or more, or 0.23 cc / g or more, and the upper limit may be 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 first particle 1a can be determined, for example, from the pore size distribution by nitrogen gas adsorption method or DFT method.

[0013] The porosity of the first particle 1a is not particularly limited. For example, the porosity of the first particle 1a may be 1% or more and 80% or less. The lower limit may be 5% or more, 10% or more, or 20% or more, and the upper limit may be 70% or less, 60% or less, 50% or less, 40% or less, or 30% or less. The porosity of the first particle 1a can be determined, for example, by observation using a scanning electron microscope (SEM). A large number of samples is preferable, for example, 100 or more. The porosity can be the average value obtained from these samples.

[0014] 1.1.4 Size of the first particle The size of the first particle 1a is not particularly limited. The particle diameter D1 of the first particle 1a may be, for example, 10 nm or more and 10 μm or less. The lower limit may be 30 nm or more, 50 nm or more, 100 nm or more, or 150 nm or more, and the upper limit may be 5 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less. The particle diameter D1 of the first particle 1a can be determined by observation with an electron microscope such as an SEM, and is determined as the number average value of the maximum Ferret diameter of each of the multiple particles. The number of samples is preferably large, for example 20 or more, but may be 50 or more, or 100 or more. The particle diameter D1 of the first particle 1a can be appropriately adjusted, for example, by appropriately changing the manufacturing conditions of the porous silicon particles or by performing a classification treatment.

[0015] 1.1.5 Shape of the first particle As described above, the first particle 1a may contain porous silicon, and its shape is not particularly limited. For example, the first particle 1a may be spherical or non-spherical.

[0016] 1.1.6 Number of first particles The number of first particles 1a contained in the active material composite particle 1 is not particularly limited. The number of first particles 1a contained in one active material composite particle 1 may be between 2 and 10,000. The lower limit may be 5 or more, 10 or more, 50 or more, or 100 or more, and the upper limit may be 5,000 or less, 1,000 or less, or 500 or less.

[0017] 1.2 Second particle The active material composite particle 1 contains at least one second particle 1b. The reaction potential between the second particle 1b and Li is lower than the reaction potential between the porous silicon constituting the first particle 1a and Li. In other words, the second particle 1b reacts with Li at a lower potential than the porous silicon constituting the first particle 1a. For example, if the active material composite particle 1 is used as the negative electrode active material of a secondary battery, the first particle 1a will react with Li more readily than the second particle 1b during charging of the secondary battery. The silicon constituting the first particle 1a expands upon reaction with Li. As mentioned above, the first particle 1a contains porous silicon, and the voids are expected to mitigate the apparent volume expansion. Furthermore, the inclusion of the second particle 1b along with the first particle 1a allows the second particle 1b to function as a pillar, maintaining the overall shape and voids of the active material composite particle 1, thereby further reducing the overall volume expansion of the active material composite particle 1. As a result, the increase in the confinement pressure of the secondary battery can be reduced.

[0018] 1.2.1 Chemical composition of the second particle The chemical composition of the second particle 1b is not particularly limited. As mentioned above, the reaction potential between the second particle 1b and Li should be lower than the reaction potential between the porous silicon constituting the first particle 1a and Li. In other words, the second particle 1b should react with Li at a lower potential than the porous silicon constituting the first particle 1a, and the optimal material should be selected according to the charge-discharge potential of the porous silicon constituting the first particle 1a. The second particle 1b may or may not contain silicon. However, higher performance is more likely to be achieved when the second particle 1b contains silicon. As will be described later, when the second particle 1b contains silicon, the charge-discharge potential may change depending on its crystallinity. When the second particle 1b contains silicon, the proportion of Si element in all elements contained in the second particle 1b may be, for example, 50 mol% or more and 100 mol% or less, 70 mol% or more and 100 mol% or less, or 90 mol% or more and 100 mol% or less. The second particle 1b may contain elements other than Si element. Other elements may be at least one of Li, Sn, Fe, Co, Ni, Ti, Cr, Al, B, and P. Furthermore, if the second particle 1b contains silicon, it may also contain impurities such as oxides. Examples of second particles 1b that do not contain silicon include particles containing at least one selected from graphite and lithium.

[0019] 1.2.2 Crystallinity of the second particle The second particle 1b may be amorphous or crystalline. In particular, higher performance is more likely to be obtained when the second particle 1b is crystalline. Among these, higher performance is more likely to be obtained when the porous silicon constituting the first particle 1a is amorphous and the second particle 1b contains crystalline silicon. The second particle 1b may have a diamond-type Si crystalline phase. This crystalline phase has typical peaks at 2θ = 28.4°, 47.3°, 56.1°, 69.2°, and 76.4° in XRD measurements using CuKα rays. These peak positions may vary by ±0.5° or ±0.3°. Thus, even when both the first particle 1a and the second particle 1b contain the element Si as a constituent element, by using particles with different crystallinity, the second particle 1b reacts with Li at a lower potential than the porous silicon that constitutes the first particle 1a. In particular, when the first particle 1a contains amorphous porous silicon and the second particle 1b contains crystalline silicon, the reaction potential between the second particle 1b and Li tends to be significantly lower than the reaction potential between the porous silicon that constitutes the first particle 1a and Li.

[0020] 1.2.3 Pores and voids of the second particle The second particle 1b may or may not be porous. If the second particle 1b is porous, it is thought that the expansion of silicon can be absorbed by the voids, further reducing the increase in the confinement pressure of the secondary battery. In this regard, for example, if the second particle 1b contains crystalline silicon, the crystalline silicon constituting the second particle 1b may be porous. The second particle 1b may be, for example, a particle containing crystalline nanoporous silicon. The second particle 1b may be a crystalline nanoporous silicon particle containing pores with a diameter of 55 nm or less. Pores with a diameter of 55 nm or less are difficult to crush even by pressing. That is, crystalline nanoporous silicon particles containing pores with a diameter of 55 nm or less tend to maintain their porous state even after pressing. For example, the second particle 1b may contain 0.21 cc to 0.30 cc / g of pores with a diameter of 55 nm or less per gram. The lower limit may be 0.22 cc / g or more, or 0.23 cc / g or more, and the upper limit may be 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 second particle 1b can be determined, for example, from the pore size distribution by nitrogen gas adsorption method or DFT method.

[0021] If the second particle 1b is porous, its porosity is not particularly limited. The porosity of the second particle 1b may be, for example, 1% or more and 80% or less. The lower limit may be 5% or more, 10% or more, or 20% or more, and the upper limit may be 70% or less, 60% or less, 50% or less, 40% or less, or 30% or less. The porosity of the second particle 1b can be determined, for example, by observation using a scanning electron microscope (SEM). A large number of samples is preferable, for example, 100 or more. The porosity can be the average value obtained from these samples.

[0022] 1.2.4 Size of the second particle The size of the second particle 1b is not particularly limited, as long as the ratio of particle diameter D2 to particle diameter D1, D2 / D1, is 2.0 or greater. The particle diameter D2 of the second particle 1b may be, for example, 100 nm or more, 500 nm or more, or 1 μm or more, or it may be 100 μm or less, 50 μm or less, 10 μm or less, or 5 μm or less. The particle diameter D2 of the second particle 1b can be determined by observation with an electron microscope such as an SEM, similar to the particle diameter D1, and is determined as the average value of the maximum Ferret diameter of each of the multiple particles. The number of samples is preferably large, for example 20 or more, but may be 50 or more, or 100 or more. The particle diameter D2 of the second particle 1b can be adjusted as appropriate, for example, by appropriately changing the manufacturing conditions or performing a classification process.

[0023] In the active material composite particle 1, if the second particle 1b is sufficiently larger than the first particle 1a, the second particle 1b functions more appropriately as a pillar, and the above-mentioned effect is more likely to be enhanced. In this regard, in the active material composite particle 1, the ratio D2 / D1 of the particle diameter D1 of the first particle 1a to the particle diameter D2 of the second particle 1b is 2.0 or more. The upper limit of this ratio D2 / D1 is not particularly limited. The ratio D2 / D1 may be between 2.0 and 100.0. The lower limit may be between 5.0 and 7.0 or 10.0, and the upper limit may be between 70.0 and 50.0 or 30.0.

[0024] 1.2.5 Shape of the second particle The shape of the second particle 1b is not particularly limited. For example, the second particle 1b may be spherical or non-spherical. In particular, when the second particle 1b is spherical, it is thought that the second particle 1b is more likely to function as a pillar, and the expansion of the first particle 1a in the active material composite particle 1 is more likely to be isotropic. "Spherical" means that the circularity is 0.80 or higher. The circularity of the second particle 1b may be 0.81 or higher, 0.82 or higher, 0.83 or higher, 0.84 or higher, 0.85 or higher, 0.86 or higher, 0.87 or higher, 0.88 or higher, 0.89 or higher, or 0.90 or higher. The circularity of the second particle 1b is 4πS / L2 The circularity of the second particle 1b is defined as follows: Here, S is the orthographic area of ​​the second particle 1b, and L is the perimeter of the orthographic image of the second particle 1b. The circularity of the second particle 1b can be determined by observing the appearance of the particle using a scanning electron microscope (SEM), transmission electron microscope (TEM), or optical microscope. If one active material composite particle 1 contains multiple second particles 1b, the circularity of the multiple second particles 1b is measured as the number average of the circularity of each second particle 1b.

