Slurry for forming negative electrode active material layer, negative electrode active material layer, and solid-state battery

Abstract

To provide a negative electrode active material layer and a solid-state battery that use sulfide solid electrolyte particles, which provide good electrical conductivity due to carbon nanotubes while suppressing the formation of microcracks.SOLUTION: A negative electrode active material layer 22 includes silicon active material particles, sulfide solid electrolyte particles, and single-walled carbon nanotubes, and the single-walled carbon nanotubes account for less than 0.3 mass % of the negative electrode active material layer 22. A solid state battery 100 includes the negative electrode active material layer 22, solid electrolyte layers 13 and 23, and the positive electrode active material layer 12, in this order.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a slurry for forming an anode active material layer, an anode active material layer, and a solid-state battery. [Background technology]

[0002] A solid-state battery is a battery having a solid electrolyte layer between a positive electrode active material layer and a negative electrode active material layer, and has the advantage of being easy to simplify safety devices. Among solid-state batteries, solid-state lithium-ion batteries have attracted attention because they can provide high energy density by utilizing a battery reaction involving the movement of lithium ions.

[0003] Regarding such all-solid-state batteries, Patent Document 1 discloses an all-solid-state battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, the negative electrode active material layer containing a Si-based active material, a ratio x of the negative electrode active material layer capacity to the positive electrode active material layer capacity satisfying 2≦x≦2.7, and a packing fraction y of the negative electrode active material layer satisfying 21.43x+14.14≦y≦4.29x+60.43. Patent Document 1 lists carbon materials such as acetylene black, ketjen black, and vapor-grown carbon fiber (VGCF), and metal materials such as nickel, aluminum, and stainless steel as conductive additives in the positive electrode active material layer and the negative electrode active material layer. Patent Document 1 also lists the content of such conductive additives in the positive electrode active material layer and the negative electrode active material layer as being in the range of 0.1% to 10% by weight, for example, and 0.1% to 20% by weight, for example. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-162396 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, known conductive additives for the positive electrode active material layer and the negative electrode active material layer of a solid-state battery include carbon materials such as acetylene black, ketjen black, and vapor-grown carbon fiber (VGCF), and metal materials such as nickel, aluminum, and stainless steel. Among these, carbon nanotubes, typified by vapor-grown carbon fiber (VGCF), have favorable electrical conductivity and are therefore being considered as promising candidates for the conductive additive in the positive electrode active material layer and the negative electrode active material layer of a solid-state battery.

[0006] Known carbon nanotubes include single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). However, only multi-walled carbon nanotubes have been investigated as conductive additives in the positive and negative electrode active material layers of solid-state batteries, particularly in the positive and negative electrode active material layers of solid-state batteries using sulfide solid electrolyte particles. Single-walled carbon nanotubes have not been investigated. This is because butyl butyrate, which can disperse sulfide solid electrolyte particles without reacting with them, is commonly used as a dispersion medium to form a slurry for the active material layer. However, it is difficult to stably disperse single-walled carbon nanotubes in this butyl butyrate.

[0007] In the manufacture of a negative electrode active material layer for a solid-state battery, the negative electrode active material layer must be compressed to improve interparticle contact. Furthermore, when a silicon-based active material is used in the negative electrode active material layer of a solid-state battery, the silicon-based active material expands and contracts with the charging and discharging of the battery. When carbon nanotubes are used in the negative electrode active material layer, the carbon nanotubes deform and then elastically return to their original shape (spring back) due to the compression and subsequent return of the negative electrode active material layer during the manufacture and the expansion and contraction of the silicon-based active material, which can promote the formation of microcracks in the negative electrode active material layer.

[0008] The present disclosure aims to provide good electrical conductivity due to carbon nanotubes in an active material layer having a sulfide solid electrolyte while suppressing the generation of microcracks. [Means for solving the problem]

[0009] The present inventors have conducted extensive research and found that the above problems can be solved as follows, and have completed the present invention.

