Anode mixture, solid-state battery, and method for producing anode mixture

Abstract

A main object of the present disclosure is to provide an anode mixture capable of obtaining an anode layer in which both of suppression of volume change due to charge and discharge and reduction of resistance are achieved.SOLUTION: The present disclosure solves the problem by providing an anode mixture comprising an anode active material, wherein the anode mixture comprises a primary particle A and a secondary particle in which a plurality of primary particles B are aggregated, as the anode active material, the primary particle A and the primary particle B are a Si-based active material comprising a Si element, and a ratio of the primary particle A with respect to a total of the primary particle A and the secondary particle is 5 volume% or more and 50 volume% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode composite, a solid-state battery, and a method for manufacturing the negative electrode composite. [Background technology]

[0002] In recent years, the development of batteries has been actively pursued. For example, in the automotive industry, development of batteries for use in electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), or hybrid electric vehicles (HEVs) is progressing. A battery typically has a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer. Also, an active material containing Si element (Si-based active material) is known as a negative electrode active material used in the negative electrode layer. For example, Patent Document 1 discloses a negative electrode for a secondary battery containing composite particles including a plurality of porous silicon particles and a binder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2024-017797 Summary of the Invention [Problem to be solved by the invention]

[0004] Although Si-based active materials are high-capacity active materials, they undergo large volume changes during charge and discharge. Large volume changes during charge and discharge can easily cause cracks to form in the negative electrode layer, and the cracks can easily cause performance degradation of the negative electrode layer (e.g., increased resistance and decreased cycle characteristics). Therefore, there is a need to suppress volume changes during charge and discharge in negative electrode layers containing Si-based active materials. Furthermore, from the perspective of improving battery performance, there is a need for negative electrode layers with low resistance.

[0005] The present disclosure has been made in consideration of the above-described circumstances, and has as its main object to provide a negative electrode composite that can obtain a negative electrode layer that achieves both suppression of volume change due to charge and discharge and reduction in resistance. [Means for solving the problem]

[0006] [1] A negative electrode mixture containing a negative electrode active material, The negative electrode composite contains, as the negative electrode active material, primary particles A and secondary particles formed by aggregation of a plurality of primary particles B, the primary particles A and the primary particles B are Si-based active materials containing Si element, The negative electrode mixture, wherein the proportion of the primary particles A to the total of the primary particles A and the secondary particles is 5% by volume or more and 50% by volume or less.

[0007] [2] Particle diameter D of the above primary particles A 50 , and the particle diameter D of the primary particles B 50 and each independently have a size of 0.3 μm or more and 3.0 μm or less.

[0008] [3] The primary particles A and the primary particles B are of the same type and have a particle diameter D 50 The negative electrode mixture according to [1] or [2] is also the same.

[0009] [4] The particle diameter D of the above secondary particles 50 The negative electrode mixture according to any one of [1] to [3], wherein the average particle size is 2.5 μm or more and less than 20 μm.

[0010] [5] The negative electrode mixture according to any one of [1] to [4], wherein at least one of the primary particles A and the primary particles B is a porous particle.

[0011] [6] The particle diameter D of the above secondary particles 50 The particle diameter D of the primary particles A50 The negative electrode mixture according to any one of [1] to [5], wherein the proportion of is 3% or more and 60% or less.

[0012] [7] The negative electrode mixture according to any one of [1] to [6], wherein the secondary particles are particles formed by aggregating the plurality of primary particles B with a binder.

[0013] [8] The negative electrode mixture according to any one of [1] to [7], further containing a solid electrolyte.

[0014] [9] The negative electrode mixture according to [8], wherein the solid electrolyte is a sulfide solid electrolyte.

[0015]

[10] The negative electrode composite according to [9], wherein the sulfide solid electrolyte contains Li, P, and S elements.

[0016]

[11] A solid-state battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer and containing a solid electrolyte, A solid-state battery, wherein the negative electrode contains the negative electrode mixture according to any one of [1] to

[10] .

[0017]

[12] A method for producing a negative electrode mixture containing a negative electrode active material, comprising: a preparation step of preparing, as the negative electrode active material, primary particles A and secondary particles formed by agglomeration of a plurality of primary particles B; a mixing step of mixing the primary particles A and the secondary particles; and the primary particles A and the primary particles B are Si-based active materials containing Si element, A method for producing a negative electrode composite, wherein the proportion of the primary particles A to the total of the primary particles A and the secondary particles is 5% by volume or more and 50% by volume or less. [Effects of the Invention]

[0018] The negative electrode mixture according to the present disclosure has the effect of being able to obtain a negative electrode layer that is suppressed from undergoing volumetric change due to charge and discharge. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. [Figure 2] FIG. 2 is an explanatory diagram illustrating a method for identifying primary particles. [Figure 3] FIG. 1 is a flow diagram illustrating a method for producing a negative electrode composite material according to the present disclosure. [Figure 4] 1 is a graph showing the results of the confining pressure fluctuation and resistance in the batteries produced in Examples 1 to 4 and Comparative Examples 1 to 4. [Figure 5] 1 is a cross-sectional SEM image of the negative electrode layer produced in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0020] The negative electrode composite, the solid-state battery, and the method for producing the negative electrode composite according to the present disclosure will be described in detail below.

