Slurry

Abstract

To provide a slurry that can increase dispersibility.SOLUTION: The slurry includes a solvent, amorphous silicon particles, a solid electrolyte, and a dispersion agent. The solvent includes a low-polarity solvent for which the polarity item δp of the Hansen solubility parameter is not larger than 4, and the dispersion agent includes a surfactant with a molecule amount of less than 1000. The relative relaxation speed ratio, Rsp' / Rsp is at least 1.3 when the relative relaxation speed measured by the pulse NMR of a dispersion medium in which the solvent and the amorphous silicon particles are mixed is denoted by Rsp and the relative relaxation speed measured by the pulse NMR of a dispersion medium in which the solvent, the amorphous silicon particles, and the dispersion agent are mixed is denoted by Rsp'.SELECTED DRAWING: None

Description

Technical Field

[0001] This application relates to a slurry.

Background Art

[0002] When forming an active material layer of a battery, a slurry containing a material constituting the active material layer may be used. When using a slurry, an active material layer can be obtained by applying the slurry to a predetermined substrate and drying it.

[0003] Patent Document 1 discloses a slurry containing a sulfide solid electrolyte and two solvents. Further, the document describes that the slurry may contain an active material. Patent Document 2 discloses a method for producing a slurry containing an oxide active material, a solid electrolyte, a dispersion medium, and at least one of a conductive auxiliary material and a binder. Patent Document 3 discloses a suspension containing silicon nanoparticles, an organic solvent, and a dispersant.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] When preparing a slurry containing a solvent, silicon particles, a solid electrolyte, and a dispersant, there is a problem that the dispersant preferentially adsorbs to the solid electrolyte, causing the silicon particles to aggregate. This is because, generally, the number of acid sites (Li) and base sites (S) contained in the sulfide solid electrolyte is larger than the number of acid sites and base sites present on the surface of the silicon particles (the dispersant adsorbs to the acid and base sites). Further, when the silicon particles aggregate, there is a problem that the dispersed solid electrolyte and silicon particles aggregate with the aggregate as a nucleus, forming aggregates. In particular, if aggregates of 100 μm or more are present, there is a risk of coating defects.

[0006] Therefore, in view of the above circumstances, a main object of the present disclosure is to provide a slurry capable of improving dispersibility.

Means for Solving the Problems

[0007] As one aspect for solving the above problems, the present disclosure provides a slurry containing a solvent, amorphous silicon particles, a solid electrolyte, and a dispersant, wherein the solvent includes a low-polarity solvent having a Hansen solubility parameter polarity term δP of 4 or less, the dispersant contains a surfactant having a molecular weight of less than 1000, and when the relative relaxation rate Rsp measured by pulsed NMR of a dispersion medium obtained by mixing the solvent and the amorphous silicon particles and the relative relaxation rate Rsp' measured by pulsed NMR of a dispersion medium obtained by mixing the solvent, the amorphous silicon particles, and the dispersant are defined, a slurry is provided in which the relative relaxation rate ratio Rsp' / Rsp is 1.3 or more.

Effects of the Invention

[0008] According to the slurry of the present disclosure, dispersibility can be improved.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0010] [Slurry] The slurry of the present disclosure contains a solvent, amorphous silicon particles, a solid electrolyte, and a dispersant. The solvent includes a low-polarity solvent having a polar term δP of the Hansen solubility parameter of 4 or less. The dispersant contains a surfactant having a molecular weight of less than 1000. When the relative relaxation rate measured by pulsed NMR of the dispersion medium obtained by mixing the solvent and the amorphous silicon particles is defined as Rsp, and the relative relaxation rate measured by pulsed NMR of the dispersion medium obtained by mixing the solvent, the amorphous silicon particles, and the dispersant is defined as Rsp', the relative relaxation rate ratio Rsp' / Rsp is 1.3 or more.

[0011] By using amorphous silicon particles, surface defects and crystal grain boundaries can be reduced compared to crystalline silicon particles, and the surface energy can be lowered, so that aggregation can be suppressed. In addition, since the solvent includes a low-polarity solvent having a polar term δP of the Hansen solubility parameter of 4 or less, the reaction between the solvent and the solid content in the slurry, particularly the solid electrolyte, can be suppressed. Furthermore, since the dispersant contains a surfactant having a molecular weight of less than 1000 and the relative relaxation rate ratio Rsp' / Rsp is 1.3 or more, the ratio of the amorphous silicon particles solvated through the dispersion medium can be increased, and the materials contained in the slurry can be appropriately dispersed. Therefore, according to the slurry of the present disclosure, the dispersibility can be improved.