[0010] <Aspect 1> Ketones as dispersion media, and Silicon active material particles, sulfide solid electrolyte particles, and single-walled carbon nanotubes dispersed in the ketone and The ratio of the single-walled carbon nanotubes to the ketone is 0.15% by mass or less. Slurry for forming a negative electrode active material layer. <Aspect 2> 2. The negative electrode active material layer forming slurry according to aspect 1, wherein the proportion of the single-walled carbon nanotubes relative to the total solid content is less than 0.3 mass %. <Aspect 3> The slurry for forming a negative electrode active material layer according to aspect 1 or 2, wherein the ketone is represented by the following formula: [ka] In the formula, R1 and R2 can be independently selected from the group consisting of an alkyl group having 1 to 5 carbon atoms, a benzyl group, and a phenyl group. <Aspect 4> silicon active material particles, sulfide solid electrolyte particles, and single-walled carbon nanotubes; The single-walled carbon nanotubes are less than 0.3% by mass. Negative electrode active material layer. <Aspect 5> A negative electrode active material layer according to aspect 4, wherein the silicon active material particles are porous silicon active material particles, clathrate silicon active material particles, or porous clathrate silicon active material particles. <Aspect 6> A solid-state battery comprising the negative electrode active material layer according to aspect 4 or 5, a solid electrolyte layer, and a positive electrode active material layer in this order. <Aspect 7> A solid state battery according to aspect 6 or 7, wherein after initial charge and discharge, the cross section of the negative electrode active material layer has an average of less than one in-plane crack having a length of 10 μm or more in a region of 50 μm in the thickness direction and 50 μm in the width direction. <Aspect 8> 7. The solid-state battery of embodiment 6, wherein the solid-state battery is a solid-state lithium-ion battery. [Effects of the Invention]

[0011] According to the present disclosure, in an active material layer having a sulfide solid electrolyte, it is possible to suppress the generation of microcracks while providing good electrical conductivity due to carbon nanotubes. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a solid state battery according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] <<Slurry for forming negative electrode active material layer and negative electrode active material layer>> The slurry for forming a negative electrode active material layer according to the present disclosure contains a ketone as a dispersion medium, Silicon active material particles, sulfide solid electrolyte particles, and single-walled carbon nanotubes dispersed in the ketone and The ratio of the single-walled carbon nanotubes to the ketone is 0.08% by mass or less.

[0014] Here, in the negative electrode active material layer forming slurry of the present disclosure, the proportion of the single-walled carbon nanotubes to the total solid content may be less than 0.3 mass %.

[0015] In addition, the negative electrode active material layer of the present disclosure is The present invention relates to a method for manufacturing a semiconductor device, comprising: a silicon-based active material particle, a sulfide solid electrolyte particle, and a single-walled carbon nanotube; The single-walled carbon nanotubes are contained in an amount of less than 0.3% by mass.

[0016] The present inventors have discovered that a ketone dispersion medium can disperse sulfide solid electrolyte particles without reacting with the sulfide solid electrolyte particles, that a small amount of ketone can stably disperse single-walled carbon nanotubes, and that a small amount of single-walled carbon nanotubes can provide good conductivity while suppressing the generation of microcracks in the negative electrode active material layer, and have therefore conceived the presently disclosed slurry for forming a negative electrode active material layer. The presently disclosed negative electrode active material layer can be produced by applying the presently disclosed slurry for forming a negative electrode active material layer to a substrate, for example, a negative electrode current collector layer.

[0017] The reason why a small amount of single-walled carbon nanotubes can provide good conductivity while suppressing the generation of microcracks in the negative electrode active material layer is not limited to a theory, but is thought to be due to the fact that the single-walled carbon nanotubes are flexible and the amount is small, so the force required to elastically return to their original shape is small, and the single-walled carbon nanotubes have a large conductivity-imparting effect per weight.

[0018] In contrast, multi-walled carbon nanotubes, which are commonly used in solid-state batteries, have a strong ability to elastically return to their original shape after being deformed, and their conductivity-imparting effect per weight is smaller than that of single-walled carbon nanotubes. Therefore, they must be used in relatively large quantities, which is thought to promote the formation of microcracks in the negative electrode active material layer.

