Method for manufacturing electrode material

Abstract

This method for manufacturing an electrode material for a power storage device comprises: a cleaning step for cleaning porous silicon with a polar organic solvent; and a slurry formation step for forming a slurry by mixing the porous silicon that has been subjected to the cleaning step with a linear alkane that is liquid at room temperature.

Description

Method for manufacturing electrode materials

[0001] This disclosure relates to a method for manufacturing electrode materials for energy storage devices.

[0002] Patent Document 1 discloses porous silicon used as an active material for electrodes in energy storage devices. It discloses that the particle size of the porous silicon is 5 μm to 100 μm. The porous silicon is mixed with a conductive material and a binder and a solvent to form a paste which is then applied onto a current collector.

[0003] Japanese Patent Publication No. 2021-014380

[0004] When manufacturing porous silicon as a powder with small particle sizes, improving its handling characteristics is a challenge.

[0005] The present disclosure is a method for manufacturing an electrode material for an energy storage device, comprising a cleaning step of cleaning porous silicon with a polar organic solvent, and a slurry formation step of mixing the porous silicon that has undergone the cleaning step with a linear alkane that is liquid at room temperature to form a slurry.

[0006] One embodiment of a method for manufacturing an electrode material is a method for manufacturing an electrode material in which the energy storage device is an energy storage device using a solid electrolyte. Another embodiment of a method for manufacturing an electrode material is a method for manufacturing an electrode material which, before the slurry formation step, includes a solvent replacement step in which the wet porous silicon that has undergone the washing step is washed with the linear alkane and the polar organic solvent is replaced with the linear alkane.

[0007] In one embodiment of the method for manufacturing the electrode material, the linear alkane has 6 to 16 carbon atoms. In another embodiment of the method for manufacturing the electrode material, the porous silicon has a carbon film formed on its surface, the slurry contains a dispersant for dispersing the porous silicon, and the dispersant is soluble in the liquid linear alkane.

[0008] In one embodiment of the method for manufacturing the electrode material, the average particle size (D50) of the primary particles of the porous silicon is 10 nm or more and 10 μm or less. In another embodiment of the method for manufacturing the electrode material, the polar organic solvent is at least one selected from ethanol, isopropyl alcohol, and acetone.

[0009] According to the present invention, the handling properties of porous silicon can be improved.

[0010] Figure 1 is a schematic diagram of porous silicon. Figure 2 is a flowchart of the manufacturing method of the electrode material. Figure 3 is a schematic diagram of each step in the manufacturing method of porous silicon. Figure 4 is a schematic cross-sectional view of the negative electrode of an energy storage device.

[0011] <First Embodiment> A first embodiment of the electrode material of the present invention will be described below. The electrode material is a slurry (hereinafter also simply referred to as "slurry") containing porous silicon and a linear alkane that is liquid at room temperature, and is an electrode material for an energy storage device.

[0012] (Porous Silicon) As shown in Figure 1, porous silicon is a secondary particle formed by the aggregation and integration of primary porous silicon particles. The primary porous silicon particles have a carbon coating on their surface. The primary porous silicon particles have pores that are connected in three dimensions. These pores penetrate the carbon coating and are exposed on the surface of the secondary porous silicon particles. The secondary porous silicon particles also have pores that are formed as voids between the aggregated primary porous silicon particles.

[0013] Hereinafter, the secondary particles of porous silicon will also be referred to as porous silicon particles. Porous silicon particles are used as active materials for electrodes in energy storage devices. The silicon content of porous silicon particles is, for example, 95% by mass or more and 99% by mass or less. The silicon content is preferably 96% by mass or more, and more preferably 97% by mass or more. Furthermore, the silicon content is preferably 98.5% by mass or less, and more preferably 98% by mass or less. The silicon content refers to the mass ratio of silicon atoms contained in the porous silicon particles.

[0014] The carbon content of the porous silicon particles is, for example, 1% by mass or more and 3% by mass or less. Preferably, the carbon content is 1.5% by mass or more, and more preferably 1.8% by mass or more. Also, preferably, the carbon content is 2.5% by mass or less, and more preferably 2.2% by mass or less. The carbon content refers to the mass ratio of carbon atoms contained in the porous silicon particles.

[0015] The average particle size (D50) of the porous silicon particles is, for example, 5 μm or more and 20 μm or less. Preferably, the average particle size (D50) of the porous silicon particles is 8 μm or more, and more preferably 10 μm or more. Also, preferably, the average particle size (D50) of the porous silicon particles is 15 μm or less, and more preferably 13 μm or less.

[0016] The average particle diameter (D50) of the primary particles of porous silicon particles is, for example, 10 nm or more and 10 μm or less. The average particle diameter (D50) of the primary particles of porous silicon particles is preferably 0.3 μm or more, more preferably 0.6 μm or more. Furthermore, the average particle diameter (D50) of the primary particles of porous silicon particles is preferably 5 μm or less, more preferably 2.5 μm or less, and even more preferably 1.3 μm or less.

[0017] The aspect ratio of the porous silicon particles is, for example, 1.0 to 1.5. Preferably, the aspect ratio of the porous silicon particles is 1.0 to 1.2, and more preferably 1.0 to 1.1. The above aspect ratio is, for example, an average value.

