JP7666341B2 - slurry - Google Patents

Description

This application relates to slurries.

In order to form the active material layer of a battery, a slurry containing the materials that make up the active material layer may be used. When using a slurry, the active material layer is obtained by applying the slurry to a specified substrate and drying it.

Patent Document 1 discloses a slurry containing a sulfide solid electrolyte and two kinds of solvents. The same document also describes that the slurry may contain an active material. Patent Document 2 discloses silicon-based particles having a specific surface area of 40 to 300 ^{m 2} /g measured by the BET method and a value obtained by dividing the oxygen content (wt %) by the specific surface area (m ² /g) of 0.1 or less. The same document also describes a slurry containing silicon-based particles. Patent Document 3 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 assistant and a binder.

JP 2021-68673 A JP 2017-112057 A JP 2020-177755 A

In the slurry for forming the active material layer, a low-polarity solvent may be used to prevent reaction with the solid electrolyte. On the other hand, when silicon particles are used as the active material, there is a problem that the dispersibility of the slurry deteriorates and the particles tend to aggregate due to the low affinity between the silicon particles and the low-polarity solvent. To suppress aggregation, a dispersant is added to the slurry, but if the silicon particle surface is not oxidized, the dispersibility of the slurry is not improved much.

Therefore, the main objective of this disclosure is to provide a slurry that can improve dispersibility in light of the above circumstances.

As one aspect for solving the above-mentioned problems, the present disclosure provides a slurry containing a solvent, silicon particles, a solid electrolyte, and a dispersant, wherein the solvent includes a low-polarity solvent having a polarity term δP of the Hansen solubility parameter of 4 or less, the dispersant includes a first dispersant having a basic functional group, and the silicon particles have peaks in the range of 1600±10 cm ⁻¹ and the range of 1443 ±10 cm ⁻¹ in an FT-IR spectrum after pyridine adsorption.

The slurry disclosed herein can improve dispersibility.

FT-IR spectra of silicon particles of Example 1 and Comparative Example 1.

[slurry]
The slurry of the present disclosure contains a solvent, silicon particles, a solid electrolyte, and a dispersant, the solvent includes a low-polarity solvent having a polarity term δP of the Hansen solubility parameter of 4 or less, the dispersant includes a first dispersant having a basic functional group, and the silicon particles have peaks in the range of 1600±10 cm ⁻¹ and the range of 1443 ±10 cm ⁻¹ in an FT-IR spectrum after pyridine adsorption.

First, by including a low-polarity solvent with a polarity 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. In addition, the silicon particles have a certain peak in the FT-IR spectrum after pyridine adsorption. This means that acid sites exist on the particle surface. Therefore, the first dispersant having a basic functional group can be efficiently adsorbed to the acid sites on the silicon particle surface, improving the dispersibility of the slurry.

In addition, active material layers obtained from slurries with low dispersibility have a problem of low peel strength, but the slurry disclosed herein can solve this problem. In other words, because the slurry disclosed herein has high dispersibility, the active material layers obtained from the slurry have a peel strength that is applicable to battery manufacturing.

The slurry of this disclosure is further described below.

<Solvent>
The solvent in the present disclosure includes a low polarity solvent having a polarity term δP of the Hansen solubility parameter of 4 or less. The solvent may include a solvent other than the low polarity solvent. The solvent other than the low polarity solvent is not particularly limited, and may be a known solvent that is usually used for slurries.

(Low polarity solvent)
A low polarity solvent has a polarity term δP of the Hansen solubility parameter of 4 or less. The polarity 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 .

Low polarity solvents 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.

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.

By containing a low polarity solvent, the reaction between the solvent and the solids in the slurry, particularly the solid electrolyte, can be suppressed.

<Silicon particles>
The slurry of the present disclosure contains silicon particles. The silicon particles have peaks in the range of 1600±10 cm ⁻¹ and 14 43 ±10 cm ⁻¹ in the FT-IR spectrum after pyridine adsorption. This means that acid sites exist on the silicon particle surface. An "acid site" is a site on the surface that functions as an acid (Bronsted acid or Lewis acid). Such acid sites can be developed by oxidizing the silicon particles and increasing the amount of oxygen on the surface to a predetermined amount.