[0019] Hereinafter, the configurations of the negative electrode active material layer-forming slurry and the negative electrode active material layer according to the present disclosure will be described.

[0020] (ketone) The negative electrode active material layer-forming slurry of the present disclosure contains a ketone as a dispersion medium, which unexpectedly can disperse sulfide solid electrolyte particles without reacting with the sulfide solid electrolyte particles, and can stably disperse single-walled carbon nanotubes in a small amount.

[0021] The ketone that can be used in the slurry for forming the negative electrode active material layer of the present disclosure can have the following formula:

[0022] [ka]

[0023] In the formula, R1 and R2 can be independently selected from the group consisting of an alkyl group having 1 to 5 carbon atoms, a benzyl group, and a phenyl group. R1 and R2 are preferably selected within a range such that the resulting ketone is liquid at room temperature (25°C).

[0024] Specifically, the ketone can be selected from the group consisting of, for example, methyl isobutyl ketone, diisobutyl ketone, 5-nonanone, ethyl isobutyl ketone, benzyl isopropyl ketone, butyrophenone, and combinations thereof.

[0025] (Silicon active material particles) The negative electrode active material layer-forming slurry and the negative electrode active material layer of the present disclosure contain silicon active material particles as the negative electrode active material.

[0026] The size of the silicon active material particles is not particularly limited. The median diameter (D50 particle diameter) of the porous silicon active material particles may be, for example, 0.1 μm or more, 0.3 μm or more, or 0.5 μm or more, and may be 50.0 μm or less, 30.0 μm or less, 10.0 μm or less, 5.0 μm or less, 3.0 μm or less, or 1.0 μm or less. The median diameter of the porous silicon active material particles is the particle diameter (D50 diameter) at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction / scattering method.

[0027] The silicon active material particles can be any silicon active material particles. Therefore, the silicon active material particles can be solid silicon active material particles or porous silicon active material particles. Furthermore, the silicon active material particles can be amorphous silicon active material particles or clathrate silicon active material particles.

[0028] The porous silicon active material particles are primary particles having pores inside, and these pores can suppress expansion and contraction of the negative electrode active material particles during charge and discharge.

[0029] In this regard, for example, the porous silicon active material particles may have an amount of pores having a pore diameter of 100 nm or less of 0.01 cc / g or more, 0.05 cc / g or more, or 0.10 cc / g or more, and may have an amount of pores having a pore diameter of 100 nm or less of 0.50 cc / g or less, 0.40 cc / g or less, 0.30 cc / g or less, 0.20 cc / g or less, 0.15 cc / g or less, or 0.10 cc / g or less. The amount of pores having a pore diameter of 100 nm or less is the cumulative pore volume of pores having a pore diameter of 100 nm or less. The cumulative pore volume can be determined, for example, by mercury porosimeter measurement.

[0030] The porous silicon active material particles can be produced by any method. Specifically, the porous silicon active material particles can be produced by a known method. For example, the porous silicon active material particles can be produced by forming particles of an alloy of silicon and another metal such as magnesium or lithium, and then eluting and removing the other metal from the alloy particles.

[0031] The porous silicon active material particles may be porous clathrate silicon active material particles (porous clathrate silicon active material particles) having a clathrate structure. It is preferable that the porous silicon active material particles have a clathrate structure, since this further reduces the expansion and contraction of the porous silicon active material particles during charging and discharging of the battery. Whether or not the porous silicon active material particles have a clathrate structure can be easily determined by Raman spectroscopy, XRD, or the like. The porous silicon active material particles may have an oxide coating, or may contain impurities such as carbon.

[0032] The porous clathrate silicon active material particles can be obtained by a known method, for example, by mixing the above-mentioned porous silicon active material particles with a sodium source, such as NaH, and then heat-treating the mixture in a non-oxidizing atmosphere to remove sodium.

