Method for manufacturing negative electrode active material, method for manufacturing lithium ion battery

Abstract

To provide a manufacturing method of a negative electrode active material easy to handle, and a manufacturing method of a lithium-ion battery including the manufacture of such a negative electrode active material.SOLUTION: A disclosed method of manufacturing a negative electrode active material includes: causing porous silicon clathrate to contact with a lithium-containing non-aqueous electrolyte; and drying and removing a solvent of the lithium-containing non-aqueous electrolyte. A disclosed method of manufacturing a lithium-ion battery includes: preparing a negative electrode active material by using the disclosed method; and forming a negative electrode active material layer containing the negative electrode active material.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a negative electrode active material and a method for manufacturing a lithium ion battery.

Background Art

[0002] In recent years, battery development has been actively carried out. For example, in the automotive industry, the development of batteries used in electric vehicles or hybrid vehicles has been promoted. Also, silicon (Si) is known as a negative electrode active material used in batteries, particularly lithium ion batteries.

[0003] For example, Patent Document 1 discloses a silicon clathrate negative electrode active material having a silicon clathrate II-type crystal phase, having voids inside primary particles, and having a void volume of voids with a pore diameter of 100 nm or less of 0.05 cc / g or more and 0.15 cc / g or less. Patent Document 2 discloses a silicon clathrate negative electrode active material having a silicon clathrate II-type crystal phase and having a composition of Na x Si 136 (1.98 < x < 2.54).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] There is a demand for improved energy density in lithium-ion batteries. One of the factors hindering improvements in energy density is irreversible capacity. Irreversible capacity comes from the lithium (Li) ions supplied from the positive electrode to the negative electrode during the initial charge that cannot be used thereafter. The higher the capacity of the negative electrode active material, such as Si, the larger the irreversible capacity tends to be. The existence of irreversible capacity limits the effective charge / discharge capacity of the battery.

[0006] A method called "pre-doping" has been investigated, in which Li ions are supplied to Si in an amount equivalent to the irreversible capacity before the battery is completed. For example, Li ions can be supplied to Si by placing Li metal (e.g., Li foil) on the surface of the Si and leaving it. However, this method can cause heat generation and changes in appearance in the resulting negative electrode active material, and therefore, improvements in the handleability of pre-doped Li ions are needed.

[0007] An object of the present disclosure is to provide a method for producing a negative electrode active material that is easy to handle, and a method for producing a lithium ion battery that includes producing such a negative electrode active material. [Means for solving the problem]

[0008] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> contacting the porous silicon clathrate with a lithium-containing non-aqueous electrolyte; and and drying and removing the solvent from the lithium-containing nonaqueous electrolyte solution. A method for producing a negative electrode active material. <Aspect 2> 2. The method of embodiment 1, wherein the solvent is an aprotic polar solvent. <Aspect 3> The method of embodiment 2, wherein the aprotic polar solvent is an ether. <Aspect 4> The method of embodiment 3, wherein the ether has a tetrahydrofuran skeleton. <Aspect 5> A method according to any one of Aspects 1 to 4, wherein the negative electrode active material is for use as a negative electrode active material in a lithium ion battery. <Aspect 6> Producing a negative electrode active material by the method according to any one of aspects 1 to 5; and forming a negative electrode active material layer containing the negative electrode active material; A method for manufacturing a lithium-ion battery, comprising: [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a method for producing a negative electrode active material that is easy to handle, and a method for producing a lithium ion battery that includes producing such a negative electrode active material. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present disclosure.

[0011] <<Method for producing negative electrode active material>> The disclosed method for producing a negative electrode active material includes contacting a porous silicon clathrate with a lithium-containing non-aqueous electrolyte solution, and then drying and removing the solvent from the lithium-containing non-aqueous electrolyte solution.

[0012] The present inventors have discovered that using porous silicon clathrate as Si and pre-doping the porous silicon clathrate with Li ions by liquid-phase synthesis improves the handleability of the Li ion-pre-doped negative electrode active material. While not intending to be bound by any theory, the reason for this is presumed to be as follows. It is believed that pre-doping with Li ions by liquid-phase synthesis causes Si and Li to react, self-generating a surface coating of lithium silicon oxide that is stable in air. Furthermore, since porous silicon clathrate has a larger surface area than regular Si, the stabilizing effect of the surface coating is significant, which is believed to improve handleability.