[0025] 1.2.6 Number of second particles The number of second particles 1b contained in the active material composite particle 1 is not particularly limited. The number of second particles 1b contained in one active material composite particle 1 may be 1 or more, 2 or more, 10 or less, 7 or less, or 5 or less. In one embodiment, the number of second particles 1b contained in one active material composite particle 1 is 1 or 2. Also, in one embodiment, the number of second particles 1b contained in one active material composite particle 1 is 1.

[0026] 1.3 Reaction potentials of the first and second particles with respect to Li As described above, the reaction potential between the second particle 1b and Li is lower than the reaction potential between the porous silicon constituting the first particle 1a and Li. For example, the reaction potential between the second particle 1b and Li may be 0.10V or less or 0.05V or less, and the reaction potential between the porous silicon constituting the first particle 1a and Li may be 0.20V or more or 0.30V or more. Here, "reaction potential" refers to the average reaction potential. The reaction potential between the first particle 1a and Li can be calculated from the charging curve when only the first particle 1a is used as the active material of a lithium-ion secondary battery and is charged as a counter electrode Li metal. Similarly, the reaction potential between the second particle 1b and Li can be calculated from the charging curve when only the second particle 1b is used as the active material of a lithium-ion secondary battery and is charged as a counter electrode Li metal.

[0027] 1.4 Positional relationship between the first and second particles The positional relationship between the first particle 1a and the second particle 1b in the active material composite particle 1 is not particularly limited. For example, as shown in Figure 1A, the second particle 1b may be located inside the first particle 1a in the active material composite particle 1. In other words, the active material composite particle 1 may have a core and a shell, the core may contain at least one second particle 1b, and the shell may contain a plurality of first particles 1a and not contain any second particles 1b. Alternatively, as shown in Figure 1B, the second particle 1b may be exposed on the outer surface of the composite particle 1 in the active material composite particle 1. In particular, as shown in Figure 1A, when the second particle 1b is located inside the first particle 1a, the expansion of the first particle 1a tends to be isotropic, and the overall expansion of the active material composite particle 1 tends to be reduced.

[0028] 1.5 Content ratio of the first particle to the second particle The content ratio of the first particle 1a to the second particle 1b in the active material composite particle 1 is not particularly limited. For example, if the total of the first particle 1a and the second particle 1b is 100 volume%, the volume percentage of the first particle 1a may be 1 volume% to 99 volume%, 10 volume% to 90 volume%, 20 volume% to 80 volume%, 30 volume% to 70 volume%, or 40 volume% to 60 volume%.

[0029] 1.6 Other Ingredients The active material composite particle 1 includes at least the first particle 1a and the second particle 1b described above. The active material composite particle 1 may also optionally contain other components.

[0030] 1.6.1 Binder The active material composite particle 1 may contain a binder along with the first particle 1a and the second particle 1b described above. The binder may have, for example, the function of binding the first particles 1a together or the function of binding the first particle 1a and the second particle 1b together. The location of the binder in the active material composite particle 1 is not particularly limited. The binder may be located on the surface side of the active material composite particle 1, on the central side, or in both locations. The type of binder is not particularly limited. Various binders known as constituent materials for secondary batteries may be used as the binder. For example, at least one binder may be selected from butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, styrene butadiene rubber (SBR) binders, polyvinylidene fluoride (PVdF) binders, polytetrafluoroethylene (PTFE) binders, polyimide (PI) binders, carboxymethylcellulose (CMC) binders, polyacrylic acid binders, polyacrylic acid ester binders, etc. PVdF binders, in particular, exhibit high performance. PVdF binders may also be copolymers having units derived from monomers other than VdF. A single binder may be used alone, or two or more may be used in combination.

[0031] In the active material composite particle 1, if a binder is included along with the first particle 1a and the second particle 1b, the total mass ratio of the first particle 1a and the second particle 1b in the active material composite particle 1 is not particularly limited. For example, the active material composite particle 1 may contain 50% to 99% by mass of the first particle 1a and the second particle 1b in total. The mass ratio of the binder in the active material composite particle 1 is not particularly limited. For example, the active material composite particle 1 may contain 1% to 50% by mass of the binder. Furthermore, the proportions of the first particle 1a, the second particle 1b, and the binder contained in the active material composite particle 1 are not particularly limited as long as they are sufficient to form the composite particle 1. For example, the proportion of the binder to the total of the first particle 1a, the second particle 1b, and the binder may be between 1% by mass and 50% by mass, the lower limit may be between 5% by mass or 8% by mass, and the upper limit may be between 40% by mass, 35% by mass or 30% by mass. When the proportion of the binder is between 1% by mass and 50% by mass, it is easier to secure a larger charge and discharge capacity.

[0032] 1.6.2 Other ingredients besides the binder The active material composite particle 1 may consist only of the first particle 1a, the second particle 1b, and an optional binder (and voids), or it may contain other components. Examples of other components include various solid components and liquid components.

[0033] 1.7 Particle size of active material composite particles The active material composite particle 1 can be considered as a secondary particle formed by the aggregation of a plurality of first particles 1a and at least one second particle 1b. 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 be 100 μm or less, 50 μm or less, 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 an SEM, and can be determined, for example, as the average value of the maximum Ferret diameter of a plurality of composite particles. The number of samples is preferably large, for example 20 or more, but may be 50 or more, or 100 or more. Alternatively, the average particle diameter (D50, median diameter) of composite particle 1, measured using a laser diffraction particle distribution analyzer, may be 100 nm or more, 1 μm or more, 2 μm or more, or 3 μm or more, and may also be 100 μm or less, 50 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0034] 1.8 Structure and shape of active material composite particles The active material composite particles 1 may have a major axis and a minor axis in their state before being applied to a secondary battery, for example. 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, or 1.3 or less or 1.2 or less. On the other hand, when the active material composite particles 1 are 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 mixture containing the active material composite particles 1. In this case, the composite particles 1 may be crushed in the pressing direction and have an aspect ratio of a predetermined value or higher. By pressing the composite particles 1 to the extent that they have an aspect ratio of a predetermined value or higher, the contact resistance within the composite particles, the contact resistance between the composite particles, and the contact resistance between the composite particles and other materials are easily reduced. Specifically, from the viewpoint of further reducing the resistance of the negative electrode, when observing the cross-section of the negative electrode active material layer, more than half (more than 50% in number) of the multiple composite particles 1 extracted by the extraction method described below may have an aspect ratio of 1.5 or higher.

[0035] Extraction method: The cross-section of the active material layer is observed, and the composite particles contained in the cross-section are extracted in descending order of cross-sectional area. Extraction is terminated when the total area of ​​the extracted composite particles exceeds 80% of the total area of ​​all composite particles contained in the cross-section.

[0036] Furthermore, the above extraction method may be performed by image analysis based on cross-sectional images 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 as ellipses, and the aspect ratio of each composite particle may be determined.

[0037] 2. Secondary battery Figure 2 schematically shows the configuration of a secondary battery 100 according to one embodiment. As shown in Figure 2, the secondary battery 100 has a positive electrode active material layer 20, an electrolyte layer 30, and a negative electrode active material layer 40, and the negative electrode active material layer 40 contains the above-mentioned active material composite particles 1. Furthermore, the problem of increased confinement pressure is more likely to become apparent when the secondary battery 100 contains a solid electrolyte. In this regard, in the secondary battery 100, at least one of the positive electrode active material layer 20, the electrolyte layer 30, and the negative electrode active material layer 40 may contain a solid electrolyte. Also, in the secondary battery 100, at least the negative electrode active material layer 40 may contain a solid electrolyte. Furthermore, in the secondary battery 100, all of the positive electrode active material layer 20, the electrolyte layer 30, and the negative electrode active material layer 40 may contain a solid electrolyte. Moreover, the secondary battery 100 may be a solid battery. A solid battery is one in which the electrolyte having carrier ion conductivity is mainly composed of a solid electrolyte. However, it may contain a liquid component in part. Alternatively, the secondary battery 100 may be an all-solid-state battery that substantially does not contain a liquid component. Furthermore, as shown in Figure 2, the secondary battery 100 may include a positive electrode current collector 10 that is in contact with the positive electrode active material layer 20. The secondary battery 100 may also include a negative electrode current collector 50 that is in contact with the negative electrode active material layer 40.

[0038] 2.1 Positive electrode current collector The positive electrode current collector 10 can be any of the commonly used positive electrode current collectors for secondary batteries. The positive electrode current collector 10 may also have at least one shape selected from foil, plate, mesh, perforated metal, and foam. The positive electrode current collector 10 may be composed of metal foil or metal mesh. Metal foil, in particular, offers superior handling. The positive electrode current collector 10 may consist of multiple foils. Examples of metals constituting the positive electrode current collector 10 include at least one selected from Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, V, Mg, Pb, Ge, In, Sn, Zr, and stainless steel. In particular, the positive electrode current collector 10 may contain Al to ensure oxidation resistance. The positive electrode current collector 10 may have some kind of coating layer on its surface for purposes such as adjusting resistance. For example, the positive electrode current collector 10 may have a carbon coating layer. Alternatively, the positive electrode current collector 10 may be a metal foil or substrate on which the above metal is plated or deposited. Furthermore, if the positive electrode current collector 10 consists of multiple metal foils, there may be some layer between the multiple metal foils. The thickness of the positive electrode current collector 10 is not particularly limited. For example, it may be 0.1 μm or more and 1 mm or less, with a lower limit of 1 μm or more and an upper limit of 100 μm or less.