[0033] (Sulfide solid electrolyte particles) The negative electrode active material layer-forming slurry and the negative electrode active material layer of the present disclosure contain sulfide solid electrolyte particles as the solid electrolyte.

[0034] Any sulfide solid electrolyte particles can be used. Specific examples of sulfide solid electrolyte particles include sulfide solid electrolyte particles such as Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Si2S-P2S5, Li2S-P2S5-LiI-LiBr, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, and Li2S-P2S5-GeS2. Sulfide solid electrolyte particles, especially sulfide solid electrolyte particles containing at least Li, S, and P as constituent elements, are preferred due to their high performance. The inorganic solid electrolyte particles may be amorphous or crystalline. Only one type of inorganic solid electrolyte particle may be used alone, or two or more types may be used in combination.

[0035] (single-walled carbon nanotubes) The negative electrode active material layer-forming slurry and the negative electrode active material layer of the present disclosure contain single-walled carbon nanotubes as a conductive additive.

[0036] In the slurry for forming a negative electrode active material layer of the present disclosure, the ratio of the single-walled carbon nanotubes to the ketone as a dispersion medium may be 0.01% by mass or more, 0.02% by mass or more, or 0.03% by mass or more, and may be 0.15% by mass or less, 0.12% by mass or less, 0.11% by mass or less, 0.10% by mass or less, 0.09% by mass or less, 0.08% by mass or less, 0.07% by mass or less, or 0.06% by mass or less.

[0037] The ratio of single-walled carbon nanotubes to the total solid content in the negative electrode active material layer-forming slurry of the present disclosure and the ratio of single-walled carbon nanotubes in the negative electrode active material layer of the present disclosure may be 0.01% by mass or more, 0.02% by mass or more, 0.04% by mass or more, 0.06% by mass or more, 0.08% by mass or more, or 0.10% by mass or more, and may be less than 0.30% by mass, 0.28% by mass or less, 0.26% by mass or less, 0.24% by mass or less, 0.22% by mass or less, or 0.20% by mass or less.

[0038] Any single-walled carbon nanotube can be used. Here, while multi-walled carbon nanotubes are composed of multiple graphene sheets, single-walled carbon nanotubes are composed of a single graphene sheet. Furthermore, single-walled carbon nanotubes are classified into chiral (spiral) type, zigzag type, and armchair type based on the difference in the structure of the graphene sheet. As the single-walled carbon nanotube in the present disclosure, any of these can be used, and a single type of single-walled carbon nanotube or a mixture of multiple types of single-walled carbon nanotubes can also be used.

[0039] The diameter (fiber diameter) of the single-walled carbon nanotubes is not particularly limited, and the average diameter may be, for example, 0.4 nm or more, 0.5 nm or more, or 1.0 nm or more, and may be 100.0 nm or less, 50.0 nm or less, 10.0 nm or less, or 5.0 nm or less. The length of the single-walled carbon nanotubes is not particularly limited, and the average length may be, for example, 0.1 μm or more, 0.5 μm or more, 1.0 μm or more, or 5.0 μm or more, and may be 1000 μm or less, 500 μm or less, 100 μm or less, or 50 μm or less. The aspect ratio of the single-walled carbon nanotubes (ratio of average length to average diameter) is not particularly limited, and may be, for example, 10 or more, 100 or more, 500 or more, or 1000 or more.

[0040] The average diameter and average length of single-walled carbon nanotubes can be determined by measuring the dimensions of 50 or more randomly selected single-walled carbon nanotubes using a scanning electron microscope (SEM), transmission electron microscope (TEM), etc., and taking the arithmetic mean.

[0041] When multi-walled carbon nanotubes are used in combination with single-walled carbon nanotubes, the mass proportion of single-walled carbon nanotubes in the total carbon nanotubes may be, for example, 1 mass% or more, 3 mass% or more, 5 mass% or more, 10 mass% or more, 20 mass% or more, 30 mass% or more, 40 mass% or more, 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, 90 mass% or more, 95 mass% or more, or 99 mass% or more. Preferably, only single-walled carbon nanotubes can be used as the carbon nanotubes.