[0018] The primary particles that make up porous silicon particles have pores that are connected in three dimensions. The total pore size of porous silicon particles is, for example, 0.2 cm. ３ / g or more 1.0cm ３ The amount is less than or equal to / g. The total pore size of the porous silicon particles is preferably 0.3 cm². ３ It is 0.4 cm or more per g, and more preferably 0.4 cm ３ The amount is 1 / g or more. Furthermore, the total pore size of the porous silicon particles is preferably 0.8 cm². ３ It is less than or equal to / g, and more preferably 0.6 cm ３It is 0 g or less. In the present specification, the pore volume means the pore volume per unit mass calculated based on the BJH (Barret-Joyner-Halenda) method.

[0019] The specific surface area of the porous silicon particles is, for example, 100 m ２ / g or more and 250 m ２ / g or less. The specific surface area of the porous silicon particles is preferably 120 m ２ / g or more, and more preferably 150 m ２ / g or more.\ Also, the specific surface area of the porous silicon particles is preferably 220 m ２ / g or less, and more preferably 200 m ２ / g or less. In the present specification, the specific surface area of the porous silicon particles means the BET surface area per unit mass measured by BET (Brunauer-Emmett-Teller) method with N ２ adsorption.

[0020] The porous silicon particles may contain other components other than silicon and carbon. Examples of the other components include oxygen and magnesium compounds. The proportion of the other components is, for example, 0 mass% or more and 10 mass% or less, and preferably 0 mass% or more and 5 mass% or less.

[0021] The porous silicon particles preferably have an oxygen content of 0 mass% or 8.0 mass% or less. The oxygen content means the mass ratio of oxygen atoms contained in the porous silicon particles. In the porous silicon particles, oxygen is contained, for example, as a surface oxide formed on the surface of the primary particles of the porous silicon particles.

[0022] The content of the porous silicon particles in the slurry is not particularly limited, and a content that can preferably disperse the porous silicon particles can be appropriately selected. The content of the porous silicon particles in the slurry is, for example, 45 mass% or more and 60 mass% or less. [[ID=​(Linear Alkanes that are Liquid at Room Temperature) Linear alkanes that are liquid at room temperature mean linear alkanes that are liquid at 1 atmosphere and 25°C. Linear alkanes that are liquid at room temperature (hereinafter also simply referred to as "linear alkanes") readily disperse porous silicon particles, thus facilitating the formation of slurries in which porous silicon particles are dispersed. Furthermore, porous silicon particles are prone to oxidation when they absorb moisture. In contrast, linear alkanes have relatively low hygroscopicity, thus suppressing moisture absorption by porous silicon particles. Therefore, oxidation of porous silicon particles can be suppressed. In addition, linear alkanes have low reactivity with solid electrolytes, so even if a solid electrolyte is mixed into the slurry when manufacturing electrodes for an energy storage device, the reaction with the solid electrolyte can be suppressed. Alternatively, even if the slurry comes into contact with a solid electrolyte when manufacturing electrodes for an energy storage device, the reaction with the solid electrolyte can be suppressed.

[0024] Examples of linear alkanes include pentane (5 carbon atoms, also referred to as C5 hereafter), hexane (C6), heptane (C7), octane (C8), nonane (C9), decane (C10), undecane (C11), dodecane (C12), tridecane (C13), tetradecane (C14), pentadecane (C15), hexadecane (C16), and heptadecane (C17). Among these, linear alkanes with 6 to 16 carbon atoms are preferred. More preferably, the linear alkane is dodecane (C12).

[0025] The linear alkanes described above may be present individually or in appropriate combinations of two or more. The content of linear alkanes in the slurry is not particularly limited, and an appropriate content can be selected to form a slurry containing porous silicon particles. For example, the content of linear alkanes in the slurry is 20% by mass or more and 90% by mass or less. Preferably, the content of linear alkanes is 30% by mass or more and 80% by mass or less.

[0026] The slurry may contain other components in addition to the porous silicon particles and linear alkanes mentioned above. Examples of other components include dispersants, thickeners, and solvents other than the linear alkanes (hereinafter also simply referred to as "solvents"). Furthermore, conductive materials and solid electrolytes may be mixed into the slurry when used in the manufacture of an energy storage device. That is, the slurry may contain conductive materials and solid electrolytes. However, it is preferable that the slurry does not contain conductive materials or solid electrolytes in its storage or distribution state, and that conductive materials and solid electrolytes are mixed in when manufacturing the energy storage device.

[0027] (Dispersant) Dispersants are used to improve the dispersibility of porous silicon particles in a slurry. Therefore, dispersants have dispersibility with silicon. Furthermore, if a carbon film is formed on the surface of the porous silicon particles, the dispersant has dispersibility with carbon in addition to dispersibility with silicon. It is preferable that the dispersant has excellent solubility with the linear alkanes contained in the slurry. It is also preferable that the dispersant can improve the dispersibility of conductive materials such as carbon when they are mixed into the slurry. Furthermore, it is preferable that the dispersant has low reactivity with solid electrolytes when they are mixed into the slurry.

[0028] As a dispersant, for example, an organic solvent-based dispersant containing styrene, sodium styrene sulfonate, polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, polyethylene, carboxymethylcellulose, polyphosphate ester, or polyester can be used.