[0013] <Contact process> The disclosed method for producing a negative electrode active material includes contacting a porous silicon clathrate with a lithium-containing non-aqueous electrolyte.

[0014] The method for contacting the porous silicon clathrate with the lithium-containing non-aqueous electrolyte solution includes, but is not limited to, adding the porous silicon clathrate to the lithium-containing non-aqueous electrolyte solution and mixing them.

[0015] (Porous silicon clathrate) In the method of the present disclosure, porous silicon clathrate is used as Si. The porous silicon clathrate can be obtained, for example, by mixing Si and Li to obtain a lithium-silicon alloy and then reacting the obtained lithium-silicon alloy with ethanol.

[0016] (Lithium-containing non-aqueous electrolyte) The lithium-containing non-aqueous electrolyte solution in the method of the present disclosure may contain an aprotic polar solvent. The aprotic polar solvent is not ionized and does not react with Li ions, which is preferable in that it can prevent a decrease in the pre-doped Li ions.

[0017] Examples of aprotic polar solvents that can be used include carbonates, esters, ethers, nitriles, sulfones, lactones, etc. Examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol, dimethyl ether, ethylene glycol, acetonitrile, propionitrile, nitromethane, N,N-dimethylformamide, dimethyl sulfoxide, sulfolane, and γ-butyrolactone.

[0018] The lithium-containing non-aqueous electrolyte may contain a solvent other than the aprotic polar solvent. Examples of such an electrolyte include biphenyls. Examples of biphenyls include 2-methylbiphenyl. It is preferable that the electrolyte contains biphenyls because it can prevent overcharging of the battery.

[0019] The proportion of the aprotic polar solvent relative to the entire lithium-containing nonaqueous electrolyte solution may be 50% by volume or more, 60% by volume or more, 70% by volume or more, or 80% by volume or more.

[0020] <Drying process> The disclosed method for producing a negative electrode active material includes drying and removing the solvent from a lithium-containing non-aqueous electrolyte solution.

[0021] An example of a method for drying and removing the solvent of the lithium-containing nonaqueous electrolyte solution is a method of performing solid-liquid separation between Li ion-doped Si and the lithium-containing nonaqueous electrolyte solution, followed by drying, but the method is not limited to this.

[0022] The solid-liquid separation method may be exemplified by suction filtration.

[0023] An example of a drying method is vacuum drying. When vacuum drying is used, the drying temperature may be 25°C to 100°C, 35°C to 90°C, or 45°C to 80°C, and the drying time may be 0.5 hours or more, 1 hour or more, or 1.5 hours or more.

[0024] <Application> The negative electrode active material obtained by the method of the present disclosure can be used as a negative electrode active material for lithium ion batteries.

[0025] <<Lithium-ion battery manufacturing method>> The disclosed method of making a lithium ion battery includes making an active anode material and forming an active anode material layer containing the active anode material.

[0026] For the method for producing the negative electrode active material, reference can be made to the above description regarding the method for producing the negative electrode active material of the present disclosure.

[0027] The method for forming the negative electrode active material layer is not particularly limited, and a known method can be adopted. For example, a negative electrode active material layer formed on the negative electrode current collector layer can be obtained by applying a slurry containing the negative electrode active material to the negative electrode current collector and drying it.

[0028] The method for forming the battery is not particularly limited, and any known method can be adopted. The method for manufacturing a battery according to the present disclosure may include, in addition to manufacturing a negative electrode active material and forming a negative electrode active material layer containing the negative electrode active material, arranging a negative electrode current collector layer, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer in this order.

[0029] <Negative electrode current collector layer> Examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon.

[0030] <Negative electrode active material layer> The negative electrode active material layer contains at least a negative electrode active material.

[0031] (Negative electrode active material) For the negative electrode active material, reference can be made to the above description regarding the negative electrode active material of the present disclosure.