[0021] A. Negative electrode mixture The negative electrode composite in the present disclosure contains a negative electrode active material. The negative electrode composite also contains, as the negative electrode active material, primary particles A and secondary particles formed by aggregation of a plurality of primary particles B. The primary particles A and primary particles B are Si-based active materials containing Si element. The ratio of the primary particles A to the total of the primary particles A and the secondary particles is within a specific range.

[0022] According to the present disclosure, the negative electrode active material contains secondary particles formed by aggregation of a plurality of primary particles B (Si-based active material), and also contains primary particles A that do not constitute secondary particles, resulting in a negative electrode composite that can obtain a negative electrode layer that achieves both suppression of volume change due to charge and discharge and reduction of resistance. As described above, while Si-based active materials are high-capacity active materials, they also undergo large volume changes during charge and discharge. Large volume changes during charge and discharge can easily cause cracks to occur in the negative electrode layer, and the occurrence of cracks can easily lead to performance degradation of the negative electrode layer (e.g., increased resistance, decreased cycle characteristics). Therefore, there is a need to suppress volume changes during charge and discharge in negative electrode layers containing Si-based active materials.

[0023] Therefore, the present inventors investigated a method of agglomerating multiple primary particles B (Si-based active material) to form secondary particles (composite particles). Such secondary particles have voids between the primary particles B. The voids can absorb the volume change of the primary particles B and reduce the volume change of the secondary particles due to charge and discharge, and as a result, the volume change of the negative electrode layer due to charge and discharge can also be reduced.

[0024] On the other hand, from the viewpoint of improving battery performance, a negative electrode layer with low resistance is required. The present inventors have conducted extensive research into achieving both suppression of volume change due to charge and discharge and reduction of resistance, and have found that adding primary particles A, which do not constitute secondary particles, in addition to secondary particles is effective in achieving both. Although the detailed mechanism is not completely clear, it is presumed that adding primary particles A, which do not constitute secondary particles, in addition to secondary particles improves the contact area between the negative electrode active material and the electrolyte, thereby achieving both suppression of volume change due to charge and discharge and reduction of resistance. Furthermore, adding primary particles A, which do not constitute secondary particles, in addition to secondary particles can improve the packing ratio of the negative electrode layer, thereby increasing the energy density per volume.

[0025] 1.Negative electrode active material The negative electrode mixture contains a negative electrode active material. The negative electrode active material includes primary particles A and secondary particles formed by aggregation of a plurality of primary particles B. The proportion of primary particles A relative to the total of primary particles A and secondary particles is typically 5% by volume or more and 50% by volume or less. The proportion of primary particles A may be 7.5% by volume or more, or may be 10% by volume or more. If the proportion of primary particles A is too low, the resistance of the negative electrode layer may not be sufficiently reduced. On the other hand, the proportion of primary particles A may be 45% by volume or less, or may be 40% by volume or less. If the proportion of primary particles A is too high, the volume change of the negative electrode layer due to charge and discharge may not be sufficiently suppressed.

[0026] (1) Primary particle A The primary particles A in the present disclosure are Si-based active materials containing elemental Si. Examples of Si-based active materials include simple Si, Si alloys, Si oxides, Si carbides, and Si oxide carbides (silicon oxycarbides). The Si alloy is an alloy whose main component is Si. Examples of metals other than Si in the Si alloy include at least one of W, Mo, Cr, V, Nb, Fe, Ti, Zr, Hf, and Os. Examples of Si oxides include SiO. The Si-based active material may have a diamond-type crystalline phase as the main phase, a clathrate I-type crystalline phase as the main phase, or a clathrate II-type crystalline phase as the main phase.

[0027] The primary particles A in the present disclosure may be solid particles or porous particles, with the latter being preferred. Porous particles have voids inside, which can absorb volume changes of the particles and, as a result, can reduce volume changes of the negative electrode layer due to charge and discharge.

[0028] The porosity of the porous particles is, for example, 4% or more, and may be 10% or more. On the other hand, the porosity of the porous particles is, for example, 40% or less, and may be 20% or less. The porosity can be determined by the following procedure. First, a cross section of an electrode layer containing an active material is prepared by ion milling. The cross section is then observed with a scanning electron microscope (SEM) to obtain a photograph of the particles. From the obtained photograph, the silicon portion and the void portion are clearly distinguished using image analysis software and binarized. The areas of the silicon portion and the void portion are determined, and the porosity (%) is calculated using the following formula: Porosity (%) = (void area) / ((silicon area) + (void area)) × 100

[0029] The porous particles preferably have many micropores with a pore diameter of 100 nm or less. Pores with a pore diameter of 100 nm or less can be more prevented from collapsing due to pressing than pores with a pore diameter greater than 100 nm. The pore volume X (cumulative pore volume) of pores with a pore diameter of 100 nm or less is, for example, 0.05 cc / g or more, or may be 0.10 cc / g or more, or may be 0.12 cc / g or more. On the other hand, the pore volume X is, for example, 0.40 cc / g or less. The pore volume in the present disclosure can be determined, for example, by BET measurement.