[0029] The above-mentioned dispersants may be present as a single type or as a combination of two or more types as appropriate. The content of the dispersant in the slurry is not particularly limited, and an appropriate content can be selected to suitably disperse porous silicon particles, etc. The content of the dispersant in the slurry is, for example, 0.5% by mass or more and 10% by mass or less. Preferably, the content of the dispersant is 1% by mass or more and 5% by mass or less.

[0030] (Thickeners) Thickeners are used to stabilize the dispersion state of porous silicon particles and the like in a slurry, that is, to improve the dispersion stability of porous silicon particles and the like. When a slurry contains a thickener, viscosity can be imparted to the slurry. In other words, the viscosity of the slurry can be increased. By increasing the viscosity of the slurry, it becomes easier to maintain the dispersion state of each component.

[0031] The thickening agent, like the dispersant described above, preferably has excellent solubility with respect to the linear alkanes contained in the slurry. Furthermore, the thickening agent is preferable to ensure good dispersion stability of conductive materials such as carbon when they are mixed into the slurry. Additionally, it is preferable that the thickening agent has low reactivity with solid electrolytes when they are mixed into the slurry.

[0032] Specific examples of thickeners include, for example, butadiene rubber (hereinafter also referred to as BR), butylene rubber (IIR), acrylate butadiene rubber (ABR), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP).

[0033] The above-mentioned thickening agents may be present as a single type or as a combination of two or more types as appropriate. The amount of thickening agent in the slurry is not particularly limited, and an appropriate amount can be selected that can suitably improve the dispersion stability of porous silicon particles, etc. The amount of thickening agent in the slurry is, for example, 0.5% by mass or more and 20% by mass or less. Preferably, the amount of thickening agent is 1% by mass or more and 5% by mass or less.

[0034] The viscosity of the slurry is not particularly limited, but for example, it is between 10 mPa·s and 1000 mPa·s. A viscosity of 10 mPa·s or higher makes it easier to maintain the dispersion state of each component. Furthermore, a viscosity of 1000 mPa·s or lower makes it easier to apply the slurry when manufacturing the energy storage device, in other words, it improves the work efficiency when manufacturing the energy storage device.

[0035] The method for measuring the viscosity of the slurry is not particularly limited and can be measured using a known viscometer. Examples of known viscometers include the B-type viscometer (Brookfield, DV2T).

[0036] (Solvent) As a solvent, a solvent that readily disperses porous silicon particles and has relatively low reactivity with solid electrolytes can be used, similar to the linear alkanes described above. Alternatively, a solvent that is soluble in the linear alkanes described above can be used. For example, xylene can be given as a solvent that satisfies these conditions.

[0037] The solvent content in the slurry is not particularly limited, but is preferably 90% by mass or less, and more preferably 80% by mass or less. The slurry does not need to contain a solvent. (Conductive material) The conductive material is not particularly limited, and known conductive materials used in energy storage devices can be used. Examples of conductive materials include natural graphite such as scaly graphite and flake graphite, artificial graphite, acetylene black, carbon black, Ketjenblack, carbon whiskers, needle coke, carbon fiber, copper, nickel, aluminum, silver, gold, etc.

[0038] The conductive material described above may be contained as a single type or as a combination of two or more types as appropriate. When the slurry contains a conductive material, the content of the conductive material is not particularly limited. The content of the conductive material is, for example, 0.01% by mass or more and 20% by mass or less, relative to the total solid content of the slurry. Preferably, the content of the conductive material is 0.05% by mass or more and 1% by mass or less, relative to the total solid content of the slurry.

[0039] (Solid Electrolyte) The solid electrolyte is not particularly limited, and known solid electrolytes used in energy storage devices can be used. As the solid electrolyte, for example, a garnet-type oxide containing at least Li, La, and Zr may be used. The basic composition of this solid electrolyte is Li ７．０＋ｘ－ｙ (La ３－ｘ ,Ax)(Zr ２－ｙ , T ｙ ) O １２It may be assumed that A is one or more of Sr and Ca, T is one or more of Nb and Ta, and satisfies 0 < x ≤ 1.0 and 0 < y < 0.75. Alternatively, the solid electrolyte is the basic composition (Li ７－３ｚ＋ｘ－ｙ Mz) (La ３－ｘ A ｘ ) (Zr ２－ｙ T ｙ ) O １２ Yes, (Li ７－３ｚ＋ｘ－ｙ M ｚ ) (La ３－ｘ A ｘ ) (Y ２－ｙ T ｙ ) O １２ It may be a garnet-type oxide represented by the formula. However, in the formula, element M is one or more of Al and Ga, element A is one or more of Ca and Sr, T is one or more of Nb and Ta, and 0 ≤ z ≤ 0.2, 0 ≤ x ≤ 0.2, and 0 ≤ y ≤ 2. In this basic composition formula, it is more preferable that 0.05 ≤ z ≤ 0.1 is satisfied. In this basic composition formula, it is more preferable that 0.05 ≤ x ≤ 0.1 is satisfied. Also, in this basic composition formula, it is more preferable that 0.1 ≤ y ≤ 0.8 is satisfied. Within such ranges, the ionic conductivity can be made more preferable.