[0042] The conductive agent other than carbon nanotubes is not particularly limited, and for example, carbon black such as acetylene black or ketjen black can be used.

[0043] 《Solid-state battery》 The solid-state battery of the present disclosure includes, in this order, the negative electrode active material layer, the solid electrolyte layer, and the positive electrode active material layer of the present disclosure. The solid-state battery of the present disclosure is preferably a solid-state lithium-ion battery.

[0044] In the solid-state battery of the present disclosure, after initial charge and discharge, the cross section of the negative electrode active material layer may have an average of less than one in-plane crack with a length of 10 μm or more in an area of ​​50 μm in the thickness direction × 50 μm in the width direction. Here, the in-plane crack may be the average of three visual fields observed. Furthermore, the in-plane crack can be confirmed by determining that a laterally elongated void with a width of 2 μm or more in the stacking direction of the solid-state battery and an aspect ratio of 5 or more is a crack.

[0045] Here, in the above, the "width direction" means a direction perpendicular to the thickness direction in the cross section of the negative electrode active material layer.

[0046] In addition, in this specification, "after initial charge and discharge" means that the fabricated solid-state battery is CCCV charged (constant current, constant voltage charged) at 1 / 10C to 4.35V and then CCCV discharged at 1 / 3C to 3.35V.

[0047] The solid-state battery according to the present disclosure may have an anode current collector layer on the side of the anode active material layer opposite the solid electrolyte layer, and may have a cathode current collector layer on the side of the cathode active material layer opposite the solid electrolyte layer. That is, the solid-state battery according to the present disclosure may have an anode current collector layer, an anode active material layer, a solid electrolyte layer, a cathode active material layer, and a cathode current collector layer in this order.

[0048] <Negative electrode current collector layer> The negative electrode layer used in the solid-state battery of the present disclosure may include a negative electrode current collector layer in contact with the negative electrode active material layer. Any of the negative electrode current collector layers commonly used in batteries can be used as the negative electrode current collector layer. The negative electrode current collector layer may be in the form of a foil, plate, mesh, punched metal, porous, foam, or the like. The negative electrode current collector layer may be a metal foil or metal mesh, or a carbon sheet. Metal foil is particularly advantageous in terms of ease of handling. The negative electrode current collector layer may be composed of multiple foils or sheets. Examples of metals constituting the negative electrode current collector layer include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. In particular, from the viewpoints of ensuring reduction resistance and being less likely to be alloyed with lithium, the negative electrode current collector layer may contain at least one metal selected from Cu, Ni, and stainless steel.

[0049] <Solid electrolyte layer> The solid electrolyte layer may contain a solid electrolyte.

[0050] The material of the solid electrolyte is not particularly limited, and any material that can be used as a solid electrolyte for a lithium-ion battery can be used. For example, the solid electrolyte may be, but is not limited to, a sulfide solid electrolyte, an oxide solid electrolyte, or a polymer electrolyte. Furthermore, these solid electrolytes may be used alone or in combination of two or more.

[0051] As the sulfide solid electrolyte, for example, the sulfide solid electrolyte particles mentioned in relation to the negative electrode active material layer can be used.

[0052] The oxide solid electrolyte is, for example, Li7La3Zr2O 12、 Li 7-x La3Zr 1-x Nb x O 12、 Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Alx Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, or Li 3+x PO 4-x N x Examples include, but are not limited to, LiPON (LiPON), etc. These may be amorphous or crystalline.

[0053] Examples of polymer electrolytes include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

[0054] <Cathode active material layer> The positive electrode active material layer used in the solid-state battery of the present disclosure contains a positive electrode active material, and may further contain, optionally, an electrolyte, a conductive additive, a binder, etc. Furthermore, the positive electrode active material layer may also contain various other additives. The contents of the positive electrode active material, electrolyte, conductive additive, binder, etc. in the positive electrode active material layer may be appropriately determined depending on the desired battery performance.

