Negative electrode active material layer, solid state battery, and method for manufacturing the same

Abstract

To provide a negative electrode active material layer that can prevent expansion in a thickness direction during charging without sacrificing battery performance.SOLUTION: A negative electrode active material layer of the present invention includes silicon active material particles, sulfide solid electrolyte particles, and multilayer carbon nanotubes, and has, on a cross section, one or more cracks in a surface direction having a length of 10 μm or more in average in an area of 50 μm in a thickness direction by 50 μm in a width direction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode active material layer, a solid state battery, and a method for manufacturing the same. [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 solid-state batteries, Patent Documents 1 and 2 disclose all-solid-state batteries in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are laminated in this order, the negative electrode layer containing a negative electrode active material having a silicon clathrate II type crystalline phase, and the all-solid-state battery is applied with a confining pressure of 0 MPa or more and less than 5 MPa in the lamination direction. The all-solid-state battery of Patent Document 1 is characterized in that, when A is the capacity ratio of the negative electrode capacity to the positive electrode capacity, the capacity ratio A is 2.5 or more and 4.8 or less, and the all-solid-state battery of Patent Document 2 is characterized in that the specific surface area of ​​the negative electrode active material is 8 m 2 / g or more 17m 2 / g or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-92723 [Patent Document 2] Japanese Patent Publication No. 2022-92725 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure provides a negative electrode active material layer that can suppress expansion in the thickness direction during charge without sacrificing battery performance. [Means for solving the problem]

[0006] As a result of intensive research, the present inventors have found that the above problems can be solved by the following means, and have completed the present disclosure. That is, the present disclosure is as follows: <Aspect 1> A composite material including silicon active material particles, sulfide solid electrolyte particles, and multi-walled carbon nanotubes, A negative electrode active material layer having, on average, one or more in-plane cracks 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 in a cross section. Aspect 2: The negative electrode active material layer according to aspect 1, having a porosity of 7% or less during discharge. Aspect 3: The anode active material layer according to Aspect 1 or 2, wherein the multi-walled carbon nanotubes have a fiber diameter of 100 nm or more and a fiber length of 5 μm or more, and the content of the multi-walled carbon nanotubes is 8 mass% or more relative to the mass of the anode active material layer. <Aspect 4> The negative electrode active material layer according to any one of Aspects 1 to 3, 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 5> A solid-state battery having the anode active material layer according to any one of aspects 1 to 4, a solid electrolyte layer, and a cathode active material layer in this order. <Aspect 6> Providing a negative electrode active material layer, and densifying the negative electrode active material layer; Including, the negative electrode active material layer contains at least silicon active material particles, sulfide solid electrolyte particles, and multi-walled carbon nanotubes; and The negative electrode active material layer is densified by a roll press with a linear pressure of 2 t / cm or more. How solid-state batteries are manufactured. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a negative electrode active material layer that can suppress expansion in the thickness direction during charge without sacrificing battery performance. [Brief explanation of the drawings]

[0008] [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

[0009] 《Negative electrode active material layer》 The negative electrode active material layer of the present invention is silicon active material particles, sulfide solid electrolyte particles, and multi-walled carbon nanotubes; In the cross section, there is an average of one or more in-plane cracks with a length of 10 μm or more in an area of ​​50 μm in the thickness direction × 50 μm in the width direction.

[0010] The cracks may be present either immediately after the negative electrode active material layer is formed or after initial charge / discharge. In addition, in the above, the "width direction" means a direction perpendicular to the thickness direction in a thickness direction cross section of the negative electrode active material layer.

[0011] In solid-state batteries using silicon active material particles, the expansion of the silicon active material particles during charging can cause the expansion of the negative electrode active material layer, which in turn can cause the entire battery to expand. This expansion can sometimes be suppressed by reducing the load applied during the densification stage of the negative electrode active material layer and increasing the porosity of the negative electrode active material layer, but in this case, the battery performance, for example, electrical resistance, can deteriorate.

[0012] In contrast, in the present invention, by forming predetermined planar cracks in the negative electrode active material layer, it is possible to efficiently absorb the volume change due to the expansion of the silicon active material particles while maintaining the battery performance. In particular, absorption of the volume change due to such cracks can be achieved even when the porosity of the negative electrode active material layer is small.

[0013] To generate such cracks, for example, a predetermined amount of relatively thick and long carbon nanotubes, i.e., multi-walled carbon nanotubes, can be added to the negative electrode active material layer, and the negative electrode active material layer can be roll-pressed with an appropriate pressure. Specifically, with such multi-walled carbon nanotubes and roll-pressing, the negative electrode active material layer can be subjected to an appropriate springback after roll-pressing, thereby generating such cracks.