[0039] 2.2 Cathode active material layer The positive electrode active material layer 20 contains at least positive electrode active material. The positive electrode active material layer 20 may also optionally contain an electrolyte, a conductive additive, a binder, and various other additives. The content of each component in the positive electrode active material layer 20 can be appropriately determined according to the desired battery performance. For example, with the total solid content of the positive electrode active material layer 20 being 100% by mass, the content of 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, or 100% by mass or less, less than 100% by mass, 95% by mass or less, or 90% by mass or less. Alternatively, with the total volume of the positive electrode active material layer 20 being 100% by volume, the positive electrode active material and optionally the electrolyte, conductive additive, and binder may together be 85% by volume or more, 90% by volume or more, or 95% by volume or more, with the remainder being void or other components. The shape of the positive electrode active material layer 20 is not particularly limited and may, for example, be a sheet having a substantially flat surface. The thickness of the positive electrode active material layer 20 is not particularly limited and may be, for example, 0.1 μm or more and 2 mm or less, with a lower limit of 1 μm or more, 10 μm or more, or 30 μm or more, and an upper limit of 1 mm or less, 500 μm or less, or 100 μm or less.

[0040] 2.2.1 Cathode active material The positive electrode active material can adopt any of those known as the positive electrode active material of a secondary battery. Among the known active materials, a material with a relatively high potential (charge-discharge potential) for occluding and releasing a predetermined carrier ion can be used as the positive electrode active material, and a material with a relatively low potential can be used as the negative electrode active material. When the secondary battery 100 is a lithium ion battery, 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 may be a lithium-containing oxide containing at least one element M, Li, and O. The element M may be, for example, at least one selected from Mn, Ni, Co, Al, Mg, Ca, Sc, V, Cr, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, Bi, Fe, and Ti, or at least one selected from the group consisting of Mn, Ni, Co, Al, Fe, and Ti. More specifically, the lithium-containing oxide may be lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium nickel cobalt oxide, lithium nickel manganate, lithium cobalt manganate, lithium nickel cobalt manganate (Li 1±α Ni x Co y Mn z O 2±δ (for example, 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1)), spinel-type lithium compounds (Li[[ID=|11]] 1+x Mn 2-x-y M y O4 (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 by this formula), lithium nickel cobalt aluminum oxide (for example, Li 1±α Ni p Co q Al r O 2±δThe positive electrode active material may be at least one selected from (for example, p+q+r=1), lithium titanate, metallic lithium phosphate (LiMPO4, etc., where M is one or more selected from Fe, Mn, Co, and Ni), etc. In particular, the performance of the secondary battery tends to be further improved when the positive electrode active material contains a lithium-containing oxide as a constituent element that includes at least one of Ni, Co, and Mn, Li, and O. Alternatively, the performance of the secondary battery tends to be further improved when the positive electrode active material contains a lithium-containing oxide as a constituent element that includes at least one of Ni, Co, and Al, Li, and O. The positive electrode active material may be used alone or in combination of two or more types.

[0041] The shape of the positive electrode active material may be any shape that is common for positive electrode active materials in secondary batteries. The positive electrode active material may be particulate, for example. The positive electrode active material may have voids, for example, it may be porous or hollow. The positive electrode active material may be primary particles or secondary particles formed by the aggregation of multiple primary particles. The average particle diameter D50 of the positive electrode active material may be, for example, 1 nm or more and 500 μm or less, with a lower limit of 5 nm or more or 10 nm or more, and an upper limit of 100 μm or less, 50 μm or less, or 30 μm or less. In this application, the average particle diameter D50 refers to the particle diameter (median diameter) at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction-scattering.

[0042] 2.2.2 Protective layer An ion-conductive protective layer may be formed on the surface of the positive electrode active material. That is, the positive electrode active material layer 20 may include a composite of the positive electrode active material and the protective layer, and in this composite, at least a portion of the surface of the positive electrode active material may be covered by the protective layer. This makes it easier to suppress reactions between the positive electrode active material and other battery materials (such as the sulfide solid electrolyte described later). The ion-conductive protective layer may include various ion-conductive compounds. The ion-conductive compound may be at least one selected from, for example, ion-conductive oxides and ion-conductive halides.

[0043] Ion-conducting oxides may, for example, contain at least one element selected from B, C, Al, Si, P, S, Ti, La, Zr, Nb, Mo, Zn, and W, as well as Li and O. Ion-conducting oxides may also be oxynitrides containing N. More specifically, ion-conducting oxides include Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, and Li4Ti5O 12 It may be at least one selected from Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, Li2WO4, LiPON, Li2O-LaO2, Li2O-ZnO2, etc. The ion-conducting oxide may have some elements substituted by various doping elements.

[0044] The ion-conducting halide may be, for example, at least one of the various compounds exemplified as halide solid electrolytes described later. The ion-conducting halide may include, for example, at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sn, Al, Sc, Ga, Bi, Sb, Zr, Hf, Ti, Ta, Nb, W, Y, Gd, Tb, and Sm, at least one halogen element selected from the group consisting of Cl, Br, I, and F, and Li. The ion-conducting halide may include at least one element selected from the group consisting of Ti, Al, Gd, Ca, Zr, and Y, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. Furthermore, the ion-conducting halide may include at least one element selected from the group consisting of Ti and Al, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. Furthermore, the ion-conducting halide may be, for example, a composite halide of Li, Ti, Al, and F.

[0045] 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 and 100 nm or less, with a lower limit of 1 nm or more and an upper limit of 20 nm or less.

[0046] 2.2.3 Electrolytes The positive electrode active material layer 20 may contain an electrolyte. The electrolyte contained in the positive electrode active material layer 20 may be a solid electrolyte, a liquid electrolyte, or a combination of a solid electrolyte and a liquid electrolyte.

[0047] 2.2.3.1 Solid electrolyte As the solid electrolyte, any known solid electrolyte 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 excellent ionic conductivity and heat resistance. Examples of inorganic solid electrolytes include oxide solid electrolytes, sulfide solid electrolytes, and ionically bonded inorganic solid electrolytes. Among inorganic solid electrolytes, sulfide solid electrolytes, and among those, sulfide solid electrolytes containing at least Li, S, and P as constituent elements, have high performance. Alternatively, among inorganic solid electrolytes, ionically bonded solid electrolytes, and among those, solid electrolytes containing at least Li, Y, and a halogen (at least one of Cl, Br, I, and F) as constituent elements, have high performance. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be particulate. The average particle size (D50) of the solid electrolyte may be, for example, 10 nm to 10 μm. The ionic conductivity of the solid electrolyte at 25°C is, for example, 1 × 10⁻¹⁶ -5 S / cm or more, 1×10 -4 S / cm or more, or 1 × 10 -3 The ratio may be S / cm or higher. The solid electrolyte may be used alone or in combination of two or more types.

[0048] Oxide solid electrolytes include lithium lanthanum zirconate, LiPON, and Li 1+X AlX Ge 2-X (PO4)3, Li-SiO glass, Li-Al-SO glass, and one or more other materials may be selected. Furthermore, when an oxide solid electrolyte and a liquid electrolyte are combined, ionic conductivity may be improved.

[0049] The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte (sulfide glass), a glass-ceramic-based sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. The sulfide glass is amorphous. The sulfide glass may have a glass transition temperature (Tg). Furthermore, if the sulfide solid electrolyte has a crystalline phase, examples of the crystalline phase include a thio-LISICON type crystalline phase, an LGPS type crystalline phase, and an argyrodite type crystalline phase.

[0050] The sulfide solid electrolyte may contain, for example, Li, X (where 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 halogen elements. Furthermore, the sulfide solid electrolyte may contain S as the main component of the anionic element.

[0051] Sulfide solid electrolytes include, for example, 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, Li2S-P2S5-ZmSn (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-Li x MO y(However, x and y are positive numbers. M may be at least one selected from P, Si, Ge, B, Al, Ga, In.)

[0052] The composition of the sulfide solid electrolyte is not particularly limited. For example, xLi2S·(100 - x)P2S5 (70 ≤ x ≤ 80), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.7 ≤ x ≤ 0.8, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30), etc. can be mentioned. Alternatively, the sulfide solid electrolyte has a composition represented by the general formula: Li 4-x Ge 1-x P x S4 (0 < x < 1). In the above general formula, at least a part of Ge may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, at least a part of P may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, a part of Li may be substituted with at least one of Na, K, Mg, Ca, and Zn. In the above general formula, a part of S may be substituted with a halogen (at least one of F, Cl, Br, and I). Alternatively, the sulfide solid electrolyte is Li 7-a PS 6-a X a (X is at least one of Cl, Br, and I, and a is a number from 0 or more to 2 or less) and may have a composition represented by. a may be 0, or may be greater than 0. In the latter case, a may be 0.1 or more, may be 0.5 or more, and may be 1 or more. Also, a may be 1.8 or less, may be 1.5 or less.