Here, the method of measuring the FT-IR spectrum will be described. First, the silicon particles are heated to 500°C in an inert atmosphere (for example, in a _N2 atmosphere). This state is maintained for 30 to 60 minutes. Next, the temperature of the silicon particles is lowered to 100°C, and the atmosphere is reduced pressure. Next, the silicon particles are exposed to pyridine vapor. Then, the atmosphere is returned to the inert atmosphere, and FT-IR measurement is performed by the diffuse reflectance method. This allows the FT-IR spectrum of the silicon particles after pyridine adsorption to be obtained.

As described above, in order to obtain such an FT-IR spectrum, the silicon particles must be oxidized to increase the amount of oxygen. One method for oxidizing silicon particles is to heat them in air or water vapor to 500°C or higher. There is no particular upper limit to the temperature, but it is, for example, 1000°C or lower.

The oxygen content of the silicon particles is not particularly limited as long as the above FT-IR spectrum can be obtained, but may be, for example, 3% by weight or more, 5% by weight or more, 5.9% by weight or more, 10% by weight or less, 8% by weight or less, or 7% by weight or less.

The amount of oxygen in silicon particles can be calculated as follows: First, silicon particles are placed in a graphite crucible, heated and melted, and the amount of _CO2 generated is detected by the NDIR method, and the amount of oxygen can be calculated from the results.

The specific surface area of the silicon particles is not particularly limited, but may be, for example, 30 m ² /g or more, 40 m ² /g or more, 60 m ² /g or less, or 53 m ² /g or less. The specific surface area of the silicon particles can be measured by the BET method.

The ratio of oxygen content to the specific surface area of the silicon particles (oxygen content/specific surface area) is not particularly limited as long as the above FT-IR spectrum can be obtained, but may be, for example, 0.1 or more, 0.111 or more, 0.2 or less, or 0.175 or less.

The shape of the silicon particles is not particularly limited, and examples of the shape include spheres, ellipsoids, columns, and scales. Silicon may be crystalline or amorphous. Furthermore, silicon particles may be porous.

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

In this specification, "particle size" can be determined by observing particles with a scanning electron microscope (SEM), counting the diameter of the long side of the rectangle circumscribing each particle, and dividing the average 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.

The content of silicon particles relative to the total solid content in the slurry is not particularly limited, but 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.

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

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

Examples of the sulfide solid electrolyte include Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -LiI, Li ₂ S-P ₂ S ₅ -GeS ₂ , Li ₂ S-P ₂ S ₅ -Li ₂ O, Li ₂ S-P ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-P ₂ S ₅ -LiI-LiBr, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ S-B ₂ S ₃ , Li ₂ S-P ₂ S ₅ -Z _m S _n (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , and Li ₂ S-SiS ₂ -Li _x MO _y (where x and y are positive numbers, and M is P, Si, Ge, B, Al, Ga, or In).

Examples of oxide solid electrolytes include lithium lanthanum zirconium-containing composite oxide (LLZO), Al-doped LLZO, lithium lanthanum titanium-containing composite oxide (LLTO), Al-doped LLTO, and lithium oxynitride phosphate (LIPON). Examples of nitride solid electrolytes include Li ₃ N and Li ₃ N-LiI-LiOH. Examples of halide solid electrolytes include LiF, LiCl, LiBr, LiI, and LiI-Al ₂ O ₃ .

The shape of the solid electrolyte is not particularly limited, and examples include spheres, ellipsoids, columns, and scales.

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

The ratio of the solid electrolyte to the total solid content contained in the slurry is not particularly limited, but 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.

<Dispersant>
The dispersant in the present disclosure contains a first dispersant having a basic functional group. The dispersant may contain a dispersant other than the first dispersant. The dispersant other than the first dispersant is not particularly limited, and may be a known dispersant that is usually used in slurries. For example, a known surfactant may be mentioned.

The content of the dispersant relative to the total solid content in the slurry is not particularly limited, but 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.

(First Dispersant)
The first dispersant has a basic functional group. The basic functional group is contained in the solvent-phobic portion of the first dispersant. Examples of the basic functional group contained in the first dispersant include reactive nitrogen-containing functional groups that do not have hydrogen, such as tertiary amino groups, pyridyl groups, and imidazole groups. Examples of the hydrophobic portion include hydrocarbon groups such as alkyl groups. Such a first dispersant is not particularly limited as long as it is soluble in the above-mentioned solvent, and examples thereof include alkylimidazoline. The number of carbon atoms in the alkyl group of the alkylimidazoline is not particularly limited, and is, for example, in the range of 5 to 30.