[0012] In addition, the active material layer obtained from a slurry with low dispersibility had a problem of low peel strength, but this problem can also be solved by the slurry of the present disclosure. That is, since the slurry of the present disclosure has high dispersibility, the active material layer obtained from the slurry has a peel strength applicable to battery manufacturing.

[0013] Hereinafter, the slurry of the present disclosure will be further described.

[0014] [Solvent] The solvent in the present disclosure includes a low-polarity solvent with a polar term δP of the Hansen solubility parameter of 4 or less. The solvent may include solvents other than the low-polarity solvent. The solvents other than the low-polarity solvent are not particularly limited and may be known solvents usually used in slurries.

[0015] (Low-polarity solvent) The low-polarity solvent has a polar term δP of the Hansen solubility parameter of 4 or less. The polar term δP of the Hansen solubility parameter can be obtained from Hansen Solubility Parameters: A user's handbook, Second Edition. Boca Raton, Fla: CRC Press. (Hansen, Charles (2007)). The unit of solubility is MPa 0.5 is.

[0016] Examples of the low-polarity solvent include tetralin (δP = 2), butyl butyrate (δP = 2.9), diisobutyl ketone (δP = 3.7), mesitylene (δP = 0.6), heptane (δP = 0), dibutyl ether (δP = 3.4), decane (δP = 0), toluene (δP = 1.4), etc. These may be used alone or in combination of multiple.

[0017] The content of the low-polarity solvent in the solvent is not particularly limited, but may be, for example, 50% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 100% by weight.

[0018] By containing the low-polarity solvent in the solvent, the reaction between the solvent and the solid content in the slurry, particularly the solid electrolyte, can be suppressed.

[0019] <Amorphous silicon particles> The slurry of the present disclosure contains amorphous silicon particles. As described above, the amorphous silicon particles can reduce surface defects and crystal grain boundaries and lower the surface energy compared to crystalline silicon particles, so that aggregation can be suppressed.

[0020] The shape of the amorphous silicon particles is not particularly limited, and examples thereof include spherical, ellipsoidal, columnar, and flaky shapes. Further, the amorphous silicon particles may be porous.

[0021] The particle size of the amorphous silicon particles is not particularly limited, but it may be 0.1 μm or more, 1 μm or more, 20 μm or less, 10 μm or less, or 5 μm or less.

[0022] The "particle size" in this specification can be determined by observing the particles with a scanning electron microscope (SEM), aggregating the long sides of the rectangles circumscribing each particle as the diameter, and averaging by dividing by the number of particles. The number of particles to be measured should be at least 10 or more. Preferably, it is 100 or more.

[0023] The content of the amorphous silicon particles with respect to the total solid content contained in the slurry is not particularly limited, but it may be, for example, 30% by weight or more, 50% by weight or more, 80% by weight or less, or 60% by weight or less.

[0024] <Solid electrolyte> The solid electrolyte of the present disclosure has Li-ion conductivity and is not particularly limited as long as it is a solid electrolyte applicable to all-solid-state lithium-ion batteries. The solid electrolyte may be glassy (amorphous), crystallized glassy, or crystalline. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes. Preferably, it is a sulfide solid electrolyte.

[0025] The sulfide solid electrolyte preferably contains an Li element, an M element (M is preferably at least one of P, Ge, Si, Sn, B, and Al), and an S element. The sulfide solid electrolyte may further contain a halogen element. Examples of the halogen element include F element, Cl element, Br element, and I element. Further, the amorphous sulfide solid electrolyte may further contain an O element.

[0026] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers. Z is any of Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers. M is any of P, Si, Ge, B, Al, Ga, and In).

[0027] Examples of oxide solid electrolytes include lithium lanthanum zirconium-containing composite oxides (LLZO), Al-doped LLZO, lithium lanthanum titanium-containing composite oxides (LLTO), Al-doped LLTO, lithium phosphorus oxynitride (LIPON), etc. Examples of nitride solid electrolytes include Li3N, Li3N-LiI-LiOH. Examples of halide solid electrolytes include LiF, LiCl, LiBr, LiI, LiI-Al2O3.

[0028] The shape of the solid electrolyte is not particularly limited, and examples include spherical, ellipsoidal, columnar, and flaky shapes.