[0040] Alternatively, as a solid electrolyte, for example, a common one is Li ３ N, Li called LISICON １４ Zn (GeO ４ ) ４ Li sulfide ３．２５ Ge ０．２５ P ０．７５ S ４ , perovskite type La ０．５ Li ０．５ TiO ３ , (La ２／３ Li ３ｘ □ １／３－２ｘ )TiO ３ (□: atomic vacancy), garnet-type Li ７ La ３ Zr ２ O １２ LiTi, known as NASICON type ２ (PO ４ ) ３, Li １．３ M ０．３ Ti １．７ (PO ３ ) ４ (M = Sc, Al), etc. can be mentioned. Also, 80Li ２ S・20P ２ S ５ (mol%) composition of glass, Li ７ P ３ S １１ , and further, substances with high conductivity in the sulfide system, such as Li １０ Ge ２ PS ２ etc. can be mentioned. In glass-based inorganic solid electrolytes, Li ２ S - SiS ２ , Li ２ S - SiS ２ - LiI, Li ２ S - SiS ２ - Li ３ PO ４ , Li ２ S - SiS ２ - Li ４ SiO ４ , Li ２ S - P ２ S ５ , Li ３ PO ４ - Li ４ SiO ４ , Li ３ BO ４ - Li ４ SiO ４ , and SiO ２ , GeO ２ , B ２ O ３ , P ２ O ５ as glass-based substances and Li ２ O as a network modifier substance, etc. can be mentioned. Also, as thio-lithium solid electrolytes, Li ２ S - GeS ２ system, Li ２ S - GeS ２ - ZnS system, Li ２ S - Ga ２ S ２ system, Li ２ S - GeS ２ - Ga２ S ３ system, Li ２ S-GeS ２ -P ２ S ５ system, Li ２ S-GeS ２ -SbS ５ system, Li ２ S-GeS ２ - Al ２ S ３ system, Li ２ S-SiS ２ system, Li ２ S-P ２ S ５ system, Li ２ S-Al ２ S ３ system, LiS-SiS ２ - Al ２ S ３ system, Li ２ S-SiS ２ -P ２ S ５ Examples include systems and such.

[0041] If the slurry contains a solid electrolyte, the solid electrolyte content is not particularly limited. The solid electrolyte content is, for example, 10% by mass or more and 90% by mass or less, relative to the total solid content of the slurry. Preferably, the solid electrolyte content is 30% by mass or more and 70% by mass or less, relative to the total solid content of the slurry.

[0042] <Applications of Electrode Materials> The electrode material is for use in energy storage devices. Preferably, the electrode material is for use in energy storage devices that use a solid electrolyte. The energy storage device may be an all-solid-state battery, a semi-solid-state battery, or an electric double-layer capacitor. The electrode material can be used, for example, in the active material layer of the negative electrode of an energy storage device.

[0043] Figure 4 is a schematic diagram of the negative electrode 20 of the energy storage device. The negative electrode 20 comprises a negative electrode current collector 21 and a negative electrode active material layer 22 formed on one side surface of the negative electrode current collector 21. The negative electrode active material layer 22 is formed by coating the surface of the negative electrode current collector 21 with a slurry-like negative electrode mixture, which is made by mixing porous silicon particles as the negative electrode active material, other components constituting the negative electrode active material layer 22, and a dispersion medium with a linear alkane, and then drying it to evaporate the linear alkane and dispersion medium.

[0044] <Operation and Effects of the First Embodiment> (1-1) The electrode material of the first embodiment is a slurry containing porous silicon particles and a linear alkane that is liquid at room temperature. Compared to conventional methods of handling porous silicon particles as a powder, handling performance can be improved. That is, in conventional methods, it was necessary to carry out transport etc. while suppressing the scattering of powder, whereas the electrode material of the first embodiment can be carried out etc. in slurry form. Therefore, it becomes possible to handle porous silicon particles more efficiently. In addition, safety can be improved compared to methods of handling porous silicon particles as a powder.

[0045] (1-2) Since linear alkanes that are liquid at room temperature have low reactivity with solid electrolytes, when the electrode material of the first embodiment is used for an energy storage device using a solid electrolyte, it is possible to suppress performance degradation due to reaction with the solid electrolyte.

[0046] (1-3) The porous silicon particles have a carbon film formed on their surface, and the slurry contains a dispersant for dispersing the porous silicon particles, and the dispersant is soluble in liquid linear alkanes. Therefore, porous silicon particles having a carbon film can be suitably dispersed in the slurry.

[0047] <Second Embodiment> A second embodiment of the method for manufacturing the electrode material of the present invention will be described below. As shown in Figure 2, the method for manufacturing the electrode material of this embodiment is a method for manufacturing a slurry containing porous silicon particles and a linear alkane that is liquid at room temperature.

[0048] The slurry manufacturing method of this embodiment includes a precursor slurry preparation step (S1), a granulation step (S2), a calcination step (S3), a reduction step (S4), a washing step (S5), and a slurry formation step (S6). The details of each step will be described below.

[0049] <Precursor Slurry Preparation Process (S1)> The precursor slurry preparation process is a process for preparing a precursor slurry containing silicon dioxide powder, a carbon source, and a dispersion medium. The details of each component constituting the precursor slurry are described below.