[0030] The porous particles preferably have many minute voids with a pore diameter of 50 nm or less. Pores with a pore diameter of 50 nm or less can be more effectively prevented from collapsing due to pressing than voids with a pore diameter greater than 50 nm and a pore diameter of 100 nm or less. The void volume Y of voids with a pore diameter of 50 nm or less is, for example, 0.05 cc / g or more, or may be 0.075 cc / g or more, or may be 0.10 cc / g or more. On the other hand, the void volume Y is, for example, 0.25 cc / g or less.

[0031] The porous particles preferably have many minute voids with a pore diameter of 10 nm or less. Pores with a pore diameter of 10 nm or less can accommodate precipitated Li at a higher filling rate than voids with a pore diameter greater than 10 nm, thereby suppressing volume changes due to charge and discharge. The void volume Z of voids with a pore diameter of 10 nm or less is, for example, 0.015 cc / g or more, or may be 0.02 cc / g or more, or even 0.03 cc / g or more. On the other hand, the void volume Z is, for example, 0.09 cc / g or less.

[0032] One example of a method for forming porous particles is to react metallic Li with solid primary particles A (Si-based active material) to produce a LiSi alloy, and then remove Li from the LiSi alloy. The LiSi alloy can be obtained, for example, by mixing primary particles A (Si-based active material) with metallic Li. The molar ratio of Li to Si (Li / Si) is, for example, 1.0 or more, or may be 2.0 or more, 3.0 or more, or even 4.0 or more. Meanwhile, Li / Si is, for example, 8.0 or less. One example of a method for removing Li from a LiSi alloy is to react the LiSi alloy with a Li extractant. Examples of Li extractants include alcohols such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol; and acids such as acetic acid, formic acid, propionic acid, and oxalic acid.

[0033] Another example of a method for forming porous particles is to react metallic Mg with solid primary particles A (Si-based active material) to produce an MgSi alloy, and then remove the Mg from the MgSi alloy. The MgSi alloy can be obtained, for example, by heating a mixture of primary particles A (Si-based active material) and metallic Mg. The ratio of Mg to Si (Mg / Si) is, for example, 1.0 or more, or may be 1.5 or more, or even 2.0 or more. On the other hand, the Mg / Si ratio is, for example, 6.0 or less. An example of a method for removing Mg from an MgSi alloy is to heat the MgSi alloy in an oxygen-containing inert gas atmosphere to convert the Mg in the Mg-Si alloy to MgO, and then remove the MgO with an acid solution. An example of the acid solution is an aqueous solution containing hydrochloric acid (HCl) and hydrogen fluoride (HF).

[0034] Particle diameter D of primary particle A 50 is not particularly limited, but may be, for example, 0.3 μm or more, or 0.5 μm or more. 50 is, for example, 3.0 μm or less, and may be 2.5 μm or less. 50 is the cumulative 50% particle size in the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer. Also, from the fine particle side, the cumulative 10% particle size in the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer is the particle size D 10 The cumulative 90% particle diameter is the particle diameter D 90 (D 90 -D 10 ) / D 50 means the spread of the distribution, and (D 90 -D 10 ) / D 50 The smaller the value of (D 90 -D 10 ) / D 50 is not particularly limited, but may be, for example, 0.1 or more and 3.0 or less, or 0.3 or more and 2.0 or less.

[0035] The BET specific surface area of ​​the primary particles A is not particularly limited, but is, for example, 1 m 2 / g or more, and 10m 2 / g or more, 2 / g or more, and 2 On the other hand, the BET specific surface area of ​​the primary particles A may be, for example, 200 m 2 / g or less, and 150m 2 / g or less.

[0036] (2) Primary particle B The primary particles B in the present disclosure are Si-based active materials containing elemental Si. Details of the primary particles B are the same as those described above for the primary particles A.

[0037] The type of primary particles B may be the same as the type of primary particles A. For example, primary particles B may be simple Si, and primary particles A may also be simple Si. Similarly, primary particles B may be a Si alloy, and primary particles A may also be a Si alloy. Furthermore, when the type of primary particles B is the same as the type of primary particles A, the composition of primary particles B may be the same as the composition of primary particles A. Furthermore, primary particles B may be a Si alloy, and primary particles A may also be a Si alloy, and the compositions of these Si alloys may be the same. On the other hand, the compositions of these Si alloys may be different.

[0038] The type of primary particles B may be different from the type of primary particles A. For example, primary particles B may be simple Si and primary particles A may be a Si alloy. Similarly, primary particles B may be a Si alloy and primary particles A may be simple Si. Furthermore, primary particles B may be porous particles and primary particles A may also be porous particles. Similarly, primary particles B may be porous particles and primary particles A may be solid particles. Similarly, primary particles B may be solid particles and primary particles A may be porous particles.