By including a first dispersant having a basic functional group in the slurry, the basic functional group of the dispersant can be adsorbed to the acid sites of the silicon particles, improving the dispersibility of the slurry.

The molecular weight of the first dispersant is not particularly limited, but may be 1000 or less, 800 or less, or 600 or less. The lower limit of the molecular weight of the first dispersant is not particularly limited, but for example, the molecular weight of the first dispersant may be 100 or more, 300 or more, or 400 or more. The molecular weight of the first dispersant can be measured using various NMR (e.g., 1H-NMR, 13C-NMR) or various MS (e.g., ESI-MS), etc.

The number of carbon atoms in the hydrophobic portion of the first dispersant is not particularly limited, but may be, for example, 5 or more, 10 or more, 30 or less, or 20 or less.

<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 applicable to lithium ion batteries. For example, butadiene rubber (BR), butylene 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.

The binder content relative to the total solid content in the slurry is not particularly limited, but may be, for example, 0.1% by weight or more, 0.3% by weight or more, 0.6% by weight or more, 0.8% by weight or more, 5% by weight or less, 2% by weight or less, 1.1% by weight or less, or 1% by weight or less.

<Conductive assistant>
The slurry of the present disclosure may contain a conductive assistant as an optional component. The conductive assistant is not particularly limited as long as it is a binder that can be applied to lithium ion batteries. 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.

The content of the conductive additive relative to the total solid content 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.

<Other ingredients>
The slurry may contain other components, such as various additives, as necessary.

<Slurry>
The viscosity of the slurry of the present disclosure is not particularly limited, and may be, for example, 10 mPa·s or more, 30 mPa·s or more, 100 mPa·s or less, or 80 mPa·s or less.

The viscosity of the slurry is measured as follows: The slurry is placed on a cone plate with a diameter of 35 mm and an inclination of 2°, and the cone plate is rotated for 30 seconds at a shear rate of 40/s, after which the viscosity of the slurry is measured using a rheometer.

The particle size of the slurry of the present disclosure is not particularly limited, but may be 1 μm or more, 10 μm or more, 100 μm or more, 500 μm or less, 300 μm or less, or 200 μm or less, and the particle size of the slurry can be measured in accordance with JIS K 5600-2-5:1999.

The slurry of the present disclosure can be obtained by mixing each component with a solvent. The mixing method is not particularly limited, and can be performed by a known method. For example, the slurry of the present disclosure can be obtained by adding each component to a solvent while mixing. The mixing method is not particularly limited, and a blender or ultrasound may be used.

The slurry of the present disclosure is used to form an active material layer for a lithium ion battery, particularly 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.

[Method of manufacturing negative electrode active material layer]
The method for producing an anode active material layer according to the present disclosure includes a step of applying the slurry of the present disclosure to a substrate (application step) and a step of drying the applied slurry (drying step). The slurry of the present disclosure has high dispersibility, so that the anode active material layer obtained from the slurry has a peel strength applicable to battery production. Therefore, according to the method for producing an anode active material layer according to the present disclosure, an anode active material layer in which the occurrence of slurry application defects is suppressed can be obtained.

The coating process can be carried out by a known method. For example, common methods such as doctor blade method, die coating method, gravure coating method, spray coating method, electrostatic coating method, and bar coating method can be mentioned. In addition, the substrate to which the slurry is applied is not particularly limited, and may be a metal foil, a current collector, or a solid electrolyte layer.

The drying process can be carried out by a known method. For example, the slurry may be heated to a temperature range of 50°C to 200°C. The atmosphere may also be set to an inert atmosphere or a reduced pressure atmosphere.

The shape of the obtained negative electrode active material layer is not particularly limited, but it is preferably in the form of a sheet. The thickness of the negative electrode active material layer is not particularly limited and may be set appropriately according to the desired battery performance. For example, it is in the range of 0.1 μm to 1 mm.