[0014] The negative electrode active material layer of the present disclosure may have a porosity of 7% or less, 6% or less, or 5% or less during discharge. This porosity can be calculated using the following formula: Porosity (%)=(1-x / y)×100 x: The total volume of each material obtained by dividing the weight of each material constituting the negative electrode active material layer by the true density of each material y: Apparent volume obtained from the actual dimensions of the negative electrode active material layer

[0015] The negative electrode active material layer may further contain a conductive additive and a binder, and may also contain other optional components.

[0016] Each component of the present disclosure will be described below.

[0017] <Silicon active material particles> 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.

[0018] Porous silicon active material particles are silicon active material particles having pores inside the primary particles, and these pores can suppress expansion and contraction of the negative electrode active material particles during charge and discharge.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] <Sulfide solid electrolyte particles> Any sulfide solid electrolyte particles can be used. Specific examples of sulfide solid electrolyte particles include 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 sulfide 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.

[0025] Multi-walled carbon nanotubes Any multi-walled carbon nanotube can be used. While a single-walled carbon nanotube is composed of a single graphene sheet, a multi-walled carbon nanotube is composed of multiple graphene sheets. The graphene sheets constituting the multi-walled carbon nanotube may be chiral (spiral), zigzag, or armchair. The multi-walled carbon nanotube in the present disclosure may be composed of a single type of graphene sheet, or multiple types of graphene sheets.

[0026] The content of multi-walled carbon nanotubes may be 5 mass% or more, 6 mass% or more, 7 mass% or more, or 8 mass% or more, and may be 15 mass% or less, 14 mass% or less, 13 mass% or less, or 12 mass% or less, relative to the mass of the negative electrode active material layer. This mass of the negative electrode active material layer means the solid content.

[0027] The diameter (fiber diameter) of the multi-walled carbon nanotubes is not particularly limited, and the average diameter may be, for example, 100 nm or more, 130 nm or more, or 150 nm or more, and 1000 nm or less, 500 nm or less, 300 nm or less, or 200 nm or less. The length of the multi-walled carbon nanotubes is not particularly limited, and the average length may be, for example, 1000 nm or more, 2000 nm or more, 3000 nm or more, 4000 nm or more, or 20000 nm or less, 15000 nm or less, 12000 nm or less, 10000 nm or less, 9000 nm or less, 8000 nm or less, or 7000 nm or less. Multi-walled carbon nanotubes having an average diameter and average length within these ranges are preferred from the viewpoint of generating appropriate springback after roll pressing of the negative electrode active material layer, thereby preventing cracks.

[0028] The aspect ratio (ratio of average length to average diameter) of the multi-walled carbon nanotubes is not particularly limited and may be, for example, 10 or more, 20 or more, or 30 or more, and may be 1000 or less, 800 or less, 500 or less, 400 or less, 300 or less, 200 or less, 100 or less, 90 or less, 70 or less, or 50 or less.

[0029] The average diameter and average length of multi-walled carbon nanotubes can be determined by measuring the dimensions of 50 or more randomly selected multi-walled carbon nanotubes using a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc., and taking the arithmetic mean.

[0030] When single-walled carbon nanotubes are used in combination with multi-walled carbon nanotubes, the mass proportion of multi-walled carbon nanotubes in all carbon nanotubes may be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more. Preferably, only multi-walled carbon nanotubes can be used as the carbon nanotubes.

[0031] <Conductive additive> The conductive additive is not particularly limited, and examples thereof include carbon materials such as VGCF (Vapor Grown Carbon Fiber), carbon nanofiber, and carbon black such as acetylene black and ketjen black, as well as metal materials.

[0032] <binder> The binder is not particularly limited, and may be, for example, polyvinylidene fluoride (PVDF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), or derivatives thereof, or a combination thereof. Examples of derivatives thereof that may be used include polyvinylidene fluoride-hexafluoropropylene copolymer.

[0033] <Other ingredients> As the other component, for example, a conductive agent other than carbon nanotubes can be used. Such a conductive agent is not particularly limited, and for example,

[0034] 《Solid-state battery》 The solid-state battery of the present disclosure has the above-described negative electrode active material layer, solid electrolyte layer, and positive electrode active material layer in this order.

[0035] 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.

[0036] Furthermore, the solid-state battery of the present disclosure may be constrained by constraining members such as end plates from both sides of the stacking direction of each of the above-mentioned layers.

[0037] <Solid electrolyte layer> The solid electrolyte layer may contain a solid electrolyte.

[0038] 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.

[0039] 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.

[0040] 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 Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, or Li 3+x PO 4-x N xExamples include, but are not limited to, LiPON (LiPON), etc. These may be amorphous or crystalline.

[0041] Examples of polymer electrolytes include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

[0042] <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.

[0043] 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.

[0044] 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.

[0045] <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.

[0046] <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.