[0053] The ionic solid electrolyte may contain, for example, at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sn, Al, Sc, Ga, Bi, Sb, Zr, Hf, Ti, Ta, Nb, W, Y, Gd, Tb, and Sm. These elements can generate cations in water. The ionic solid electrolyte material may also further contain, for example, at least one halogen element selected from the group consisting of Cl, Br, I, and F. These elements can generate anions in water. The ionic solid electrolyte may contain at least one element selected from the group consisting of Gd, Ca, Zr, and Y, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. Alternatively, the ionic solid electrolyte may contain Li and Y, and at least one element selected from the group consisting of Cl, Br, I, and F. More specifically, the ionic solid electrolyte may contain Li, Y, Cl, and Br, or Li, Ca, Y, Gd, Cl, and Br, or Li, Zr, Y, and Cl. More specifically, the ionic solid electrolyte may be Li3YBr2Cl4, Li 2.8 Ca 0.1 Y 0.5 Gd 0.5 Br2Cl4 and Li 2.5 Y 0.5 Zr 0.5 It may be at least one of the Cl6 species.

[0054] The ionic solid electrolyte may be a halide solid electrolyte. Halide solid electrolytes have excellent ionic conductivity. For example, formula (1): Li α M β X γ ...(A) It may have a composition represented by Here, α, β, and γ are each independently values greater than 0, M is at least one selected from the group consisting of metal elements other than Li and metalloid elements, and X is at least one selected from the group consisting of Cl, Br, and I. Note that the "metalloid element" may be at least one selected from the group consisting of B, Si, Ge, As, Sb, and Te. Further, the "metal element" may include (i) all elements (excluding hydrogen) contained in Groups 1 to 12 of the periodic table and (ii) all elements (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se) contained in Groups 13 to 16 of the periodic table. The metal element can form an inorganic compound with a halide ion and become a cation.

[0055] In formula (A), M may contain Y (i.e., yttrium). The halide solid electrolyte containing Y is Li a Me b Y c It may have a composition represented by X6 (where a + mb + 3c = 6, c > 0, Me is at least one selected from the group consisting of metal elements and metalloid elements other than Li and Y, and m is the valence of Me). Me may be at least one selected from the group consisting of, for example, Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0056] The halide solid electrolyte may have a composition represented by formula (A1): Li 6-3d Y d X6. In formula (A1), X is one or more elements selected from the group consisting of Cl, Br, and I. d may satisfy 0 < d < 2, or d = 1. The halide solid electrolyte may have a composition represented by formula (A2): Li 3-3δ Y 1+δ Cl6. In formula (A2), 0 < δ ≦ 0.15 may hold. The halide solid electrolyte may have a composition represented by formula (A3): Li 3-3δ Y 1+δIt may have a composition represented by Br6. In formula (A3), 0 < δ ≦ 0.25 may be satisfied. The halide solid electrolyte has the formula (A4): Li 3-3δ+a Y 1+δ-a Me a Cl 6-x-y Br x I y It may have a composition represented by. In formula (A4), Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, and Zn. In formula (A4), for example, -1 < δ < 2, 0 < a < 3, 0 < (3 - 3δ + a), 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 are satisfied. The halide solid electrolyte has the formula (A5): Li 3-3δ Y 1+δ-a Me a Cl 6-x-y Br x I y It may have a composition represented by. In formula (A5), Me may be at least one selected from the group consisting of Al, Sc, Ga, and Bi. In formula (A5), -1 < δ < 1, 0 < a < 2, 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 may be satisfied. The halide solid electrolyte has the formula (A6): Li 3-3δ-a Y<所 1+δ-a Me a Cl 6-x-y Br x I y It may have a composition represented by. In formula (A6), Me may be at least one selected from the group consisting of Zr, Hf, and Ti. In formula (A6), -1 < δ < 1, 0 < a < 1.5, 0 < (3 - 3δ - a), 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 may be satisfied. The halide solid electrolyte has the formula (A7): Li 3-3δ-2a Y 1+δ-a Me a Cl 6-x-y Br x I y It should be noted that in the translation, for the tags like 3-3δ+a etc., they are preserved as they are because they are specific tags in the original text and need to be kept unchanged according to the requirements. Also, the text seems to have some inconsistent or unclear notations in the original (such as "所0000062"), but the translation is done based on the rules of keeping the original format and content as much as possible.It may have a composition represented by. In formula (A7), Me may be at least one selected from the group consisting of Ta and Nb. In formula (A7), -1 < δ < 1, 0 < a < 1.2, 0 < (3 - 3δ - 2a), 0 < (1 + δ - a), 0 ≤ x ≤ 6, 0 ≤ y ≤ 6, and (x + y) ≤ 6 may hold.

[0057] The ionic solid electrolyte may be a complex hydride solid electrolyte. The complex hydride solid electrolyte may be composed of Li ions and a complex ion containing H. The complex ion containing H may, for example, have at least one of a non-metal element, a semi-metal element, and a metal element, namely, element M, and H bonded to the element M. Also, in the complex ion containing H, the element M as the central element and the H surrounding the element M may be bonded to each other via a covalent bond. Also, the complex ion containing H may be represented by (M m H n ) α- . In this case, m is an arbitrary positive number, and n and α can take arbitrary positive numbers according to m and the valence of element M, etc. Element M may be a non-metal element or a metal element capable of forming a complex ion. For example, element M may contain at least one of B, C, and N as a non-metal element, and may contain B. Also, for example, element M may contain at least one of Al, Ni, and Fe as a metal element. Particularly, when the complex ion contains B, or when it contains C and B, higher ionic conductivity is more easily ensured. Specific examples of the complex ion containing H include (CB9H 10 ) - , (CB 11 H 12 ) - , (B 10 H 10 ) 2- , (B 12 H 12 ) 2- , (BH4) - , (NH2) - , (AlH4) - , and combinations thereof. Particularly, (CB9H 10 ) - , (CB 11H 12 ) - Alternatively, using a combination of these can easily ensure higher ionic conductivity. In other words, the complex hydride solid electrolyte may contain Li, C, B, and H.

[0058] 2.2.3.2 Liquid electrolyte The liquid electrolyte is a liquid containing carrier ions. If the secondary battery 100 is a lithium-ion battery, the electrolyte contains lithium ions. The electrolyte may be an aqueous or non-aqueous electrolyte. The composition of the electrolyte may be the same as that known for secondary battery electrolytes. The electrolyte may be a solution of lithium salt in water or a non-aqueous solvent. Examples of non-aqueous solvents include carbonate-based solvents. Examples of carbonate-based solvents include fluoroethylene carbonate (FEC), ethylene carbonate (EC), and dimethyl carbonate (DMC). Examples of lithium salts include LiPF6, LiTFSI, and LiFSI.

[0059] 2.2.4 Conductive additives Examples of conductive additives that may be included in the positive electrode active material layer 20 include carbon materials such as vapor-processed carbon fiber (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metallic materials such as nickel, titanium, aluminum, and stainless steel. The conductive additive may be in the form of parts or fibers, and its size is not particularly limited. One type of conductive additive may be used alone, or two or more types may be used in combination.

[0060] 2.2.5 Binder Examples of binders that may be included in the positive electrode active material layer 20 include butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, styrene butadiene rubber (SBR) binders, polyvinylidene fluoride (PVdF) binders, polytetrafluoroethylene (PTFE) binders, and polyimide (PI) binders. A single binder may be used alone, or two or more binders may be used in combination.

[0061] 2.2.6 Others The positive electrode active material layer 20 may contain various additives in addition to the above-mentioned components. For example, dispersants and lubricants.

[0062] The positive electrode active material layer 20 can be manufactured by applying known methods. For example, the positive electrode active material layer 20 can be easily formed by molding a positive electrode mixture containing the above-mentioned components in a dry or wet manner. The positive electrode active material layer 20 may be molded together with the positive electrode current collector 10, or it may be molded separately from the positive electrode current collector 10.

[0063] 2.3 Electrolyte layer The electrolyte layer 30 is placed between the positive electrode active material layer 20 and the negative electrode active material layer 40. The electrolyte layer 30 contains at least an electrolyte. The electrolyte layer 30 may contain one or both of a solid electrolyte and a liquid electrolyte (electrolyte), and may also optionally contain a binder and various additives. The content of electrolyte and binder etc. in the electrolyte layer 30 is not particularly limited. Alternatively, the electrolyte layer 30 may have a separator etc. to hold the electrolyte and prevent contact between the positive electrode active material layer 20 and the negative electrode active material layer 40. The thickness of the electrolyte layer 30 is not particularly limited; for example, it may be 0.1 μm or more and 2 mm or less, with a lower limit of 1 μm or more and an upper limit of 1 mm or less.

[0064] The electrolyte layer 30 may consist of one layer or multiple layers. For example, the electrolyte layer 30 may comprise a first layer located on the positive electrode active material layer 20 side and a second layer located on the negative electrode active material layer 40 side, wherein the first layer contains a first electrolyte and the second layer contains a second electrolyte. The first electrolyte and the second electrolyte may be of different types. The first electrolyte and the second electrolyte may each be at least one selected from the oxide solid electrolyte, sulfide solid electrolyte and ionic solid electrolyte described above. For example, the first layer may contain an ionic solid electrolyte, and the second layer may contain at least one of the ionic solid electrolyte and sulfide solid electrolyte.

