Electrode active material and battery

Abstract

The invention relates to an electrode active material and a battery. In the present disclosure, the problem is solved by providing an electrode active material obtained by aggregating a plurality of primary particles using a binder, in which: the primary particles are an Si-based active material containing an Si element; the binder is an organic polymer having a tensile modulus of from 0.10 MPa to 1100 MPa (inclusive); the ratio of the binder to the sum of the primary particles and the binder is 1% by weight or more and 20% by weight or less; and the electrode active material has a particle size D50 of 2.5 [mu] m or more and 20 [mu] m or less.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electrode active material and a battery. BACKGROUND

[0002] In recent years, batteries are being actively developed. For example, in the automobile industry field, batteries for a battery electric vehicle (BEV), a plug-in hybrid electric vehicle (PHEV), or a hybrid electric vehicle (HEV) are being developed. A battery generally contains a positive electrode layer, a negative electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer. Further, as an electrode active material, an active material containing a Si element (Si-based active material) is known. For example, Japanese Patent Application Publication No. 2024-017797 (JP 2024-017797 A) discloses a negative electrode for a secondary battery, which contains composite particles containing a plurality of porous silicon particles and a binder. SUMMARY

[0003] Although the Si-based active material is a high-capacity active material, it has a large volume change in charge and discharge. The large volume change in charge and discharge tends to cause the occurrence of cracks in the electrode layer, and the occurrence of cracks tends to cause the performance of the battery to deteriorate (for example, an increase in resistance and / or deterioration in cycle characteristics). Therefore, for the Si-based active material, it is required to suppress the volume change due to charge and discharge.

[0004] The present disclosure was designed in view of the above circumstances, and its main object is to provide an electrode active material capable of suppressing the volume change of an electrode layer.

[0005] [1] An electrode active material obtained by agglomerating a plurality of primary particles with a binder, wherein:

[0006] the primary particles are a Si-based active material containing a Si element;

[0007] the binder is an organic polymer having a tensile modulus of 0.10 MPa or more and 1100 MPa or less;

[0008] the ratio of the binder to the total of the primary particles and the binder is 1% by mass or more and 20% by mass or less; and

[0009] the particle size D 50 of the electrode active material is 2.5 μm or more and 20 μm or less.

[0010] [2] The electrode active material according to [1], wherein the tensile modulus can be 300 MPa or less.

[0011] [3] The electrode active material according to [1] or [2], wherein the binder can be at least one of poly(vinylidene-fluoride-co-hexafluoropropylene) (PVdF-HFP), polyvinyl butyral (PVB), styrene butadiene rubber (SBR), and an epoxy resin.

[0012] [4] The electrode active material according to any one of [1] to [3], wherein the primary particles can be porous particles.

[0013] [5] The electrode active material according to any one of [1] to [4], wherein the electrode active material can be a negative electrode active material.

[0014] [6] A battery comprising: a positive electrode layer; a negative electrode layer; and an electrolyte layer provided between the positive electrode layer and the negative electrode layer, wherein

[0015] one of the positive electrode layer and the negative electrode layer contains the electrode active material according to any one of [1] to [5].

[0016] In the present disclosure, the following effects are obtained: an electrode active material capable of suppressing a volume change of an electrode layer can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0017] Features, advantages, technical and industrial significance of exemplary embodiments of the present application will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:

[0018] Figure 1 is a schematic cross-sectional view showing a battery in the present disclosure. DETAILED DESCRIPTION

[0019] Hereinafter, an electrode active material and a battery in the present disclosure will be described in detail.

[0020] A. Electrode active material

[0021] The electrode active material in the present disclosure is an electrode active material obtained by agglomerating a plurality of primary particles with a binder. Further, the primary particles are Si-based active materials containing a Si element. In particular, the electrode active material in the present disclosure has the following features. The binder is an organic polymer having a tensile modulus of 0.10 MPa or more and 1100 MPa or less. The ratio of the binder to the total of the primary particles and the binder is 1% by mass or more and 20% by mass or less. The particle size D 50 is 2.5 μm or more and 20 μm or less.