[0055] The positive electrode active material may be a known positive electrode active material, particularly a positive electrode active material used in lithium ion batteries, and may be selected from, for example, metal oxides containing lithium and at least one transition metal selected from manganese, cobalt, nickel, and titanium, such as lithium cobalt oxide, lithium nickel oxide, lithium manganate, or lithium nickel cobalt manganate (NCM), heteroelement-substituted Li-Mn spinel, lithium titanate, lithium metal phosphate, or a combination thereof.

[0056] The electrolyte that can be contained in the positive electrode active material layer may be a solid electrolyte, a liquid electrolyte (electrolytic solution), or a combination thereof.

[0057] <Positive electrode current collector layer> The positive electrode current collector layer used in the solid-state battery of the present disclosure can be any of those commonly used as positive electrode current collector layers for secondary batteries. The positive electrode current collector layer may be in the form of a foil, plate, mesh, punched metal, porous, foam, or the like. The positive electrode current collector layer may be a metal foil or a metal mesh. Metal foil is particularly excellent in terms of ease of handling. The positive electrode current collector layer may be made of multiple sheets of metal foil. Examples of metals constituting the positive electrode current collector layer include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. [Example]

[0058] Example 1 <Fabrication of solid-state batteries> The solid state battery of Example 1 was fabricated as follows.

[0059] (Preparation of negative electrode active material layer) To 2.7 g of diisobutyl ketone as a dispersion medium, 0.002 g of single-walled carbon nanotubes (SWCNTs), 1.0 g of silicon active material, 1.2 g of sulfide solid electrolyte, and 0.8 g of a 5% by mass diisobutyl ketone solution of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) (PVDF-HFP: 0.04 g, diisobutyl ketone: 0.76 g) were added, and the mixture was dispersed for 10 minutes using ultrasonic waves at an amplitude of 40 μm and a frequency of 20 kHz to obtain a slurry for forming the negative electrode active material layer. The single-walled carbon nanotubes (SWCNTs) used had an average fiber diameter of less than approximately 10 nm and an average fiber length of approximately 5 μm.

[0060] The content of single-walled carbon nanotubes in the dispersion medium (isobutyl ketone) was 0.0578 mass% (0.002 g / (2.7 g + 0.8 g × 0.95)). The ratio of single-walled carbon nanotubes to the total solid content was less than 0.3 mass% (0.002 g / (2.7 g + 0.002 g + 1.0 g + 0.8 g × 0.05)). Li2S-P2S5-based glass ceramic was used as the sulfide solid electrolyte.

[0061] The silicon active material was porous silicon (porous Si) produced as follows. Specifically, Si powder (Si powder without voids inside the primary particles) was prepared as the Si source. This Si source and Li metal were weighed out in a molar ratio of Li / Si = 4.0 and mixed in a mortar in an Ar atmosphere to obtain an alloy compound. The obtained alloy compound was reacted with ethanol in an Ar atmosphere to obtain porous silicon with voids inside the primary particles, i.e., a porous structure.

[0062] The negative electrode active material layer forming slurry obtained as described above was applied to a roughened nickel foil serving as a negative electrode current collector layer using a blade with a gap of 100 μm to obtain a negative electrode active material layer.

[0063] (Preparation of solid electrolyte layer) The sulfide solid electrolyte (0.4 g) and a 5 mass % heptane solution (0.05 g) of acrylonitrile butadiene rubber (ABR) were added to heptane (0.8 g) as a dispersion medium, and the mixture was dispersed for 10 minutes using ultrasonic waves with an amplitude of 40 μm and a frequency of 20 kHz to obtain a slurry for forming a solid electrolyte layer. The slurry for forming a solid electrolyte layer thus obtained was applied to a stainless steel foil for transfer using a blade with a gap of 50 μm to obtain a solid electrolyte layer.