[0029] The particle size of the solid electrolyte is not particularly limited, but it may be 0.1 μm or more, 1 μm or more, 20 μm or less, 10 μm or less, or 5 μm or less.

[0030] The ratio of the solid electrolyte to the total solids contained in the slurry is not particularly limited, and may be, for example, 20% by weight or more, 30% by weight or more, 40% by weight or more, 60% by weight or less, or 50% by weight or less.

[0031] <Dispersant> The dispersant in the present disclosure contains a surfactant having a molecular weight of less than 1000. The dispersant may contain a dispersant other than this surfactant. The dispersant other than the surfactant is not particularly limited and may be a known dispersant usually used in slurries.

[0032] The content of the dispersant with respect to the total solids contained in the slurry is not particularly limited, and may be, for example, 0.1% by weight or more, 0.5% by weight or more, 0.8% by weight or more, 5% by weight or less, 2% by weight or less, or 1% by weight or less.

[0033] (Surfactant) The surfactant has a molecular weight of 1000 or less. By the surfactant having a molecular weight of 1000 or less, the solubility in a low-polarity solvent can be improved, and an increase in viscosity can be suppressed. For example, when using a surfactant with a molecular weight exceeding 1000, there are concerns about thickening due to the surfactant itself or thickening due to cross-linking, but these concerns are suppressed by using a surfactant with a molecular weight of 1000 or less.

[0034] The surfactant has a hydrophilic functional group (adsorbing group) and a hydrophobic functional group. Examples of the hydrophilic functional group include nitrogen-containing functional groups having no reactive hydrogen such as a tertiary amino group, a pyridyl group, and an imidazole group. Examples of the hydrophobic functional group include hydrocarbon groups such as an alkyl group (for example, having 5 to 30 carbon atoms). The surfactant is not particularly limited as long as it is soluble in the above solvent, and examples include alkyl imidazoline. The number of carbon atoms of the alkyl group of the alkyl imidazoline is not particularly limited and is, for example, in the range of 5 to 30.

[0035] Since the surfactant has a hydrophilic group and a hydrophobic group, it can adsorb to both the solid electrolyte and the amorphous silicon particles. Therefore, when the slurry contains a surfactant, aggregation can be suppressed and the dispersibility of the slurry can be improved.

[0036] The molecular weight of the surfactant is 1000 or less, and may be 800 or less, or may be 600 or less. The lower limit of the molecular weight of the surfactant is not particularly limited. For example, the molecular weight of the surfactant may be 100 or more, may be 300 or more, or may be 400 or more. The molecular weight of the surfactant can be measured using various NMRs (e.g., 1H-NMR, 13C-NMR) and various MSs (e.g., ESI-MS).

[0037] The content of the surfactant in the dispersant is not particularly limited. For example, it may be 50% by weight or more, may be 80% by weight or more, may be 90% by weight or more, may be 95% by weight or more, or may be 100% by weight.

[0038] <Binder> The slurry of the present disclosure may contain a binder as an optional component. The binder is not particularly limited as long as it is a binder applicable to a lithium ion battery. For example, butadiene rubber (BR), isobutylene rubber (IIR), acrylate butadiene rubber (ABR), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), etc. may be mentioned. These may be used alone or in combination of multiple types. Preferably, it is PVdF-HFP. This is because PVdF is polarized, easily adsorbs to the active material and the solid electrolyte, and is likely to have high adhesion.

[0039] The content of the binder relative to the total solid content contained in the slurry is not particularly limited. For example, it may be 0.1% by weight or more, may be 0.3% by weight or more, may be 0.6% by weight or more, may be 0.8% by weight or more, may be 5% by weight or less, may be 2% by weight or less, may be 1.1% by weight or less, or may be 1% by weight or less.

[0040] <Conductive aid The slurry of the present disclosure may contain a conductive aid as an optional component. The conductive aid is not particularly limited as long as it is a binder applicable to a lithium ion battery. For example, carbon materials such as acetylene black, ketjen black, and vapor grown carbon fiber (VGCF), and metal materials such as nickel, aluminum, and stainless steel can be mentioned.

[0041] The content of the conductive aid relative to the total solid content contained in the slurry is not particularly limited, but may be, for example, 1% by weight or more, 2% by weight or more, 4% by weight or more, 10% by weight or less, 8% by weight or less, or 6% by weight or less.