[0022] According to the present disclosure, since the tensile modulus of the binder (organic polymer), the ratio of the binder (the ratio of the binder to the sum of the primary particles and the binder), and the particle size D 50 Within respective predetermined ranges, thus an electrode active material capable of suppressing the volume change of the electrode layer is provided.

[0023] From the viewpoint of absorbing the expansion and contraction of Si-based active materials and then at least partially preventing cracks of the electrode layer, the use of an electrode active material (secondary particles, granulated active material) obtained by agglomerating Si-based active materials (primary particles) with the use of a binder is being studied. On the other hand, the inventors have found that when such an electrode active material is used in a battery, there are cases where the volume change of the electrode active material cannot be sufficiently suppressed. Further studies on the reason have revealed that due to the densification press in the manufacturing of the electrode layer and the manufacturing of the battery, there is a possibility that the secondary particles are deformed. When all or some of the secondary particles are deformed due to the press, there are cases where the voids (spaces where neither the primary particles nor the binder are present) inside the secondary particles collapse, and there are concerns that the expansion and contraction of the primary particles in the battery are not completely absorbed. Furthermore, when all or some of the secondary particles are deformed and broken due to the press, there are concerns that the structure of the secondary particles in the battery cannot be maintained, and the expansion and contraction of the primary particles are not completely absorbed.

[0024] The researchers of the present disclosure have found, after conducting intensive studies, that by adjusting the tensile modulus of the binder, the ratio of the binder, and the particle size D 50 By adjusting to respective predetermined ranges, even when a pressure is applied to the electrode active material, the deformation of the secondary particles and the collapse of the voids can be suppressed, and the volume change of the electrode layer can be well suppressed.

[0025] 1. Primary particles

[0026] The primary particles in the present disclosure are Si-based active materials containing Si elements.

[0027] The primary particles (Si-based active materials) can be Si simple substance, can be alloys containing Si as a main component (Si alloys), or can be Si oxides. The ratio of Si elements in the Si alloys is, for example, 50 mol% or more and 95 mol% or less.

[0028] The primary particles can be solid particles. On the other hand, the primary particles can be porous particles having voids inside. Si-based active materials having voids are referred to as porous Si herein. The presence of such voids can be confirmed by observation with a scanning electron microscope (SEM). In addition, the porosity is not particularly limited, and is, for example, 4% or more, or can be 10% or more. In addition, the porosity can be, for example, 40% or less, or can be 20% or less. The porosity can be obtained, for example, by the following procedure. First, a cross-sectional image of the Si-based active material is acquired by SEM. Image analysis software is used to separate the silicon portion and the void portion in the acquired image, and they are binarized. The areas of the silicon portion and the void portion are obtained, and the porosity (%) is calculated from the following formula.

[0029] Porosity (%) = 100 x (void portion area) / ((silicon portion area) + (void portion area))

[0030] In the porous Si, the void amount of voids having a pore diameter of 50 nm or less is, for example, 0.05 cc / g or more and 0.30 cc / g or less. In addition, the BET specific surface area of the porous Si is, for example, 20 m 2 / g or more and 200 m 2 / g or less.

[0031] Examples of the method of producing the porous Si include a method of producing an alloy of Li and Si (LiSi alloy), and then removing Li from the LiSi alloy. The LiSi alloy is obtained, for example, by mixing Li and Si. Examples of the method of removing Li from the LiSi alloy include a method of reacting the LiSi alloy with a Li extraction material. Examples of the Li extraction material include alcohols such as methanol, and acids such as acetic acid.

[0032] The primary particles (Si-based active material) can be crystalline or can be amorphous. In the case of a crystalline substance, the Si-based active material generally has a Si crystal phase. Examples of the Si crystal phase include a diamond crystal phase. Typical Si contains a diamond crystal phase as a Si crystal phase. The Si-based active material can contain a diamond crystal phase as a main phase of the Si crystal phase.