[Method of manufacturing all-solid-state battery]
The method for producing an all-solid-state battery according to the present disclosure includes a step of producing an anode active material layer by the method for producing an anode active material layer according to the present disclosure (anode active material layer producing step), a step of producing a cathode active material layer (cathode active material layer producing step), a step of producing a solid electrolyte layer (solid electrolyte layer producing step), and a step of stacking the anode active material layer, the solid electrolyte layer, and the cathode active material layer in this order (stacking step). According to the method for producing an all-solid-state battery according to the present disclosure, an all-solid-state battery including an anode active material layer in which the occurrence of slurry coating defects is suppressed can be obtained.

<Negative electrode active material layer preparation process>
The negative electrode active material layer preparation step is carried out by the method for producing a negative electrode active material layer of the present disclosure. In the negative electrode active material preparation step, a negative electrode current collector may be used as a substrate to which the slurry is applied. This allows the negative electrode to be prepared.

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

<Positive electrode active material layer preparation process>
The positive electrode active material layer preparation step can be carried out by a known method. For example, the materials constituting the positive electrode active material layer are mixed in a dry state 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. A positive electrode current collector may be used as the substrate. This allows the positive electrode to be prepared. The positive electrode current collector and the positive electrode active material layer will be described below.

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

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. Examples include lithium cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), and lithium manganese oxide. The particle size of the positive electrode active material is not particularly limited, but is, for example, 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 is, for example, in the range of 50% by weight to 99% by weight. In addition, the surface of the positive electrode active material may be covered with an oxide layer such as a lithium niobate layer, a lithium titanate layer, or a lithium phosphate layer.

The positive electrode active material layer may optionally include a solid electrolyte. The solid electrolyte may be appropriately selected from among known solid electrolytes used in all-solid-state lithium-ion batteries. For example, the solid electrolyte may be one that can be contained in the above-mentioned slurry. 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% to 50% by weight.

The positive electrode active material layer may optionally contain a conductive assistant. The conductive assistant can be appropriately selected from known conductive assistants used in all-solid-state lithium-ion batteries. For example, the conductive assistants that can be contained in the slurry described above can be used. 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.

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

The shape of the positive electrode active material layer is not particularly limited, but a sheet shape is preferable. The thickness of the positive electrode active material layer is not particularly limited and may be set appropriately according to the desired battery performance. For example, it is in the range of 0.1 μm to 1 mm.

<Solid electrolyte layer production process>
The solid electrolyte layer preparation step can be carried out by a known method. For example, the materials constituting the solid electrolyte layer are mixed in a dry state 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.

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

The solid electrolyte layer may also optionally include a binder. The binder may be appropriately selected from known binders used in all-solid-state lithium-ion batteries. For example, the binder may be one that can be contained in the above-mentioned slurry. The amount of binder contained in the solid electrolyte layer is not particularly limited, but is, for example, in the range of 0.1% to 10% by weight.

The shape of the solid electrolyte layer is not particularly limited, but it is preferably in the form of a sheet. The thickness of the solid electrolyte layer is not particularly limited and may be set appropriately according to the desired battery performance. For example, it is in the range of 0.1 μm to 1 mm.

<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, the laminate may be pressed. The pressing method is not particularly limited, but examples thereof include roll pressing and flat plate 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 plate pressing may be, for example, 800 MPa or more and 3000 MPa or less.

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

When a negative electrode current collector and a positive electrode current collector are used as the substrate in the negative electrode active material layer preparation process and the positive electrode active material layer preparation process, the negative electrode, solid electrolyte layer, and positive electrode may be laminated in this order in the lamination process.

The all-solid-state battery obtained by the manufacturing method of the all-solid-state battery disclosed herein may be a single cell or a stacked battery. The stacked battery may be a monopolar stacked battery (a stacked battery connected in parallel) or a bipolar stacked battery (a stacked battery connected in series). The shape of the all-solid-state battery may be, for example, a coin type, a laminate type, a cylindrical type, or a square type.

The slurry of this disclosure will be further explained using examples.

<Preparation of slurry>
The slurries of Examples 1-2 and Comparative Examples 1-2 were prepared using the materials and contents listed in Table 1. First, the materials were charged into a 5 mL container at once so that the total volume was 3.5 mL. Next, while the resulting mixture was cooled to 10°C, an ultrasonic horn with a diameter of 3.5 mm was used to irradiate ultrasonic waves with an amplitude of 40 μm and 20 kHz for 40 minutes to disperse the mixture. In this way, the slurries of Examples 1-2 and Comparative Examples 1-2 were prepared.