[0042] <Other components The slurry may contain other components, such as various additives, as necessary.

[0043] <Slurry For the slurry of the present disclosure, when the relative relaxation rate measured by pulsed NMR of a dispersion medium in which a solvent and amorphous silicon particles are mixed is Rsp, and the relative relaxation rate measured by pulsed NMR of a dispersion medium in which a solvent, amorphous silicon particles, and a dispersant are mixed is Rsp', the relative relaxation rate ratio Rsp' / Rsp is 1.3 or more.

[0044] The relative relaxation rate ratio Rsp' / Rsp is calculated as follows. First, a blank of only the solvent, a sample 1 in which the solvent and amorphous Si particles are mixed at a weight ratio of 80:20, and a sample 2 in which the solvent, amorphous silicon particles, and a dispersant are mixed at a weight ratio of 80:19.7:0.3 are prepared. Next, using the blank and samples 1 and 2, the T2 relaxation time by the CPMG method using pulsed NMR is measured respectively. Then, the relative relaxation rates Rsp and Rsp' are calculated from (blank relaxation time) / (sample relaxation time) - 1. And then, the relative relaxation rate ratio Rsp' / Rsp is calculated.

[0045] When the relative relaxation speed ratio Rsp' / Rsp is 1.3 or more, a dispersant is likely to adsorb onto the amorphous silicon particles. Therefore, the amorphous silicon particles are likely to be solvated, and the dispersibility of the slurry is improved.

[0046] The relative relaxation speed ratio Rsp' / Rsp is not particularly limited as long as it is 1.3 or more. For example, it may be 1.5 or less, 1.45 or less, or 1.31 or more.

[0047] The particle size of the slurry of the present disclosure is not particularly limited, but may be less than 100 μm, 50 μm or less, 20 μm or less, less than 20 μm, 0.1 μm or more, or 1 μm or more. The particle size of the slurry can be measured according to JIS K 5600-2-5:1999.

[0048] The slurry of the present disclosure can be obtained by mixing each component and a solvent. The mixing method is not particularly limited and can be carried out by a known method. For example, the slurry of the present disclosure can be obtained by mixing while adding each component to the solvent. The mixing method is not particularly limited, and a blender or ultrasonic waves may be used.

[0049] The slurry of the present disclosure is used to form an active material layer for a lithium-ion battery, particularly for an all-solid-state lithium-ion battery. The active material layer may be a positive electrode active material layer or a negative electrode layer, but is preferably a negative electrode active material layer.

[0050] [Method for manufacturing a negative electrode active material layer] The method for manufacturing a negative electrode active material layer of the present disclosure includes a step of coating the slurry of the present disclosure on a substrate (coating step) and a step of drying the coated slurry (drying step). Since the slurry of the present disclosure has high dispersibility, the negative electrode active material layer obtained from the slurry has a peel strength applicable to battery manufacturing. Therefore, according to the method for manufacturing a negative electrode active material layer of the present disclosure, a negative electrode active material layer in which coating defects of the slurry are suppressed can be obtained.

[0051] The coating process can be carried out by known methods. For example, general methods such as the doctor blade method, die coating method, gravure coating method, spray coating method, electrostatic coating method, bar coating method, etc. can be mentioned. Further, the substrate on which the slurry is coated is not particularly limited and may be a metal foil, a current collector, or a solid electrolyte layer.

[0052] The drying process can be carried out by known methods. For example, the slurry may be heated in the range of 50°C to 200°C or lower. Also, the atmosphere may be set to an inert atmosphere or a reduced pressure atmosphere.

[0053] The shape of the obtained negative electrode active material layer is not particularly limited, but it is preferably sheet-like. The thickness of the negative electrode active material layer is not particularly limited and may be appropriately set according to the desired battery performance. For example, it is in the range of 0.1 μm or more and 1 mm or less.

[0054] [Method for manufacturing all-solid-state battery] The method for manufacturing an all-solid-state battery of the present disclosure includes a step of manufacturing a negative electrode active material layer (negative electrode active material layer manufacturing step) by the method for manufacturing a negative electrode active material layer of the present disclosure, a step of manufacturing a positive electrode active material layer (positive electrode active material layer manufacturing step), a step of manufacturing a solid electrolyte layer (solid electrolyte layer manufacturing step), and a step of laminating the negative electrode active material layer, the solid electrolyte layer, and the positive electrode active material layer in this order (laminating step). According to the method for manufacturing an all-solid-state battery of the present disclosure, an all-solid-state battery including a negative electrode active material layer in which coating defects of the slurry are suppressed can be obtained.