[0033] Other examples of the Si crystal phase include a silicon clathrate crystal phase. The silicon clathrate crystal phase can be a silicon clathrate type I crystal phase, or can be a silicon clathrate type II crystal phase. In the silicon clathrate crystal phase, a plurality of Si atoms constitute a polyhedron (cage) including pentagons and / or hexagons. The polyhedron has a space inside that can contain metal ions such as Li ions. By inserting metal ions into the space, volume change due to charge and discharge can be suppressed. The Si-based active material can contain a silicon clathrate type I crystal phase, or can contain a silicon clathrate type II crystal phase, as the main phase of the Si crystal phase. Examples of a method of producing the silicon clathrate crystal phase include a method in which a Na-Si alloy is produced by a reaction of Na and Si, and then the Na-Si alloy is fired to remove Na from the Na-Si alloy.

[0034] The particle size D of the primary particles 50 There is no particular limitation, and it is, for example, 0.3 μm or more and 5.0 μm or less.

[0035] Examples of a method of forming the porous Si (porous particles) include a method in which a LiSi alloy is produced by a reaction of a primary particle (Si-based active material) that is a solid particle and metal Li, and then Li is removed from the LiSi alloy. For example, a LiSi alloy is obtained by mixing a primary particle (Si-based active material) and metal Li. The molar ratio of Li to Si (Li / Si) is, for example, 1.0 or more, can be 2.0 or more, can be 3.0 or more, or can be 4.0 or more. On the other hand, Li / Si is, for example, 8.0 or less. Examples of a method of removing Li from the LiSi alloy include a method in which the LiSi alloy is reacted with a Li extraction material. Examples of the Li extraction material include alcohols such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol; and acids such as acetic acid, formic acid, propionic acid, and oxalic acid.

[0036] Other examples of a method of forming the porous particles include a method in which a MgSi alloy is produced by a reaction of a primary particle (Si-based active material) that is a solid particle and metal Mg, and then Mg is removed from the MgSi alloy. For example, a MgSi alloy is obtained by heating a mixture of a primary particle (Si-based active material) and metal Mg. The ratio of Mg to Si (Mg / Si) is, for example, 1.0 or more, can be 1.5 or more, or can be 2.0 or more. On the other hand, Mg / Si is, for example, 6.0 or less. Examples of a method of removing Mg from the MgSi alloy include a method in which Mg in the Mg-Si alloy is changed to MgO by heating the MgSi alloy in an inert gas atmosphere containing oxygen, and then MgO is removed using an acid solution. Examples of the acid solution include an aqueous solution containing hydrochloric acid (HCl) and hydrogen fluoride (HF).

[0037] Examples of obtaining primary particles having a clathrate crystal phase (clathrate Si) include the following method: mixing Si and a Na source (e.g., NaH) and heating to thereby produce a Na-Si alloy, and heating the Na-Si alloy to thereby reduce the amount of Na in the Na-Si alloy, resulting in the silicon clathrate crystal phase. Primary particles having voids and having a clathrate crystal phase (porous clathrate Si) can be produced by using porous Si as the Si described above.

[0038] 2. Binder

[0039] The binder in the present disclosure is an organic polymer having a predetermined tensile modulus.

[0040] The tensile modulus of the binder (organic polymer) is 0.10 MPa or more. The tensile modulus can be 0.50 MPa or more, can be 1.00 MPa or more, can be 5.00 MPa or more, or can be 10.00 MPa or more. In addition, the tensile modulus is 1100 MPa or less. The tensile modulus can be 1000 MPa or less, can be 800 MPa or less, can be 300 MPa or less, can be 100 MPa or less, or can be 50 MPa or less. When the tensile modulus is too high, in other words, when the binder is too hard, it is considered that the binder is easily broken by pressing or the like. In this case, it is considered that the breakage of the secondary particles is caused by a crack in the binder, and the structure of the secondary particles in the battery cannot be maintained. This leads to the consideration that the volume change suppression effect is not sufficiently obtained. In addition, when the tensile modulus is too low, in other words, when the binder is too soft, it is considered that the electrode active material is deformed due to pressing, and the voids in the secondary particles tend to collapse. The tensile modulus can be measured by a tensile test in accordance with JIS K 7161, for example. In addition, the tensile modulus can be adjusted by the kind of the binder (organic polymer compound) described later, the degree of polymerization, or the like, for example.