[0039] Particle diameter D of primary particle B 50 and the particle diameter D of primary particle A 50 The above "particle diameter D of primary particles B" may be the same as 50and the particle diameter D of primary particle A 50 "The same as" means that the particle diameter D 50 On the other hand, the absolute value of the difference between the particle diameter D of primary particle B and that of primary particle B is 0.5 μm or less. 50 is the particle diameter D of primary particle A 50 It may be larger or smaller.

[0040] (3) Secondary particles The secondary particles are particles formed by agglomeration of a plurality of primary particles B. The secondary particles are, for example, particles formed by agglomeration of a plurality of primary particles B with a binder. Examples of binders include rubber-based binders such as butadiene rubber (BR) and styrene butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVdF). In the secondary particles, the proportion of the binder relative to the total of the plurality of primary particles B and the binder is, for example, 1% by mass or more and 30% by mass or less, and may be 5% by mass or more and 25% by mass or less. On the other hand, the secondary particles may be a sintered body formed by agglomeration of a plurality of primary particles.

[0041] Secondary particle diameter D 50 The particle diameter D of the secondary particles is, for example, 2.5 μm or more and less than 20 μm. 50 On the other hand, the particle diameter D of the secondary particles may be 3.0 μm or more, or 5.0 μm or more. 50 The diameter of the secondary particles (D 90 -D 10 ) / D 50 is not particularly limited, but may be, for example, 0.1 or more and 5.0 or less, or 0.3 or more and 1.0 or less.

[0042] The particle diameter D of the secondary particles 50 Particle diameter D of primary particle A 50 The ratio of is not particularly limited, but may be, for example, 3% or more and 60% or less, 5% or more and 40% or less, or 7% or more and 25% or less. 50 Particle diameter D of primary particle B50 The ratio is not particularly limited, but is, for example, 3% or more and 60% or less, or may be 5% or more and 40% or less, or may be 7% or more and 25% or less.

[0043] The method for forming secondary particles is not particularly limited, but examples thereof include spray drying. In the spray drying method, a slurry containing a plurality of primary particles B, a binder, and a dispersion medium is sprayed into hot air to dry. When forming secondary particles containing porous particles as primary particles B, primary particles B that are porous particles may be first prepared, and then secondary particles may be formed using the primary particles B. Alternatively, primary particles B that are solid particles may be first prepared, and then secondary particles may be formed using the primary particles B, and then the primary particles B that constitute the secondary particles may be made porous.

[0044] 2.Solid electrolyte The negative electrode mixture may contain a solid electrolyte, such as an inorganic solid electrolyte, such as a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, or a halide solid electrolyte.

[0045] The sulfide solid electrolyte is a solid electrolyte containing sulfur element (S element) as a main anion element. Examples of the sulfide solid electrolyte include solid electrolytes containing Li element, X element (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S element. The sulfide solid electrolyte may contain one element as the X element, or may contain two or more elements. The sulfide solid electrolyte preferably contains P element as the X element. The sulfide solid electrolyte may further contain at least one of O element and a halogen element. Examples of the halogen element include F element, Cl element, Br element, and I element.

[0046] The sulfide solid electrolyte may be glass (amorphous), glass ceramics, or crystalline. The sulfide solid electrolyte may have a crystalline phase. Examples of the crystalline phase include, for example, Thio-LISICON type crystalline phase, argyrodite type crystalline phase, and LGPS type crystalline phase.

[0047] The composition of the sulfide solid electrolyte is not particularly limited. For example, xLi2S·(1 - x)P2S5 (0.5 ≤ x < 1), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.5 ≤ x < 1, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30) can be mentioned. In these compositions, x preferably satisfies 0.7 ≤ x ≤ 0.8. Also, as other examples of the composition of the sulfide solid electrolyte, Li 7-x PS 6-x X X can be mentioned. X is at least one of F, Cl, Br, and I, and x satisfies 0 ≤ x ≤ 2. Also, as other examples of the composition of the sulfide solid electrolyte, Li 4-x Me 1-x P x S4 (0 < x < 1) can be mentioned. Me is at least one of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0048] The oxide solid electrolyte is a solid electrolyte containing oxygen element as the main component of the anion element, the nitride solid electrolyte is a solid electrolyte containing nitrogen element as the main component of the anion element, and the halide solid electrolyte is a solid electrolyte containing halogen element as the main component of the anion element. Any known solid electrolyte can be adopted as these solid electrolytes. The solid content ratio of the solid electrolyte in the negative electrode composite material is, for example, 10% by mass or more and 50% by mass or less, and may be 20% by mass or more and 40% by mass or less.

[0049] The particle diameter D of the solid electrolyte 50 is not particularly limited. For example, it is 0.05 μm or more and less than 2.0 μm. The particle diameter D of the solid electrolyte 50On the other hand, the particle diameter D of the solid electrolyte may be 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more. 50 may be 1.8 μm or less, may be 1.5 μm or less, may be 1.2 μm or less, or may be 1.0 μm or less.