[0064] (Preparation of positive electrode active material layer) NCM (2 g), VGCF-H (0.03 g), sulfide solid electrolyte (0.3 g), and a 5% by mass butyl butyrate solution (0.3 g) of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) copolymer were added to butyl butyrate (1 g) as a dispersion medium, and the mixture was dispersed for 10 minutes using ultrasonic waves with an amplitude of 40 μm and a frequency of 20 kHz to obtain a positive electrode active material layer forming slurry. The positive electrode active material layer forming slurry thus obtained was applied to an aluminum foil as a positive electrode current collector layer using a blade with a gap of 100 μm to obtain a positive electrode active material layer.

[0065] (Fabrication of solid-state batteries) A solid electrolyte layer was placed on the negative electrode active material layer, and roll-pressed at room temperature with a linear pressure of 3 t / cm to obtain a negative electrode laminate 20 having a negative electrode current collector layer 21, a negative electrode active material layer 22, and a solid electrolyte layer 23 in this order. A solid electrolyte layer was placed on the positive electrode active material layer, and roll-pressed at 170°C with a linear pressure of 4 t / cm to obtain a positive electrode laminate 10 having a positive electrode current collector layer 11, a positive electrode active material layer 12, and a solid electrolyte layer 13 in this order. Each was placed in a thickness of 1 cm. 2 The solid electrolyte layer 23 of the negative electrode laminate 20 and the solid electrolyte layer 13 of the positive electrode laminate 10 were then overlapped and bonded to obtain a solid battery 100 having a laminate of the negative electrode current collector layer 21, the negative electrode active material layer 22, the solid electrolyte layer 23, the solid electrolyte layer 13, the positive electrode active material layer 12, and the positive electrode current collector layer 11. That is, the obtained battery laminate has a laminate configuration as shown in FIG.

[0066] <evaluation> The solid state battery of Example 1 obtained as described above was evaluated as follows. The evaluation results are shown in Table 1.

[0067] (Dispersibility of Slurry for Forming Negative Electrode Active Material Layer) The dispersibility of the negative electrode active material layer forming slurry was evaluated. Specifically, it was evaluated whether the negative electrode active material layer forming slurry was uniformly dispersed or not.

[0068] (internal resistance) The fabricated solid-state battery was CCCV charged (constant current, constant voltage charged) at 1 / 10 C to 4.35 V and then CCCV discharged at 1 / 3 C to 3.35 V. It was then further CCCV charged at 1 / 10 C to 4.35 V and CCCV discharged at 1 / 3 C to 3.35 V, while discharging at 7 C at a state of charge of 70% (SOC 70%) and a state of charge of 30% (SOC 30%), and the internal resistance was calculated from the change in voltage and current value over 10 seconds.

[0069] (Number of cracks and porosity) After measuring the internal resistance as described above, the number of cracks in the negative electrode active material layer was evaluated. Specifically, after measuring the internal resistance as described above, the solid-state battery was cut in the stacking direction, and the cut cross section was observed at 2000x magnification using an FE-SEM. The number of cracks was counted within an area of ​​40 μm in the stacking direction (thickness direction) and 60 μm in the width direction of the solid-state battery. Three fields of view were observed for each sample, and the average of the three fields of view was used to count the number of cracks. Note that a horizontally elongated void with a width of 2 μm or more in the stacking direction of the solid-state battery and an aspect ratio of 5 or more was determined as a crack. Regardless of the length of the crack, a continuous crack was counted as one crack. Similarly, three fields of view were observed for each sample, and the porosity of the negative electrode active material layer was calculated.

[0070] Examples 2 to 3 and Comparative Examples 1 to 6 Solid state batteries of Examples 2 to 3 and Comparative Examples 1 to 6 were obtained and evaluated in the same manner as in Example 1, except that the negative electrode active material, dispersion medium, and conductive additive used were changed as shown in the following Table 1. The multi-walled carbon nanotubes (MWCNTs) used had an average fiber diameter of about 150 nm and an average fiber length of about 6 μm.

[0071] In Table 1, "MWCNT" refers to multi-walled carbon nanotubes having an average fiber diameter of about 150 nm and an average fiber length of about 6 μm.