[0050] [Silicon Oxide Powder] Silicon oxide powder contains silicon oxide as its main component. Examples of silicon oxide include SiO₂, SiO₂ ２ Examples include the following. Silicon oxide is preferably SiO. The powder may also contain components other than silicon oxide. The proportion of silicon oxide in the powder is, for example, 50% by mass or more, preferably 90% by mass or more, and more preferably 99% or more.

[0051] The average particle diameter (D50) of the above powder is, for example, 10 nm or more and 10 μm or less. The average particle diameter (D50) of the above powder is preferably 300 nm or more, more preferably 600 nm or more. Furthermore, the average particle diameter (D50) of the above powder is preferably 5 μm or less, more preferably 2.5 μm or less, and even more preferably 1.3 μm or less. In this specification, "average particle diameter (D50)" means the median diameter measured by laser diffraction scattering method.

[0052] [Carbon Source] The carbon source is, for example, an organic compound. Examples of organic compounds include sugars such as glucose, fructose, galactose, mannose, maltose, sucrose, lactose, glycogen, pectin, alginic acid, glucomannan, chitin, hyaluronic acid, chondroitin, and agarose, as well as polyethers, polyhydric alcohols, polyvinyl alcohol, polyvinylpyrrolidone, cellulose, starch, gelatin, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, polyacrylic acid, polystyrene sulfonic acid, polyacrylamide, and polyvinyl acetate. Examples of polyhydric alcohols include polyethylene glycol, polypropylene glycol, polyglycerin, and glycerin. The carbon source may be used alone or in combination of two or more types.

[0053] The carbon source is preferably a sugar such as fructose. By using a sugar as the carbon source, it functions as a binder for forming granules in the granulation process described later. Therefore, granules can be formed in the granulation process even without adding a separate binder to the precursor slurry, or even if only a small amount of a separate binder is added.

[0054] The carbon source content in the precursor slurry is adjusted so that the mass of carbon in the carbon source is a specific amount. For example, when the silicon content in the powder in the precursor slurry is 100 parts by mass, the carbon content in the carbon source in the precursor slurry is 3.7 parts by mass or more and 11.3 parts by mass or less. The carbon content is preferably 5.5 parts by mass or more, and more preferably 6.7 parts by mass or more. Also, the carbon content is preferably 9.3 parts by mass or less, and more preferably 8.2 parts by mass or less. The silicon content refers to the mass ratio of silicon atoms contained in the precursor slurry. The carbon content refers to the mass ratio of carbon atoms constituting the carbon source contained in the precursor slurry.

[0055] Increasing the carbon content improves the conductivity of the porous silicon particles produced. Conversely, decreasing the carbon content increases the proportion of silicon in the porous silicon particles produced, resulting in a larger volume per unit area of ​​the porous silicon particles.

[0056] Furthermore, when a carbon source is used as a binder, it is preferable to determine the carbon source content based on the average particle size (D50) of the powder. In other words, it is preferable to determine the carbon source content based on the specific surface area of ​​the powder. For example, suppose the average particle size (D50) of the powder is 10 nm or more and 5 μm or less, and the carbon source is a sugar such as fructose. In this case, the carbon source content in the precursor slurry is, for example, 3.7 parts by mass or more, preferably 5.5 parts by mass or more, and more preferably 6.7 parts by mass or more, when the powder content in the precursor slurry is 100 parts by mass. The carbon source content is, for example, 11.3 parts by mass or less. By setting the carbon source content within the above range, granules can be formed in the granulation process even without adding a binder separately to the precursor slurry, or even if only a small amount of binder is added separately.

[0057] [Dispersion medium] The dispersion medium is water, or a mixed solvent of water and a non-aqueous solvent. The water is not particularly limited, but preferred examples include ion-exchanged water, which is water treated with an ion-exchange resin, and ultrapure water, which is water treated by a reverse osmosis membrane water purification system. Examples of non-aqueous solvents that make up the mixed solvent include solvents that are miscible with water, such as lower alcohols, acetone, tetrahydrofuran, ethylene glycol, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, acetonitrile, and dimethyl sulfoxide. The non-aqueous solvent may be used alone or in combination of two or more types.

[0058] The volume percentage of water in the mixed solvent is preferably, for example, 50% by volume or more and 99.9% by volume or less, and more preferably 60% by volume or more and 99% by volume or less. The content of the dispersion medium in the precursor slurry is not particularly limited, but for example, it is an amount such that the solid content ratio is 10% by mass or more and 65% by mass or less.

[0059] [Other Components] The precursor slurry may contain other components besides those mentioned above, as needed. Examples of other components include dispersants and binders.

[0060] [Specific Example of Precursor Slurry Preparation Process] As shown in Figures 2 and 3, an example of the precursor slurry preparation process (S1) includes a grinding process (S1A) and a mixing process (S1B).