[0050] In addition, the particle diameter of the secondary particles D 50 Solid electrolyte particle diameter D 50 The ratio (SE / Si2) is not particularly limited, but may be, for example, 0.5% or more, 1.0% or more, 1.2% or more, or 1.5% or more. On the other hand, the ratio (SE / Si2) is, for example, 15% or less, 12% or less, 10% or less, or 5% or less.

[0051] 3.Negative electrode composite material The negative electrode mixture may further contain a conductive material. Examples of the conductive material include carbon-based conductive materials and metal-based conductive materials. Examples of the carbon-based conductive material include particulate carbon-based conductive materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon-based conductive materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF). The fibrous carbon-based conductive material is preferably a carbon nanotube (CNT) such as a single-walled carbon nanotube (SWCNT) or a multi-walled carbon nanotube (MWCNT). When the conductive material is particulate, the particle diameter D of the conductive material is 50 is not particularly limited, but is, for example, 10 nm to 10 μm, or alternatively, 20 nm to 1 μm, or 30 nm to 500 nm. The solid content ratio of the conductive material in the negative electrode mixture is, for example, 0.05 mass % to 3 mass %.

[0052] The negative electrode mixture may further contain a binder (second binder) that does not form secondary particles, in addition to the binder (first binder) that forms the secondary particles. The type of the second binder is the same as that described for the first binder. The solid content of the second binder in the negative electrode mixture is, for example, 0.1 mass % or more and 5 mass % or less.

[0053] The negative electrode mixture may or may not further contain a dispersion medium. Examples of the dispersion medium include butyl acetate, butyl butyrate, mesitylene, tetralin, heptane, and N-methyl-2-pyrrolidone (NMP). When the negative electrode mixture contains a dispersion medium, the solid content of the negative electrode mixture is, for example, 20% by mass or more and 80% by mass or less. Furthermore, the negative electrode mixture is generally used in batteries, and is preferably used in solid-state batteries.

[0054] The method for producing the negative electrode composite is not particularly limited. As described later in "C. Method for producing the negative electrode composite," the negative electrode composite may be obtained by separately preparing primary particles A and secondary particles, and then mixing the primary particles A and secondary particles. On the other hand, for example, when producing secondary particles by a spray-drying method, by adjusting the production conditions (for example, by relatively reducing the amount of binder added), it is possible to form secondary particles from primary particles B and the binder, while leaving some of the primary particles B untransformed into secondary particles. The primary particles B that are not transformed into secondary particles become primary particles A, and as a result, a negative electrode composite containing primary particles A and secondary particles is obtained.

[0055] B. Solid state battery Fig. 1 is a schematic cross-sectional view illustrating a solid-state battery according to the present disclosure. The solid-state battery 10 shown in Fig. 1 includes a positive electrode layer 1, a negative electrode layer 2, an electrolyte layer 3 containing a solid electrolyte and disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive electrode current collector 4 that collects current from the positive electrode layer 1, and a negative electrode current collector 5 that collects current from the negative electrode layer 2. In the present disclosure, the negative electrode layer 2 contains the negative electrode composite described above in "A. Negative electrode composite."

[0056] According to the present disclosure, by using the above-described negative electrode composite, a solid-state battery can be obtained that achieves both suppression of volume change due to charge and discharge and reduction of resistance.

[0057] 1. Negative electrode layer The negative electrode layer contains the negative electrode composite described above. The negative electrode composite is similar to the above description of "A. Negative Electrode Composite." The ratio of primary particles A to the total of primary particles A and secondary particles in the negative electrode layer can be determined from a cross-sectional image of the negative electrode layer. In the cross-sectional image, primary particles A and secondary particles (aggregates of multiple primary particles B) are distinguished as follows. Specifically, as shown in FIG. 2 , a single primary particle P is focused on in the cross-sectional image, and the distance from the center (center of gravity) C of the primary particle P to the edge E of the primary particle is defined as r. A virtual edge E' is defined as a position 1.5r from the center C of the primary particle, and a virtual primary particle Q is identified with the virtual edge E' as its outer edge. If no other primary particles exist within the range of the virtual primary particle Q, the single primary particle P is identified as a primary particle A. On the other hand, if other primary particles exist within the range of the virtual primary particle Q, the single primary particle P is identified as a primary particle B that constitutes a secondary particle. In this way, primary particles A and secondary particles (aggregates of multiple primary particles B) can be distinguished, and the ratio of primary particles A to the total of primary particles A and secondary particles can be calculated from the area ratio. It is assumed that some of the primary particles B that make up the secondary particles will detach from the secondary particles due to volume changes caused by charging and discharging. If the detached primary particles B satisfy the above-mentioned identification conditions, they will be identified as primary particles A.

[0058] The thickness of the negative electrode layer is, for example, 0.1 μm to 500 μm, or may be 0.1 μm to 100 μm, or may be 0.1 μm to 50 μm. In addition, examples of a method for forming the negative electrode layer include a method in which a negative electrode mixture containing a dispersion medium is applied to a negative electrode current collector and then dried.