[0055] <Negative electrode active material layer manufacturing step> The negative electrode active material layer manufacturing step is carried out by the method for manufacturing a negative electrode active material layer of the present disclosure. In the negative electrode active material manufacturing step, a negative electrode current collector may be used as the substrate on which the slurry is coated. Thereby, a negative electrode can be manufactured.

[0056] The material of the negative electrode current collector can be appropriately selected from known materials according to the purpose. For example, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. can be mentioned. The thickness of the negative electrode current collector is not particularly limited and can be appropriately set according to the desired battery performance. For example, it is in the range of 0.1 μm or more and 1 mm or less.

[0057] <Positive electrode active material layer manufacturing process> The positive electrode active material layer manufacturing process can be carried out by known methods. For example, the materials constituting the positive electrode active material layer are mixed dry and pressed to obtain the positive electrode active material layer. Alternatively, the materials constituting the positive electrode active material layer are dispersed in a solvent to form a slurry, and the obtained slurry is applied to a substrate and dried to obtain the positive electrode active material layer. The positive electrode current collector may be used as the substrate. Thereby, a positive electrode can be manufactured. Hereinafter, the positive electrode current collector and the positive electrode active material layer will be described.

[0058] The material of the positive electrode current collector is not particularly limited and can be appropriately selected from known materials according to the purpose. For example, Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. can be mentioned. The thickness of the positive electrode current collector is not particularly limited and can be appropriately set according to the desired battery performance. For example, it is in the range of 0.1 μm or more and 1 mm or less.

[0059] The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material can be appropriately selected from known positive electrode active materials used in all-solid-state lithium-ion batteries. For example, lithium cobaltate, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganate, etc. can be mentioned. The particle size of the positive electrode active material is not particularly limited, but for example, it is in the range of 1 μm to 100 μm. The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but for example, it is in the range of 50% by weight to 99% by weight. Also, the surface of the positive electrode active material may be coated with an oxide layer such as a lithium niobate layer, a lithium titanate layer, or lithium phosphate.

[0060] The positive electrode active material layer may optionally include a solid electrolyte. The solid electrolyte can be appropriately selected from known solid electrolytes used in all-solid-state lithium-ion batteries. For example, the solid electrolytes that can be contained in the above-described slurry can be mentioned. The content of the solid electrolyte in the positive electrode active material layer is not particularly limited, but is, for example, in the range of 1% by weight to 50% by weight.

[0061] The positive electrode active material layer may optionally include a conductive assistant. The conductive assistant can be appropriately selected from known conductive auxiliary materials used in all-solid-state lithium-ion batteries. For example, the conductive assistants that can be contained in the above-described slurry can be mentioned. The content of the conductive assistant in the positive electrode active material layer is not particularly limited, but is, for example, in the range of 0.1% by weight to 10% by weight.

[0062] The positive electrode active material layer may optionally include a binder. The binder can be appropriately selected from known binders used in all-solid-state lithium-ion batteries. For example, the binders that can be contained in the above-described slurry can be mentioned. The content of the binder in the positive electrode active material layer is not particularly limited, but is, for example, in the range of 0.1% by weight to 10% by weight.

[0063] The shape of the positive electrode active material layer is not particularly limited, but is preferably sheet-like. The thickness of the positive electrode active material layer is not particularly limited and may be appropriately set according to the desired battery performance. For example, it is in the range of 0.1 μm or more and 1 mm or less.

[0064] <Solid electrolyte layer manufacturing process> The solid electrolyte layer manufacturing process can be carried out by known methods. For example, the materials constituting the solid electrolyte layer are mixed dry and pressed to obtain the solid electrolyte layer. Alternatively, the materials constituting the solid electrolyte layer are dispersed in a solvent to form a slurry, and the obtained slurry is applied to a substrate and dried to obtain the solid electrolyte layer. The solid electrolyte layer will be described below.

[0065] The solid electrolyte layer contains at least a solid electrolyte. The solid electrolyte can be appropriately selected from known solid electrolytes used in all-solid-state lithium-ion batteries. For example, the solid electrolytes that can be contained in the above-mentioned slurry can be mentioned. The content of the solid electrolyte in the solid electrolyte layer is not particularly limited, but is, for example, in the range of 50% by weight to 99% by weight.