[0041] The kind of the binder in the present disclosure is not particularly limited as long as it is included in an organic polymer having the aforementioned tensile modulus. The organic polymer can be a thermoplastic resin, or can be a thermosetting resin. Examples of the thermoplastic resin include PVdF-HFP, PVB, and SBR. Examples of the thermosetting resin include an epoxy resin. The electrode active material can contain a single kind of binder, or can contain two or more kinds of binders.

[0042] Further, the binder ratio (the ratio of the binder to the total of the primary particles and the binder) in the present disclosure is 1% by weight or more. The binder ratio can be 3% by weight or more, can be 5% by weight or more, or can be 8% by weight or more. Further, the binder ratio in the present disclosure is 20% by weight or less. The binder ratio can be 18% by weight or less, can be 15% by weight or less, can be 13% by weight or less, or can be 10% by weight or less. When the binder ratio is too low, the agglomeration of the primary particles is considered to be too weak, deformation and / or breakage of the electrode active material easily occur due to densification pressing in the manufacturing steps of the battery, as a result, volume change suppression is not sufficiently obtained. On the other hand, when the binder ratio is too high, it is considered that this results in too few voids (spaces in which neither primary particles nor a binder are present) inside the secondary particles. It is also considered that this results in less room for absorbing expansion and shrinkage of the primary particles inside the secondary particles, and the volume change suppression effect is not sufficiently obtained. In particular, when the primary particles are porous Si, there is a concern that voids inside the primary particles are filled with the binder, and there is a concern that volume change suppression cannot be achieved more.

[0043] 3. Electrode active material

[0044] The electrode active material in the present disclosure can be considered to be a secondary particle obtained by agglomerating the primary particles with the binder.

[0045] The particle size D 50 of the electrode active material in the present disclosure is 2.5 μm or more. 50 The particle size D 50 of the electrode active material in the present disclosure can be 3.0 μm or more, can be 5.0 μm or more, or can be 10 μm or more. Further, the particle size D 50 of the electrode active material in the present disclosure is 20 μm or less. 50 When the particle size D 50 is too small, although the pressure resistance is considered to be excellent, it is considered that this results in less room for absorbing expansion and shrinkage of the primary particles inside the secondary particles, and the volume change suppression effect is not sufficiently obtained. Further, when the particle size D 50 is too large, it is considered that this results in more influence due to pressing, and the electrode active material easily deforms and / or cracks. Further, when the particle size D 50 of the electrode active material is too large, it is considered that the effect of suppressing volume change is not sufficiently obtained because reaction unevenness occurs in the secondary particles and local expansion and shrinkage occur.

[0046] The particle size D 50The D of the primary particles (Si-based active material) described above can be controlled by adjusting the D 50 Further, for example, the control can be performed by adjusting the conditions of the spray drying method described later (such as the spray pressure, the slurry concentration, and the slurry feed rate).

[0047] The production method of the electrode active material in the present disclosure is not particularly limited, and examples thereof include a spray drying method. The spray drying method is a method of drying by spraying a slurry containing the primary particles, the binder, and a dispersion medium into a hot gas stream.

[0048] The electrode active material in the present disclosure is generally used for a battery. Although the electrode active material can be a positive electrode active material and / or can be a negative electrode active material, the latter is preferred. This is because a battery with a high capacity can be obtained.

[0049] B. Battery

[0050] Figure 1 is a schematic cross-sectional view exemplarily showing a battery in the present disclosure. Note that, Figure 1 is a schematic view, and the dimensions and shapes of the respective portions are appropriately exaggerated for ease of understanding. Figure 1 The battery 10 shown in FIG. 1 includes a positive electrode layer 1, a negative electrode layer 2, an electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive electrode current collector 4 that collects electrons in the positive electrode layer 1, and a negative electrode current collector 5 that collects electrons in the negative electrode layer 2. In particular, in the battery 10 in the present disclosure, the positive electrode layer 1 or the negative electrode layer 2 contains the electrode active material described in the above “A. Electrode active material”. As described above, the electrode active material in the present disclosure is preferably a negative electrode active material, in other words, the negative electrode layer preferably contains the aforementioned electrode active material. Hereinafter, details of the battery in which the negative electrode layer contains the aforementioned electrode active material are described.