[0059] 2. Positive electrode layer The positive electrode layer usually contains a positive electrode mixture, which contains at least a positive electrode active material and may further contain at least one of a solid electrolyte, a conductive material, and a binder.

[0060] Examples of the positive electrode active material include oxide active materials, such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, etc., rock salt layered active materials, LiMn2O4, Li4Ti5O 12 , Li(Ni 0.5 Mn 1.5 )O4, and olivine type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0061] A coating layer containing a Li-ion conductive oxide may be formed on the surface of the oxide active material. This is because it can suppress the reaction between the oxide active material and the solid electrolyte (especially the sulfide solid electrolyte). An example of the Li-ion conductive oxide is LiNbO3. The thickness of the coating layer is, for example, 1 nm or more and 30 nm or less.

[0062] The solid electrolyte, conductive material, and binder used in the positive electrode composite are the same as those described above in "A. Negative Electrode Composite." The thickness of the positive electrode layer is, for example, 0.1 μm to 500 μm, or may be 0.1 μm to 100 μm, or may be 0.1 μm to 50 μm. The positive electrode layer may be formed, for example, by applying a positive electrode composite containing a dispersion medium to a positive electrode current collector and drying the applied coating.

[0063] 3. Electrolyte layer The electrolyte layer is formed between the positive electrode layer and the negative electrode layer and contains a solid electrolyte. The electrolyte layer may further contain a binder. The solid electrolyte and the binder are the same as those described above in "A. Negative Electrode Composite." The thickness of the electrolyte layer is, for example, 0.1 μm to 500 μm, or may be 0.1 μm to 100 μm, or may be 0.1 μm to 50 μm.

[0064] 4. Other configurations The solid-state battery according to the present disclosure preferably includes a positive electrode current collector that collects current from the positive electrode layer and a negative electrode current collector that collects current from the negative electrode layer. Examples of materials for the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, and carbon. Examples of materials for the negative electrode current collector include stainless steel, copper, nickel, and carbon.

[0065] The solid-state battery according to the present disclosure may further include a constraining jig that applies a constraining pressure to the positive electrode layer, the electrolyte layer, and the negative electrode layer in the thickness direction. The constraining pressure is, for example, 0.1 MPa or more, or may be 1 MPa or more, or may be 5 MPa or more. On the other hand, the constraining pressure is, for example, 100 MPa or less, or may be 50 MPa or less, or may be 20 MPa or less.

[0066] 5. Solid state battery The type of solid-state battery in the present disclosure is not particularly limited, but is typically a lithium-ion battery. The solid-state battery in the present disclosure may be a primary battery or a secondary battery, with secondary batteries being preferred. This is because they can be repeatedly charged and discharged and are useful, for example, as automotive batteries. The solid-state battery may be a semi-solid battery or an all-solid battery.

[0067] Examples of uses of solid-state batteries include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, solid-state batteries are preferably used as driving power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). Solid-state batteries may also be used as power sources for mobile objects other than vehicles (for example, trains, ships, and aircraft), or as power sources for electrical appliances such as information processing devices. There are no particular limitations on the method for producing solid-state batteries, and known methods can be used.

[0068] C. Method of manufacturing negative electrode composite Fig. 3 is a flow diagram illustrating a method for producing a negative electrode composite according to the present disclosure. As shown in Fig. 3, primary particles A and secondary particles formed by aggregation of a plurality of primary particles B are prepared as a negative electrode active material (preparation step). The primary particles A and primary particles B are Si-based active materials containing Si element. Next, the primary particles A and secondary particles are mixed (mixing step). In the mixing step, the ratio of the primary particles A to the total of the primary particles A and the secondary particles is within a specific range.

[0069] According to the present disclosure, by carrying out the above steps, it is possible to obtain a negative electrode mixture that can provide a negative electrode layer that achieves both suppression of volume change due to charge and discharge and reduction in resistance.

[0070] 1. Preparation process The preparation step in the present disclosure is a step of preparing, as the negative electrode active material, primary particles A and secondary particles formed by aggregation of a plurality of primary particles B. The primary particles A and the secondary particles are the same as those described above in "A. Negative electrode composite."

[0071] 2.Mixing process The mixing step in the present disclosure is a step of mixing primary particles A and secondary particles. Furthermore, in the mixing step, the ratio of primary particles A to the total of primary particles A and secondary particles is within a predetermined range. The ratio of primary particles A is the same as that described above in "A. Negative electrode composite." Furthermore, in the mixing step, at least one of a solid electrolyte, a conductive material, a binder, and a dispersion medium may be added to the mixture of primary particles A and secondary particles. The solid electrolyte, the conductive material, the binder, and the dispersion medium are also the same as those described above in "A. Negative electrode composite."

[0072] 3.Negative electrode composite material The negative electrode composite obtained by each of the above steps is the same as that described above in "A. Negative electrode composite."