[0066] In addition, the solid electrolyte layer may optionally be provided with a binder. The binder can be appropriately selected from known binders used in all-solid-state lithium-ion batteries. For example, the binders that can be contained in the above-mentioned slurry can be mentioned. The content of the binder in the solid electrolyte layer is not particularly limited, but is, for example, in the range of 0.1% by weight to 10% by weight.

[0067] The shape of the solid electrolyte layer is not particularly limited, but is preferably sheet-shaped. The thickness of the solid electrolyte layer is not particularly limited and may be appropriately set according to the desired battery performance. For example, it is in the range of 0.1 μm or more and 1 mm or less.

[0068] <Lamination process> The lamination process is a process of laminating the negative electrode active material layer, the solid electrolyte layer, and the positive electrode active material layer in this order. After laminating these layers, a laminate can be obtained by pressing. The pressing method is not particularly limited, and examples include roll pressing and flat pressing. The linear pressure applied during roll pressing may be, for example, 1 t / cm or more and 10 t / cm or less. The surface pressure applied during flat pressing may be, for example, 800 MPa or more and 3000 MPa or less.

[0069] After the lamination process, the negative electrode current collector may be disposed on the surface of the negative electrode active material layer, and the positive electrode current collector may be disposed on the surface of the positive electrode active material layer.

[0070] In the negative electrode active material layer manufacturing process and the positive electrode active material layer manufacturing process, when the negative electrode current collector and the positive electrode current collector are used for the base material, in the lamination process, the negative electrode, the solid electrolyte layer, and the positive electrode are laminated in this order.

[0071] The all-solid-state battery obtained by the manufacturing method of the all-solid-state battery of the present disclosure may be a single cell or a stacked battery. The stacked battery may be a monopolar type stacked battery (parallel-connected stacked battery) or a bipolar type stacked battery (series-connected stacked battery). Examples of the shape of the all-solid-state battery include coin type, laminate type, cylindrical type, and rectangular type.

Examples

[0072] The slurry of the present disclosure will be further described using examples.

[0073] <Preparation of slurry> Slurries of Examples 1 to 2 and Comparative Examples 1 to 12 were prepared using the materials and contents shown in Table 1. First, the materials were put into a 5 mL container at once so that the total volume became 3.5 mL to prepare a slurry. Next, while cooling the obtained mixture to 10°C, ultrasonic waves with an amplitude of 40 μm and a frequency of 20 kHz were irradiated for 40 minutes using a φ3.5 mm ultrasonic horn to disperse. Thereby, slurries of Examples 1 to 2 and Comparative Examples 1 to 12 were prepared.

[0074] The materials in Table 1 will be described. As the silicon active material (Si active material), amorphous silicon active material and crystalline silicon active material were used. As the solid electrolyte, a sulfide solid electrolyte was used. As the binder, PVdF-HFP or SBR was used. As the dispersant, a low molecular weight surfactant or an amphiphilic polymer was used. As the low molecular weight surfactant, alkyl imidazoline (molecular weight: about 500) was used. As the amphiphilic polymer, polyalkyleneamine (molecular weight: about 5000) was used. As the conductive aid, VGCF was used. As the solvent, diisobutyl ketone (DIBK), tetralin, or butyl butyrate was used. Note that (δP) described in the solvent column is the numerical value of the polar term of the Hansen solubility parameter.

[0075] Also, in Table 1, the contents of the binder and the dispersant with respect to the total solid content are shown.

[0076] <XRD measurement> For the amorphous silicon particles and crystalline silicon particles used in the slurry, the diffraction intensity in the range of 2θ = 10 to 80° was measured. Rigaku SmartLab was used as the XRD apparatus. The results are shown in Fig. 1.

[0077] As shown in Fig. 1, the peak of the crystalline silicon particles was sharp, confirming that they were crystalline. On the other hand, the peak of the amorphous silicon particles was broad, confirming that they were amorphous.

[0078] <Pulse NMR measurement> First, a blank containing only the solvent, Sample 1 in which the solvent and the Si active material were mixed at a weight ratio of 80:20, and Sample 2 in which the solvent, the Si active material, and the dispersant were mixed at a weight ratio of 80:19.7:0.3 were prepared.