[0047] <<Solid-state battery manufacturing method>> The disclosed method of making a solid-state battery includes: Providing a negative electrode active material layer; and densifying the negative electrode active material layer; Including, the negative electrode active material layer contains at least silicon active material particles, sulfide solid electrolyte particles, and multi-walled carbon nanotubes; and The negative electrode active material layer is densified by a roll press with a linear pressure of 2 t / cm or more.

[0048] In particular, the method of the present disclosure may include providing an anode active material layer, providing a solid electrolyte layer, and providing a cathode active material layer.

[0049] Each step of the method of the present disclosure and the materials used therein will be described below.

[0050] <Providing the negative electrode active material layer> The negative electrode active material layer can be provided by a known method, for example, by applying a negative electrode active material layer-forming slurry to the negative electrode current collector layer.

[0051] The negative electrode active material layer-forming slurry can be obtained by mixing the components constituting the negative electrode active material layer in a dispersion medium. For details of each component, see the description of the negative electrode active material layer.

[0052] The dispersion medium may be, for example, water or various organic solvents, including non-polar organic solvents, polar organic solvents, or a combination thereof.

[0053] Examples of non-polar organic solvents that can be used include aliphatic hydrocarbons such as hexane and heptane, and aromatic hydrocarbons such as xylene and toluene. Examples of polar organic solvents that can be used include ketone solvents such as diisobutyl ketone, tertiary amine solvents such as triethylamine, ether solvents such as cyclopentyl methyl ether, thiol solvents such as ethane mercaptan, and ester solvents such as butyl butyrate.

[0054] The negative electrode active material layer-forming slurry can be applied by a known method, such as a doctor blade method, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a gravure coating method, a screen printing method, etc. These methods may be used alone or in combination.

[0055] <Densification of the negative electrode active material layer> The negative electrode active material layer is densified by a roll press with a linear pressure of 2 t / cm or more.

[0056] The negative electrode active material layer may be densified alone or simultaneously with other layers. For example, the negative electrode active material layer and the solid electrolyte layer may be densified as a single unit.

[0057] The densification is performed at a linear pressure of 2.0 t / cm or more, 2.5 t / cm or more, 3.0 t / cm or more, 3.5 t / cm or more, 4.0 t / cm or more, or 4.5 t / cm or more. This linear pressure may be 10.0 t / cm or less, 9.0 t / cm or less, 8.0 t / cm or less, 7.0 t / cm or less, 6.0 t / cm or less, or 5.5 t / cm or less. By densifying the negative electrode active material layer containing multi-walled carbon nanotubes at the above linear pressure, the negative electrode active material layer after densification can be caused to spring back appropriately, thereby generating the above cracks.

[0058] <Provision of solid electrolyte layer> The solid electrolyte layer can be provided by a known method, for example, by applying a solid electrolyte layer-forming slurry to a substrate to be transferred, such as a metal foil such as a stainless steel foil.

[0059] The provided solid electrolyte layer can be laminated and integrated with the negative electrode active material layer and / or the positive electrode active material layer.

[0060] <Providing the positive electrode active material layer> The positive electrode active material layer can be provided by a known method, for example, by applying a positive electrode active material layer-forming slurry to the positive electrode current collector layer.

[0061] The slurry for forming the positive electrode active material layer can be obtained by mixing a positive electrode active material, a solid electrolyte, and an optional binder, conductive additive, etc., in a dispersion medium. The positive electrode active material and solid electrolyte can be the same as those listed for the positive electrode active material layer. The silicon active material particles, sulfide solid electrolyte particles, and multi-walled carbon nanotubes can be the same as those listed for the negative electrode active material layer.

[0062] For the coating method and dispersion medium of the positive electrode active material forming slurry, the description of the negative electrode active material forming slurry can be referred to. [Example]

[0063] The present disclosure will be specifically explained with reference to examples and comparative examples, but the present disclosure is not limited to these.

[0064] The solid state battery of Example 1 was fabricated as follows.

[0065] (Preparation of negative electrode active material layer) Multi-walled carbon nanotubes (MWCNTs) (0.33 g), silicon active material (1.0 g), sulfide solid electrolyte (1.2 g), and a 5 wt% diisobutyl ketone solution of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) (0.8 g (PVDF-HFP: 0.04 g, diisobutyl ketone: 0.76 g)) were added to diisobutyl ketone (2.7 g) as a dispersion medium, 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 multi-walled carbon nanotubes (SWCNTs) used had an average fiber diameter of approximately 150 nm and an average fiber length of approximately 6000 nm.

[0066] 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.

[0067] The ratio of the single-walled carbon nanotubes to the total solid content was approximately 13 mass % (0.33 g / (2.7 g + 0.33 g + 1.0 g + 0.8 g × 0.05)). Li2S-P2S5-based glass ceramic was used as the sulfide solid electrolyte.