[0051] According to the present disclosure, since the positive electrode layer or the negative electrode layer contains the aforementioned electrode active material, a battery in which performance degradation caused by cracks in the electrode layer is suppressed is provided.

[0052] 1. Positive electrode layer

[0053] The positive electrode layer contains at least the positive electrode active material, and contains at least one of a conductive aid, a binder, and an electrolyte, as necessary.

[0054] Examples of the positive electrode active material include a layered rock salt type active material such as LiCoO2, LiNi 0.8 Co 0.15 Mn 0.05 O2, and LiNi 0.33 Co 0.33 Mn0.33 O2; spinel active materials such as LiMn2O4and Li4Ti5O 12 ; and olivine active materials such as LiFePO4. Examples of the shape of the positive electrode active material include a particle shape. The proportion of the positive electrode active material in the positive electrode layer is, for example, 50% by weight or more and 90% by weight or less.

[0055] Examples of the conductive aid include carbon materials. Examples of the carbon material include: particulate carbon materials such as acetylene black (AB) and ketjen black (KB); and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). The proportion of the conductive aid in the positive electrode layer is, for example, 0.5% by weight or more and 10% by weight or less.

[0056] Examples of the binder in the positive electrode layer include the binder in the aforementioned electrode active material. In addition, examples of the binder in the positive electrode layer include: polyimide-based binders; rubber-based binders such as amine-modified butadiene rubber (ABR), butadiene rubber (BR), and styrene butadiene rubber (SBR); cellulose-based binders such as carboxymethyl cellulose (CMC); acrylic-based binders such as polyacrylic acid, polyacrylate, and polyacrylate ester; and fluorinated binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). The proportion of the binder in the positive electrode layer is, for example, 0.5% by weight or more and 10% by weight or less.

[0057] The electrolyte is described in "3. Electrolyte layer". The thickness of the positive electrode layer is not particularly limited, and is, for example, 0.1 μm or more and 1000 μm or less.

[0058] 2. Negative electrode layer

[0059] The negative electrode layer contains at least the negative electrode active material, and, as necessary, at least one of a conductive aid, a binder, and an electrolyte. In addition, the negative electrode layer preferably contains the aforementioned electrode active material as the negative electrode active material. Matters described in "1. Positive electrode layer" are applicable to the conductive aid, the binder, and the electrolyte here.

[0060] The thickness of the negative electrode layer is not particularly limited, and is, for example, 0.1 μm or more and 1000 μm or less.

[0061] 3. Electrolyte layer

[0062] The electrolyte layer is a layer provided between the positive electrode layer and the negative electrode layer. The electrolyte layer contains at least an electrolyte, and, as necessary, can contain a binder. Matters described in "1. Positive electrode layer" are applicable to the binder.

[0063] Although the electrolyte can be a liquid electrolyte (electrolytic solution), or can be a solid electrolyte, the latter is preferred.

[0064] Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, and complex hydrides. The sulfide solid electrolyte, the oxide solid electrolyte, the nitride solid electrolyte, and the halide solid electrolyte generally contain sulfur (S), oxygen (O), nitrogen (N), and halogen (X) as main components of anionic elements, respectively. Among them, the use of a sulfide solid electrolyte is particularly preferred because of high ion conductivity.

[0065] Examples of the solid electrolyte can also include organic solid electrolytes such as polymer electrolytes and gel electrolytes.