[0073] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0074] [Example 1] (Preparation of primary particles) 0.65 g of Si particles (Kojundo Chemical) and 0.60 g of Li metal (Honjo Metal) were mixed in an agate mortar under an Ar atmosphere to obtain a LiSi precursor. In a glass reactor under an Ar atmosphere, 1.0 g of LiSi precursor and 125 ml of a dispersion medium (1,3,5-trimethylbenzene, Nacalai Tesque) were mixed using an ultrasonic homogenizer (UH-50, SMT). The resulting LiSi precursor dispersion was cooled to 0°C, and 125 ml of ethanol (Nacalai Tesque) as a Li extraction solvent was added dropwise. The reaction was continued for 120 minutes. After the reaction, 50 ml of acetic acid (Nacalai Tesque) was added dropwise and the reaction continued for 60 minutes. After the reaction, the liquid and solid reactants were separated by suction filtration. The resulting solid reactant was vacuum dried at 120°C for 2 hours to recover porous primary particles (nanoporous Si). The recovered primary particles are classified and the particle diameter D50 was adjusted to 1.5 μm.

[0075] (Creation of secondary particles) The obtained primary particles (nanoporous Si) and a PVDF-HFP binder (manufactured by Kureha) were dispersed and partially dissolved in dimethyl carbonate (manufactured by Nacalai Tesque) so that the ratio (mass ratio) of primary particles to binder was 100:13.3. This slurry was sprayed into a spray dryer in a nitrogen gas atmosphere at 140°C and dried to obtain secondary particles in which multiple primary particles were aggregated. The obtained secondary particles were classified to determine the particle diameter D of the secondary particles. 50 was adjusted to 10 μm.

[0076] (Production of negative electrode layer) The obtained primary particles and secondary particles were mixed in a volume ratio of primary particles:secondary particles = 5:95 to obtain a negative electrode active material. 1.0 g of the obtained negative electrode active material, 0.04 g of a conductive material (VGCF, manufactured by Showa Denko), and a sulfide solid electrolyte (LiI-LiBr-Li3PS4-based sulfide solid electrolyte, D 50 0.776 g of cellulose acetate (0.2 μm), 0.02 g of binder (PVdF, manufactured by Kureha), and 1.7 g of butyl butyrate (manufactured by Kishida Chemical) were mixed using an ultrasonic homogenizer (UH-50, manufactured by SMT) to prepare a negative electrode slurry (negative electrode composite). This negative electrode slurry was applied to a negative electrode current collector (Ni foil) by the blade method and dried on a hot plate at 100°C for 30 minutes to obtain a negative electrode layer (thickness 30 μm).

[0077] (Preparation of positive electrode layer) Positive electrode active material (LiNi coated with LiNbO3) 1 / 3 Co 1 / 3 Mn 1 / 3 O2) 1.5 g, conductive material (VGCF, Showa Denko) 0.023 g, sulfide solid electrolyte (LiI-LiBr-Li3PS4 sulfide solid electrolyte, D 500.239 g of cellulose acetate (0.2 μm), 0.011 g of binder (PVdF, manufactured by Kureha), and 0.8 g of butyl butyrate (manufactured by Kishida Chemical) were mixed using an ultrasonic homogenizer (UH-50, manufactured by SMT) to prepare a positive electrode slurry. This positive electrode slurry was applied to a positive electrode current collector (Al foil) by the blade method and dried on a hot plate at 100°C for 30 minutes to obtain a positive electrode layer.

[0078] (Preparation of solid electrolyte layer) A sulfide solid electrolyte (LiI-LiBr-Li3PS4-based sulfide solid electrolyte), a binder (PVdF, manufactured by Kureha), and a dispersion medium (butyl butyrate) were dispersed using an ultrasonic disperser to prepare a slurry for the solid electrolyte layer. This slurry was applied to a transfer foil (Al foil) using a blade method and dried on a hot plate at 100°C for 30 minutes to obtain a transfer foil with a solid electrolyte layer.

[0079] (Battery construction) The positive electrode layer and the solid electrolyte layer were stacked so that they faced each other. After pressing with a roll press at a pressure of 50 kN / cm and a temperature of 160°C, the transfer foil (Al foil) was peeled off from the solid electrolyte layer and a 1 cm 2 A positive electrode laminate was obtained by punching out the laminate to a size of 1.08 cm. Next, the negative electrode layer and the solid electrolyte layer were laminated so that they faced each other. After pressing with a roll press at a pressure of 50 kN / cm, the transfer foil (Al foil) was peeled off from the solid electrolyte layer to obtain a negative electrode laminate. Furthermore, a solid electrolyte layer was laminated on the solid electrolyte layer side of the negative electrode laminate so that it faced each other. This laminate was pre-pressed with a flat uniaxial press at a pressure of 100 MPa and a temperature of 25°C, after which the transfer foil (Al foil) was peeled off from the solid electrolyte layer and a 1.08 cm laminate was obtained. 2 By punching out the sheet into a size of 100 mm, a negative electrode laminate having an additional solid electrolyte layer was obtained.