[0068] The silicon active material was porous clathrate silicon (PC-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 at 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 silicon with voids inside the primary particles, i.e., porous silicon with a porous structure.

[0069] Next, a NaSi alloy was produced using porous silicon powder and NaH as a Na source. The NaH was previously washed with hexane. 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.

[0070] 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.

[0071] (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.

[0072] (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.

[0073] (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 5 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.

[0074] <evaluation> The solid state battery of Example 1 obtained as described above was evaluated as follows. The evaluation results are shown in Table 2.

[0075] (Number of cracks and porosity) The number of cracks in the negative electrode active material layer of the resulting battery stack was evaluated. Specifically, the fabricated 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 as 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. The porosity of the negative electrode active material layer was calculated using the sum of the volumes of each material, calculated from the weight and true density of each material constituting the negative electrode active material layer, and the apparent volume, calculated from the actual dimensions of the negative electrode active material.

[0076] (confining pressure, cell volume, and internal resistance) A solid-state battery fabricated separately from the one used to evaluate the number of cracks and porosity was confined at a confining pressure of 5 MPa using a confinement jig, CCCV charged at 1 / 10 C to 4.35 V (constant current, constant voltage charge), and CCCV discharged at 1 / 3 C to 3.35 V. The battery was then CCCV charged again at 1 / 10 C to 4.35 V, and the confining pressure was measured. This was used as the confining pressure after charge to calculate the increase in confining pressure. The battery was then CCCV discharged at 1 / 3 C to 3.35 V, and the cell capacity was measured. The battery was then CCCV charged again at 1 / 10 C to 4.35 V and discharged at 7 C. The internal resistance was calculated from the change in voltage and current over 10 seconds.

[0077] Examples 2 to 4 and Comparative Examples 1 to 4 Solid state batteries of Examples 2 to 4 and Comparative Examples 1 to 4 were obtained and evaluated in the same manner as in Example 1, except that the conductive additive used was changed as shown in Tables 1 and 2 below and the densification load of the negative electrode active material layer was changed as shown in Table 2.

[0078] In Table 1, "MWCNT" refers to multi-walled carbon nanotubes with an average fiber diameter of approximately 150 nm and an average fiber length of approximately 6000 nm, and "SWCNT" refers to single-walled carbon nanotubes with an average fiber diameter of approximately 2 nm and an average fiber length of approximately 5000 nm. Also, in Table 1, "AB" refers to acetylene black with an average particle diameter of 35 nm.

[0079] The outlines and evaluation results of the Examples and Comparative Examples are shown in Tables 1 and 2 below. [Table 1]

[0080] [Table 2]

[0081] From Table 1, it can be seen that the secondary batteries of the examples having the negative electrode active material layer of the present disclosure, which has, on average, one or more planar cracks with a length of 10 μm or more in a cross section in an area of ​​50 μm in the thickness direction × 50 μm in the width direction, can suppress expansion and have low resistance.

[0082] Furthermore, the number of cracks was counted in an area of ​​40 μm in the thickness direction and 60 μm in the width direction. Because this area is narrower than 50 μm in the thickness direction and 50 μm in the width direction, even 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 material of the solid state battery of the example is naturally one or more on average. [Explanation of symbols]

[0083] 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. silicon active material particles, sulfide solid electrolyte particles, and multi-walled carbon nanotubes; In the cross section, there is an average of one or more in-plane cracks having a length of 10 μm or more in an area of ​​50 μm in the thickness direction × 50 μm in the width direction, The planar crack is a void that is elongated in the horizontal direction and has a width of 2 μm or more in the stacking direction of the solid-state battery and an aspect ratio of 5 or more. Anode active material layer for solid-state batteries.

2. The negative electrode active material layer according to claim 1 , wherein the porosity during discharge is 7% or less.

3. 3. The negative electrode active material layer according to claim 1, wherein a content of the multi-walled carbon nanotubes is 8 mass% or more relative to a mass of the negative electrode active material layer, the multi-walled carbon nanotubes have a fiber diameter of 100 nm or more, and a fiber length of 5 μm or more.

4. The negative electrode active material layer according to claim 1 or 2, wherein the silicon active material particles are porous silicon active material particles, clathrate silicon active material particles, or porous clathrate silicon active material particles.

5. A solid-state battery comprising the anode active material layer according to claim 1 or 2, a solid electrolyte layer, and a cathode active material layer in this order.

6. Providing a negative electrode active material layer; and densifying the negative electrode active material layer; Including, the negative electrode active material layer contains at least silicon active material particles, sulfide solid electrolyte particles, and multi-walled carbon nanotubes; and The negative electrode active material layer is densified by a roll press with a linear pressure of 2 t / cm or more. The method for manufacturing the solid state battery according to claim 5 .

Images