[0066] Examples of the electrolytic solution can include conventionally known electrolytic solutions for lithium ion batteries. Specifically, examples can include electrolytic solutions containing a lithium salt such as LiPF6, and a nonaqueous solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0067] The electrolyte layer can be a solid electrolyte layer containing the aforementioned solid electrolyte. On the other hand, when the aforementioned electrolytic solution is contained as an electrolyte, the electrolyte layer can be a layer obtained by impregnating a separator with the electrolytic solution. The material of the separator can be an organic material, or can be an inorganic material. Specifically, examples thereof include porous membranes of polyethylene (PE), polypropylene (PP), cellulose, polyvinylidene fluoride, polyamide, and polyimide; nonwoven fabrics such as resin nonwoven fabrics and glass fiber nonwoven fabrics; ceramic porous membranes, and the like. Furthermore, the separator can have a single-layer structure, or can have a laminated structure.

[0068] The thickness of the electrolyte layer is not particularly limited, and is, for example, 0.1 μm or more and 1000 μm or less.

[0069] 4. Other configurations

[0070] The battery in the present disclosure preferably includes a positive electrode current collector that collects electric current of the positive electrode layer, and a negative electrode current collector that collects electric current of the negative electrode layer. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon.

[0071] The battery in the present disclosure can further include a constraint jig that applies a constraint pressure to the positive electrode layer, the electrolyte layer, and the negative electrode layer in the thickness direction. In particular, when the electrolyte layer is a solid electrolyte layer, it is preferable to apply a constraint pressure in order to form excellent ion conduction paths and electron conduction paths. For example, the constraint pressure is 0.1 MPa or more, can be 1 MPa or more, or can be 5 MPa or more. On the other hand, for example, the constraint pressure is 100 MPa or less, can be 50 MPa or less, or can be 20 MPa or less.

[0072] 5. The battery

[0073] The kind of the battery in the present disclosure is not particularly limited, and is typically a lithium ion battery. Furthermore, the battery in the present disclosure can be a liquid battery in which the electrolyte layer contains an electrolytic solution, or can be a solid-state battery in which the electrolyte layer contains a solid electrolyte. The solid-state battery can be a semi-solid-state battery, or can be a full solid-state battery. In the present disclosure, the semi-solid-state battery is a battery in which the electrolyte layer has a solid electrolyte and a liquid component (for example, an ionic liquid). In the present disclosure, the full solid-state battery is a battery in which the electrolyte layer has only an inorganic solid electrolyte as the electrolyte. Furthermore, although the battery in the present disclosure can be a primary battery, or can be a secondary battery, a secondary battery is preferable in which. The reason is that it can be repeatedly charged and discharged, and can be used for a vehicle-mounted battery.

[0074] Examples of the use of the battery include a power source for a vehicle, such as a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), a pure electric vehicle (BEV), a gasoline automobile, and a diesel automobile. In particular, it is preferably used as a power source for driving a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), or a pure electric vehicle (BEV). Furthermore, the battery can be used as a power source for a moving body other than a vehicle (for example, a railway, a ship, and an airplane), and can be used as a power source for an electrical device such as an information processing device.

[0075] Note that the present disclosure is not limited to the foregoing embodiments. The foregoing embodiments are illustrative, and any mode having a constitution substantially equivalent to that within the technical idea disclosed in the claims in the present disclosure and achieving a similar effect is included in the technical scope of the present disclosure.

[0076] Example 1

[0077] Manufacture of primary particles

[0078] Under an Ar atmosphere, 0.65 g of Si particles (High Purity Chemicals Co., Ltd.) and 0.60 g of Li metal (Hitoji Metal Co., Ltd.) were mixed in a marver mortar to obtain a LiSi precursor. Under an Ar atmosphere, 1.0 g of the LiSi precursor and 125 ml of a dispersion medium (1,3,5-trimethylbenzene, Nacalai Tesque Co.) were mixed in a glass reactor using an ultrasonic homogenizer (UH-50, SMT Co.). The LiSi precursor dispersion liquid obtained after mixing was cooled to 0°C, and 125 ml of ethanol (Nacalai Tesque Co.) was added dropwise as a Li extraction solvent, and reacted for 120 minutes. After the reaction, 50 ml of acetic acid (Nacalai Tesque Co.) was further added dropwise, and reacted for 60 minutes. After the reaction, the liquid and solid reactants were separated by filtration under reduced pressure. The obtained solid reactant was dried at 120°C for 2 hours to recover porous primary particles (porous Si).