[0065] The electrolyte included in the electrolyte layer 30 may be appropriately selected from the examples of electrolytes that can be included in the positive electrode active material layer 20 (solid electrolytes and / or liquid electrolytes). Similarly, the binder that can be included in the electrolyte layer 30 may be appropriately selected from the examples of binders that can be included in the positive electrode active material layer 20. The electrolyte and binder may be used individually or in combination of two or more types. The separator may be any separator commonly used in secondary batteries, such as those made of polyethylene (PE), polypropylene (PP), polyester, and polyamide resins. The separator may have a single-layer structure or a multi-layer structure. Examples of multi-layer separators include a PE / PP two-layer separator, or a PP / PE / PP or PE / PP / PE three-layer separator. The separator may also be made of a nonwoven fabric such as cellulose nonwoven fabric, resin nonwoven fabric, or glass fiber nonwoven fabric.

[0066] 2.4 Negative electrode active material layer The negative electrode active material layer 40 contains at least the above-described active material composite particles 1 as the negative electrode active material. The negative electrode active material layer 40 may also optionally contain an electrolyte, a conductive additive, a binder, and various additives. The content of each component in the negative electrode active material layer 40 can be appropriately determined according to the desired battery performance. For example, taking the total solid content of the negative electrode active material layer 40 as 100% by mass, the content of the negative 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, or it may be 100% by mass or less, less than 100% by mass, 95% by mass or less, or 90% by mass or less. Alternatively, taking the entire negative electrode active material layer 40 as 100% by volume, the negative electrode active material and optionally the electrolyte, conductive additive, and binder may total 85% by volume or more, 90% by volume or more, or 95% by volume or more, with the remainder being void or other components. The shape of the negative electrode active material layer 40 is not particularly limited and may, for example, be a sheet having a substantially flat surface. The thickness of the negative electrode active material layer 40 is not particularly limited and may be, for example, 0.1 μm or more and 2 mm or less, with a lower limit of 1 μm or more, 10 μm or more, or 30 μm or more, and an upper limit of 1 mm or less, 500 μm or less, or 100 μm or less.

[0067] 2.4.1 Negative electrode active material The negative electrode active material layer 40 may contain only the above-described active material composite particles 1 as the negative electrode active material, or it may contain other negative electrode active materials together with the above-described active material composite particles 1. When the total amount of negative electrode active material contained in the negative electrode active material layer 40 is taken as 100% by mass, the proportion of negative electrode active material derived from the above-described active material composite particles 1 may be, for example, 50% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, or 90% by mass or more and 100% by mass or less. Any other negative electrode active material known as a negative electrode active material for secondary batteries can be used. Among the known active materials, various materials can be used in which the potential for intercalating and releasing predetermined carrier ions (charge / discharge potential) is lower than that of the above-described positive electrode active material. If the secondary battery 100 is a lithium-ion battery, the other negative electrode active material may be at least one selected from, for example, silicon-based active materials such as Si, Si alloys, or silicon oxide; carbon-based active materials such as graphite or hard carbon; various oxide-based active materials such as lithium titanate; or metallic lithium or lithium alloys. The other negative electrode active material may be used alone or in combination of two or more types. The shape of the other negative electrode active material may be any shape that is common for negative electrode active materials in secondary batteries. For example, the negative electrode active material may be particulate. The negative electrode active material particles may be primary particles or secondary particles formed by the aggregation of multiple primary particles. The average particle diameter (D50) of the negative electrode active material particles may be, for example, 1 nm or more and 500 μm or less, with a lower limit of 5 nm or more, or 10 nm or more, and an upper limit of 100 μm or less, 50 μm or less, or 30 μm or less. Alternatively, the negative electrode active material layer 40 may contain a sheet-like (foil-like, film-like) active material such as lithium foil as the negative electrode active material.

[0068] 2.4.2 Others The electrolyte that may be included in the negative electrode active material layer 40 can be appropriately selected from among the examples of electrolytes that may be included in the positive electrode active material layer 20 (solid electrolytes and / or liquid electrolytes). The conductive additive that may be included in the negative electrode active material layer 40 can be appropriately selected from among the examples of conductive additives that may be included in the positive electrode active material layer 20. The binder that may be included in the negative electrode active material layer 40 can be appropriately selected from among the examples of binders that may be included in the positive electrode active material layer 20. Electrolytes, conductive additives, and binders may each be used individually or in combination of two or more types.

[0069] The negative electrode active material layer 40 may contain various additives in addition to the above-mentioned components. For example, dispersants and lubricants.

[0070] The negative electrode active material layer 40 can be manufactured by applying known methods. For example, the negative electrode active material layer 40 can be easily formed by molding a negative electrode mixture containing the above-mentioned components in a dry or wet manner. The negative electrode active material layer 40 may be molded together with the negative electrode current collector 50, or it may be molded separately from the negative electrode current collector 50.

[0071] 2.5 Negative electrode current collector The negative electrode current collector 50 can be any of the materials commonly used as negative electrode current collectors for secondary batteries. The negative electrode current collector 50 may also be in the form of foil, plate, mesh, perforated metal, or foam. The negative electrode current collector 50 may be metal foil or metal mesh, or a carbon sheet. Metal foil is particularly advantageous in terms of handling. The negative electrode current collector 50 may consist of multiple foils or sheets. The metal constituting the negative electrode current collector 50 can be at least one selected from Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, V, Mg, Pb, Ge, In, Sn, Zr, and stainless steel. In particular, from the viewpoint of ensuring reduction resistance and avoiding alloying with lithium, the negative electrode current collector 50 may contain at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector 50 may have some kind of coating layer on its surface for purposes such as adjusting resistance. For example, the negative electrode current collector 50 may have a carbon coating layer. The negative electrode current collector 50 may be aluminum foil having a carbon coating layer. Alternatively, the negative electrode current collector 50 may be a metal foil or a substrate on which the above metal has been plated or deposited. Furthermore, if the negative electrode current collector 50 consists of multiple metal foils, there may be some kind of layer between the multiple metal foils. The thickness of the negative electrode current collector 50 is not particularly limited. For example, it may be 0.1 μm or more and 1 mm or less, with a lower limit of 1 μm or more and an upper limit of 100 μm or less.

[0072] 2.6 Other Configurations In addition to the above configuration, the secondary battery 100 may have configurations common to secondary batteries, such as tabs and terminals. The secondary battery 100 may have each of the above configurations housed inside an outer casing. Any known battery casing can be used. Furthermore, multiple secondary batteries 100 may be electrically connected and stacked as desired to form a battery pack. In this case, the battery pack may be housed inside a known battery case. The secondary battery 100 may also have other obvious configurations such as necessary terminals. Examples of shapes for the secondary battery 100 include coin type, laminate type, cylindrical type, and prismatic type.

[0073] 3. Manufacturing method of secondary batteries The secondary battery 100 can be manufactured by applying known methods. For example, it can be manufactured as follows. However, the manufacturing method of the secondary battery 100 is not limited to the following method, and each layer may be formed by, for example, dry molding. (1) A negative electrode slurry is obtained by dispersing the active material composite particles, etc., constituting the negative electrode active material layer in a solvent. 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 onto 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, thus forming the negative electrode. The negative electrode active material layer may be press-formed. (2) A positive electrode slurry is obtained by dispersing the positive electrode active material and other materials constituting the positive electrode active material layer in a solvent. 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 onto 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 forming the positive electrode. The positive electrode active material layer may be press-formed. (3) The layers are stacked 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 obtained, for example, by molding an electrolyte mixture containing an electrolyte and a binder, or by press molding. The laminate may also be press molded. Other members such as terminals are attached to the laminate as needed. When an electrolyte solution is used, a separator may be used in the electrolyte layer. (4) A secondary battery is obtained by housing the laminate in a battery case and sealing it.

[0074] 4. Method for manufacturing active material composite particles The active material composite particles of the present disclosure can be manufactured, for example, in the flow shown in Figure 3. That is, as shown in Figure 3, a method for manufacturing active material composite particles according to one embodiment includes: dropletizing a slurry containing a plurality of first particles, at least one second particle, and a solvent to obtain slurry droplets (step S1); and air-drying the slurry droplets in a heated gas to obtain active material composite particles containing a plurality of the first particles and at least one second particle (step S2). Here, the first particles contain porous silicon, the reaction potential between the second particle and Li is lower than the reaction potential between the porous silicon and Li, and the ratio D2 / D1 of the particle diameter of the second particle to the particle diameter D1 of the first particle is 2.0 or more. In the manufacturing method of the present disclosure, as will be described later, dropletization of the slurry and air-drying of the slurry droplets may be performed by spray drying.

[0075] 4.1 Process S1 In step S1, a slurry containing multiple first particles and at least one second particle is formed into droplets to obtain slurry droplets. The first and second particles are as described above.