[0032] The proportion of the negative electrode active material in the negative electrode active material layer may be 20 wt % or more, 30 wt % or more, or 40 wt % or more. If the proportion of the negative electrode active material is too low, sufficient energy density may not be obtained. The proportion of the negative electrode active material may be 80 wt % or less, 70 wt % or less, or 60 wt % or less. If the proportion of the negative electrode active material is too high, the ionic conductivity and electronic conductivity of the negative electrode active material layer may be relatively reduced.

[0033] The negative electrode active material layer may contain at least one of an electrolyte, a conductive material, and a binder, as needed.

[0034] (electrolyte) Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, and organic polymer electrolytes such as polymer electrolytes.

[0035] Examples of sulfide solid electrolytes include solid electrolytes containing Li, X (wherein X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and a halogen. Examples of halogen include F, Cl, Br, and I. The sulfide solid electrolyte may be glass (amorphous) or glass ceramic. Examples of sulfide solid electrolytes include Li2S-P2S5, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-SiS2, Li2S-GeS2, and Li2S-P2S5-GeS2.

[0036] The electrolyte preferably contains a supporting salt and a solvent.

[0037] Examples of supporting salts (lithium salts) for the electrolyte solution having lithium ion conductivity include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3.

[0038] Examples of solvents used in the electrolytic solution include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), and chain esters (chain carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).The electrolytic solution preferably contains two or more solvents.

[0039] (Conductive material) Examples of conductive materials include carbon materials, metal particles, and conductive polymers.

[0040] Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0041] (binder) Examples of binders include rubber-based binders and fluoride-based binders.

[0042] The thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

[0043] <Electrolyte layer> The electrolyte layer contains at least an electrolyte. For the electrolyte, reference can be made to the above description regarding the negative electrode active material layer of the present disclosure.

[0044] The thickness of the electrolyte layer is, for example, not less than 0.1 μm and not more than 1000 μm.

[0045] <Cathode active material layer> The positive electrode active material layer contains at least a positive electrode active material, and may also contain at least one of an electrolyte, a conductive material, and a binder, as necessary.

[0046] Examples of the positive electrode active material include oxide active materials, such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, LiMn2O4, Li4Ti5O 12 , Li(Ni 0.5 Mn 1.5 )O4, and olivine type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0047] A coating layer containing a Li-ion conductive oxide may be formed on the surface of the oxide active material. This is because it can suppress the reaction between the oxide active material and the solid electrolyte (especially the sulfide solid electrolyte). An example of the Li-ion conductive oxide is LiNbO3. The thickness of the coating layer is, for example, 1 nm or more and 30 nm or less.

[0048] Furthermore, for example, Li2S can also be used as the positive electrode active material.

[0049] The positive electrode active material may be, for example, particulate. The average particle size (D50) of the positive electrode active material is not particularly limited, but may be, for example, 10 nm or more, or 100 nm or more. On the other hand, the average particle size (D50) of the positive electrode active material is, for example, 50 μm or less, or may be 20 μm or less. The average particle size (D50) can be calculated, for example, from measurements using a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM).

[0050] For the electrolyte, conductive material, and binder used in the positive electrode active material layer, reference can be made to the above descriptions regarding the negative electrode active material of the present disclosure.

[0051] The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

[0052] <Positive electrode current collector layer> Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon.

[0053] The lithium ion battery produced by the method of the present disclosure may be a liquid-based battery containing an electrolytic solution as the electrolyte layer, or may be a solid-state battery having a solid electrolyte layer as the electrolyte layer. In the context of the present disclosure, the term "solid-state battery" refers to a battery that uses at least a solid electrolyte as the electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as the electrolyte. The solid-state battery of the present disclosure may also be an all-solid-state battery, i.e., a battery that uses only a solid electrolyte as the electrolyte.

[0054] The lithium ion battery produced by the method of the present disclosure may be a primary battery or a secondary battery.

[0055] Examples of the shape of the lithium ion battery include coin type, laminate type, cylindrical type, and square type. [Example]

[0056] <<Synthesis of negative electrode active material>> The negative electrode active materials of the respective examples were obtained as follows.