[0079] Manufacture of secondary particles

[0080] The obtained primary particles (porous Si) and a binder (PVdF-HFP) were dispersed in dimethyl carbonate (Nacalai Tesque Co.) to partially dissolve to obtain a slurry. Note that the content ratio of the binder (the ratio of the binder to the sum of the primary particles and the binder) in this slurry was set to 20% by weight. This slurry was sprayed into a spray dryer at 140°C in a nitrogen atmosphere to dry (spray drying method). By adjusting the spray pressure and slurry feed rate in the spray drying method, secondary particles having a particle size D 50 as shown in Table 1 were obtained. The binder was subjected to a tensile test to measure the tensile modulus, which was 0.62 MPa.

[0081] Manufacture of evaluation battery

[0082] An evaluation battery was manufactured using the above-described secondary particles as a negative electrode active material as described below.

[0083] Using an ultrasonic homogenizer (UH-50, SMT Co.), 1.0 g of the above-described secondary particles, 0.04 g of a conductive material (VGCF, Showa Denko Co. (Resonac Co.)), 0.776 g of a sulfide solid electrolyte (LiI-LiBr-Li3PS4-based sulfide solid electrolyte, D 50= 0.2 pm), 0.02 g of a binder (PVdF, Kureha Corporation), and 1.7 g of butyl butyrate (Kishida Chemical Corporation) were mixed to thereby produce a negative electrode slurry. The negative electrode slurry was applied to the negative electrode current collector (Cu foil) by a doctor blade method, and dried on a hot plate at 100°C for 30 minutes. Thus, a negative electrode having a negative electrode current collector and a negative electrode layer was obtained.

[0084] Next, 1.5 g of a positive electrode active material (LiNi 0.8 Co 0.15 Mn 0.05 O2), 0.023 g of a conductive material (VGCF, Showa Denko (Resonac Corporation)), 0.239 g of a sulfide solid electrolyte (LiI-LiBr-Li3PS4-based sulfide solid electrolyte, D 50 = 0.2 pm), 0.011 g of a binder (PVdF, Kureha Corporation), and 0.8 g of butyl butyrate (Kishida Chemical Corporation) were mixed to thereby produce a positive electrode slurry. The positive electrode slurry was applied to the positive electrode current collector (Al foil) by a doctor blade method, and dried on a hot plate at 100°C for 30 minutes. Thus, a positive electrode having a positive electrode current collector and a positive electrode layer was obtained.

[0085] Next, a sulfide solid electrolyte (LiI-LiBr-Li3PS4-based sulfide solid electrolyte), a binder (PVdF, Kureha Corporation), and a dispersion medium (butyl butyrate) were dispersed using an ultrasonic homogenizer to thereby produce a slurry for a solid electrolyte layer. The slurry was applied to a transfer foil (Al foil) by a doctor blade method, and they were dried on a hot plate at 100°C for 30 minutes. Thus, transfer foils each having a solid electrolyte layer were obtained.

[0086] The positive electrode and the transfer foils were stacked so that the positive electrode layer and the solid electrolyte layer faced each other. After pressing them by a roll press at a pressing pressure of 50 kN / cm and a temperature of 160°C, the solid transfer foils (Al foils) were peeled off, and they were punched into 1 cm 2The dimensions are determined. Thus, a positive electrode stack is obtained. Next, the negative electrode and the transfer foil are stacked such that the negative electrode layer and the solid electrolyte layer face each other. After pressing them with a rolling press at a pressure of 50 kN / cm, the transfer foil (Al foil) is peeled off. Thus, a negative electrode stack is obtained. Furthermore, the transfer foil is stacked on the solid electrolyte layer side of the negative electrode stack such that the solid electrolyte layer of the transfer foil faces the solid electrolyte layer side. After pre-pressing the stack with a pressing pressure of 100 MPa and a temperature of 25°C using a uniaxial flatbed press, the transfer foil (Al foil) is peeled from the solid electrolyte layer and stamped to a size of 1.08 cm. 2 The dimensions are adjusted to obtain a negative electrode stack with an additional solid electrolyte layer.