[0061] The grinding process involves adding a dispersion medium to silicon dioxide mother particles and performing wet grinding to obtain a mixture containing silicon dioxide powder and a dispersion medium. Wet grinding can be carried out using a grinding device such as a bead mill. It is preferable to perform the grinding process under conditions where the lump-like mother particles are volume-ground. For example, in the first half of the grinding process, the ground particles produced by surface grinding using frictional or shearing forces are further ground under conditions where they are volume-ground by impact or compressive forces in the second half of the grinding process. Performing the grinding process under volume-ground conditions reduces the aspect ratio of the resulting powder. Using powder with a small aspect ratio reduces the aspect ratio of the resulting porous silicon particles. The specific method of wet grinding in the grinding process is not particularly limited, and known methods applicable to grinding silicon dioxide can be used.

[0062] The mixing step is a process of preparing a precursor slurry by adding a carbon source to the mixture after the grinding step. In the mixing step, the solid content ratio of the precursor slurry may be adjusted by further adding a dispersion medium. Also, when preparing a precursor slurry containing other components, the other components may be mixed in during the mixing step. The specific mixing method in the mixing step is not particularly limited, and known methods applicable when preparing a slurry can be used.

[0063] The precursor slurry preparation process is not limited to the method described above. For example, wet grinding may be performed in the grinding step with the carbon source added beforehand. In this case, the mixing step can be omitted. Alternatively, the precursor slurry may be prepared by separately preparing silicon dioxide powder, a carbon source, and a dispersion medium, and then mixing them. In this case, for example, commercially available silicon dioxide powder that has been pre-adjusted to a predetermined particle size may be used.

[0064] <Granulation Process (S2)> As shown in Figure 3, the granulation process is a process in which a granulated material is obtained by spray-drying the precursor slurry. The granulated material consists of secondary particles in which the silicon oxide powder contained in the precursor slurry is the primary particle and the surface of the primary particle is covered with a carbon source. In other words, the granulated material consists of secondary particles in which primary particles made of silicon oxide powder are aggregated via a carbon source.

[0065] Examples of spraying methods in spray drying include those using disc-type nozzles, pressurized nozzles, pressurized two-fluid nozzles, and pressurized four-fluid nozzles. The spray temperature in spray drying is, for example, between 150°C and 250°C.

[0066] The average particle size (D50) of the granulated material obtained by the granulation process is, for example, 3 μm or more and 20 μm or less. Preferably, the average particle size (D50) of the granulated material is 5 μm or more, more preferably 8 μm or more, and even more preferably 10 μm or more. Also, preferably the average particle size (D50) of the granulated material is 15 μm or less, and more preferably 13 μm or less.

[0067] The aspect ratio of the granules obtained by the granulation process is, for example, 1.0 or more and 1.5 or less. Preferably, the aspect ratio of the granules is 1.0 or more and 1.2 or less, and more preferably 1.0 or more and 1.1 or less. The above aspect ratio is, for example, an average value.

[0068] <Firing Process (S3)> As shown in Figure 3, the firing process is a process of firing the granules to obtain precursor particles in which a carbon film derived from a carbon source is formed on the surface of the primary particles of the granules. In other words, the firing process is a process of changing the carbon source attached to the surface of the primary particles of the granules into a carbon film. The precursor particles include primary particles made of silicon oxide and a carbon film covering the surface of the primary particles. The precursor particles are not limited to a configuration in which the carbon film completely covers the surface of the primary particles made of silicon oxide, but also include a configuration in which the carbon film partially covers the surface of the primary particles made of silicon oxide.

[0069] The firing temperature in the firing process is, for example, between 500°C and 1100°C. When silicon dioxide is SiO, the disproportionation reaction of SiO at high temperatures (SiO → Si + SiO) ２ To suppress this, the firing temperature is preferably between 500°C and 1000°C.

[0070] The firing time in the firing process is, for example, 0.5 hours or more and 12 hours or less. The atmosphere in the firing process is, for example, a non-oxidizing atmosphere. A non-oxidizing atmosphere is, for example, nitrogen (N ２ ), an inert atmosphere such as argon (Ar), and hydrogen (H ２ Examples include reducing atmospheres containing reducing gases such as ).

[0071] During the firing process, the particle size of the precursor particles and the particle size of the primary particles of the precursor particles remain largely unchanged from those of the granulated material. Therefore, the average particle size (D50) of the precursor particles is approximately equal to the average particle size (D50) of the granulated material described above. Furthermore, the average particle size (D50) of the primary particles of the precursor particles is approximately equal to the average particle size (D50) of the primary particles of the granulated material.

[0072] <Reduction Process (S4)> As shown in Figure 3, the reduction process is a process in which reduced particles are obtained by contacting precursor particles with Mg vapor to obtain a mixture containing Si and MgO as primary particles. In the reduction process, the primary particles made of silicon oxide that constitute the precursor particles are reduced by Mg vapor to SiO or SiO ２ Through a reduction reaction, the precursor particles are transformed into primary particles consisting of a mixture of Si and MgO. Therefore, the reduction step can also be described as a step in which each of the primary particles constituting the precursor particles is transformed from a primary particle made of silicon oxide to a primary particle consisting of a mixture of Si and MgO. The reduced particles consist of primary particles made of a mixture of Si and MgO and a carbon film covering the surface of the primary particles. The Mg vapor passes through the carbon film and reacts with the silicon oxide of the precursor particles.