[0076] In step S1, the first particles constituting the slurry may be produced through, for example, obtaining a LiSi precursor containing Li and Si, and removing Li from the LiSi precursor to obtain porous silicon particles. The LiSi precursor contains Li and Si as constituent elements. The LiSi precursor may be, for example, an alloy of Li and Si. The LiSi precursor may be any material that can form voids and become porous by removing Li. The LiSi precursor may have a crystal phase of Si (diamond type). The crystal phase of Si has typical peaks at positions of 2θ = 28.4°, 47.3°, 56.1°, 69.2°, and 76.4° in XRD measurement using CuKα radiation. These peak positions may shift within a range of ±0.5° respectively, or may shift within a range of ±0.3°. The LiSi precursor may have a crystal phase of Si (diamond type) as the main phase. The "main phase" refers to the crystal phase to which the peak with the highest intensity belongs in the XRD chart. The LiSi precursor contains Li 22 a crystal phase of Si5 and Li 15 may have a crystal phase of Si4. Li 22 The crystal phase of Si5 has typical peaks at positions of 2θ = 24.8° and 40.8° in XRD measurement using CuKα radiation, and Li 15 the crystal phase of Si4 has typical peaks at positions of 2θ = 20.3°, 26.2°, 39.4°, 41.2°, and 42.9° in XRD measurement using CuKα radiation. These peak positions may shift within a range of ±0.5° respectively, or may shift within a range of ±0.3°.

[0077] The composition of the LiSi precursor is not particularly limited. The LiSi precursor may contain only Li and Si elements, or it may contain other elements in addition to Li and Si elements. The total proportion of Li and Si elements to all elements contained in the LiSi precursor may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. In the LiSi precursor, the proportion of Li elements to the total proportion of Li and Si elements may be, for example, 30 mol% or more, 50 mol% or more, or 80 mol% or more, or 95 mol% or less, or 90 mol% or less. The LiSi precursor may be obtained by mixing a raw material containing Li elements with a raw material containing Si elements. For example, in the manufacturing method of this disclosure, a LiSi precursor may be obtained by mixing Si particles and Li metal. Examples of mixing methods include mixing Si particles and Li metal using an agate mortar, or mixing Si particles and Li metal using a mechanical milling method. The temperature and pressure during mixing are not particularly limited. Heating or cooling may or may not be applied during mixing, and pressurization or depressurization may or may not be applied. The atmosphere during mixing is not particularly limited; for example, an inert gas atmosphere such as an Ar atmosphere may be used. The shape and size of the Si particles and Li metal to be mixed are also not particularly limited and may be appropriately selected according to the shape and size of the desired porous silicon particles.

[0078] Porous silicon particles are obtained by removing Li from a LiSi precursor. Here, it is not necessary to remove all Li from the LiSi precursor, and Li may partially remain in the porous silicon particles. The method for removing Li from the LiSi precursor is not particularly limited. For example, Li may be extracted from the LiSi precursor. A Li extraction solvent may be used for Li extraction. For example, by contacting the LiSi precursor with a Li extraction solvent, the Li extraction solvent and Li react, and Li is extracted from the LiSi precursor into the Li extraction solvent. The form in which the LiSi precursor is contacted with the Li extraction solvent is not particularly limited; the LiSi precursor may be immersed in the Li extraction solvent, the Li extraction solvent may be sprayed onto the LiSi precursor, the LiSi precursor and the Li extraction solvent may be mixed, or the LiSi precursor may be dispersed in a dispersion medium to form a dispersion, and this dispersion may be mixed with the Li extraction solvent. As the Li extraction solvent, for example, alcohols such as methanol, ethanol, and propanol can be used. The Li extraction solvent may contain a secondary solvent along with the alcohol. Examples of secondary solvents include various acids. The extraction rate of lithium (Li) varies depending on the type of Li extraction solvent, and this affects the diameter of the pores formed after Li extraction. For example, comparing the extraction of Li using methanol, ethanol, and propanol, the extraction rate is fastest when methanol is used, followed by ethanol, then 1-propanol, and then isopropanol. Furthermore, the pore diameter after Li extraction tends to be largest when methanol is used, followed by ethanol, then 1-propanol, and then isopropanol. The type of Li extraction solvent and extraction time should be selected according to the desired pore diameter.

[0079] The voids formed in porous silicon particles after lithium extraction have various pore sizes. By adjusting the pore size in the porous silicon particles after lithium extraction, the pores become less likely to collapse even when the porous silicon particles are subjected to pressure (for example, when the negative electrode is pressed during battery manufacturing). For example, as mentioned above, increasing the amount of pores with a diameter of 55 nm or less in the porous silicon particles makes the pores less likely to collapse, and the expansion and contraction of the active material during charging and discharging becomes even easier to suppress.

[0080] The porous silicon particles, as the first particles, may be manufactured by dispersing a LiSi precursor in a dispersion medium to obtain a dispersion, and then mixing the dispersion with a Li extraction solvent to extract Li from the LiSi precursor and form voids. In this case, the pore size in the porous silicon particles after Li extraction can be adjusted more appropriately. Examples of dispersion mediums include one or more solvents selected from saturated hydrocarbons such as n-heptane, n-octane, n-decane, 2-ethylhexane, and cyclohexane; unsaturated hydrocarbons such as hexene and heptene; aromatic hydrocarbons such as 1,3,5-trimethylbenzene, toluene, xylene, ethylbenzene, propylbenzene, cumene, 1,2,4-trimethylbenzene, and 1,2,3-trimethylbenzene; and ethers such as n-butyl ether, n-hexyl ether, isoamyl ether, diphenyl ether, methylphenyl ether, and cyclopentyl methyl ether. Among these, one or more selected from n-butyl ether, 1,3,5-trimethylbenzene, and n-heptane are preferred, with 1,3,5-trimethylbenzene being particularly preferred. Furthermore, it is preferable that the water content in the dispersion medium be low, as water reacts with the LiSi precursor. The water content in the dispersion medium may be, for example, 100 ppm or less, 50 ppm or less, 30 ppm or less, or 10 ppm or less. The proportion (solid content) of the LiSi precursor in the dispersion is not particularly limited and should be sufficient to disperse the LiSi precursor in the dispersion medium. The dispersion can be obtained, for example, by mixing the LiSi precursor with the dispersion medium. The mixing method in this case is not particularly limited.

[0081] The temperature and pressure used when extracting Li from a LiSi precursor using a Li extraction solvent are not particularly limited. Heating or cooling may or may not be applied during Li extraction, and pressurization or depressurization may or may not be applied. The atmosphere and Li extraction time during Li extraction are also not particularly limited. Furthermore, the ratio of LiSi precursor to Li extraction solvent is not particularly limited. The temperature, pressure, time, ratio, etc., should be adjusted so that the required amount of Li is extracted from the LiSi precursor. The removal of Li from the LiSi precursor may be carried out in one step or in two or more steps. For example, porous silicon particles may be obtained in one step by simply reacting the LiSi precursor with the Li extraction solvent, or porous silicon particles may be obtained through two or more extraction processes, such as forming voids using the Li extraction solvent and then extracting Li again using the Li extraction solvent, or extracting Li using an acid. Using an acid after using the Li extraction solvent allows for more appropriate extraction of Li from the LiSi precursor. Examples of acids include one or more of acetic acid, formic acid, propionic acid, and oxalic acid. Acetic acid is particularly preferred. The temperature, pressure, time, and volume ratio during Li extraction using acid are not particularly limited. The porous silicon particles after Li extraction may be optionally washed. This can reduce the amount of impurities contained in the porous silicon particles. If the concentration of LiSi precursor in the total of LiSi precursor and Li extraction solvent is high, the manufacturing efficiency will be high, but the amount of impurities generated will also tend to be high. For example, if the concentration of LiSi precursor is 3.3 g or more per 1 L of Li extraction solvent, washing the active material after Li extraction can improve manufacturing efficiency and reduce impurities at the same time. Washing may be, for example, acid washing, in which the porous silicon particles are brought into contact with an acid. In addition, the extraction of the element Li using the acid described above may also serve as the acid washing of the porous silicon particles.

[0082] In step S1, the second particles constituting the slurry should be selected from materials that are optimal in accordance with the reaction potential between the porous silicon constituting the first particles and Li, as described above. When particles containing crystalline silicon are used as the second particles, the crystalline silicon can be synthesized by known methods.

[0083] In step S1, the solvent constituting the slurry only needs to be capable of dispersing the first and second particles. The slurry may also contain a binder along with the first and second particles. In this case, the binder may be dissolved in the solvent. Various organic solvents, such as dimethyl carbonate, can be used as solvents capable of dissolving the binder.

[0084] In step S1, "slurry" refers to a suspension or aerosol containing the first particle, the second particle, a solvent, and optionally a binder, provided that it has sufficient fluidity to be formed into droplets. In step S1, the slurry may have sufficient fluidity to be formed into droplets using, for example, a spray nozzle or a rotary atomizer. In addition to the components described above, the slurry may also contain any solid or liquid components.

[0085] In step S1, "dropletization" of the slurry means that the slurry containing the first particle, the second particle, and the solvent is converted into particles containing the first particle, the second particle, and the solvent (and any binder). The method for dropletizing the slurry in step S1 is not particularly limited. For example, dropletization can be achieved by spraying the slurry. When spraying the slurry, a spray nozzle may be used. Methods for spraying the slurry using a spray nozzle include, but are not limited to, the pressurized nozzle method and the two-fluid nozzle method.

[0086] In step S1, 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, or 10 mm or less, or 1 mm or less. Furthermore, the slurry spraying speed (the rate at which the slurry is supplied to the spray nozzle) is not particularly limited. The spraying speed may be adjusted according to the viscosity of the slurry, the solid content concentration, the nozzle dimensions, etc.