[0072] Furthermore, "porous clathrate Si" refers to porous clathrate silicon produced as follows. Specifically, a NaSi alloy was produced using the above-mentioned porous silicon powder and NaH as a Na source. The NaH used had been washed with hexane in advance. The Na source and Si source were weighed out to a molar ratio of 1.05:1.00 and mixed using a cutter mill. This mixture was heated in a heating furnace under an Ar atmosphere at 400°C for 40 hours to obtain a powdered NaSi alloy.

[0073] The obtained NaSi alloy was heated in an Ar atmosphere at 270°C for 120 hours to remove Na, and porous clathrate silicon with a clathrate II crystal phase was obtained.

[0074] The outlines and evaluation results of the Examples and Comparative Examples are shown in Tables 1 and 2 below.

[0075] [Table 1]

[0076] [Table 2]

[0077] As shown in Table 1, in Examples 1 to 3, in which single-walled carbon nanotubes were used as the conductive additive in an amount of less than 0.3 mass% relative to the total solid content, it was possible to disperse the slurry for forming the negative electrode active material layer. Furthermore, in the solid batteries of Examples 1 to 3, the internal resistance of the solid battery was low at a state of charge of 30% (SOC 30%), i.e., in a relatively discharged state. Furthermore, in the solid batteries of Examples 1 to 3, the number of cracks in the negative electrode active material layer and the porosity of the negative electrode active material layer were small.

[0078] The number of cracks was counted in an area of ​​40 μm in the thickness direction and 60 μm in the width direction. This area is narrower than 50 μm in the thickness direction and 50 μm in the width direction, but when converted to an area of ​​50 μm in the thickness direction and 50 μm in the width direction, the number of cracks in the negative electrode active materials of the solid-state batteries of Examples 1 to 3 was less than one on average.

[0079] Furthermore, for the convenience of evaluation, the number of cracks was counted after the initial charge / discharge and then after further charge / discharge for measuring the internal resistance. However, even when counted immediately after the initial charge / discharge, the number of cracks in the negative electrode active material of the solid state batteries of Examples 1 to 3 was less than one on average. [Explanation of symbols]

[0080] 10 Positive electrode laminate 11 Positive electrode current collector layer 12 Cathode active material layer 13, 23 Solid electrolyte layer 20 negative electrode laminate 21 Negative electrode current collector layer 22 Negative electrode active material layer 100 solid state battery

Claims

1. Ketones as dispersion media, and Silicon active material particles, sulfide solid electrolyte particles, and single-walled carbon nanotubes dispersed in the ketone and The ratio of the single-walled carbon nanotubes to the ketone is 0.15% by mass or less. Slurry for forming a negative electrode active material layer.

2. 2. The negative electrode active material layer forming slurry according to claim 1, wherein the ratio of the single-walled carbon nanotubes to the total solid content is less than 0.3 mass %.

3. 3. The slurry for forming a negative electrode active material layer according to claim 1, wherein the ketone is represented by the following formula: 【Chemistry 1】 In the formula, R １ and R ２ can be independently selected from the group consisting of an alkyl group having 1 to 5 carbon atoms, a benzyl group, and a phenyl group.

4. silicon active material particles, sulfide solid electrolyte particles, and single-walled carbon nanotubes; The single-walled carbon nanotubes are less than 0.3% by mass. Negative electrode active material layer.

5. The negative electrode active material layer according to claim 4 , wherein the silicon active material particles are porous silicon active material particles, clathrate silicon active material particles, or porous clathrate silicon active material particles.

6. A solid-state battery comprising the anode active material layer according to claim 4 or 5, a solid electrolyte layer, and a cathode active material layer in this order.

7. 7. The solid state battery according to claim 6, wherein after initial charge and discharge, the cross section of the negative electrode active material layer has an average of less than one in-plane crack having a length of 10 μm or more in an area of ​​50 μm in the thickness direction × 50 μm in the width direction.

8. The solid-state battery according to claim 6 or 7, which is a solid-state lithium-ion battery.

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