[0073] In the reduction process, the particle size of the reduced particles and the particle size of the primary reduced particles remain largely unchanged from those of the precursor particles. Therefore, the average particle size (D50) of the reduced particles is approximately equal to the average particle size (D50) of the granulated material and precursor particles described above. Furthermore, the average particle size (D50) of the primary reduced particles is approximately equal to the average particle size (D50) of the primary reduced particles and precursor particles.

[0074] <Washing Process (S5)> As shown in Figure 3, the washing process is a process to obtain porous silicon particles in which porous silicon is the primary particle by removing MgO from the reduced particles. In the washing process, the primary particles, which consist of a mixture containing Si and MgO that constitute the reduced particles, are transformed into primary particles made of porous silicon having pores by the removal of MgO.

[0075] Therefore, the washing process can also be described as a process of changing each of the primary particles constituting the reduced particles from primary particles made of a mixture containing Si and MgO to primary particles made of porous silicon.

[0076] As shown in Figures 2 and 3, an example of the cleaning process includes a first cleaning step (S5A), a second cleaning step (S5B), and a third cleaning step (S5C). By going through the first cleaning step (S5A) to the third cleaning step (S5C), porous silicon particles are obtained.

[0077] (First Washing Step) The first washing step is a step in which the reduced particles obtained in the reduction step are treated with acid. In the first washing step, magnesium salts are generated from the MgO contained in the reduced particles, and the generated magnesium salts are washed away to obtain porous silicon particles. The acid used in the first washing step is not particularly limited and any acid capable of generating magnesium salts from MgO is acceptable. Examples of acids that can be used in the first washing step include hydrochloric acid, nitric acid, and sulfuric acid. The concentration of the acid used in the first washing step can be appropriately selected depending on the type of acid. As an example, the reaction equation when hydrochloric acid is used is shown below.

[0078] MgO+2HCl→MgCl ２ +H ２ The specific method for the first washing step is not particularly limited, and known washing methods can be employed. For example, it can be carried out by preparing a container filled with acid, adding reduced particles to this container, and stirring.

[0079] (Second Washing Step) The second washing step is a step in which magnesium salts and the like remaining in the first washing step are washed away using a rinsing solution. The second washing step is performed on porous silicon particles that have been wet after the first washing step. The rinsing solution is water or an acidic aqueous solution with a pH of 6 or less and a polar organic solvent. The acid contained in the acidic aqueous solution is preferably an acid that can be removed with an alcohol such as ethanol, for example, an organic acid such as acetic acid. An example of an acidic aqueous solution is a 1% acetic acid aqueous solution.

[0080] Examples of polar organic solvents include ethanol, isopropyl alcohol, and acetone. In other words, it is preferable that the polar organic solvent is at least one selected from ethanol, isopropyl alcohol, and acetone.

[0081] The second washing step involves first washing away the acid used in the first washing step and any remaining magnesium salts adhering to the porous silicon particles using water or an acidic aqueous solution with a pH of 6 or lower. Next, the water or acidic aqueous solution with a pH of 6 or lower adhering to the porous silicon particles is washed away using a polar organic solvent. Multiple washes using water or an acidic aqueous solution with a pH of 6 or lower may be performed, followed by multiple washes using a polar organic solvent. Alternatively, washing with only a polar organic solvent such as ethanol, isopropyl alcohol, or acetone may be performed without washing with water or an acidic aqueous solution with a pH of 6 or lower. Through the second washing step, the water or acidic aqueous solution with a pH of 6 or lower adhering to the porous silicon particles is replaced by a polar organic solvent.

[0082] The specific method for the second washing step is not particularly limited, and known washing methods can be employed. For example, it can be carried out in the same way as the first washing step, by introducing porous silicon particles into a container filled with a washing solution such as water and stirring. Alternatively, a dilution washing may be performed by pouring water or an acidic aqueous solution with a pH of 6 or less over the porous silicon particles deposited on the filter film to filter the porous silicon particles, and then pouring a polar organic solvent over them to filter the porous silicon particles. Dilution washing may also be performed while stirring the porous silicon particles on the filter film using a stirring blade.

[0083] Here, because linear alkanes have low solubility in water, it is difficult to directly replace the water or acidic aqueous solution with a pH of 6 or lower attached to the porous silicon particles with linear alkanes. Therefore, in the second washing step, a polar organic solvent that is soluble in both water and linear alkanes is used to temporarily replace the water or acidic aqueous solution with a pH of 6 or lower attached to the porous silicon particles with the polar organic solvent. Then, in the following third washing step, the polar organic solvent is replaced with linear alkanes.

[0084] (Third Washing Step) The third washing step is a process of washing away the polar organic solvent that adhered to the porous silicon particles in the second washing step using a linear alkane. The third washing step is performed on the porous silicon particles in a wet state after the second washing step. Washing with a linear alkane may be performed multiple times. By going through the third washing step, the polar organic solvent that adhered to the porous silicon particles is replaced by a linear alkane. Therefore, the third washing step can be said to be a solvent replacement step that replaces the polar organic solvent that adhered to the porous silicon particles with a linear alkane.

[0085] The specific method for the third cleaning step is not particularly limited, and known cleaning methods can be employed. For example, dilution cleaning may be performed in the same manner as in the second cleaning step. Instead of the third cleaning step, polar organic solvents may be removed by vacuum treatment or heating treatment after the second cleaning step.