Here, the solid electrolyte in Table 1 is a sulfide solid electrolyte. The dispersant is an alkyl imidazoline (molecular weight: about 500). The solvent is diisobutyl ketone (DIBK).

<FT-IR Measurement>
Using a Varian 7000 FT-IR device, the FT-IR spectra of the silicon particles of Example 1 and Comparative Example 1 were measured as follows. First, the silicon particles were heated to 500°C in an _N2 atmosphere. This state was maintained for 30 minutes or more. Next, the temperature of the silicon particles was lowered to 100°C, and the atmosphere was reduced pressure. Subsequently, the silicon particles were exposed to pyridine vapor. Then, the atmosphere was returned to _N2 again, and FT-IR measurements were performed by the diffuse reflectance method. As a result, the FT-IR spectrum of the silicon particles after pyridine adsorption was obtained.

Figure 1 shows the FT-IR spectra of Example 1 and Comparative Example 1. As shown in Figure 1, in Comparative Example 1, no peaks were observed near 1600 cm ^-1 and 1400 cm ^-1 . In contrast, in Example 1, sharp peaks were observed near 1600 cm ^-1 and 1443 cm ^-1 . Therefore, it was confirmed that acid sites exist on the surface of the silicon particles of Example 1.

<Specific surface area measurement>
The BET method was used to measure the specific surface area of the silicon particles of Examples 1 and 2 and Comparative Examples 1 and 2. The results are shown in Table 1.

<Oxygen measurement>
Using an oxygen content analyzer EMGA920, the oxygen content of silicon particles in Examples 1-2 and Comparative Examples 1-2 was measured as follows. The silicon particles were placed in a graphite crucible and heated to melt the silicon particles. The amount of _CO2 generated during this process was detected by the NDIR method. The amount of oxygen was calculated from the results obtained. The results are shown in Table 1. Table 1 also shows the ratio of the amount of oxygen to the specific surface area of the silicon particles.

<Viscosity measurement>
The viscosity of Examples 1 and 2 and Comparative Examples 1 and 2 was measured using a viscosity measuring device MCR302 as follows. The slurry was placed on a cone plate with a diameter of 35 mm and an inclination of 2°, and the cone plate was rotated at a shear rate of 40/s for 30 seconds, after which the viscosity of the slurry was measured. The results are shown in Table 1.

In addition, the points marked with "-" in Table 1 indicate that the aggregates had settled and could not be measured.

<Particle size measurement>
The particle sizes of the slurries of Examples 1 and 2 and Comparative Examples 1 and 2 were measured. The particle size measurement method was performed in accordance with JIS K 5600-2-5: 1999. The results are shown in Table 1.

In addition, the points marked with "-" in Table 1 indicate that the aggregates had settled and could not be measured.

<Dispersibility evaluation>
The state of the slurry was evaluated visually, and the absence of agglomerates was evaluated as "good", and the presence of agglomerates was evaluated as "bad". In addition, when agglomerates were present, the state of the agglomerates was evaluated. The results are shown in Table 1.

<Results>
From Table 1, it can be seen that the dispersion evaluation results were good in Examples 1 and 2. On the other hand, the dispersion evaluation results for Comparative Examples 1 and 2 were "x".

In Comparative Example 1, the silicon particles had a low oxygen content and the ratio of oxygen content to specific surface area was also low. Therefore, the silicon particles did not have acid sites (Figure 1) and the dispersant was not properly adsorbed, which is thought to have resulted in low dispersibility of the slurry. Comparative Example 2 used the same silicon particles as Example 1, but did not contain a dispersant, which is thought to have resulted in low dispersibility of the slurry.

Claims (1)

The composition contains a solvent, silicon particles, a solid electrolyte, and a dispersant,
The solvent includes a low polarity solvent having a polarity term δP of the Hansen solubility parameter of 4 or less;
The dispersant contains a first dispersant having a basic functional group,
the first dispersant is an alkyl imidazoline;
The ratio of the amount of oxygen to the specific surface area of the silicon particles is 0.1 or more;
The silicon particles have peaks in the range of 1600±10 cm ⁻¹ and 1443±10 cm ⁻¹ in the FT-IR spectrum after pyridine adsorption .
slurry.