[0057] <Porous silicon synthesis> Example 1 1 g of silicon (Si) (Kojundo Chemical, particle size 5 μm) and 1 g of lithium (Li) metal (Honjo Metals) were mixed in an agate mortar under an argon atmosphere to obtain a lithium silicon (LiSi) precursor. In a glass reactor under an argon atmosphere, 1.0 g of LiSi precursor and 200 ml of 1,3,5-trimethylbenzene (Nacalai Tesque) as a dispersion solvent were mixed using an ultrasonic homogenizer (SMT, UH-50) to obtain a mixed solution. This mixed solution was cooled to 0°C, and 200 ml of ethanol (Nacalai Tesque) as a solvent for extracting Li was added dropwise. The mixture was then reacted for 2 hours to obtain a reaction solution. 100 ml of acetic acid (Nacalai Tesque) was added dropwise to the reaction solution and reacted for 1 hour. The solid reactant and liquid were then separated by suction filtration. The reaction product was then vacuum dried at 120°C for 2 hours to obtain porous silicon.

[0058] <Synthesis of porous silicon clathrate> 0.5 g of the obtained porous silicon and 0.5 g of sodium hydride (Wako Pure Chemical Industries) were mixed in an agate mortar under an argon atmosphere, placed in a tantalum crucible (Nilaco), and sealed in a stainless steel 304 airtight container. The airtight container was placed in an electric furnace and fired at 500°C for 40 hours to obtain a sodium silicon (NaSi) precursor. The NaSi precursor was transferred to a stainless steel 304 vacuum container under an argon atmosphere and vacuum fired at 400°C for 40 hours to obtain a porous silicon clathrate.

[0059] Porous silicon clathrate was doped with Li ions in the liquid phase using the following procedure. First, 200 ml of 2-methyltetrahydrofuran (Tokyo Chemical Industry Co., Ltd.), 50 ml of 2-methylbiphenyl (Tokyo Chemical Industry Co., Ltd.), and 1 g of Li metal (Honjo Metals Co., Ltd.) were mixed in a glass reactor under an argon atmosphere to obtain a Li ion-doped solution. 1 g of porous silicon clathrate was added to the Li ion-doped solution and stirred for 40 hours. The solid reactant and the Li ion-doped solution were then separated by suction filtration. Furthermore, the reactant was vacuum-dried at 60°C for 2 hours to obtain the negative electrode active material of Example 1.

[0060] (Comparative Example 1) The Si raw material in Example 1 (high purity chemical, particle size 5 μm) was used as the negative electrode active material in Comparative Example 1.

[0061] (Comparative Example 2) In the doping of Li ions, the porous silicon clathrate was doped with Li ions in the solid phase by the following procedure: 1 g of porous silicon clathrate and 1 g of Li metal (Honjo Metals) were mixed in an agate mortar under an argon atmosphere to obtain a negative electrode active material of Comparative Example 2.

[0062] "evaluation" Handling test The negative electrode active material of each example was exposed to the air atmosphere to evaluate the handleability of the negative electrode active material. Regarding the handleability, when the material did not generate heat or change in appearance upon exposure to the air, it was evaluated as ◯, and when the material generated heat or changed in appearance, it was evaluated as ×.

[0063] "result" The results are shown in Table 1.

[0064] [Table 1]

[0065] As shown in Table 1, the negative electrode active material of Example 1, in which the Si used was porous silicon clathrate and Li ions were doped in a liquid phase, was easy to handle.

Claims

1. contacting the porous silicon clathrate with a lithium-containing non-aqueous electrolyte; and and drying and removing the solvent from the lithium-containing nonaqueous electrolyte solution. A method for producing a negative electrode active material.

2. The method of claim 1 , wherein the solvent is a polar aprotic solvent.

3. The method of claim 2, wherein the aprotic polar solvent is an ether.

4. The method according to claim 3, wherein the ether has a tetrahydrofuran skeleton.

5. 10. The method of claim 1, wherein the negative electrode active material is for use as a negative electrode active material in a lithium ion battery.

6. Producing a negative electrode active material by the method according to any one of claims 1 to 5; and forming a negative electrode active material layer containing the negative electrode active material; A method for manufacturing a lithium-ion battery, comprising:

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