[0087] In step S1, in addition to the method of spraying the slurry using a spray nozzle as described above, other examples of methods for forming droplets from the slurry include supplying a slurry containing first particles, second particles, and solvent (and an optional binder) onto a rotating disk at a constant speed and forming droplets by centrifugal force. In this case as well, the slurry supply speed should be adjusted according to the viscosity and solid content concentration of the slurry. Alternatively, a method of forming droplets by applying a high voltage to the surface of the slurry can also be employed.

[0088] In one embodiment of the manufacturing method, for example, a spray dryer may be used to perform the dropletization of the slurry (step S1) and the subsequent airflow drying (step S2). The type of spray dryer is not particularly limited and examples include the type using the spray nozzle described above, or the type using a rotating disc.

[0089] A "slurry droplet" is a particle of slurry containing a first particle, a second particle, and a solvent (and binder). 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, or 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 it can be measured using a laser diffraction particle size analyzer. Alternatively, the droplet diameter can be estimated from the operating conditions of the apparatus that forms the slurry droplet.

[0090] In step S1, without pre-compounding the multiple first particles 1a, a slurry may be obtained by dispersing the primary particles of the multiple first particles 1a and at least one second particle 1b in a solvent, and the slurry may be formed into droplets. This yields the active material composite particle 1 shown in Figure 1A. Alternatively, in step S1, a first composite particle may be obtained by pre-compounding (secondary particle formation) the multiple first particles 1a together, and then the first composite particle and the second particle 1b may be dispersed in a solvent to obtain a slurry, and the slurry may be formed into droplets. This yields the active material composite particle 1 shown in Figure 1B.

[0091] 4.2 Process S2 In step S2, the slurry droplets are air-dried in a heated gas to obtain active material composite particles containing a plurality of first particles and at least one second particle.

[0092] In a manufacturing method according to one embodiment, "airflow drying" means drying slurry droplets while they are suspended in a high-temperature airflow. "Airflow drying" may include not only drying but also incidental operations using dynamic airflow. By continuously applying hot air to the slurry droplets through airflow drying, a force is continuously applied to the slurry droplets. Taking advantage of this, for example, step S2 may include disintegrating (crushing) the slurry droplets or granules by airflow drying. In other words, in the method of this disclosure, even if granulation of slurry droplets occurs, the granules can be crushed by airflow drying. Therefore, slurries with low solid content can be used, and the processing speed can be easily increased. In step S2, the drying and crushing described above may be performed simultaneously or separately. In step S2, a first airflow drying in which drying of slurry droplets is prioritized and a second airflow drying in which crushing of granules is prioritized may be performed. Step S2 may also be repeated.

[0093] In step S2, the temperature of the heated gas should be such that the solvent can be evaporated 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 it may also be 180°C or lower, 170°C or lower, 160°C or lower, or 150°C or lower.

[0094] In step S2, the amount (flow rate) of heated gas supplied can be appropriately set considering the size of the equipment used, the amount of slurry droplets supplied, etc. For example, the flow rate of heated gas may be 0.10 m³. 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 3 It may be more than / min, and also 5.00m 3 / min or less, 4.00m 3 / min or less, 3.00m 3 / min or less, 2.00m 3 Less than / min, or 1.00m 3 It can be less than / minute.

[0095] In step S2, the supply rate (flow rate) of the heated gas can also be set appropriately, taking into consideration the size of the equipment used and the amount of slurry droplets supplied. For example, the flow rate of the heated gas may be 1 m / sec or more or 5 m / sec or more in at least a part of the system, or it may be 50 m / sec or less or 10 m / sec or less.

[0096] In step S2, the processing time (drying time) with heated gas can be appropriately set considering the size of the equipment used, the amount of slurry droplets supplied, etc. For example, the processing time may be 5 seconds or less, or 1 second or less.

[0097] In step S2, a heated gas that is substantially inert to the first particle, the second particle, and the solvent (and any binder) may be used. For example, an oxygen-containing gas such as air, an inert gas such as nitrogen or argon, or dry air with a low dew point can be used. In that case, the dew point may be -10°C or lower, -50°C or lower, or -70°C or higher.

[0098] For example, a spray dryer can be used as the device for air-flow drying, but it is not limited to this.

[0099] According to the above manufacturing method, an active material composite particle 1 as shown in Figure 1A or Figure 1B is obtained. That is, a secondary particle is obtained in which a plurality of first particles 1a and at least one second particle 1b are composited.

[0100] 5. Method for charging and discharging secondary batteries and method for improving the cycle characteristics of secondary batteries When the active material composite particles of this disclosure are included in the negative electrode of a secondary battery, the increase in the confinement pressure of the secondary battery is suppressed, and for example, the cycle characteristics of the secondary battery are easily improved. That is, the charging and discharging method of a secondary battery and the method for improving the cycle characteristics of a secondary battery of this disclosure include repeatedly charging and discharging the secondary battery, and the secondary battery has a positive electrode active material layer, an electrolyte layer and a negative electrode active material layer, and the negative electrode active material layer contains the active material composite particles of this disclosure. Here, the charging termination potential of the negative electrode of the secondary battery may be higher than the reaction potential between the second particle and Li.

[0101] 6. Vehicles equipped with secondary batteries As described above, when the active material composite particles of this disclosure are included in the negative electrode of a secondary battery, improvements in the cycle characteristics of the secondary battery can be expected. A secondary battery with such excellent charge-discharge cycle characteristics can be suitably used in, for example, at least one type of vehicle selected from hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). In other words, the technology of this disclosure also has an aspect as a vehicle having a secondary battery, wherein the secondary battery has a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, and the negative electrode active material layer contains the active material composite particles of this disclosure. [Examples]

[0102] The technology of this disclosure will be described in more detail below with reference to examples, but the technology of this disclosure is not limited to the following examples.

[0103] 1. Preparation of the negative electrode active material 1.1 Comparative Example A LiSi precursor was obtained by mixing 0.65 g of Si particles (particle size 0.5 μm, manufactured by Kojunsei Kagaku Co., Ltd.) and 0.60 g of Li metal (manufactured by Honjo Kinzoku) in an agate mortar under an Ar atmosphere. In a glass reactor under an Ar atmosphere, 1.0 g of the LiSi precursor and 125 ml of dispersion medium (1,3,5-trimethylbenzene, manufactured by Nacalai Tesque) were mixed using an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.). The resulting LiSi precursor dispersion was cooled to 0°C, and 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 added dropwise, and the mixture was reacted for another 60 minutes. After the reaction, the liquid and solid reactants (nanoporous Si particles) were separated by suction filtration. The obtained solid reactants were vacuum-dried at 120°C for 2 hours, and nanoporous Si particles (particle size: 500 nm) were recovered. Analysis of the crystalline structure of the nanoporous Si by X-ray diffraction and other methods revealed that the nanoporous Si was amorphous.

[0104] 1.2 Example 1 The above-mentioned nanoporous Si and PVdF-HFP binder (manufactured by Kureha Corporation) were dispersed and dissolved in dimethyl carbonate (manufactured by Nacalai Tesque) in a mass ratio of nanoporous 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, and while being dropletized, it was air-dried to obtain composite particles 1.

[0105] The above composite particle 1, crystalline Si particles (particle size: approximately 2 μm, manufactured by Kojunsei Kagaku Co., Ltd.), and PVdF-HFP binder (manufactured by Kureha Corporation) were dispersed and dissolved in dimethyl carbonate (manufactured by Nacalai Tesque) in a mass ratio of composite particle 1:crystalline Si particles:binder = 50:50:7 to obtain a slurry. This slurry was sprayed into a spray dryer under a nitrogen gas atmosphere at a temperature of 140°C and air-dried while being formed into droplets to obtain the active material composite particles according to Example 1.

[0106] 1.3 Example 2 The above-mentioned nanoporous Si, crystalline Si particles (particle size: approximately 2 μm, manufactured by Kojunsei Kagaku Co., Ltd.), and PVdF-HFP binder (manufactured by Kureha Corporation) were dispersed and dissolved in dimethyl carbonate (manufactured by Nacalai Tesque) in a mass ratio of nanoporous Si particles:crystalline Si particles:binder = 50:50:26.7 to obtain a slurry. This slurry was sprayed into a spray dryer under a nitrogen gas atmosphere at a temperature of 140°C and air-dried while being formed into droplets to obtain the active material composite particles according to Example 2.

[0107] 2. Preparation of solid electrolytes 0.550 g of Li2S (Furuuchi Chemical), 0.887 g of P2S5 (Aldrich), 0.285 g of LiI (Nippo Chemical), and 0.277 g of LiBr (High Purity Chemical) were mixed in an agate mortar for 5 minutes. 4 g of n-heptane (dehydrated grade, Kanto Chemical) was added to the resulting mixture, and the mixture was mechanically milled for 40 hours using a planetary ball mill to obtain a sulfide solid electrolyte.

[0108] 3. Preparation of the positive electrode composite material LiRing 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode active material was obtained by surface-treating O2 (manufactured by Nichia Corporation) with LiNbO3. 1.5 g of this positive electrode active material, 0.023 g of a conductive additive (VGCF, manufactured by Showa Denko Corporation), 0.239 g of the above-mentioned 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 Corporation) to obtain a positive electrode composite material.