[0080] The positive electrode laminate and the negative electrode laminate with an additional solid electrolyte layer were stacked facing each other. This laminate was pressed in a flat uniaxial press at a pressure of 600 MPa and a temperature of 160°C to obtain a battery laminate. The resulting battery laminate was sandwiched between two restraint plates, which were then clamped together with fasteners at a pressure of 1 MPa to fix the distance between them, thereby obtaining a battery.

[0081] [Examples 2 to 4 and Comparative Examples 1 to 4] Batteries were fabricated in the same manner as in Example 1, except that the volume ratio of the primary particles to the secondary particles was changed as shown in Table 1.

[0082] [evaluation] (Confining pressure fluctuation) The batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were CC / CV charged at 0.245 mA to 4.55 V, and then CC / CV discharged at 0.245 mA to 3.0 V. The confining pressure fluctuation (ΔMPa / mAh) per unit battery capacity was determined. The results are shown in Table 1 and FIG. 4.

[0083] (resistance) The batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were CC / CV charged to 4.35 V at 0.3 mA and then CC / CV discharged to 2.5 V at 0.3 mA, and this charge / discharge cycle was repeated five times. The voltage was then adjusted to 3.7 V, and a current of 10 mA was applied for five seconds. The direct current internal resistance (DCIR) was calculated from the relationship between the voltage drop and the current during discharge. The results are shown in Table 1 and Figure 4.

[0084] (Filling rate) The packing fraction of the negative electrode layers obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was determined. Specifically, the following formula was used, where A is the porosity of the negative electrode layer, x is the sum of the volumes obtained by dividing the mass of each material constituting the negative electrode layer by the true density of each material, and y is the volume obtained from the dimensions of the negative electrode layer (area × thickness). The results are shown in Table 1. Porosity of the negative electrode layer A (%) = (1-x / y) × 100

[0085] [Table 1]

[0086] As shown in Table 1 and FIG. 4, Examples 1 to 4 had smaller confining pressure fluctuations than Comparative Examples 3 and 4. Furthermore, Examples 1 to 4 had smaller resistances than Comparative Examples 1 and 2. Thus, it was confirmed that the negative electrode composites produced in Examples 1 to 4 can provide negative electrode layers that both suppress volume change due to charge and discharge and reduce resistance. Furthermore, Examples 1 to 4 had higher packing rates and higher energy densities per volume than Comparative Examples 1 to 4.

[0087] Furthermore, a cross section of the negative electrode layer produced in Example 1 was observed with a scanning electron microscope (SEM), and the results are shown in Figure 5. As shown in Figure 5, it was confirmed that primary particles and secondary particles formed by aggregation of a plurality of primary particles were dispersed in the negative electrode layer. [Explanation of symbols]

[0088] 1...Positive electrode layer 2...Anode layer 3...electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...solid battery

Claims

1. A negative electrode mixture containing a negative electrode active material, The negative electrode composite includes, as the negative electrode active material, primary particles A and secondary particles formed by aggregation of a plurality of primary particles B, the primary particles A and the primary particles B are Si-based active materials containing Si element, a ratio of the primary particles A to the total of the primary particles A and the secondary particles is 5% by volume or more and 50% by volume or less.

2. Particle diameter D of the primary particles A ５０ , and the particle diameter D of the primary particles B ５０ and each independently are 0.3 μm or more and 3.0 μm or less.

3. The primary particles A and the primary particles B are of the same type and have a particle diameter D ５０ The negative electrode mixture according to claim 1 , wherein

4. The particle diameter D of the secondary particles ５０ The negative electrode mixture according to claim 1 , wherein the average particle diameter is 2.5 μm or more and less than 20 μm.

5. The negative electrode composite according to claim 1 , wherein at least one of the primary particles A and the primary particles B is a porous particle.

6. The particle diameter D of the secondary particles ５０ The particle diameter D of the primary particles A ５０ The negative electrode mixture according to claim 1 , wherein the ratio of

7. The negative electrode mixture according to claim 1 , wherein the secondary particles are particles formed by aggregating the plurality of primary particles B with a binder.

8. The negative electrode composite according to claim 1 , further comprising a solid electrolyte.

9. The negative electrode composite according to claim 8 , wherein the solid electrolyte is a sulfide solid electrolyte.

10. The negative electrode composite according to claim 9 , wherein the sulfide solid electrolyte contains Li, P, and S elements.

11. A solid-state battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer and containing a solid electrolyte, A solid-state battery, wherein the negative electrode comprises the negative electrode mixture according to any one of claims 1 to 10.

12. A method for producing a negative electrode mixture containing a negative electrode active material, comprising: a preparation step of preparing, as the negative electrode active material, primary particles A and secondary particles formed by agglomeration of a plurality of primary particles B; a mixing step of mixing the primary particles A and the secondary particles; and the primary particles A and the primary particles B are Si-based active materials containing Si element, a ratio of the primary particles A to the total of the primary particles A and the secondary particles is 5% by volume or more and 50% by volume or less.

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