[0087] The positive electrode stack and the negative electrode stack with an additional solid electrolyte layer are stacked so that they face each other. The stack is pressed using a uniaxial planar press at a pressing pressure of 600 MPa and a temperature of 160°C to obtain a battery stack. The obtained battery stack is inserted between two constraint plates, and the two constraint plates are fastened with fasteners at a constraint pressure of 1 MPa to fix the distance between the two constraint plates. Thus, an evaluation battery (all-solid-state battery) is obtained.

[0088] Examples 2 to 10 and Comparative Examples 1 to 6

[0089] As shown in Table 1, at least one of the type of binder, tensile modulus, and binder ratio (binder content ratio) in Example 1 was changed. Furthermore, in the manufacture of secondary particles, secondary particles with the particle size shown in Table 1 were obtained by adjusting the spray drying conditions (at least one of spray pressure and slurry feed rate). Various evaluation batteries were manufactured in the same manner as in Example 1, except that these secondary particles were used as negative electrode active materials.

[0090] Comparative Example 7

[0091] The evaluation battery was manufactured in the same manner as in Example 1, except that porous Si was used as the negative electrode active material.

[0092] evaluate

[0093] The volume changes of the batteries and electrode layers were evaluated by monitoring the constraint pressure changes of the batteries obtained in Examples 1 to 10 and Comparative Examples 1 to 7 using load sensors. Specifically, an initial charge was performed at 0.245 mA to 4.55 V, and the constraint pressure before the initial charge was subtracted from the constraint pressure after the initial charge (after full charge) to calculate the change in each constraint pressure. A relative evaluation was performed based on the results of Comparative Example 7. The results are shown in Table 1.

[0094]

[0095] As shown in Table 1, it was confirmed that any of the examples exhibited a small constraint pressure change compared to Comparative Examples 1 to 7, and in the present disclosure, with the electrode active material, the volume change of the electrode layer and the battery could be suppressed. Here, it was confirmed from the results of Example 3 and Comparative Example 3 and the results of Example 4 and Comparative Example 4 that even when the tensile modulus of the binder (hardness of the binder) is within the predetermined range, when the binder ratio and the particle size of the electrode active material are too large, the volume change suppression effect is not sufficiently obtained. On the other hand, from the results of Comparative Example 5 (tensile modulus: 1233 MPa) and Comparative Example 6 (tensile modulus: 0.05 MPa), even when the binder ratio and the particle size of the electrode active material are within the predetermined range, when the binder is too hard or too soft, the volume change suppression effect is not sufficiently obtained. This means that the tensile modulus of the binder plays a dominant role in the volume change suppression.

Claims

1. An electrode active material, obtained by agglomerating multiple primary particles using a binder, wherein: The primary particles are Si-based active materials containing Si elements; The adhesive is an organic polymer with a tensile modulus of 0.10 MPa or higher and 1100 MPa or lower; The ratio of the adhesive to the total amount of the primary particles and the adhesive is more than 1% by weight and less than 20% by weight; and The particle size D of the electrode active material 50 It is above 2.5μm and below 20μm.

2. The electrode active material according to claim 1, wherein the tensile modulus is below 300 MPa.

3. The electrode active material according to claim 1, wherein the binder is at least one selected from poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), polyvinyl butyral (PVB), styrene-butadiene rubber (SBR), and epoxy resin.

4. The electrode active material according to claim 1, wherein the primary particles are porous particles.

5. The electrode active material according to claim 1, wherein the electrode active material is a negative electrode active material.

6. A battery comprising: Positive electrode layer; Negative electrode layer; and An electrolyte layer is disposed between the positive electrode layer and the negative electrode layer, wherein One of the positive electrode layer and the negative electrode layer contains an electrode active material according to any one of claims 1 to 5.

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