[0109] 4. Preparation of the negative electrode composite A negative electrode composite was obtained by mixing 1.0 g of nanoporous Si according to the above comparative example, 1.0 g of active material composite particles according to Example 1, or 1.0 g of active material composite particles according to Example 2, 0.04 g of conductive additive (VGCF, manufactured by Showa Denko Corporation), 0.776 g of the above sulfide solid electrolyte, 0.02 g of binder (PVdF, manufactured by Kureha Corporation), and 1.7 g of butyl butyrate (manufactured by Kishida Chemical Co., Ltd.) using an ultrasonic homogenizer (UH-50, manufactured by SMT Corporation).

[0110] 5. Preparation of evaluation batteries 1cm 2 Place 0.065g of the above sulfide solid electrolyte into the ceramic mold, and fill with 1 ton / cm³. 2 A solid electrolyte layer was fabricated by pressing. 0.018g of the above positive electrode composite material was placed on one side, and the pressure was increased to 1 ton / cm². 2 The positive electrode active material layer was fabricated by pressing. 0.0054g of the above negative electrode composite material was placed on the opposite side of the positive electrode active material layer at a rate of 4 tons / cm². 2 The negative electrode active material layer was fabricated by pressing. Al foil was used as the positive electrode current collector, and Cu foil as the negative electrode current collector. This allowed for the fabrication of an evaluation battery (all-solid-state battery).

[0111] 6. Evaluation 6.1 Cross-sectional observation of active material composite particles For each of the active material composite particles in Examples 1 and 2, the cross-sectional structure before pressing was observed using SEM, the elements contained in the cross-section of the composite particles were analyzed using EDX, and the cross-sectional structure of the composite particles was identified by image processing. Figure 4A is the cross-sectional SEM image of the composite particle according to Example 1, Figure 4B is the EDX distribution for Si in the cross-sectional SEM image of the composite particle according to Example 1, Figure 5A is the cross-sectional SEM image of the composite particle according to Example 2, and Figure 5B is the EDX distribution for Si in the cross-sectional SEM image of the composite particle according to Example 2.

[0112] As shown in Figures 4A, 4B, 5A, and 5B, the active material composite particles in Examples 1 and 2 can be seen to be formed by the compounding of multiple relatively small nanoporous Si particles and relatively large crystalline Si particles to form secondary particles. As mentioned above, the ratio (D2 / D1) of the particle diameter of crystalline Si particles to the particle diameter of nanoporous Si particles (D1) is 2.0 or greater, and it can be seen that this relationship is maintained in the composite particles as well.

[0113] As shown in Figures 4A and 4B, in the active material composite particles according to Example 1, it can be seen that the crystalline Si particles (second particles) are exposed on the outer surface of the composite particles. On the other hand, as shown in Figures 5A and 5B, in the active material composite particles according to Example 2, it can be seen that the crystalline Si particles (second particles) are located inside the nanoporous Si particles (first particles). In other words, the active material composite particles according to Example 2 have a core and a shell, the core contains crystalline Si particles, and the shell contains a plurality of nanoporous Si particles and does not contain crystalline Si particles.

[0114] 6.2 Confirmation of the increase in confinement pressure of the evaluation battery Each evaluation battery in the comparative example and the example was confined with a confinement pressure of 5 MPa. The confined evaluation batteries were CC / CV charged to 4.55 V at a rate of 1 / 10C. During charging, the negative electrode expanded, and an increase in confinement pressure was confirmed. The increase in confinement pressure after charging compared to the confinement pressure before charging was measured. The results are shown in Table 1 below. In Table 1 below, the increase in confinement pressure of the evaluation battery in the comparative example is set to 100, and the increase in confinement pressure of the evaluation batteries in Examples 1 and 2 are shown relative to each other. A smaller value in Table 1 means a smaller increase in confinement pressure.

[0115] [Table 1]

[0116] It is known that the reaction potential between crystalline Si particles and Li is lower than that between amorphous nanoporous Si particles and Li. That is, during charging, nanoporous Si particles react with Li and expand before crystalline Si particles. In each of the batteries according to the Comparative Example and Examples 1 and 2, when charged under the above conditions, substantially only the nanoporous Si particles (first particles) react with Li and expand, while the crystalline Si particles (second particles) do not react with Li and remain substantially unchanged from their pre-charging state. That is, the amount of expansion of the nanoporous Si particles is substantially the same in the batteries according to the Comparative Example and Examples 1 and 2. Nevertheless, as shown in Table 1, the increase in confinement pressure was smaller in the batteries according to Examples 1 and 2 compared to the battery according to the Comparative Example. That is, the overall expansion of the negative electrode in the batteries according to Examples 1 and 2 was significantly smaller than that of the battery according to the Comparative Example. This is presumed to be due to the following mechanism.

[0117] Examples 1 and 2 differ from the comparative example in that they use composite particles of nanoporous Si particles and crystalline Si particles as the negative electrode active material. Here, the reaction potential between crystalline Si particles and Li is lower than the reaction potential between amorphous nanoporous Si particles and Li. Therefore, under the above charging conditions, after charging the battery, the nanoporous Si particles react with Li and expand, while the crystalline Si particles do not react with Li and remain substantially unchanged from their pre-charging state. Also, as mentioned above, the ratio D2 / D1 of the particle diameter D1 of the nanoporous Si particles to the particle diameter D2 of the crystalline Si particles is 2.0 or greater, meaning that the crystalline Si particles are sufficiently larger than the nanoporous Si particles. In such a case, it is thought that the crystalline Si particles function as pillars in the active material composite particles, and the overall structure and voids of the active material composite particles are more easily maintained by the crystalline Si particles. As a result, even if the nanoporous Si particles expand, the overall expansion of the active material composite particles is mitigated, the expansion of the negative electrode is reduced, and the increase in confinement pressure is reduced. In particular, as in Example 2, when crystalline Si particles are located inside the nanoporous Si particles, the expansion of the nanoporous Si becomes more isotropic, and the overall expansion of the active material composite particles is thought to be further relaxed. As a result, the increase in confinement pressure is thought to be more significantly reduced.

[0118] In the above embodiment, an example was given in which amorphous nanoporous Si particles were used as the first particles constituting the active material composite particles and crystalline Si particles were used as the second particles. However, the technology of this disclosure is not limited to this form. For example, as mentioned above, the second particles only need to be capable of functioning as pillars, and particles other than crystalline Si particles may be used. When particles other than crystalline Si particles are used as the second particles, the first particles do not necessarily need to be amorphous. That is, it is thought that any active material composite particle having the following configurations (1) to (4) will exhibit a certain effect through the same mechanism as described above. However, it is thought that the effect is more likely to be enhanced when amorphous nanoporous Si particles are used as the first particles constituting the active material composite particles and crystalline Si particles are used as the second particles. (1) The active material composite particle comprises a plurality of first particles and at least one second particle. (2) The first particle contains porous silicon. (3) The reaction potential between the second particle and Li is lower than the reaction potential between the porous silicon and Li. (4) The ratio D2 / D1 of the particle diameter of the second particle to the particle diameter D1 of the first particle is 2.0 or greater.

[0119] Furthermore, although the above embodiment shows the use of active material composite particles containing a binder, the presence of a binder is optional as long as the shape of the active material composite particles is maintained. However, when the active material composite particles contain a binder, the shape of the active material composite particles is more easily maintained. [Explanation of symbols]

[0120] 1 Active material composite particles 1a 1st particle 1b 2nd particle 100 Secondary battery 10 Positive electrode current collector 20 Cathode active material layer 30 Electrolyte layer 40 Negative electrode active material layer 50 Negative electrode current collector

Claims

1. An active material composite particle comprising a plurality of first particles and at least one second particle, The first particle contains porous silicon, The porous silicon constituting the first particle is amorphous, The second particle contains crystalline silicon, The reaction potential between the second particle and Li is lower than the reaction potential between the porous silicon and Li, Particle diameter D of the first particle １ The particle diameter D of the second particle relative to ２ Ratio D ２ / D １ However, it is 2.0 or higher. Active material composite particles.

2. The active material composite particle according to claim 1, The crystalline silicon constituting the second particle is porous. Active material composite particles.

3. The active material composite particle according to claim 1, The second particle is located inside the first particle, Active material composite particles.

4. The active material composite particle according to claim 1, The first particle and the second particle together include a binder, Active material composite particles.

5. The active material composite particle according to claim 1, The second particle is spherical. Active material composite particles.

6. A secondary battery comprising a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The negative electrode active material layer includes the active material composite particles described in any one of claims 1 to 5. Secondary battery.

7. A secondary battery according to claim 6, At least one of the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer includes a solid electrolyte. Secondary battery.

8. A method for producing active material composite particles according to claim 1, To obtain slurry droplets by forming a slurry containing multiple first particles, at least one second particle, and a solvent into droplets, and, The process includes: air-drying the slurry droplets in a heated gas to obtain an active material composite particle comprising a plurality of first particles and at least one second particle. The first particle contains porous silicon, The reaction potential between the second particle and Li is lower than the reaction potential between the porous silicon and Li, Particle diameter D of the first particle １ The particle diameter D of the second particle relative to ２ Ratio D ２ / D １ However, it is 2.0 or higher. Manufacturing method.

9. A manufacturing method according to claim 8, Spray drying is used to form droplets of the slurry and to perform air-flow drying of the slurry droplets. Manufacturing method.

10. A manufacturing method according to claim 8 or 9, The slurry contains a binder along with the first and second particles. Manufacturing method.

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