[0086] <Slurry Formation Process (S6)> As shown in Figure 2, the slurry formation process is a process in which porous silicon particles in a wet state after the third washing process are mixed with linear alkanes that are liquid at room temperature to form a slurry.

[0087] The specific method for the slurry formation process is not particularly limited, and known methods can be employed. For example, it can be carried out by placing wet porous silicon particles that have undergone the third washing process and linear alkanes into a container and stirring. In this case, other components such as the dispersant and thickener mentioned above may be mixed in as appropriate. By mixing in the dispersant mentioned above, porous silicon particles having a carbon coating can be suitably dispersed in the slurry. When the electrode material of the present invention is used in the negative electrode active material layer of an energy storage device, it is preferable that the other components mixed in the slurry formation process do not contain Si. Specifically, it is preferable that the other components such as thickeners and binders do not contain the element silicon. By not including the element silicon in the components, it is possible to avoid the reaction between the element Li contained in the solid electrolyte and the element silicon. The binder is also called a binder.

[0088] It is preferable that the slurry contains a small amount of water. For example, the amount of water in the slurry is 300 ppm or less. The amount of water in the slurry can be measured by a known method. <Effects and Effects of the Second Embodiment> (2-1) The method for manufacturing the electrode material of the second embodiment comprises a washing step (second washing step) in which porous silicon particles are washed with a polar organic solvent, and a slurry forming step in which the porous silicon particles that have undergone the washing step are mixed with a linear alkane that is liquid at room temperature to form a slurry. Therefore, an electrode material with suppressed reactivity with solid electrolytes can be manufactured for use in energy storage devices. When manufacturing an energy storage device using this electrode material, even if the electrode material comes into contact with the solid electrolyte, a decrease in the performance of the energy storage device can be suppressed.

[0089] (2-2) Prior to the slurry formation step, the process includes a solvent replacement step (third washing step) in which the wet porous silicon particles, which have undergone a washing step (second washing step), are washed with a linear alkane to replace the polar organic solvent with the linear alkane. Therefore, water or acidic aqueous solution with a pH of 6 or less attached to the porous silicon particles can be efficiently replaced with a linear alkane.

[0090] <Examples of Modifications> The first embodiment and the second embodiment (hereinafter collectively referred to as "this embodiment") can be implemented with the following modifications. This embodiment and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0091] ○The viscosity of the electrode material slurry may be less than 10 mPa·s. It may also be greater than 1000 mPa·s. ○The method for manufacturing the electrode material of the second embodiment included a precursor slurry preparation step, a granulation step, a calcination step, a reduction step, and a washing step, but these steps may be omitted. For example, commercially available porous silicon or porous silicon obtained without going through the manufacturing method of the second embodiment may be used. A slurry may be formed by mixing commercially available porous silicon with a linear alkane that is liquid at room temperature. Alternatively, commercially available porous silicon may be prepared, and the second washing step, the third washing step, and the slurry formation step may be performed on this porous silicon. By performing the second washing step and the third washing step on commercially available porous silicon, adsorbed water etc. attached to the commercially available porous silicon can be efficiently replaced with linear alkane. Commercially available porous silicon may be prepared, and the second washing step and the slurry formation step may be performed on this porous silicon.

[0092] If the granulation process is omitted, the average particle size (D50) of the primary particles of the porous silicon particles used can be, for example, 1 μm or more and 10 μm or less. ○ In the second embodiment, the second washing step was performed on the wet porous silicon particles that had undergone the first washing step, but the invention is not limited to this embodiment. The wet porous silicon particles that had undergone the first washing step may be dried before the second washing step is performed. Similarly, the wet porous silicon particles that had undergone the second washing step may be dried before the third washing step is performed. By performing the next washing step after drying, the time required for the washing step (S5) can be shortened.

[0093] 20...Negative electrode 21...Negative electrode current collector 22...Negative electrode active material layer

Claims

1. A method for manufacturing an electrode material for an energy storage device, comprising: a cleaning step of cleaning porous silicon with a polar organic solvent; and a slurry formation step of mixing the porous silicon that has undergone the cleaning step with a linear alkane that is liquid at room temperature to form a slurry.

2. The method for manufacturing an electrode material according to claim 1, wherein the energy storage device is an energy storage device using a solid electrolyte.

3. The method for producing an electrode material according to claim 1, further comprising a solvent replacement step, before the slurry formation step, in which the wet porous silicon that has undergone the washing step is washed with the linear alkane to replace the polar organic solvent with the linear alkane.

4. The method for producing an electrode material according to claim 1, wherein the linear alkane has 6 or more carbon atoms and 16 or less carbon atoms.

5. The method for producing an electrode material according to claim 1, wherein the porous silicon has a carbon film formed on its surface, the slurry contains a dispersant for dispersing the porous silicon, and the dispersant is soluble in the liquid linear alkane.

6. The method for producing an electrode material according to claim 1, wherein the average particle size (D50) of the primary particles of the porous silicon is 10 nm or more and 10 μm or less.

7. The method for producing an electrode material according to claim 1, wherein the polar organic solvent is at least one selected from ethanol, isopropyl alcohol, and acetone.

Images