[0079] Next, for each sample, the T2 relaxation time by the CPMG method using pulse NMR was measured. Bruker minispec mq20 was used as the measuring apparatus. Then, the relative relaxation rate was measured from (blank relaxation time) / (sample relaxation time) - 1. Here, the relative relaxation rate obtained from the blank and Sample 1 was defined as Rsp, and the relative relaxation rate obtained from the blank and Sample 2 was defined as Rsp'. Also, the relative relaxation rate ratio Rsp' / Rsp was calculated. The results are shown in Table 2.

[0080] Note that the places indicated by "-" in Table 2 mean that they were not measured.

[0081] <Particle size measurement> The particle size of each slurry was measured. The particle size measurement method was carried out in accordance with JIS K 5600-2-5:1999. The results are shown in Table 2.

[0082] Note that the places indicated by "-" in Table 2 mean that the aggregates had sedimented and could not be measured.

[0083] <Dispersibility evaluation> The state of the slurry was visually evaluated, and when there were no aggregates, it was evaluated as "〇", and when there were aggregates, it was evaluated as "×". Also, when there were aggregates, the state of the aggregates was evaluated. When there were aggregates and the aggregates did not settle, it was evaluated as "agglomeration", and when the aggregates had settled, it was evaluated as "sedimentation". The results are shown in Table 2.

[0084] <Peel Strength Evaluation> The slurry was applied to the substrate and dried to obtain a coating film. Whether peeling or crumbling occurred when the obtained coating film was punched out with a hand punch was visually confirmed. Also, whether peeling or crumbling occurred when roll pressing was performed on the coating film was visually confirmed. In both the hand punch and roll press, when no peeling occurred, it was evaluated as "〇", and when peeling occurred in either one or both, it was evaluated as "×". The results are shown in Table 2.

[0085] <Cross-Section Observation> The cross-sections of the coating films formed from the slurries of Example 1 and Comparative Example 3 were evaluated. The results are shown in Figure 2. As can be seen from Figure 2, in Example 1, each material was dispersed, but in Comparative Example 3, aggregates were confirmed.

[0086]

Table 1

[0087]

Table 2

[0088] <Results> From Table 1 and Table 2, in Examples 1 and 2, the dispersion evaluation and peel evaluation had good results. On the other hand, in Comparative Examples 1 to 12, at least one of the dispersion evaluation and peel strength evaluation was "×".

[0089] In Comparative Example 1, the binder amount with respect to the total solid content was larger compared to the conditions of Example 1, the particle size became 100 μm or more, and aggregation occurred in the slurry. In Comparative Example 2, the binder amount with respect to the total solid content was smaller compared to the conditions of Example 1, and peeling occurred in the coating film. In Comparative Example 3, since SBR with low affinity for particles was employed compared to the conditions of Comparative Example 2, the particle size further became 100 μm or more, and aggregation occurred in the slurry. In Comparative Examples 4 and 5, the type of solvent was changed from the conditions of Comparative Example 3, and a solvent with a lower δP was employed, but the results were not improved. In Comparative Examples 6 and 7, the content of the dispersant was reduced from the conditions of Comparative Example 4, but the results were not improved. In Comparative Examples 8 and 9, the content of the dispersant was reduced from the conditions of Comparative Example 3, but the results were not improved. In Comparative Example 10, the type of Si active material was changed from the conditions of Comparative Example 3, and crystalline silicon particles were employed, but the results were not improved. In Comparative Example 11, the type of Si active material was changed from the conditions of Comparative Example 4, and crystalline silicon particles were employed, but the results were not improved. In Comparative Example 12, the type of dispersant was changed from the conditions of Comparative Example 4, and an amphiphilic polymer was employed, but the results were not improved.

Claims

【Claim 1】 A slurry containing a solvent, amorphous silicon particles, a solid electrolyte, a dispersant, and a binder, wherein the solvent includes a low-polarity solvent having a polar term δP of the Hansen solubility parameter of 4 or less, the dispersant contains a surfactant having a molecular weight of less than 1000, the content of the binder with respect to the total solid content contained in the slurry is 0.8% by weight or more and 1.0% by weight or less, the surfactant is alkylimidazoline, the relative relaxation rate measured by pulsed NMR of the dispersion medium obtained by mixing the solvent and the amorphous silicon particles is defined as Rsp, when the relative relaxation rate measured by pulsed NMR of the dispersion medium obtained by mixing the solvent, the amorphous silicon particles, and the dispersant is defined as Rsp', a slurry in which the relative relaxation rate ratio Rsp' / Rsp is 1.3 or more. ​

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